Honors Chemistry Lab Fall

Honors Chemistry Lab Fall

By:Mary McHale

Honors Chemistry Lab Fall

By:Mary McHale

Online:< http://cnx.org/content/col10456/1.16/ >

C O N N E X I O N S

Rice University, Houston, Texas

This selection and arrangement of content as a collection is copyrighted by Mary McHale. It is licensed under the

Creative Commons Attribution 2.0 license (http://creativecommons.org/licenses/by/2.0/).

Collection structure revised: November 15, 2007

PDF generated: October 26, 2012

For copyright and attribution information for the modules contained in this collection, see p. 111.

Table of Contents

1 Initial Lab: Avogradro and All That . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Stoichiometry: Laws to Moles to Molarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 VSEPR: Molecular Shapes and Isomerism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Beer's Law and Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 Hydrogen and Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 The Best Table in the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497 Bonding 07 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 Solid State and Superconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679 Organic Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8510 Transition Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9511 Physical Properties of Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 105Attributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

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Available for free at Connexions <http://cnx.org/content/col10456/1.16>

Chapter 1

Initial Lab: Avogradro and All That1

Initial Lab: Avogadro and All ThatExperiment 1Objective

• The purpose of this laboratory exercise is to help you familiarize yourself with the layout of thelaboratory including safety aids and the equipment that you will be using this year.

• Then, to make an order-of-magnitude estimate of the size of a carbon atom and of the number of atomsin a mole of carbon based on simple assumptions about the spreading of a thin �lm of stearic acid ona water surface

Grading

• Pre-lab � not required for the �rst lab• Lab Report (90%)• TA points (10%)

Before coming to lab. . .. . .

• Read the following:

· Lab instructions· Background Information· Concepts of the experiment

• Print out the lab instructions and report form.• You may �ll out the lab survey, due at the beginning of the lab, for extra credit if you wish.• Read and sign the equipment responsibility form and the safety rules, email Ms Duval at ndu-

[email protected] to con�rm completing this requirement by noon on August 31st

IntroductionSince chemistry is an empirical (experimental) quantitative science, most of the experiments you will

do involve measurement. Over the two semesters, you will measure many di�erent types of quantities �temperature, pH, absorbance, etc. � but the most common quantity you will measure will be the amount ofa substance. The amount may be measured by (1) weight or mass (grams), (2) volume (milliliters or liters),or (3) determining the number of moles. In this experiment we will review the methods of measuring massand volume and the calculations whereby number of moles are determined.

Experimental ProcedureWe will start in the amphitheater of DBH (above DBH 180) for demonstrations: oxygen, hydrogen and

a mixture of the two in balloons and more besides.1This content is available online at <http://cnx.org/content/m15093/1.1/>[email protected]


1

2 CHAPTER 1. INITIAL LAB: AVOGRADRO AND ALL THAT

Mandatory Safety talk by Kathryn Cavender, Director of Environmental Health and Safety at Rice.1. Identi�cation of ApparatusOn your benches, there are a number of di�erent pieces of common equipment. With your TA's help,

identify each and sketch - I know this may sound a trivial exercise but it is necessary so that we are all onthe same page.

1. beaker2. erlenmeyer �ask3. graduated (measuring) cylinder4. pipette5. burette6. Bunsen burner7. test tube8. boiling tube9. watch glass

2. Balance UseIn these general chemistry laboratories, we only use easy-to-read electronic balances � saving you a lot of

time and the TA's a lot of headaches. However, it is important that you become adept at the use of them.Three aspects of a balance are important:

1. The on/o� switch. This is either on the front of the balance or on the back.2. The "Zero" or "Tare" button. This resets the reading to zero.3. CLEANLINESS. Before and after using a balance, ensure that the entire assembly is spotless. Dirt on

the weighing pan can cause erroneous measurements, and chemicals inside the machine can damage it.4. Turn the balance on.5. After the display reads zero, place a piece of weighing paper on the pan.6. Read and record the mass. (2)7. With a spatula, weigh approximately 0.2 g of a solid, common salt NaCl, the excess salt is discarded,

since returning the excess salt may contaminate the rest of the salt - in this exercise, this is not a bigdeal but in strict analytical procedures it is.

8. Record the mass (1). To determine how much solid you actually have, simply subtract the mass of theweighing paper(2) from the mass of the weighing paper and solid (1). Record this mass (3).You havejust determined the mass of an "unknown amount of solid."

9. Now place another piece of weighing paper on the balance and press the Zero or Tare button thenweigh out approximately 0.2 g of the salt (4). Thus, the zero/tare button eliminates the need forsubtraction.

3. Measuring the volume of liquidsWhen working with liquids, we usually describe the quantity of the liquid in terms of volume, usual

units being milliliters (mL). We use three types of glassware to measure volume � (1) burette, (2) volumetricpipette, and (3) graduated cylinder.

• Examine each piece of equipment. Note that the sides of each are graduated for the graduated cylinderand the burette. You can read each to the accuracy of half a division.

• Put some water into the graduated cylinder. Bend down and examine the side of the water level. Notethat it has a "curved shape." This is due to the water clinging to the glass sides and is called themeniscus. When reading any liquid level, use the center of the meniscus as your reference point.

Graduated cylinder

1. Look at the graduations on the side of the cylinder. Note that they go from 0 on the bottom andincrease upwards. Thus, to get the mass of 10 mL of a liquid from a graduated cylinder, do thefollowing:


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2. Add water up to the 10 mL line as accurately as possible.3. Dry a small beaker and weigh it (2).4. Pour the 10 mL of water from the cylinder into the beaker. Reweigh (1).5. Subtract the appropriate values to get the weight of the water (3).

Pipette

1. You may �nd either that 0 is at the spout end or at the top of the pipette. You should be aware ofhow these graduations go when using each pipette. Thus, to get the mass of 10 mL of a liquid from apipette, do the following:

2. Half-�ll a beaker with water.3. Squeeze the pipette bulb and attach to the top of the pipette. Put the spout of the pipette under

water and release the bulb. It should expand, drawing the water into the pipette, do not let the waterbe drawn into the bulb.

4. When the water level is past the last graduation, remove the bulb, replace with your �nger, and thenremove the pipette from the water.

5. Removal of your �nger will allow liquid to leave the pipette. Always run some liquid into a wastecontainer in order to leave the level at an easy-to-read mark.

6. Add 10 mL of water to a pre-weighed dry beaker (5).7. Weigh (4).8. Subtract to get the weight of the water (6).

Burette

1. Examine the graduations. Note that 0 is at the top.2. Using a funnel, add about 10 mL of water. To do this, �rst lower the burette so that the top is easy

to reach.3. Run a little water from the burette into a waste container. Then turn the burette upside down and

allow the rest of the water to run into the container (you will have to open the top to equalize thepressure).

4. You have just "rinsed your burette." This should be done every time before using a burette � �rst rinsewith water, then repeat the process using whatever liquid is needed in the experiment.

5. Fill the burette to any convenient level (half-way is �ne). It is a good technique to "over�ll" and thenallow liquid to run into a waste container until you reach the appropriate level so that you �ll the spacefrom the top to the tip of the burette.

6. Dry a beaker and weigh (8).7. Add 10 mL of water to a pre-weighed dry beaker (7).8. Subtract to get the weight of the water (9).

4. Estimation of Avogadro's numberBrie�y, as a group with your TA, you will make an approximate (order of magnitude) estimate of Avo-

gadro's number by determining the amount of stearic acid that it takes to form a single layer (called amonolayer) on the surface of water. By making simple assumptions about the way the stearic acid moleculespack together to form the monolayer, we can determine its thickness, and from that thickness we can estimatethe size of a carbon atom. Knowing the size of a carbon atom, we can compute its volume; and if we knowthe volume occupied by a mole of carbon (in the form of a diamond), we can divide the volume of a mole ofcarbon by the volume of an atom of carbon to get an estimate of Avogadro's number.

ProcedureSpecial Supplies: 14 cm watch glass; cm ruler; polyethylene transfer pipets; 1-mL syringes; pure distilled

water free of surface active materials; disposable rubber gloves (for cleaning own watch glasses in 0.1 MNaOH in 50:50 methanol/water): 13 X 100 mm test tubes with rubber stoppers to �t.

Chemicals: pure hexane, 0.108 g/L stearic acid (puri�ed grade) solution in hexane. 0.1 M NaOH in 50:50methanol/water used for washing the watch glasses.



SAFETY PRECAUTIONS: Hexane is �ammable! There must be no open �ames in the laboratory whilehexane is being used.

WASTE COLLECTION: At the end of the experiment, unused hexane solvent and stearic acid in hexanesolution should be placed in a waste container, marked "Waste hexane/stearic acid solution in hexane."

Measurement of the volume of stearic acid solution required to cover the water surfaceYour TA will do this as a group demonstration:

1. Using a transfer pipette, obtain about 3-4 mL 0.108 g/L stearic acid solution in hexane in a clean, dry13 X 100 mm test tube. Keep the tube corked when not in use.

2. Fill the clean watch glass to brim with deionized water. One recommended way to do this is to set upyour 25 mL burette on a ring stand. Wash and drain the burette with deionized water. (the deionizedwater comes from the white handled spouts at each sink)

3. In a freshly cleaned and rinsed beaker, obtain more distilled water and �ll the burette. Place yourwatch glass directly under the burette (about 1 inch or less from the tip) and dispense the water untilthe entire watch glass is full. You may have to re�ll the burette 4 or 5 times to do this. With carefuldispensing, the surface tension of the water should allow you to �ll the entire watch glass with relativeease.

4. Carefully measure the diameter of the water surface with a centimeter ruler. It should be close to 14cm, + or - a couple of millimeters. Next, rinse and �ll your 1 mL syringe with stearic acid solution,taking care to eliminate bubbles in the solution inside the syringe.

5. Read and record the initial volume of the syringe (1 mL is always a good place to start.)6. Then add the stearic acid solution drop by drop to the water surface. Initially, the solution will spread

across the entire surface, and it will continue to do so until a complete monolayer of stearic acid hasbeen formed. If your �rst few drops do not spread and evaporate quickly, either your water or watchglass is still dirty. As this point is approached, the spreading will become slower and slower, until�nally a drop will not spread out but will instead sit on the surface of the water (looking like a littlecontact lens). If this "lens" persists for at least 30 s, you can safely conclude that you have added 1drop more than is required to form a complete monolayer.

7. Now, read and record the �nal volume reading of the syringe.Takes 10 min8. Thoroughly clean the watch glass (or get another one), and repeat the experiment. Repeat until the

results agree to within 2 or 3 drops (0.04 ml).

When you have completed all of your measurements, rinse your syringe with pure hexane, and dispose of allthe hexane-containing solutions in the waste collection bottle provided.

Calculation Of Avogadro's NumberThe calculation proceeds in several steps.

• We calculate the volume of stearic acid solution in hexane required to deliver enough stearic acid toform a monolayer.

• All of the hexane evaporates, leaving only the thin monolayer �lm of stearic acid, so we next calculatethe actual mass of pure stearic acid in the monolayer.

• We calculate the thickness of the stearic acid monolayer, using the known density of stearic acid andthe area of the monolayer.

• Assuming the stearic acid molecules are stacked on end and are tightly packed, and knowing that thereare 18 carbon atoms linked together in the stearic acid molecule, calculate the diameter and volume ofa carbon atom.

• Calculate the volume of a mole of carbon atoms in diamond; divide the molar volume of carbon (dia-mond) by the volume of a single carbon atom to obtain an estimate of Avogadro's number. Rememberthat the units of Avogadro's number are mol-1, so you can use unit analysis to check your answer.

Initial Lab: Avogadro and All ThatReport 1


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Note: In preparing this report you are free to use references and consult with others. However, you maynot copy from other students' work (including your laboratory partner) or misrepresent your own data (seehonor code).

Name(Print then sign): ___________________________________________________Lab Day: ___________________Section: ________TA__________________________Note: In preparing this report you are free to use references and consult with others. However, you may

not copy from other students' work (including your laboratory partner) or misrepresent your own data (seehonor code).

Demonstrations:Balloons:

1. Oxygen

1. Hydrogen2. Mixture of Hydrogen and Oxygen with relevant equation: H2 + O2 →

Thermite:Include description and relevant equation: Fe2 O3 + Al →Dry Ice and Magnesium:Include description and relevant equation: MgO + C →1. Identi�cation of Apparatus

1. beaker

1. erlenmeyer �ask

1. graduated (measuring) cylinder

1. pipette

1. burette

1. Bunsen burner

1. test tube2. watch glass

2. Balance Use

1. Mass of weighing paper and solid, ________ g2. Mass of weighing paper, __________ g



3. Mass of solid, ___________g4. Mass of solid on tared weighing paper ____________g

3. Measuring the volume of a liquid

1. Mass of 50 mL beaker and water, g ______________2. Mass of 50 mL beaker, g ______________________3. Mass of water from graduated cylinder, g___________4. Mass of 50 mL beaker and water, g ______________5. Mass of 50 mL beaker, g ______________________6. Mass of water from pipette, g ____________________7. Mass of 50 mL beaker and water, g ______________8. Mass of 50 mL beaker, g ______________________9. Mass of water from burette, g ____________________

From a consideration of the masses of water measured above, and given that the density of water is 1 g/mL,decide on an order of which is the most accurate method of volume measurement � measuring cylinder,pipette, or burette with (1) being the most accurate?

(1)(2)(3)How precisely could each of the apparatus used be read?(1) measuring cylinder(2) pipette(3) burette4. Estimation of Avogadro's NumberMeasurement of the volume of stearic acid solution required to cover the water surface

Trial 1 Trial 2

Record the diameter of the watersurface

___________________ ___________________

Record the volume of stearic acidsolution required to cover the sur-face

___________________ ___________________

Record the concentration of thestearic acid solution

___________________ ___________________

Table 1.1

Calculation Of Avogadro's Numbera. Calculation of the thickness of a monolayer of stearic acid

Trial 1 Trial 2

continued on next page


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From your data, the volume ofstearic acid solution required toform a monolayer was

___________________ ___________________

Calculate the mass of stearicacid contained in that volume ofstearic acid solution (the concen-tration in grams per liter will begiven to you)

___________________ ___________________

Calculate the volume, V, of purestearic acid in the monolayer onthe water surface. You will needthe density of solid stearic acid,which is 0.85 g/ml (or g/cm

3).

___________________ ___________________

Calculate the area of the mono-layer (A = πr2, r is the radius ofthe water surface)

___________________ ___________________

Calculate the thickness of themonolayer (t = Volume/Area)

___________________ ___________________

Table 1.2

b. Estimation of the size and volume of a carbon atom

Trial 1 Trial 2

A stearic acid molecule consistsof 18 carbon atoms linked to-gether. Assuming that the thick-ness, t, of a monolayer is equalto the length of the stearic acidmolecule, calculate the size of acarbon atom, s = t/18

___________________ ___________________

Assuming that a carbon atom isa little cube, calculate the volumeof a carbon atom, volume = s3

___________________ ___________________

Table 1.3

c. Calculation of the volume of a mole of carbon atoms

Trial 1 Trial 2




Calculate the molar volume ofcarbon (diamond) by using the

density of diamond(3.51g/cm3

)

and the atomic mass of a mole ofcarbon

_____________________________________________

Is the volume of a mole of dia-mond the same as the actual vol-ume of a mole of carbon atoms?

_____________________________________________

Table 1.4

d. Calculation of the volume of a mole of carbon (diamond) volume of a single carbon atom (Avogadro'snumber)

Trial 1 Trial 2

Calculate Avogado's number(NA) from the appropriate ratioof volumes

______________________________________________

Calculate the average value ofNA from your results

______________________________________________

Express your results as a number1023. Are you within a power of10 of the accepted value of 6.021023?

_____________________________________________

Table 1.5


Chapter 2

Stoichiometry: Laws to Moles to

Molarity1

2.1 Experiment 2: Stoichiometry: Laws to Moles to Molarity

2.1.1 Objective

• To determine the mass of a product of a chemical reaction• To make a solution of assigned molarity � your accuracy will be tested by your TA by titration!

2.1.2 Grading

• Pre-lab (10%)• Lab Report (80%)• TA points (10%)

1This content is available online at <http://cnx.org/content/m15095/1.14/>.


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10 CHAPTER 2. STOICHIOMETRY: LAWS TO MOLES TO MOLARITY

2.1.3 Before Coming to Lab..

• Read the lab instructions• Complete the pre-lab, due at the beginning of the lab

2.1.4 Introduction

The word stoichiometry derives from two Greek words: stoicheion (meaning "element") and metron (meaning"measure"). Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants andproducts involved in a chemical reaction. Consequently, it is a very mathematical part of chemistry.

In the �rst part of this lab, sodium bicarbonate is reacted with an excess of hydrochloric acid.NaHCO3 (s) +HCl (aq)→ NaCl (aq) + CO2 (g) +H2OBy measuring the mass of NaHCO3 and balancing the equation (above), the mass of NaCl expected to

be produced can be calculated and then checked experimentally. Then, the actual amount of NaCl producedcan be compared to the predicted amount.

This process includes molar ratios, molar masses, balancing and interpreting equations, and conversionsbetween grams and moles and can be summarized as follows:

1. Check that the chemical equation is correctly balanced.2. Using the molar mass of the given substance, convert the mass given in the problem to moles.3. Construct a molar proportion (two molar ratios set equal to each other). Use it to convert to moles of

the unknown.4. Using the molar mass of the unknown substance, convert the moles just calculated to mass.

In the second part of this lab, since a great deal of chemistry is done with solutions, a solution will beprepared of allocated molarity. Molarity, or more correctly molar concentration, is de�ned to be the numberof moles of solute divided by the number of liters of solution:

cM = nsubstance

Vsolution

with units of [mole/L]. However molar concentration depends on the temperature so a higher temperaturewould result in an increased volume with a consequential decrease in molar concentration. This can be asigni�cant source of error, of the same order as the error in the volume measurements of a burette, when thetemperature increases more than 5 º C.

Steps to preparing a solution of a certain concentration:

1. First need to know the formula for the solute, e.g. potassium chromate: K2CrO4.2. Need the molecular weight of the solute: by adding up the atomic weights of potassium, chromium

and oxygen: 39.10, 52.00 and 16.00 in the correct ratios:3. 2 × 39.1, 52.0 and 4 × 16.00 = 194.2g/mole.4. Then the volume of solution, usually deionised water: e.g. for one liter of solution use a 1000 mL

volumetric �ask. So a 1M solution would require 194.2g of solid K2CrO4 in 1 L, 0.1M 19.42g of solidK2CrO4 and so on.

5. Remember to ensure that all the solute is dissolved before �nally �lling to the mark on the volumetric�ask. If there is any undissolved solute present in the solution, the water level will go down slightlybelow the mark, since the volume occupied by the solute di�ers from the actual volume it contributesto the solution once it is dissolved.

Your teaching assistant will check the accuracy of the solution that you have made by titration, whichis a method of quantitatively determining the concentration of a solution. A standard solution (knownconcentration) is slowly added from a burette to a solution of the analyte (unknown concentration � yoursolution) until the reaction between them is judged to be complete equivalence point). In colorimetrictitration, some indicator must be used to locate the equivalence point. One example is the addition ofacid to base using phenolphthalein (indicator) to turn a pink solution colorless in order to determine the


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concentration of unknown acids and bases. Record your TAs value of the molarity of your solution on yourreport form along with your percent error.

Figure 2.1

Figure 1: Reading the BuretteWhen an acid is neutralized by a base, since there is stoichiometrically equal amounts of acid and base

and the pH = 7, it is possible to accurately determine the concentration of either the acid or base solution.Since:

Moles of a substance = Concentration of solution (moles/L) x Volume (L)We can calculate the concentration of the acid or base in the solution using:

Balance Base [U+E09E] Bb [U+E09F] × Moles of Acid = Moles of Base × Balance Acid [U+E09E] Ba [U+E09F]

Bb × Ca × Va = Ba × Cb × Vb

2.1.4.1 Titration Calculations:

Step 1:Balance the neutralization equation. Determine Balance of Acid and Base.Step 2:Determine what information is given.Step 3:Determine what information is required.Step 4:Solve using the equation below.Bb × Ca × Va = Ba× Cb × Vb

2.1.4.2 Example:

Calculate the concentration of a nitric acid solution HNO3 if a 20 ml sample of the acid required an averagevolume of 55 ml of a 0.047 mol/l solution of Ba[U+E09E]OH[U+E09F]2 to reach the endpoint of the titration.



Step 1: 2HNO3 + Ba[U+E09E]OH[U+E09F]2 → Ba[U+E09E]NO3[U+E09F]2 + 2H2OBalance Base =1Balance Acid = 2

Step 2:Given informationVolume Acid = 20 mlVolume Base (average) = 55 ml Concentration of Base =0.047 mol/l

Step 3: Required informationConcentration of AcidStep 4:Solve using the equation. Bb × Ca × Va =Ba×Cb×Vb1×Ca× 20ml = 2× 0.047mol/1× 55ml Ca = 0.2585 mol/l ( considering signi�cant �gures 0.26mol/l)

2.1.5 Experimental

2.1.5.1 Materials List

sodium bicarbonate [U+E09E]NaHCO3[U+E09F]3M hydrochloric acid (HCl) solution

2.1.5.2 Procedure

2.1.5.3 Part 1

1. Weigh an empty 150-mL beaker on the electronic balance. Record this value in your data table.2. Remove the beaker from the balance and add one spoonful of sodium bicarbonate (approximately 5

g). Re-weigh and record this value.3. Pour approximately 20 mL of 3M hydrochloric acid into a 100-mL beaker. Rest a Pasteur pipette in

the beaker.4. Add 3 drops of acid to the NaHCO3beaker, moving the pipette so that no drops land on each other.

The key point is to spread out the adding of acid so as to hold all splatter within the walls of thebeaker.

5. Continue to add acid slowly drop by drop. As liquid begins to build up, gently swirl the beaker. Thisis done to make sure any unreacted acid reaches any unreacted sodium bicarbonate. Do not add acidwhile swirling.

6. Stop adding the hydrochloric acid when all bubbling has ceased. So that the minimum amount of HClhas reacted with all of the sodium bicarbonate. Check when all the bubbling has ceased, by swirlingthe beaker and to ensure that there is no more bubbling. When all the bubbling has ceased, add onedrop more of acid and swirl.

7. Weigh the beaker and contents, record.8. Using a microwave oven, dry to constant weigh, initially for 1 min, when there is plenty of solution,

and then 10 second intervals thereafter. Measure weight to the nearest milligram.

2.1.5.4 Materials List

100 mls volumetric �ask3M hydrochloric acid (HCl) solutionsodium bicarbonate [U+E09E]NaHCO3[U+E09F]methyl orange indicator

2.1.5.5 Part 2

1. Ask you TA for your assigned molarity � it will range from 0.7 M to 1.2 M.2. First need to know the formula for the solute.3. Need the molecular weight of the solute in g/mole.4. The volume of solution, 100 mLs.5. Remember to ensure that all the solute is dissolved before �nally �lling with deionised water to the

mark on the volumetric �ask.


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6. Take your solution to your TA to check the molarity by titration, record value on your report formand your percent error.



2.2 Pre-Lab 2: Stoichiometry

(Total 10 points)Click here 2 to print the Pre-Lab Note: In preparing this Pre-Lab you are free to use references and

consult with others. However, you may not copy from other students' work (including your laboratorypartner) or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________Lab Day: ___________________Section: ________TA__________________________Circle the correct answer:1) Which one of the following is a correct expression for molarity?A) mol solute/L solventB) mol solute/mL solventC) mmol solute/mL solutionD) mol solute/kg solventE) µmol solute/L solution2) What is the concentration (M) of KCl in a solution made by mixing 25.0 mL of 0.100 M KCl with

50.0 mL of 0.100 M KCl?A) 0.100B) 0.0500C) 0.0333D) 0.0250E) 1253) How many grams of CH3OH must be added to water to prepare 150 mL of a solution that is 2.0 M

CH3OH?A) 9.6 × 103

B) 4.3 × 102

C) 2.4D) 9.6E) 4.34) The concentration of species in 500 mL of a 2.104 M solution of sodium sulfate is __________

M sodium ion and __________ M sulfate ion.A) 2.104, 1.052B) 2.104, 2.104C) 2.104, 4.208D) 1.052, 1.052E) 4.208, 2.1045) Oxalic acid is a diprotic acid. Calculate the percent of oxalic acid H2C2O4 in a solid given that a

0.7984 g sample of that solid required 37.98 mL of 0.2283 M NaOH for neutralization.A) 48.89B) 97.78C) 28.59D) 1.086E) 22.836) A 31.5 mL aliquot of H2SO4(aq) of unknown concentration was titrated with 0.0134 M NaOH (aq).

It took 23.9 mL of the base to reach the endpoint of the titration. The concentration (M) of the acid was__________.

A) 0.0102B) 0.0051C) 0.0204D) 0.102

2http://cnx.org/GroupWorkspaces/wg768/m15095/Prelab07.doc


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E) 0.2277) What are the respective concentrations (M) of Fe3+ and I− a�orded by dissolving 0.200 mol FeI3 in

water and diluting to 725 mL?A) 0.276 and 0.828B) 0.828 and 0.276C) 0.276 and 0.276D) 0.145 and 0.435E) 0.145 and 0.04838) A 36.3 mL aliquot of 0.0529 M H2SO4(aq) is to be titrated with 0.0411 M NaOH (aq). What volume

(mL) of base will it take to reach the equivalence point?A) 93.6B) 46.8C) 187D) 1.92E) 3.849) A 13.8 mL aliquot of 0.176 M H3PO4(aq) is to be titrated with 0.110 M NaOH (aq). What volume

(mL) of base will it take to reach the equivalence point?A) 7.29B) 22.1C) 199D) 66.2E) 20.910) A solution is prepared by adding 1.60 g of solid NaCl to 50.0 mL of 0.100 M CaCl2. What is the

molarity of chloride ion in the �nal solution? Assume that the volume of the �nal solution is 50.0 mL.A) 0.747B) 0.647C) 0.132D) 0.232E) 0.547

2.3 Report 2: Stoichiometry

(Total 80 points)Note: In preparing this report you are free to use references and consult with others. However, you may

not copy from other students' work (including your laboratory partner) or misrepresent your own data (seehonor code). This is only an advisory template of what needs to be include in your complete lab write-up.

Name(Print then sign): ___________________________________________________Lab Day: ___________________Section: ________TA__________________________

2.3.1 Part 1

2.3.2 Data Table

Mass Grams

empty 150-mL beaker

NaHCO3 in beaker

Mass of NaHCO3

Table 2.1



Mass Grams

NaCl plus beaker �rst weighing

NaCl plus beaker second weighing

NaCl plus beaker third weighing

Table 2.2

1) The grams of NaHCO3 you had in your beaker was ________2) Calculate how many moles of NaHCO3 the mass is ________3) Write the molar ratio for the NaHCO3 / NaCl ratio _______4) Write the number of moles of NaCl you predict were produced in your experiment.5) Calculate the mass of NaCl you predict will be produced.6) Determine, by subtraction, the actual mass of NaCl produced in your experiment.a) �rst weighingb) second weighingc) third weighing7) Calculate your percentage yield.

2.3.3 Discussion Questions

1. Compare the numerical value of the observed ratio for maximum yield to the best ratio

2.3.4 Part 2

Record your TAs value of the molarity of your solution.Calculate your percent error from your assigned value.Complete the equation for the titration ofNaHCO3[U+E09E]aq[U+E09F] +HCl[U+E09E]aq[U+E09F] →


Chapter 3

VSEPR: Molecular Shapes and

Isomerism1

Molecular Shapes & IsomerismObjectives

• Understand the 3-dimensional nature of molecules• Learn about Molecular Symmetry• Be able to identify the various isomers possible for one molecular formula• Be able to identify enantiomers

3.1 Grading

• Quiz (10%).• Lab Report Form (90%).

Before Coming to Lab . . .Look over the following to make sure you have a basic understanding of the topics presented.

• Drawing Lewis Structures• Determining the Shapes of Molecules from their Lewis Structures• Some Basic Aspects of Bonding• Model Kits

IntroductionThe shape of a molecule is extremely important in determining its physical properties and reactivity. A

multitude of shapes are possible, and in today's lab, you will be looking at several.In Part 1, you will be exploring the various symmetry elements that can be present in molecules. The

symmetry elements you will be looking for are mirror planes, rotation axes, and inversion centers. Beingable to determine which symmetry elements are present in a molecule help in understanding its chemistry. Ifthere is a plane present in the molecule that has the exact same arrangement of atoms on either side of theplane, then the molecule has a mirror plane (σ). It is important to note that a molecule can have morethan one mirror plane. Rotation axes are represented as Cn (n = 1, 2, 3 . . .). The subscript indicateshow many degrees of rotation (360o/n) are needed in order to return to the same orientation of atoms withwhich you started. So if there is a C2 axis, the rotation would be 180o. An example of a molecule having aC2 axis is H2O.



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18 CHAPTER 3. VSEPR: MOLECULAR SHAPES AND ISOMERISM

Figure 3.1

The third symmetry element is an inversion center (i). In such molecules, starting at any positionand drawing a line through the center and an equal distance to the opposite side of the molecule, you willend up at a position with an identical environment to the one you started from.

Figure 3.2

Part 2 of the lab introduces the concept of enantiomers. Enantiomers are molecules sharing thesame molecular con�guration, but they are non-superimposable images of each other. This concept shouldbecome clearer as you build the models for this part of the lab. Enantiomers share many of the same physicalproperties. The property which distinguishes them is the direction in which they rotate plane-polarized light.They will rotate the light in equal amounts but in di�erent directions (plane-polarized light is just light in

which all wave vibrations have been �ltered out except for those in one plane). If both enantiomers arepresent in a 1:1 ratio, the e�ects of the rotation of light cancel and no net rotation is observed. Such a


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mixture of isomers is known as a racemic mixture or as a racemate. Because these isomers rotate plane-polarized light, they are also known as optical isomers. Compounds that form optical isomers are said tobe chiral.

The chemistry of enantiomers is of great importance in the �eld of medicine. It has been discovered thatwith many drugs, one enantiomer will be biologically active while the other will be inactive or even produceundesired side e�ects. For this reason, it has become advantageous for pharmaceutical companies to try tosynthesize the active enantiomer exclusively.

The next part of the lab deals with isomers. Isomers are molecules having the same molecular formula,but the atoms are arranged in a di�erent manner, while still obeying the rules of bonding. There are di�erentclassi�cations for isomers. For example, structural isomers di�er from one another in the order in whichthe atoms are bound to each other (connectivity is di�erent). On the other hand, geometrical isomers havethe same order of atoms, but the spatial arrangement of atoms is di�erent (connectivity is the same). Acommon example of geometrical isomers is the cis and trans forms of double bonds:

Figure 3.3

** NOTE: Remember that molecules having single carbon-carbon bonds cannot have cis/trans isomersbecause there is free rotation about single bonds.

By building the models of various molecules during this lab, you will be able to better understandmolecular symmetry and isomers. Building models is not di�cult; however, the chemical principles involvedare very important and you may �nd some surprises in how atoms can be �t together.

Finally, in Part 4, you will be applying your knowledge of VSEPR (Valence Shell Electron Pair Repulsion)Theory in order to determine the geometry of several di�erent molecules. VSEPR theory is useful in helpingto determine how atoms will orient themselves in molecules. Basically, the idea is that the arrangementadopted by a molecule will be the one in which the repulsions among the various electron domains areminimized. The two kinds of electron domains are bonding (electron pair shared by two atoms) and non-bonding (electron density centralized on one atom) pairs of electrons.

Experimental ProcedureFor Parts 1 & 2: You and your lab partner are to work with one other lab group in preparing these

models (no more than 3 - 4 students). Your TA will assign each group a certain set of molecules to makeand answer questions pertaining to those molecules. Each group will then present their answers to the class.These models will need to be completed and answers determined within 30 minutes so that we can continueto Parts 3 & 4 as soon as possible.

For Parts 1-4, the work should be divided among the group members. Be sure to discuss the questionsand answers among yourselves, but put your own conclusions on the Report Form.



1. Symmetry ElementsUsing the Molecular Framework models, make models of the following compounds:

a. CH4

b. CH3Clc. CH2Cl2d. CHCl3e. CH2ClFf. CHBrClFg. BF3h. BF2Cli. PH3

j. PH2Cl

Choose a color to represent each atom. For example, make all C atoms black, all H atoms white, etc.Once the models are created, look for symmetry elements that may be present. Ask yourselves the

following questions:

• Does the molecule contain a mirror plane (σ)? In other words, is there a plane within the moleculewhich results in one half being a mirror image of the other half?

• Does the molecule contain a two-fold rotation axis (C2)? Remember from the Introduction that thesubscript indicates the degrees of rotation necessary to reach a con�guration that is indistinguishablefrom the original one. In this case, the rotation will be 180o.

• Does the molecule contain any higher-order rotation axes?

• · C3 � rotation by 120o

· C4 � rotation by 90o

· C∞ (in�nity rotation axis) � rotation of any amount will result in an indistinguishable orientation• Does the molecule have an inversion center (i)?

Determine which of these symmetry elements are present in your assigned molecules. All of the columnsof the table on the report form should be �lled out. If you have any di�culty determining whether suchsymmetry elements are present in the molecules you are assigned, your TA can provide examples of eachsymmetry element.

Extra credit points can be earned by indicating in the table how many of each symmetry element arepresent for each molecule (i.e. How many mirror planes are present?).

2.Mirror ImagesUsing the model kits, build models which are the mirror images of the models you were assigned to build

(b, c, d, e, f, g, h, i and j) in Part 1. With the two mirror images in hand, try to place the models on top ofone another, atom for atom.

If you can do this, the model and its mirror image are superimposable mirror images of one another.If not, the molecule and its mirror image form nonsuperimposable mirror images. Nonsuperimposablemirror images are also known as enantiomers.

For each compound, decide whether the mirror image is superimposable or nonsuperimposable. Can youmake a generalization about when to expect molecules to have nonsuperimposable mirror images?

3.IsomersIn this exercise you will build models of compounds which are structural and/or geometrical isomers of

one another.Make the following models:A. Structural Isomers

1. Make a model(s) of C2H5Cl. How many di�erent structural isomers are possible?


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2. Make a model(s) of C3H7Cl. How many di�erent structural isomers are possible?3. Make a model(s) of C3H6Cl2. How many di�erent structural isomers are possible?

B. Geometrical Isomers

1. Make a model(s) of C2H3Cl. How many di�erent structural and geometrical isomers are possible?2. Make a model(s) of C2H2Cl2. How many di�erent structural and geometrical isomers are possible?3. Make a model(s) of cyclobutane (C4H8). HINT: cyclo = ring of C atoms4. Now make dichlorocyclobutane (C4H6Cl2) by replacing two H atoms on cyclopropane with Cl atoms.

How many di�erent structural and geometrical isomers are possible for dichlorocyclobutane? You maywish to make a couple of cyclobutane molecules so that you can compare the structures. Do any of theisomers have nonsuperimposable mirror images?

C. Aromatic Ring Compounds

1. Make a model of benzene, C6H6. Even though your model will contain alternating double and singlebonds, remember that in the real molecules of benzene all the C-C bonds are equivalent. Whatsymmetry elements does benzene possess?

2. Make a model(s) of chlorobenzene, C6H5Cl. How many di�erent structural and geometrical isomersare possible?

3. Make a model(s) of dichlorobenzene, C6H4Cl2. How many di�erent structural and geometrical isomersare possible?

4. Make a model(s) of trichlorobenzene, C6H3Cl3. How many di�erent structural and geometrical isomersare possible?

4. Hypervalent StructuresHypervalent compounds are those that have more than an octet of electrons around them. Such

compounds are formed commonly with the heavier main group elements such as Si, Ge, Sn, Pb, P, As, Sb,Bi, S, Se, Te, etc. but rarely with C, N or O. Refer to the rules for Electron Domain theory in order to assignLewis structures to the following molecules. Describe possible isomeric forms and the bond angles betweenthe atoms. How many lone pairs of electrons are present on the central atom of each molecule, if any? (**Your book will be very useful in aiding you with these structures **)

a. PF5b. PF3Cl2c. SF4d. XeF2e. BrF3


Chapter 4

Beer's Law and Data Analysis1

4.1 Beer's Law and Data Analysis

4.1.1 Objectives

• Learn or review typical data analysis procedures � plotting data with excel, performing linear regressionanalysis, etc.

• Explore the concepts and applications of spectrophotometry

4.1.2 Grading

• Pre-lab (10%)• Lab Report Form � including plot (80%)• TA points + Pop Quiz (10%)

4.1.3 Before coming to lab. . .

• Read the lab instructions• Print out the lab instructions and report form.• Complete the pre-lab, due at the beginning of the lab

4.1.4 Introduction

When describing chemical compounds, scientists rely on their chemical and physical properties. In lab, wemight observe that a metal reacts violently with water, that a reactant is liquid at room temperature, orthat a powder is yellow. Chemical and physical properties can be used qualitatively to identify a materialor to predict its behavior, or quantitatively to determine how much of that material is present in a solution.In this lab, we will develop a scheme to determine the concentration of copper sulfate in aqueous solutionusing spectrophotometry.

To start, we will consider light and its interaction with matter. Chemicals exhibit a diverse rangeof colors, especially when they contain transition metal ions. In order for a compound to have color, itmust absorb visible light. Visible light consists of electromagnetic radiation with wavelengths ranging from



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24 CHAPTER 4. BEER'S LAW AND DATA ANALYSIS

approximately 400 nm to 700 nm, a small section of the electromagnetic radiation spectrum shown below.

Light is characterized by its frequency ( ν), the number of times the crest of the wave passes some point inspace per second, or by its wavelength ( λ), the distance between two successive crests. These two quantitiesare related by the speed of light, a fundamental constant: λν = c = 3×108m/s. Planck related the frequencyof light to its energy (E) according to E = hν, where h is Planck's constant, h = 6.626× 10−34J/s.

A compound will absorb light when the radiation posesses the energy needed to move an electron fromits lowest energy (ground) state to some excited state. The particular energies of radiation that a substanceabsorbs dictate the colors that it exhibits. Conversely the color of a compound can help us to determine itselectronic con�guration.

White light contains all wavelengths in this visible region. When a transparent sam-ple (like most aqueous solutions) absorbs visible light, the color we perceive is thesum of the remaining colors that are transmitted by the object and strike our eyes.


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Ifan object absorbs all wavelengths of visible light, none reaches our eyes, and it appears black. If it absorbsno visible light, it will look white or colorless. If it absorbs all but orange, the material will appear orange.We also perceive an orange color when visible light of all colors except blue strikes our eyes. Orange andblue are complementary colors; the removal of blue from white light makes the light look orange, and viceversa. Thus, an object has a particular color for one of two reasons: It transmits light of only that color orit absorbs light of the complementary color.



Figure 4.1

Complementary colors can be determined using an artist's color wheel. The wheel shows the colors ofthe visible spectrum, from red to violet. Complementary colors, such as orange and blue, appear as wedgesopposite each other on the wheel.

With our eye, we can make qualitative judgments about the color(s) of light a sample absorbs. However,

given a red solution of [Ti (H2O)6 ]3+ we can not determine if it absorbs green light or if it absorbs allcolors of light but red. To quantitatively determine the amount of light absorbed by a sample as a functionof wavelength, we will measure its absorption spectrum using a UV-visible spectrophotometer. Typicalabsorption spectra of aqueous [Ti (H2O)6 ]3+ solutions are shown below.


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No-tice the absorption maximum is at 490 nm. Because the sample absorbs more strongly in the green and yellowregions of the visible spectrum, it appears red-violet. Measuring the absorption spectrum of a second, moredilute solution demonstrates that the spectrum changes as a function of the concentration of the solution.To understand how to use the absorption spectrum as a quantitative tool for chemical analysis, read on!

Spectrophotmetric BasicsThe essential components of a spectrophotometer consist of a radiation source, a wavelength selector

(monochromator), a photodetector and read-out device.



Figure 4.2

The incident light from a tungsten (visible light source) or deuterium (UV light source) lamp is focusedby a lens and passes through an entrance slit. By passing the beam through the monochromator (either aprism or a di�raction grating) it is separated into monochromatic (i.e., one-color or single-wavelength) light.One particular wavelength of monochromatic light is selected and allowed to pass through the exit slit intothe sample. Light transmitted through the sample is detected by a photodetector which converts the signalto an electrical current which is measured by a galvanometer and sent to a recording device, typically acomputer.

The measurement of transmittance (T) is made by determining the ratio of the intensity of incident (I0) and transmitted (I) light passing through pure solvent and sample solutions as a function of wavelength.[Note: The percent transmittance (%T) is obtained by multiplication of T by 100.] The logarithm of thereciprocal of the transmittance is called the absorbance (A),

A = log (1 / T)Care must be taken when small values of transmittance are being measured as stray light from either the

room or scattering within the instrument can cause large errors in your readings!

4.1.4.1 Extracting Quantitative Information

The Beer-Lambert law relates the amount of light being absorbed to the concentration of the substanceabsorbing the light and the pathlength through which the light passes:

A = εbc.In this equation, the measured absorbance (A) is related to the molar absorptivity constant ( ε), the path

length (b), and the molar concentration (c) of the absorbing. The concentration is directly proportional toabsorbance.

The single largest application of the spectrophotometer is for quantitative analysis. The prerequisite forsuch analysis is a known absorption spectrum of the compound under investigation. Of particular importanceis the maximum absorption (at λmax) [Why choose the maximum? Could the choice alter the precision ofour experiment? the accuracy?], which can be easily obtained by plotting absorbance vs. wavelength at a�xed concentration. Next, a series of solutions of known concentration are prepared and their absorbance is


29

measured at λmax. Plotting absorbance vs. concentration, a calibration curve can be determined and �t usinglinear regression (least-squares �t). An unknown concentration can be deduced by measuring absorbance atthe absorption maximum and comparing it to the standard curve. Caution: The Beer-Lambert Law is onlyobeyed (the standard curve is linear) for reasonably dilute solutions. Only those points in the linear rangeof the standard curve may be used for accurate concentration determination.

Typical results are shown for the absorbance of [Ti (H2O)6 ]3+ measured at 490 nm.

Concentration (mg/mL) %Transmittance Absorbance

0 100. 0

1 50.0 0.301

2 25.0 0.602

3 12.5 0.903

Table 4.1

Figure 4.3

Over the studied range the solutions obey Beer's Law. If a solution has a measured absorbance of 0.450,we can calculate its concentration to be 1.5 mg/mL.

4.2 Experimental Procedure

In this experiment, each lab pair will measure the absorbance of CuSO4 at six concentrations. You willcreate a calibration curve to correlate copper sulfate concentration to absorbance. This curve will be usednext week to determine the concentration of an unknown copper sulfate solution and, in turn, the percentyield of a series of chemical reactions.

Materials CuSO4 · 5H2O distilled water pipette bulb 1cm cuvette 4 - 25 mL volumetric �ask for yourdilutions

Note: You will be borrowing these and must collect them from your TA. Do not forget to return the �askat the end of the lab). All students will lose 3 points in that lab section if any go missing!

100 mL volumetric �ask for the parent solution (in your drawer)10 mL volumetric pipette or 10 mLgraduated cylinder



1. Measure out an appropriate mass of CuSO4 · 5H2O to get 100ml of ∼0.1M solution and record themass on your report form. Show your calculation to the TA before making the solution. This is yourparent solution. Calculate the molarity using the actual mass measured and record it.

2. Do the following dilutions and calculate the concentrations for each.

Dilution (ml parent : ml total)

0:25 (DI H2O)

5:25

10:25

15:25

20:25

25:25 (parent solution)

Table 4.2

1. Measure the absorbance of the 6 solutions you have prepared and the unknown given to you by yourTA.

4.2.1 Analysis

Plot the concentration as a function of absorbance for your six solutions. Perform a linear regression analysisand determine the equation of a best-�t line.


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4.3 PreLab: Spectrophotometry and Data Analysis � Beer's Law

Hopefully here2 for the Pre-LabName(Print then sign): ___________________________________________________Lab Day: ___________________Section: ________TA__________________________This assignment must be completed individually and turned in to your TA at the beginning of lab. You

will not be allowed to begin the lab until you have completed this assignment.In many of the experiments that you will do throughout the duration of this course you will be asked

to analyze your data by making plots and calculating the best �t line through your data. One programcommonly used to analyze data in this fashion is Microsoft Excel ®. The following exercise will help youthrough the process used to obtain a plot and linear regression for a set of data.

Suppose you go for a 5 mile run and you tabulate the after each mile as in the following table.

Distance Traveled (miles) Time (sec)

1 510

2 1026

3 1548

4 2077

5 2612

Table 4.3

4.3.1 Questions:

1. Plot the distance traveled in miles vs. the time in seconds.2. Use linear regression to obtain a trendline and give the equation obtained in terms of the variables

distance traveled and time and the R-squared value. Comment on the meaning of the R-squared valueand its signi�cance when doing data analysis.

3. Using the equation you obtained by doing linear regression, estimate how long the 6th mile will takeyou to run.

4. Assuming this linear trend persists, how far have you run if you �nish in 2900 sec.

EXCEL INSTRUCTIONS:

• In order to plot this data in excel, you should enter the data exactly as above in to column A (rows1-6) and column B (rows 1-6).

• To plot the data you will need to go to Insert on the tool bar and then click Chart. A Chart Wizardwill appear. Select XY(Scatter) as the Chart type and choose the sub-type that does not have anylines connecting the points, then click next.

• On Step 2, click on the series tab near the top of the screen and click Add.• You do not need to name the series unless you have multiple plots on one graph, but you can type in

a name if you wish.• To insert the X data, click on the icon at the far left of the x series box.• Select the x values by clicking on the �rst one and while the left mouse button is down dragging the

mouse down to the last value.• When the values have been selected click the icon again and repeat for the y values. You may also

manually enter the values by separating them with a comma. Don't forget you need to remember whatunits you are using when answering questions.

2http://cnx.org/content/m15131/latest/BeersPreLab07.doc



• Click next when you have x and y values entered correctly.• The next step is just entering title information and changing the appearance of your plot; click next

when �nished.• Choose your chart location and then �nish. You now need to place a linear regression line on your

plot.• Right click on a data point and pick add trendline.• Choose linear as the type and click the options tab.• Check the boxes to get the equation and R-squared value and click ok.


Chapter 5

Hydrogen and Fuel Cells1

5.1 Hydrogen and Fuel Cells Experiment

5.1.1 Objective

• Build a fuel cell in order to appreciate practically a range of important chemical and physical principles,such as galvanic cells, energy conversion, energy quality, combustion reactions, water electrolysis andbio-fuels.

• Crituique the design in order to improve the e�ciency of the fuel cell and to accomplish it practically

5.1.2 Grading

• Pre-lab (10%)• Lab Report (80%)• TA points (10%)



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34 CHAPTER 5. HYDROGEN AND FUEL CELLS

5.1.3 Before Coming to Lab. . .

• Read the lab instructions

5.1.4 Introduction

As the world's reserves of fossil fuels are diminishing and our awareness of environmental protection isincreasing, we strive to develop alternative ways of energy production. Thus in many countries research intoconstruction of stable and e�cient fuel cells has been given high priority. Indeed, President Bush in hisJanuary 28th 2003 State of the Union address, proposed a $1.2 billion fuel-cell research and developmentprogram.

Fuel cells are used for direction conversion of the energy of combustion reactions to electrical energy. Apossible fuel is hydrogen, which can be produced from water in electrolysis plants driven by solar cells orwindmills. A future interesting fuel source for operation fuel cells might be �bio-fuels� i.e fuels produced fromnon-fossil organic material such as methane from biogas plants, alcohol produced by fermentation of sugaror hydrolyzed starch (or, in the not so distant future, perhaps also from enzymatically hydrolyzed cellulose).

Conventional power plants turn approximately 40% of the fuel energy into electricity; we say that thee�ciency of the plant is 40%. (Although, in some modern plants surplus heat is reused for district heatingthus increasing the actually e�ciency somewhat). However, with fuel cells the e�ciency of chemical-to-electric energy conversion is unsurpassed, namely about 70% (or even high in some experimental plants).

U.S. energy dependence is higher today than it was during the �oil shock� of the 1970's, and oil importsare project to increase. Passenger vehicles alone consume 6 million barrels of oil every day, equivalent 85%of oil imports.

• If just 20% of cars used fuel cells, we could cut oil imports by 1.5 million barrels a day.• If every new vehicle sold in the U.S. next year was equipped with a 60kW fuel cell, we would double

the amount of the country's available electricity supply.• 10,000 fuel cell vehicles running on non-petroleum feul would reduce oil consumption by 6.98 million

gallons per year.

Fuel cells could dramatically reduce urban air pollution, decrease oil imports, reduce the trade de�cit andproduce American jobs. The U.S. Department of Energy projects that if a mere 10% of automobiles nation-wide were powered by fuel cells, regulated air pollutants would be cut by one million tons per year and 60million tons of the greenhouse gas carbon dioxide would be eliminated. DOE projects that the same numberof feel cell cars would cut oil imports by 800,000 barrels a day � about 13% of total imports. Since fuel cellsrun on hydrogen derived from a renewable source, the fuel cell emissions will be nothing but water vapor.

5.2 The Chemistry of a Fuel Cell

A fuel cell is a galvanic cell in which electricity is generated by a combustion reaction. The fuel cell consistsof two electrodes between which electrical contact is established by means of an electrolyte. Oxygen or justplain atmospheric air is fed continuously to the cathode and the fuel is fed continuously to the anode.

The fuel could be any of a vast number of combustible materials, e.g. methane, ethane or ethanol (allorganic fuels) hydrogen, hydrazine or sodium borohydride (inorganic fuels). With the hydrogen burning cellas an example we can describe the chemistry of the cell by the following reactions:

Anode � at which oxidation of the fuel takes place:H2 + 2OH- -> 2H2O + 2e-Cathode � at which reduction of oxygen takes places½ O2 + H2O + 2e- -> 2OH-The next reaction for the cell:H2 + ½ O2 -> H2O


35

With ethanol as the fuel the matter becomes somewhat more complicated, since ethanol is oxidized insteps to ethanal, ethanoic acid and carbon dioxide respectively. In an ideally working fuel cell we assumethat ethanal and ethanoic acid are further oxidized so that the only carbon compound of the overall processis carbon dioxide. We have not succeed ( by simple chemical tests) to detect either ethanol or ethanoic acid(or rather ethanoate due to the strongly basic electrolyte solution) as intermediate products in our own cells.However we still suggest a three-step oxidation of ethanol(and at the same time admitting that the last stepis dubious):

Anode:Step 1: CH3CH2OH + 2 OH- -> CH3CHO + 2 H2O + 2e-Step 2: CH3HO + 2 OH- -> CH3COOH + H2O + 2 e-Step 3: CH3COOH +8 OH- -> 2 CO2 + 6 H2O + 8 e-Sum: CH3CH2OH + 12OH- -> 2 CO2 + 9 H2O + 12 e-Cathode:3O2 + 6 H2O + 12 e- -> 12OH-Overall reaction:CH3CH2OH + 3O2 -> 2CO2 + 3H2OSodium borohydride can power a cell in either a direct or indirect manner. Indirectly sodium boroydride

will decompose in water to produce NaBO2 (borax) and hydrogenNaBH4 + 2H2O -> NaBO2 + 4H2This hydrogen will then fuel the cell as shown above. However, sodium borohydride can directly power

a cell with higher energy yields.Anode:NaBH4 + 8OH- -> NaBO2 + 6H2O + 8e-Cathode:2O2 + 4H2O + 8e- -> 8OH-While sodium borohydride costs ∼$50 per kilogram, it has projected that mass production and borax

recycling could reduce that price to as low as $1 per kilogram.

5.3 Experimental

5.4 Caution!!! Plastic can burn.

To get good results, very careful measurements are required. Be sure to wear suitable eye protection.Materials:

• 2X 50-60mL disposable hypodermic syringes without needles and pistons.• 3X pieces of nickel net (2 cut to cover the �anges of the syringe cylinders approximately 2cm X 10cm

+ 1 extra piece) The net should be a very �ne mesh.• 2X machine screws with nuts and waters (all brass)• 2X 20cm pieces of insulated 1mm copper wire with ∼1.5cm insulation removed from each end• Heating plate• Aluminum plate 4-6mm thick with 7-8mm hole drilled through center• Baking paper• Screwdriver, drill, spanner, �at bit, scissors, wooden board and small saw• tape• Lab stand with clamps• 600mL beakers• 1.5V electric motor• Red LED• digital mulitimeter• balloons



• electrical leads with alligator clips• 1M sodium hydroxide solution• 4M nitric acid• ethanol• methanol• Palladium chloride solution (very expensive and should be recycled)• NaBH4• Oxygen gas• Hydrogen gas

Building an electrode (each group should build 2)

• Cut a piece of nickel mesh to cover the �ange of the syringe cylinder completely• Place an aluminum plate on a heating plate. Place the baking paper on the Al plate and the nickel

net on the paper.• Heat the plate to a temperature that will melt the plastic but not burn it.• 4. Place the �ange of the syringe on the nickel net on the heating plate. Press down �rmly so that the

nickel net is melted onto the �ange. Make sure that the net is sealed tight to the whole of the �angesurface, but take care not to melt so much plastic that the cylinder hold itself is covered with moltenplastic.

• Remove the syringe and net form the eating plate and allow to cool.• At one of the sides of the �ange drill a hole through the �ange using the electric drill. Place a piece

of wood beneath to prevent drilling into the lab bench. (see picture) Push the machine screw throughthe hole and fasten using a washer and nut. (see picture)

• Mount a piece of insulated copper wire around the machine screw by twisting an end into a loop with a�at bit and fastening it with the nut. Tighten it so that good electrical contact is established betweenthe wire and the nickel net. Use tape to attach the wire to the syringe cylinder.

• Cut o� excess nickel net around the �ange.• Clean the nickel net by immersing the electrode in 4M nitric acid for at least �ve minutes. Also clean

the extra piece of nickel net in this manner. This much be carried out in the fume hood since poisonous�umes may evolve. Rinse thoroughly with water.

• Place the nickel net of the electrode in a solution of palladium chloride for 30 minutes and then gentlyrinse with water. Be sure to put the extra piece of nickel net in the palladium chloride solution as well.The electrode is now ready. You should have something that resembles the picture.


37

Figure 5.1

Figure 1: Drilling holes in �ange.



Figure 5.2

Figure 2: Wire connection assembly.


39

Figure 5.3Available for free at Connexions <http://cnx.org/content/col10456/1.16>


Figure 3: Final assembled cellBuilding the cell

• First cut top o� of one of the syringes. This will be the electrode you introduce the liquid/solid fuel.• Place your two electrodes into a 600mL beaker containing 1M NaOH solution. The nickel meshing

should be completely submerged in solution.• Fill a balloon with oxygen gas (from gas cylinder) and connect using rubber hosing to the syringe that

was not cut. The oxygen may bubble slowly through the syringe.• Roll up the extra piece of nickel mesh and place into the cut syringe.• Add ∼20mg of NaBH4 to the syringe with the extra piece of nickel mesh. If time permits you may test

other fuels later.

Figure 5.4

Figure 4: Functional cell layout.Testing the cell

• Measure the voltage generated by your cell by taking a digital multimeter and setting it to DC voltage.


41

Connect one probe to each wire of the cell. The reading may continue to grow for a while and thenstabilize. Record this stable voltage. It should read between 0.8V-1V.

• Measure the current your cell sources by keeping the probes connected and switching to current mode.This reading should be between 30mA-50mA.

Powering an LED

• One fuel cell does not generate enough voltage to power anything of interest. Just like you wouldconnect 2 or 4 AA batteries in series to power a portable CD player, it is necessary to connect multiplefuel cells to generate larger voltages.

• Pair up with another group and connect the positive terminal of one cell to the negative terminalof the other cell using the wires with alligator clips. Now connect the unwired positive terminal tothe positive (longer lead) of the red LED. The unwired negative terminal should be connected to thenegative (short lead) of the red LED. At this point the LED should be lit. If you do not see any light,you should use the multimeter to check the voltage generated by the two cells in series and verifythat it is greater that 1.5V. If you do not measure any voltage verify that you have wired everythingcorrectly.

Figure 5.5



Figure 5.6

Figure 5: Powering an LED circuit.Powering a small motor

• While two cells in series generate the proper voltage to operate the motor, they cannot source enoughcurrent to run a motor longer than a few seconds. By putting cells in parallel more current can beobtained.

• You will need two sets of two cells in series as described in the �Powering an LED� section (4 groupsare needed for this part).

• Take the positive connection from each series cell and connect to one terminal of the electric motor.Take the negative connection from each series cell and connect to the other terminal on the electricmotor. At this point the motor shaft should begin to turn. If not, check the wiring and verify thatyou are applying at least 1.5V. It is also possible that 2 parallel cells will not generate enough current.Additional cells can be added in parallel to generate more current.


43

Figure 5.7

Figure 6: Powering a motor circuit.



5.4.1 Pre-Lab: (Total 10 Points)

Name(Print then sign): ___________________________________________________Lab Day: ___________________Section: ________TA__________________________This assignment must be completed individually and turned in to your TA at the beginning of lab. You

will not be allowed to begin the lab until you have completed this assignment.1.Fill in the blanks:Fuel cells are used for direction conversion of the energy of combustion reactions to

______________. A fuel cell is a ______________ in which electricity is generated by acombustion reaction. A fuel cell provides a ______________ voltage that can be used to powermotors, lights or any number of electrical appliances.

2.T or F At the anode, oxidation of the fuel takes place.3.T or F The fuel cell emissions will be nothing but water vapor.4.T or F The e�ciency of fuel cells, chemical-to-electric energy conversion, is approximately 40%.Review of series and parallel circuits:In a series circuit, the electrons in the current have to pass through all the components, which are

arranged in a line. Consider a typical series circuit in which there are three resistors of value R1, R2, andR3.

Figure 5.8

There are two key points about a series circuit:

• The current throughout the circuit is the same.• The voltages add up to the battery voltage.

Therefore:VT = V1 + V2 + V3From Ohm's Law:

• VT = IRT;• V1 = IR1;• V2 = IR2;• V3 = IR3

Þ IRT = IR1 + IR2 + IR3Therefore:RTot = R1 + R2 + R35.In the circuit below, the current is 100 mA.


45

Figure 5.9

(a) What is the current in each resistor?(b) What is the voltage across each resistor?(c) What is the total resistance?(d) What is the battery voltage?

Figure 5.10

Parallel circuits have their components in parallel branches so that an individual electron can go throughone of the branches but not the others. The current splits into the available number of branches.

In this case, the current will split into three. For a parallel circuit:

• The voltage across each branch is the same.• The currents in each branch add up to the total current.

From this:Itot = I1 + I2 + I3From Ohm's Law: I T = V ; I1 = V; I2 = V; I3 = VRT R1 R2 R3Þ V = V + V + VRT R1 R2 R3Þ 1/RTot = 1/R1 + 1/R2 + 1/R36.This question refers to the circuit below.



Figure 5.11

(a) What is the total resistance of the circuit?(b) What is the current through each resistor?(c) What is the total current?

Figure 5.12

For resistors in both series and parallel, follow these guidelines:

• Work out the total resistance of the parallel combination.• Work out the total resistance of the circuit by adding your answer in the previous step to the values

of the series resistors.

7.What is the single resistor equivalent of this circuit?


47

5.4.2 Report (80 points)

Note: In preparing this report you are free to use references and consult with others. However, you maynot copy from other students' work (including your laboratory partner) or misrepresent your own data (seehonor code).

The following tables and questions should be answered in your written report. Please put the informationin the relevant section of your report (i.e. observations and results, discussion)

What would happen if zinc screws were used instead of brass?What is the purpose of the palladium coating on the anode?What is the purpose of the palladium coating on the cathode?What fuel cell worked best?Explain, in detail, why you think that the best fuel cell worked better than the others?Debate fuel cells.


Chapter 6

The Best Table in the World1

6.1 The Best Table in the World!

6.1.1 Objective

The goals of this experiment are:

• to observe the reactions of several metals with cold water, hot water, acids and then other metal ions.• to prepare an activity series of the metals based on the observations from the above reactions.

6.1.2 Grading

You will be assessed on:

• observations of the reactions of several metals with cold water, hot water, acids and then other metalions.

• preparation of an activity series of the metals based on the observations from the above reactions.• answers to the post-lab questions.

6.1.3 Background Information

First, you are going to travel back to 1869 and marvel at how the �rst periodic law and table were bornwhen only 63 elements had been discovered at the time. A 35 year old professor of general chemistry, DmitriIvanovich Mendeleev at the University of St. Petersburg (now Lennigrad) in Russia was shu�ing his cardswith the properties of each element on each card trying to organize his thoughts for his soon-to-be famoustextbook on chemistry. When he realized that if the elements were arranged in the order of their atomicweights, there was a trend in properties that repeated itself several times! His paper was delivered by hisgraduate student, Nikolai Aleksandrivich Menchutkin before the Russian Chemical Society while Medeleevwas busy visiting cheesemaking cooperatives at the time!

In order to see and �nd order among the elements, we must have some general acquaintance with them.Elements are made of matter, and matter is de�ned as anything that has mass and occupies space. Thisincludes everything that you can see and a lot that you cannot. It follows that in order to distinguish betweendi�erent types of matter (in other words di�erent elements) we have to assess their properties.

There are two types of properties: intensive and extensive. In the former case, intensive properties donot depend on the how much of an element is present but do include state (whether a substance is a solid,



49

50 CHAPTER 6. THE BEST TABLE IN THE WORLD

liquid or gas), color and chemical reactivity. Extensive properties depend on the quantity of matter present- mass and volume are extensive properties.

Properties can be further categorized as either chemical or physical. A chemical change describes howthe substance may change composition, such as spontaneously by combustion or in combination with othersubstances. On the other hand, physical changes are those properties that can be measured without changingthe composition of the matter. Condensation of steam to water is a physical change.

6.1.4 Introduction

What is there to know about the periodic table? Why is it important? Why does it appear in nearly everyscience lecture room and labs? Is it just a portrait of an aspect of chemistry or does it serve a useful purpose?Why is the name periodic appropriate? Why is the table arranged in such a way? What are the importantfeatures of the table? Does it give order to the approximately 120 known elements?

6.2 Relative Reactivity of Metals and the Activity Series

A super�cial glance at the Periodic Table will reveal that all known elements are listed by their chemicalsymbols. An in depth glance at the Periodic Table yields information on the mass of an atom of the elementin atomic mass units (amu) for the molar mass of a mole ( 6.02×1023) of atoms in grams below the chemicalsymbol for each element. Above the chemical symbol for each element, there is a second number listed,the atomic number, which gives the number of protons (positively charged particles in the nucleus), or thenumber of electrons (negatively charged outside the nucleus) for a neutral atom.

Mendeleev arranged the elements in the Periodic Table in order of increasing atomic number in horizontalrows of such length that elements with similar properties recur periodically; that is to say, they fall directlybeneath each other in the Table. The elements in a given vertical column are referred to as a family orgroup. The physical and chemical properties of the elements in a given family change gradually as one goesfrom one element in the column to the next. By observing the trends in properties, the elements can bearranged in the order in which they appear in the Periodic Table.

6.3 Procedure

6.3.1 I. Activity Series

6.3.1.1 Part 1. Reactions of Metals with Water

CAUTION! Sodium reacts very rapidly with water to evolve hydrogen and heat. This is potentially dangerousbecause of the possibility of the violent explosive reaction of H2 (g) with O2 (g) present in the air.

CAUTION! Sodium causes severe chemical burns when it comes into contact with the skin. Note: Metallicsodium must be stored below the surface of an inert liquid such as kerosene to prevent oxidation by air.

1. I will demonstrate the reaction of sodium and then potassium with water. Observe the rate of evolutionof H2 gas as I use tweezers to place a tiny pea-size piece of sodium then potassium into a 500-mL beakerfull of deionised water. Record your observation on the Report Form and write a balanced equationfor this reaction.

2. Place 5 mL H2O in each of four clean tubes and label them as follows:

A. Mg

B. Cu

C. Zn

D. Ca


51

Table 6.1

1. Use sandpaper or steel wool to remove the oxide from the surfaces of Mg, Cu, and Zn.2. Place several small pieces of Mg, Cu, and Zn in the correctly labeled test tube prepared above. Place

two or three (not more!) pieces of Ca turnings in the test tube labeled "Ca".3. Watch for evidence of reaction by noting evolution of gas bubbles and any change in the color or size

of the metal. Record your observations and write net ionic equations for each reaction.

Note: Trapped air bubbles on the metal surfaces are not indicative of a reaction.CAUTION: H2 is FLAMMABLE!CAUTION: Residual calcium should be discarded in a special container designated by your instructor.Note: Net ionic equations must balance in mass (atoms) and in total charge on each side of the equation.

6.3.1.2 Part 2. Reactions of Metals with HCl

CAUTION: The reaction of Ca with HCl is not studied. Residual calcium should be discarded in a specialcontainer designated by your instructor.

1. Decant the water from each test tube used in the procedure above and leave the pieces of metal thatremain unreacted in each test tube.

2. Place the test tubes in a test tube rack/holder.3. Add 2 mL of 3 M HCl solution to each test tube.

CAUTION: Some of the test tubes may become very hot. Leave them in the rack/holder while you aremaking observations.

1. Observe relative rate of H2 gas evolution for up to 10 minutes and record your observations on yourreport form.

2. Based on the observations in the previous steps, list the elements that react in 3M HCl in order ofincreasing strength as reducing agents and write net ionic equations for all reactions.

6.3.1.3 Part 3. Reactions of Metals with Other Metal Ions

1. Place a clean 1 inch-square of metal foil (sheet) of each of these metals Cu, Zn and Pb on a �at surface.2. Clean the metal surfaces by sanding them with �ne sandpaper or steel wool.3. Place one or two drops in spots of each of these solutions in a clockwise order on the metal surfaces:

A. 0.5 M Ag+

B. 0.5 M Cu2+

C. 0.5 M Zn2+

D. 0.5 M Pb2+

Table 6.2

1. NOTE: Do not test a cation of a metal on a square of the same metal such as Cu2+ ion and Cu metal.2. Watch for color changes in each spot as evidence of reaction. If you are not sure whether the reaction

has occurred, rinse the plate with water. A distinct spot of a di�erent color on the surface is goodevidence for the reaction.

3. Write net ionic equations for each reaction . Arrange Ag, Cu, Pb and Zn in order of their increasingstrength as reducing agents. If a metal A reacts with a cation of another metal B, metal A is a strongerreducing agent, more reactive than metal B.

4. Rinse and dry each square of metal and return it to the correct beaker on the reagent shelf for otherstudents to use.



6.3.1.4 Part 4. Flame Tests

6.3.1.5 One station set up that all sections will rotate through

Clean a spatula wire by dipping it into dilute hydrochloric acid (3M) and then holding it in a hot Bunsen�ame. Repeat this until the spatula doesn't produce any color in the �ame.

When the spatula is clean, moisten it again with some of the acid and then dip it into a small amount ofthe solid you are testing so that some sticks to the spatula. Place the spatula back in the �ame again.

If the �ame color is weak, it is often worthwhile to dip the spatula back in the acid again and put it backinto the �ame as if you were cleaning it. You often get a very short but intense �ash of color by doing that.

Chemicals/Materials:

1. Chloride salts of Li, Na, K, Rb, Cs, Ca, Ba, Cu, Pb, Fe (II) and Fe(III) Sr (nitrate salt).2. Glass rods with loops of Pt wire.3. Bunsen burner/clicker.4. Concentrated nitric acid or hydrochloric acid.

Record your observations on your report form.It should be noted that sodium is present as an impurity in many if not most metal salts. Because sodium

imparts an especially intense color to a �ame, �ashes of the sodium may be observed in nearly all solutionstested.


53

6.4 Pre-Lab 5: The Best Table in the World!

Hopefully here2 for the Pre-LabName(Print then sign): __________________________________________________Lab Day: ___________________Section: ________TA________________________This assignment must be completed individually and turned in to your TA at the beginning of lab. You

will not be allowed to begin the lab until you have completed this assignment.

1. The mass of an atom of the element in atomic mass units (amu) for the molar mass of a mole (6.02 × 1023) of atoms in grams above or below the chemical symbol for each element? Circle thecorrect one.

2. The second symbol listed for each element is the _______ __________, symbol________? Fill in the blanks.

3. The number in question 2 gives the number of

• ____________ or• the number of ________________ for a neutral atom. Fill in the blanks

4. The elements in a given vertical column are referred to as a _________ or __________. Fillin the blanks.

5. The horizontal rows are called __________? Fill in the blank6. The block of elements between groups II and III are called ___________ _________? Fill

in the blanks.7. Elements 58 to 71 are known as ____________ or __________________? Fill in the

blanks.8. Elements 90 to 103 are known as _________ ____________? Fill in the blanks.9. Do elements with larger atomic numbers than 92 occur naturally? True or false? Circle the correct

one.

6.5 Report 5: The Best Table in the World!

Hopefully here3 for the Report FormNote: In preparing this report you are free to use references and consult with others. However, you may


Name(Print then sign): __________________________________________________Lab Day: ___________________Section: ________TA________________________

2http://cnx.org/content/m15206/latest/PreLabTable07.doc3http://cnx.org/content/m15206/latest/ReportTable07.doc



6.5.1 I. Activity Series

6.5.1.1 Part 1. Reactions of Metals with Water

Metal Observations Net Ionic Equations (If NoReaction Occurs, write N.R)

Na

K

Mg

Cu

Zn

Ca

Table 6.3

6.5.1.2 Part 2. Reactions with HCl

Metal Observations Net Ionic Equations (If No Reaction Occurs, Write N.R.)

Mg

Cu

Zn

Table 6.4

2. Based on your experimental results place Mg, Cu, Zn and Ca in order of increasing strength as reducingagents.

6.5.1.3 Part 3. Reactions with Other Metal Ions

1. Write in the appropriate box either �REACTION� or �NO REACTION�.

Zn Cu Pb

Ag+

Cu2+ Do not test

Zn2+ Do not test

Pb2+ Do not test

Table 6.5

2. Write balanced equations to represent the results tabulated above.3. Based on your experimental results, arrange Ag, Cu, Zn and Pb in order of increasing strength as

reducing agents.4. Arrange Ag+, Cu2+, Zn2+ and Pb2+ in order of increasing strength as oxidizing agents.5. Combine the results from Part 2 and Part 3. Arrange Mg, Cu, Zn, Ca, Ag and Pb in order or

increasing strength as reducing agents.6. Place Ni in this row, if it is found that Ni will deposit on Zn foil, but not on Pb foil when a drop of

NiSO4 is placed on both.


55

6.5.1.4 Part 4. Flame Tests

Element Color in �ame

Li

Na

K

Rb

Cs

Ca

Sr

Ba

Cu

Pb

Table 6.6

What are the limitations of this test?


Chapter 7

Bonding 071



57

58 CHAPTER 7. BONDING 07

7.1 Lab 5: Bonding 07

7.2 Objective

• To test various compounds and determine their conductivity and bonding.• To understand how electronegativity can predict bond type.• To learn the relationship between bonding and conductivity.

7.3 Grading

• Pre-Lab (10%)• Lab Report Form (80%)• TA Points (10%)

7.4 Background Information

A chemical bond is a link between atoms that results from the mutual attraction of their nuclei for electrons.Bonding occurs in order to lower the total potential energy of each atom or ion. Throughout nature, changesthat decrease potential energy are favored.

The main types of bonds that we will be covering are ionic bonds, covalent bonds, and metallic bonds.An ionic bond is the chemical bond that results from the electrostatic attraction between positive (cations)and negative (anions) ions. The ionic relationship is a �give and take� relationship. One ion donates or�gives� electrons, while the other ion receives or �takes� electrons.

A covalent bond is a chemical bond resulting from the sharing of electrons between two atoms. There aretwo main types of covalent bonds. The �rst being non-polar covalent bonds. These are bonds in which thebonding electrons are shared equally by the united atoms-with a balanced electrical charge. Polar covalentbonds are covalent bonds in which the united atoms have an unequal attraction for the shared electrons.


59

Figure 7.1

The role of electrons in bonding has been well-studied. The ability of an atom or element to attractelectrons to itself is known as the element's electronegativity. A scale was �rst calculated by the Nobel lau-reate Linus Pauling and is commonly called the Pauling electronegativity scale. The actual electronegativityvalues aren't as important as how they compare to a di�erent element. In Part I of today's experiment, youwill compare electronegativity values to predict the type of bond that will exist between two elements.

In the solution state, ionic compounds dissociate to give a separation of charge. The separation of chargeallows for the �ow of electrons through solution. The �ow of electrons is classi�ed as conductivity. A strongelectrolyte is a compound that when dissolved in water will completely ionize or dissociate into ions. Thatis, the compound exists in water only as individual ions, and there are no intact molecules at all. Thissolution conducts electricity well. A weak electrolyte is a compound that when dissolved in water onlypartially ionizes or dissociates into ions. That is, the compound exists in water as a mixture of individualions and intact molecules. This solution conducts electricity weakly. A nonelectrolyte is a compound thatwhen dissolved in water does not ionize or dissociate into ions at all. In water, this compound exists entirelyas intact molecules. The solution does not conduct electricity at all. By measuring the conductivity ofa dissolved compound, we can classify it as a nonelectrolyte, weak electrolyte, or strong electrolyte anddetermine its ability to dissociate into ions. There are four common compounds that you will encounter intoday's lab.

ACIDS are molecular compounds which ionize (turn into ions) in water. The cation that is formed isalways H+. Therefore, in the formulas for simple acids, H is always the �rst element listed. Some acidsare strong electrolytes and some acids are weak electrolytes. There are no acids which are nonelectrolytesbecause by de�nition an acid is a H+ donor.

BASES can be molecular compounds or ionic compounds. Some bases are soluble and some are not. The



soluble bases ionize or dissociate into ions in water, and the anion formed is always OH−. The ionic baseshave hydroxide ( OH− ) as the anion. If they are soluble, the ions simply separate (dissociate) in thewater. All of the ionic bases which are soluble are strong electrolytes.

SALTS are ionic compounds which are not acids or bases. In other words, the cation is not hydrogenand the anion is not hydroxide. Some salts are soluble in water and some are not. All of the salts whichare soluble are relatively strong electrolytes.

NONELECTROLYTES are compounds which dissolve in water but do not ionize or dissociate intoions. These would be molecular compounds other than the acids or bases already discussed.

7.5 Experimental Procedure

Caution:Acids and bases are corrosive and can cause burns.

7.5.1 Part I. Predicting bond type through electronegativity di�erences.

Using the electronegativity table provided in the lab manual, predict the type of bond that each of thefollowing compounds will have by the following process:

• Find the electronegativity for each element or ion in compound using electronegativity table provided.• Subtract the electronegativites (using absolute value).• If values are between:

4.0-1.7�Ionic bond-50-100% ionic1.7-0.3�Polar Covalent bond-5-50% ionic0.3-0.0�Non-Polar Covalent-0-5% ionicDetermine the type of bonding in the following compounds: KCl, CO, CaBr2, SiH4, MgS.


61

Figure 7.2

7.5.2 Part II. Weak and strong electrolytes

7.5.3 Chemicals

• tap water• 0.1 M hydrochloric acid, HCl• 0.1 M acetic acid, HC2H3O2

• 0.1 M sulfuric acid, H2SO4

• 0.1 M sodium hydroxide, NaOH• 0.1 M ammonia, NH3

• 0.1 M sodium acetate, NaC2H3O2

• 0.1 M sodium chloride, NaCl• 0.1 M ammonium acetate, NH4C2H3O2

• 0.1 M ammonium chloride, NH4Cl• methanol, CH3OH• ethanol, C2H5OH



• sucrose solution, C12H22O11

In today's lab, you will be using a MicroLab conductivity probe to determine how well electrons �ow througha given solution. First, you will need to calibrate the probe with a non-electrolyte (distilled water) and avery strong electrolyte. To quantify how well a solution conducts, we will assign numerical values to theconductance probe. A non-conducting solution will have a conductance value of 0, a poor conducting solutionwill have a reading of 0 to 1,000, and good conductors will have readings of 3,000 up.


63

7.5.4 Instructions for MicroLab Conductivity Experiment

Open the MicroLab Program by clicking on the Shortcut to MicroLab.exe tab on the desktop.On the �Choose an Experiment Type� Tab, enter a name for the experiment, and then double click on

the MicroLab Experiment iconClick �Add Sensor�, Choose sensor = Conductivity ProbeChoose an input, click on the red box that corresponds to the port that your conductivity sensor is

connected to. Choose 20,000 microseconds�Choose a Sensor�, click radial button that says Conductivity Probe. Click next.Click �Perform New Calibration�Click �Add Calibration Point� place the conductivity probe in the non-conductive standard solution,

while swirling wait until the value is constant and then enter 0.0 into the �Actual Value� box in MicroLaband hit �ok�.

Again, Click �Add Calibration Point� place the conductivity probe in the conducting standard solution,while swirling wait until the value is constant and then enter 1020 into the �Actual Value� box in MicroLaband hit �ok�. Repeat for 3860 as the Actual Value.

Under Curve Fit Choices , click on �First order (linear)� and then �Accept and Save this Calibration�, whenprompted to �Enter the units for this calibration�, leave as is and click ok, save as your name-experiment-date.Click �nish.

In the sensor area, left click on the conductivity icon and drag it to the Y-axis over �data source two�,also click and drag to column B on the spreadsheet and also click and drag to the digital display window.

When ready to obtain data, click start.This is very important: Be sure to thoroughly since the probe with DI water between every use.Beginning with the tap water, measure the conductance of each of the following solutions. Using the

information provided in the lab manual, classify each solution as a non-, weak, or strong electrolyte. Forthose solutions that are electrolytes, record the ions present in solution.

7.5.5 Part III. Electrolyte strength and reaction rate

7.5.6 Chemicals

• calcium carbonate powder - shake once• 1 M HCl - stopper it• 1 M HC2H3O2

• 0.5 M H2SO4

• Test tube gas collection apparatus - end at 20mL

Measure 2 g of powdered calcium carbonate ( CaCO3) onto a piece of weigh paper. Obtain 30 mL of 1 MHCl in a graduated cylinder. Pour the acid into the test tube apparatus. Add the calcium carbonate to theacid and QUICKLY stopper the tube to begin collecting gas. Record the time it takes to collect 20 mL ofgas. The acid may react very fast with the CaCO3 generating the gas very rapidly. Clean out the test tubeapparatus and repeat the experiment using 1 M HC2H3O2 and 0.5 M H2SO4.

7.5.7 Part IV. Chemical reactions

7.5.8 Chemicals

• 0.01 M calcium hydroxide, Ca (OH)2• Plastic straws

Obtain ∼20 mL of saturated calcium hydroxide solution. Make sure it is clear and colorless. Place theconductivity probe in the solution and begin monitoring it conductivity. With your straw, slowly exhale intothe solution. Note any observations in the solution and the conductivity.



7.6 Pre-Lab 5: Bonding 07

7.7 (Total 10 Points)



7.7.1 Part I. Bonding of chemicals in solution

1. Write out the formulas of the following acids:

• phosphoric ____________________

• perchloric ____________________

• nitric ____________________

• sulfuric __________________

• hydrochloric ____________________

• acetic ____________________

1. Write out the formulas of the following bases:

• calcium hydroxide ____________________

• potassium hydroxide ____________________

• sodium hydroxide ____________________

• ammonia ____________________

1. Write out the formulas of the following salts:

• potassium chromate ____________________

• potassium sulfate ____________________

• copper(II) nitrate ____________________

• calcium carbonate ____________________

• potassium iodide ____________________

2http://cnx.org/content/m15205/latest/PreLabBonding07.doc


65

7.8 Report 5: Bonding 07




7.8.1 Part I. Predicting bond type through electronegativity di�erences.

Chemical Formula Electroneg (1) Electroneg (2) Di� Electroneg Type of bond

KCl

CO

CaBr2

SiH4

MgS

Table 7.1

7.8.2 Part II. Weak and strong electrolytes

Solution Tested Numerical Output Electrolyte Strength Ions Present

0.1 M HCl

0.1 M HC2H3O2

0.1 M H2SO4

0.1 M NaOH

0.1 M NH3

0.1 M NaC2H3O2

0.1 M NaCl

0.1 M NH4C2H3O2

0.1 M NH4Cl

CH3OH

C2H5OH

Sucrose

Tap water

Table 7.2

1. Why do we use deionized water instead of tap water when making solutions for conductivity measure-ments?

3http://cnx.org/content/m15205/latest/ReportBonding07.doc



7.8.3 Part III. Electrolyte strength and reaction rate

2. Time to collect 20 mL of gas using 1 M HCl _______________________. Write the reactionof HCl with CaCO3.

3. Time to collect 20 mL of gas using 1 M HC2H3O2_______________________. Write thereaction of HC2H3O2 with CaCO3.

4. Time to collect 20 mL of gas using 0.5 M H2SO4_________________________.Writethe reaction of H2SO4 with CaCO3.

5. Why does it take di�erent lengths of time to collect 20 mL of gas?6. Based on the time it took to collect 20 mL of gas, rank the acids in the order of increasing strength.7. Why did we use 0.5 M H2SO4 instead of 1.0 M H2SO4?

7.8.4 Part IV. Chemical reactions

8. Write the chemical reaction for calcium hydroxide with your exhaled breath.9. Write your observations for the reaction that took place (i.e. appearance, conductivity, etc.)10. When in separate solutions, aqueous ammonia, NH3(aq) and acetic acid HC2H3O2 conduct electricity

equally well. However, when the two solutions are mixed a substantial increase in electrical conductivity isobserved. Explain.

11. Separately, ammonium sulfate and barium hydroxide solutions are very good conductors. When thetwo solutions are mixed a substantial decrease in conductivity is observed. Rationalize this.


Chapter 8

Solid State and Superconductors1

8.1 Solid State Structures and Superconductors

8.1.1 Objectives

• Build examples of: simple cubic, body centered cubic and face centered cubic cells.• Understand and familiarize with three-dimensionality of solid state structures.• Understand how binary ionic compounds (compounds made up of two di�erent types of ions) pack in

a crystal lattice.• Observe the special electromagnetic characteristics of superconducting materials using 1,2,3-

superconductor YBa2Cu3O8−, discovered in 1986 by Dr. Paul Chu at the University of Houston.

8.1.2 Grading

Your grade will be determined according to the following

• Pre-lab (10%)• Lab report form. (80%)• TA points (10%)

8.1.3 Before coming to lab:

• Read introduction and model kits section• Complete prelab exercise

8.1.4 Introduction

From the three states of matter, the solid state is the one in which matter is highly condensed. In the solidstate, when atoms, molecules or ions pack in a regular arrangement which can be repeated "in�nitely" inthree dimensions, a crystal is formed. A crystalline solid, therefore, possesses long-range order; its atoms,molecules, or ions occupy regular positions which repeat in three dimensions. On the other hand an amor-phous solid does not possess any long-range order. Glass is an example of an amorphous solid. And eventhough amorphous solids have very interesting properties in their own right that di�er from those of crys-talline materials, we will not consider their structures in this laboratory exercise.



67

68 CHAPTER 8. SOLID STATE AND SUPERCONDUCTORS

The simplest example of a crystal is table salt, or as we chemists know it, sodium chloride (NaCl). Acrystal of sodium chloride is composed of sodium cations ( Na+) and chlorine anions ( Cl−) that are arrangedin a speci�c order and extend in three dimensions. The ions pack in a way that maximizes space and providesthe right coordination for each atom (ion). Crystals are three dimensional, and in theory, the perfect crystalwould be in�nite. Therefore instead of having a molecular formula, crystals have an empirical formula basedon stoichiometry. Crystalline structures are de�ned by a unit cell which is the smallest unit that containsthe stoichiometry and the �spatial arrangement� of the whole crystal. Therefore a unit cell can be seen asthe building block of a crystal.

The crystal lattice

In a crystal, the network of atoms, molecules, or ions is known as a crystal lattice or simply as a lattice.In reality, no crystal extends in�nitely in three dimensions and the structure (and also properties) of thesolid will vary at the surface (boundaries) of the crystal. However, the number of atoms located at thesurface of a crystal is very small compared to the number of atoms in the interior of the crystal, and so, to a�rst approximation, we can ignore the variations at the surface for much of our discussion of crystals. Anylocation in a crystal lattice is known as a lattice point. Since the crystal lattice repeats in three dimensions,there will be an entire set of lattice points which are identical. That means that if you were able to makeyourself small enough and stand at any such lattice point in the crystal lattice, you would not be ableto tell which lattice point of the set you were at � the environment of a lattice point is identical to eachcorrespondent lattice point throughout the crystal. Of course, you could move to a di�erent site (a non-correspondent lattice point) which would look di�erent. This would constitute a di�erent lattice point. Forexample, when we examine the sodium chloride lattice later, you will notice that the environment of eachsodium ion is identical. If you were to stand at any sodium ion and look around, you would see the samething. If you stood at a chloride ion, you would see a di�erent environment but that environment would bethe same at every chloride ion. Thus, the sodium ion locations form one set of lattice points and the chlorideion locations form another set. However, lattice points not only exist in atom positions. We could easilyde�ne a set of lattice points at the midpoints between the sodium and chloride ions in the crystal lattice ofsodium chloride.

The unit cell

Since the crystal lattice is made up of a regular arrangement which repeats in three dimensions, we cansave ourselves a great deal of work by considering the simple repeating unit rather than the entire crystallattice. The basic repeating unit is known as the unit cell. Crystalline solids often have �at, well-de�nedfaces that make de�nite angles with their neighbors and break cleanly when struck. These faces lie alongwell-de�ned directions in the unit cell.

The unit cell is the smallest, most symmetrical repeating unit that, when translated in three dimensions,will generate the entire crystal lattice.

It is possible to have a number of di�erent choices for the unit cell. By convention, the unit cell thatre�ects the highest symmetry of the lattice is the one that is chosen. A unit cell may be thought of as beinglike a brick which is used to build a building (a crystal). Many bricks are stacked together to create the entirestructure. Because the unit cell must translate in three dimensions, there are certain geometrical constraintsplaced upon its shape. The main criterion is that the opposite faces of the unit cell must be parallel. Becauseof this restriction there are only six parameters that we need to de�ne in order to de�ne the shape of theunit cell. These include three edge lengths a, b, and c and three angles α, β[U+F02C][U+F020]and γ. Oncethese are de�ned all other distances and angles in the unit cell are set. As a result of symmetry, some of


69

these angles and edge lengths may be the same. There are only seven di�erent shapes for unit cells possible.These are given in the chart below.

Unit Cell Type Restrictions on Unit Cell Param-eters

Highest Type of Symmetry Ele-ment Required

Triclinic a is not equal to b is not equalto c; α[U+F020]is not equal toβ[U+F020]is not equal to γ.

no symmetry is required, an in-versioncenter may be present

Monoclinic a is not equal to b is not equalto c[U+F03B][U+F020][U+F020]α[U+F020]=γ[U+F020][U+F03D][U+F020]90 ◦[U+F020] β[U+F020]is notequal to 90 ◦.

highest symmetry element al-lowed is aC2 axis or a mirrorplane

Orthorhombic a is not equal to b is not equalto c[U+F03B][U+F020][U+F020]α[U+F020]= β[U+F020]=γ[U+F020][U+F03D][U+F020]90 ◦

has three mutually perpendicu-larmirror planes and/or C2 axes

Tetragonal a =b is not equal to c[U+F03B][U+F020][U+F020]α[U+F020]= β[U+F020]=γ[U+F020][U+F03D] 90 ◦

has one C4 axis

Cubic a =b =c[U+F03B][U+F020][U+F020]α[U+F020]= β[U+F020]=γ[U+F020][U+F03D][U+F020]90 ◦[U+F020]

has C3 and C4 axes

Hexagonal, Trigonal a =b is not equal to c[U+F03B][U+F020][U+F020]α[U+F020]= β[U+F020]=90 ◦[U+F02C][U+F020][U+F020]γ[U+F03D][U+F020] 120 ◦

C6 axis (hexagonal); C3 axis(trigonal)

Rhombohedral* a =b =c[U+F03B][U+F020][U+F020]α[U+F020]= β[U+F020]=γ[U+F020]is not equal to 90 ◦

C3 axis (trigonal)

Table 8.1

*There is some discussion about whether the rhombohedral unit cell is a di�erent group or is really asubset of the trigonal/hexagonal types of unit cell.

8.1.5 Stoichiometry

You will be asked to count the number of atoms in each unit cell in order to determine the stoichiometry(atom-to-atom ratio) or empirical formula of the compound. However, it is important to remember that solidstate structures are extended, that is, they extend out in all directions such that the atoms that lie on thecorners, faces, or edges of a unit cell will be shared with other unit cells, and therefore will only contribute a



fraction of that boundary atom. As you build crystal lattices in these exercises you will note that eight unitcells come together at a corner. Thus, an atom which lies exactly at the corner of a unit cell will be sharedby eight unit cells which means that only 1/8 of the atom contributes to the stoichiometry of any particularunit cell. Likewise, if an atom is on an edge, only ¼ of the atom will be in a unit cell because four unit cellsshare an edge. An atom on a face will only contribute ½ to each unit cell since the face is shared betweentwo unit cells.

It is very important to understand that the stoichiometry of the atoms within the unit cell must re�ectthe composition of the bulk material.

8.1.5.1 Binding forces in a crystal

The forces which stabilize the crystal may be ionic (electrostatic) forces, covalent bonds, metallic bonds,van der Waals forces, hydrogen bonds, or combination of these. The properties of the crystal will changedepending upon what types of bonding is involved in holding the atoms, molecules, or ions in the lattice.The fundamental types of crystals based upon the types of forces that hold them together are: metallic inwhich metal cations held together by a sea of electrons, ionic in which cations and anions held together bypredominantly electrostatic attractions, and network in which atoms bonded together covalently throughoutthe solid (also known as covalent crystal or covalent network).

8.1.5.2 Close-packing

Close-packing of spheres is one example of an arrangement of objects that forms an extended structure.Extended close-packing of spheres results in 74% of the available space being occupied by spheres (or atoms),with the remainder attributed to the empty space between the spheres. This is the highest space-�llinge�ciency of any sphere-packing arrangement. The nature of extended structures as well as close-packing,which occurs in two forms called hexagonal close packing (hcp) and cubic close packing (ccp), will beexplored in this lab activity. Sixty-eight of the ninety naturally occurring elements are metallic elements.Forty of these metals have three-dimensional submicroscopic structures that can be described in terms ofclose-packing of spheres. Another sixteen of the sixty-eight naturally occurring metallic elements can bedescribed in terms of a di�erent type of extended structure that is not as e�cient at space-�lling. Thisstructure occupies only 68% of the available space in the unit cell. This second largest subgroup exhibits asphere packing arrangement called body-centered cubic (bcc).

You should be able to calculate the % of void space using simple geometry.

8.1.5.3 Packing of more than one type of ion (binary compounds) in a crystal lattice

A very useful way to describe the extended structure of many substances, particularly ionic compounds, isto assume that ions, which may be of di�erent sizes, are spherical. The structure then is based on sometype of sphere packing scheme exhibited by the larger ion, with the smaller ion occupying the unused space(interstitial sites). In structures of this type, coordination number refers to the number of nearest neighborsof opposite charge. Salts exhibiting these packing arrangements will be explored in this lab activity.

8.1.5.4 Coordination number and interstitial sites

When spherical objects of equal size are packed in some type of arrangement, the number of nearestneighbors to any given sphere is dependent upon the e�ciency of space �lling. The number of nearestneighbors is called the coordination number and abbreviated as CN. The sphere packing schemes with the


71

highest space-�lling e�ciency will have the highest CN. Coordination number will be explored in this labactivity. A useful way to describe extended structures, is by using the unit cell which as discussed above isthe repeating three-dimensional pattern for extended structures. A unit cell has a pattern for the objects aswell as for the void spaces. The remaining unoccupied space in any sphere packing scheme is found as voidspace. This void space occurs between the spheres and gives rise to so-called interstitial sites.

8.1.6 Synthesis of solid state materials

There exist many synthetic methods to make crystalline solids. Traditional solid state chemical reactions areoften slow and require high temperatures and long periods of time for reactants to form the desire compound.They also require that reactants are mixed in the solid state by grinding two solids together. In this mannerthe mixture formed is heterogeneous (i.e. not in the same phase), and high temperatures are required toincrease the mobility of the ions that are being formed into the new solid binary phase. Another approachto get solid state binary structures is using a precursor material such as a metal carbonate, that upondecomposition at high temperatures loses gaseous CO2 resulting in very �ne particles of the correspondingmetal oxide (e.g., BaCO3(s) → BaO(s) + CO2(g)).

8.1.7 X-ray crystallography

8.1.8

To determine the atomic or molecular structure of a crystal di�raction of X-rays is used. It was observedthat visible light can be di�racted by the use of optical grids, because these are arranged in a regularmanner. Energy sources such as X-rays have such small wavelengths that only �grids� the size of atoms willbe able to di�ract X-rays. As mentioned before a crystal has regular molecular array, and therefore it ispossible, to use X-ray di�raction to determine the location of the atoms in crystal lattice. When such anexperiment is carried out we say that we have determined the crystal structure of the substance. The studyof crystal structures is known as crystallography and it is one of the most powerful techniques used todayto characterize new compounds. You will discuss the principles behind X-ray di�raction in the lecture partof this course.

8.1.9 Superconductors

A superconductor is an element, or compound that will conduct electricity without resistance when itis below a certain temperature. Without resistance the electrical current will �ow continuously in a closedloop as long as the material is kept below an speci�c temperature. Since the electrical resistance is zero,supercurrents are generated in the material to exclude the magnetic �elds from a magnet brought near it.The currents which cancel the external �eld produce magnetic poles opposite to the poles of the permanentmagnet, repelling them to provide the lift to levitate the magnet2 . In some countries (including USA) thismagnet levitation has been used for transporation. Speci�cally trains can take advantage of this levitationto virtually eliminate friction between the vehicle and the tracks. A train levitated over a superconductorcan attain speeds over 300 mph!

8.2 Solid State Model Kits

In this experiment we will use the Institute for Chemical Education (ICE) Solid-State Model Kits which aredesigned for creating a variety of common and important solid state structures. Please be careful with these

2http://hyperphysics.phy-astr.gsu.edu/hbase/solids/maglev.html#c1



materials as they are quite expensive. There is a list of kit components on the inside of the lid of each box.Please make sure that you have all the listed pieces and that these are in their proper locations when you�nish using the kit.

The TAs will deduct points from your lab grade if the kits are not returned with all pieces present andproperly organized.

8.2.1 Use of the Solid State Model Kit:

The following instructions are abbreviated. Please consult the instruction manual found in the kits for moredetails if you need assistance in building any of the structures given. Note that some of the model kits areolder than others and the manuals' and page numbers may not correspond.

There are four major part types in each model kit:*2 o�-white, thick plastic template bases with holes (one with a circle, the other a semicircle);*cardboard templates (about 20 labeled A-T);*metal rods (to be inserted in the holes to support the plastic spheres)*plastic spheres in 4 sizes and colors.The spheres can represent atoms, ions, or even molecules depending upon the kind of solid it is.You will be given directions for the use of a speci�c base, template, placement of the rods, selection of

spheres, and arrangement of the spheres as you progress. The ICE model kits make use of Z-diagrams torepresent how the structure will be built up. Each type of sphere will be numbered with the z layer in whichit belongs.

As we build each structure in three-dimensional space, we will be drawing �gures to represent the unitcell structures. Each level or layer of atoms, ions, or molecules in a unit cell can be represented by atwo-dimensional base, that is, a square, hexagon, parallelogram, etc.

To draw the Z-diagrams the bottom layer is referred to as z=0. We then proceed layer by layer up theunit cell until we reach a layer which is identical to the z=0 layer. This is z=1. Since z=0 and z=1 areidentical by de�nition, we do not have to draw z=1, although you might want to do so as you are learninghow to work with solid state �gures. The layers between top and bottom are given z designations accordingto their positions in the crystal. So, for example, a unit cell with 4 layers (including z=0 and z=1) wouldalso have z=0.33 (1/3) and z=0.67 (2/3).

Each solid-state kit has two types of bases (one using rectangular coordinates, the other using polarcoordinates) indicated by a full circle or semicircle, or by color (yellow and green.)

You will �rst build structures that involve only one type of atom, as you would �nd in crystalline solidsof the elements, especially that of the metals. Then you will examine ionic compounds which are knownas binary solids. Binary solids are those composed of only two types of atoms, such as sodium chloride orcalcium �uoride.

If time permits there is an extra credit exercise you can do. You may not do this extra credit exerciseuntil the report form has been completed nor may you receive credit for the extra credit assignment unlessyou fully complete the report form.

8.2.2 Working groups and teams

You and your lab partner will constitute a group. Each group will receive one model kit and two groupswill work together as a team. Your TA will assign you the structures you have to do, and at the end eachteam will discuss the structures assigned on front of the class. The number of teams and the assignmentsthe TA will give you will be decided based on the number of students in a particular laboratory session. Thelaboratory is divided for six teams (A-F)


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8.2.3 Experimental Procedure

Every part of the experimental procedure has correspondent questions on the Report Form. Do not proceeduntil ALL questions accompanying each section have been answered and recorded.

1. Demonstration of the 1,2,3-superconductor YBa2Cu3O8−A pellet of the 1,2,3-superconductor YBa2Cu3O8− is placed on the top of an inverted paper cup. The

pellet is cooled down by carefully pouring liquid nitrogen over it until the bottom of the cup is �lled up. Afterapproximately 10 seconds (when the bubbling stops) the pellet should reach the liquid nitrogen temperature.Your TA will then place a very strong magnet over the pellet.

What happens to the magnet? What happens as the superconductor warms up? What is the Meissnere�ect? (Write observations and answer these questions on your report form)

Warning- LIQUID NITROGEN CAN CAUSE FROST BITE! Do not directly touch anything that hascome into contact with the liquid nitrogen until it is warmed up to room temperature.

NOTE TO TA: to remove a levitating magnet, simply wait until the liquid nitrogen fully evaporatesor use another magnet to "grab" the �oating magnet. Be careful not to lose or break these very tiny, yetexpensive, magnets!!!!

8.2.4

8.2.5 2. Cubic Cells

There are many types of fundamental unit cells, one of which is the cubic cell. In turn, there are threesubclasses of the cubic cell:

a. simple or primitive cubic (P)b. body-centered cubic (bcc, I*)c. face-centered cubic (fcc, F)*The I designation for body-centered cubic comes from the German word innenzentriert.We do not have time to build models of all of the unit cells possible, so we will focus on the cubic structure

and its variations. Our investigation will include several aspects of each cell type:

• the number of atoms per unit cell• the e�ciency of the packing of atoms in the volume of each unit cell• the number of nearest neighbors (coordination number) for each type of atom• the stoichiometry (atom-to-atom ratio) of the compound

A. Simple Cubic Unit Cells or Primitive Cubic Unit Cells (P)

8.2.5.1 Team A

Group 1. Single Unit Cell· Construct a simple cubic cell using template A and its matching base.· Insert rods in the 4 circled holes in the shaded region of the template.· Build the �rst layer (z = 0) by placing a colorless sphere on each rod in the shaded region.· Draw a picture of this layer as previously described.· Complete the unit cell by placing 4 colorless spheres on top of the �rst layer.This is the z=1 layer.

8.2.5.1.1 Group 2. Extended Structure

• Construct an extended cubic cell using template A.• Insert rods in the circled holes of template A in the area enclosed by the dotted lines.• Construct a set of unit cells as described for making a single unit cell.



Look closely at the structures generated by both groups. They are called simple (or primitive) cubic.Considering all of the cells around it, answer the corresponding questions on the report form.B. Body-Centered Cubic Structure (BCC)Team BGroup 1. Single Unit Cell· Construct a body-centered cubic (bcc) structure using template F. · Insert the rods in all 5 of the holes

in the shaded region.· Use the guide at left and place four colorless spheres in the �rst layer (1) at the corners for z=0.· Place one colorless sphere in the second layer (2) on the center rod for z=0.5· Construct the z=1 layer.Group 2.Extended Structure

• Using template F, construct an extended body-centered cubic structure.• Insert rods in every hole of the template/block.• Using the guide which follows, place colorless spheres for z=0 on every rod labeled 1.• For z=0.5 place colorless spheres on each rod labeled 2.• Complete the z=1 layer and then place another two layers on top.

1. Face-Centered Cubic (FCC) Structure

Team CGroup 1. Single Unit Cell· Construct a single face-centered cubic cell using template C, colorless spheres and the layering as

illustrated. Only put rods and spheres on one of the squares de�ned by the internal lines.

Figure 8.1

Group 2. Extended Structure· Construct an extended face-centered cubic structure using template C (You can �nd instructions on

how to do it in the manual that comes with the kit.)


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3. Close-Packing: Sphere Packing & Metallic ElementsTeam DGroup 1. Construct the hexagonal close-packing unit cell (use the one requiring the C6 template)Group 2. Construct the cubic close-packing unit cell (use the one requiring the C6 template)Team EGroup 1. Add a 2' layer on top of the existing structure.Group 2. Add a 2' layer on top of the existing structure.Team FUsing only the shaded portion on the template, construct the face-centered cubic unit cell which uses the

C4 template.Compare the structures of the face-centered cubic unit cell made on the C4 template to that made on

the C6 template.

8.2.5.2 4. Interstitial sites and coordination number (CN)

8.2.5.3 Team A

Group 1 - Construct CN 8, CN 6 and CN 4 (using the C4 template).Group 2 - Construct CN 6, CN 4 (body diagonal) (using the C6 template).

8.2.6 5. Ionic Compounds

Now we will look at some real ionic compounds which crystallize in di�erent cubic unit cells. We will usethe models to determine the stoichiometry ( atom-to-atom ratios) for a formula unit.

Team BCesium Chloride· Construct a model of cesium chloride on template A. This time use colorless spheres as layers 1 and 1'

and the green spheres for layer 2.· Start with the shaded area and then work your way outward to an extended structure. Consider both

simple and extended structures when answering the questions which follow.

8.2.6.1 Team C

8.2.6.2 Fluorite: Calcium �uoride

· Construct a model of �uorite, which is calcium �uoride, on template E.· Green spheres will be used for layers 1, 3, and 1' while colorless spheres go on layers 2 and 4.· Finish with a 1' layer on top. Build the structure by placing rods in all 13 holes in the area enclosed by

the internal line.



8.2.6.3 Team D

8.2.6.4 Lithium Nitride

8.2.6.5 · Use the L template and insert 6 rods in the parallelogram portion of the dotted lines.

8.2.6.6 · Construct the pattern shown below. Be sure to include a z=1 layer. 1 is a greensphere while 1 and 2 are blue spheres. The 0 indicates a 4.0 mm spacer tube; the 2 is an18.6 mm spacer.

Figure 8.2

8.2.6.7 Teams E and F

8.2.6.8 Zinc Blende and Wurtzite: Zinc Sul�de

Team E. Zinc Blende: Use template D to construct the crystal pattern illustrated below. Numbers 2 and 4are blue spheres while 1 and 3 are colorless spheres and 4 is a 16.1 mm spacer.

Team F. Wurtzite: Use template L to construct the Wurtzite lattice. Numbers 1, 3 and 1' are colorlessspheres and Numbers 2 and 4 are pink spheres.


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Figure 8.3



8.3 Pre-Lab: Solid State and Superconductors




1. List the existing crystal systems (unit cell types):2. Which of these unit cells will we study in this laboratory exercise?3. Which are the three subclasses of this type of unit cell?4. De�ne coordination number:5. What is the volume of a sphere? Of a cube?

8.5 Report: Solid State and Superconductors



Name(Print then sign): ___________________________________________________Lab Day: ___________________Section: ________TA__________________________Part I Demonstration and Unit cell theoryA. TA Demo of the superconductorDescribe and explain your observations (What happens with the magnet? Brie�y describe the Meissner

e�ect?)

B. The unit cell 1. A cube (see below) has _______ corners, _______ edges & _______ faces.

Figure 8.4

3http://cnx.org/content/m15259/latest/PreLabSS07.doc4http://cnx.org/content/m15259/latest/ReportSS07.doc


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2. Structure A below shows how a unit cell may be drawn where one choice of unit cell is shown in boldlines. In Structures B, C and D below, draw the outline(s) of the simplest 2-D unit cells (two-dimensionalrepeating patterns depicted by a parallelogram that encloses a portion of the structure).

If the unit cell is moved in the X,Y-plane in directions parallel to its sides and in distance incrementsequal to the length of its sides, it has the property of duplicating the original structural pattern of circles aswell as spaces between circles. Can a structure have more than one type of unit cell? ________

Figure 8.5

Structure A Structure B Structure C Structure D

Table 8.2

3. If the circle segments enclosed inside each of the bold-faced parallelograms shown below were cut outand taped together, how many whole circles could be constructed for each one of the patterns:

Figure 8.6

Table 8.3

4. Shown below is a 3-D unit cell for a structure of packed spheres. The center of each of 8 spheresis at a corner of the cube, and the part of each that lies in the interior of the cube is shown. If all of thesphere segments enclosed inside the unit cell could be glued together, how many whole spheres could beconstructed?



number of whole spheres: ________5. For each of the �gures shown below, determine the number of corners and faces. Identify and name

each as one of the regular geometric solids.

Figure 8.7

AB

A B

Number of corners

Number of faces

Name of the shape of this object

Table 8.4

Part II Experimental

1. Cubic Cells

8.5.1 A. Simple Cubic Unit Cells or Primitive Cubic Unit Cells (P)

a. How would you designate the simple cube stacking - aa, ab, abc, or some other?

b. If the radius of each atom in this cell is r, what is the equation that describes the volume of the cubegenerated in terms of r? (Note that the face of the cube is de�ned by the position of the rods and does notinclude the whole sphere.)


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c. Draw the z-diagram for the unit cell layers.

d. To how many di�erent cells does a corner atom belong? What is the fractional contribution of a singlecorner atom to a particular unit cell?

e. How many corner spheres does a single unit cell possess?

f. What is the net number of atoms in a unit cell? (Number of atoms multiplied by the fraction theycontribute)

g. Pick an interior sphere in the extended array. What is the coordination number (CN) of that atom?In other words, how many spheres are touching it? .

h. What is the formula for the volume of a sphere with radius r?

i. Calculate the packing e�ciency of a simple cubic unit cell (the % volume or space occupied by atomicmaterial in the unit cell). Hint: Consider the net number of atoms per simple cubic unit cell (question g)the volume of one sphere (question i), and the volume of the cube (question b).

8.5.2 B. Body-Centered Cubic (BCC) Structure

a. Draw the z diagrams for the layers.

b. Fill out the table below for a BCC unit cell

Atom type Number Fractional Contribution Total Contribution Coordination Number

Corner

Body

Table 8.5

c. What is the total number of atoms in the unit cell?

d. Look at the stacking of the layers. How are they arranged if we call the layers a, b, c, etc.?

e. If the radius of each atom in this cell is r, what is the formula for the volume of the cube generated interms of the radius of the atom? (See diagrams below.)

f. Calculate the packing e�ciency of the bcc cell: Find the volume occupied by the net number of spheresper unit cell if the radius of each sphere is r; then calculate the volume of the cube using r of the sphere andthe Pythagoras theorem ( a2 + b2 = c2) to �nd the diagonal of the cube.



8.5.3 C. The Face Centered Cubic (FCC) Unit Cell

8.5.4 a. Fill out the following table for a FCC unit cell.

Atom type Number Fractional Contribution Total Contribution Coordination Number

Corner

Face

Table 8.6

b. What is the total number of atoms in the unit cell?c. Using a similar procedure to that applied in Part B above; calculate the packing e�ciency of the

face-centered cubic unit cell.

1. Close-Packing

a. Compare the hexagonal and cubic close-packed structures.

b. Locate the interior sphere in the layer of seven next to the new top layer. For this interior sphere,determine the following:

Number of touching spheres: hexagonal close-packed (hcp) cubic close-packed (ccp)

on layer below

on the same layer

on layer above

TOTAL CN of the interior sphere

Table 8.7

c. Sphere packing that has this number (write below) of adjacent and touching nearest neighbors isreferred to as close-packed. Non-close-packed structures will have lower coordination numbers.

d. Are the two unit cells the identical?

e. If they are the same, how are they related? If they are di�erent, what makes them di�erent?

f. Is the face-centered cubic unit cell aba or abc layering? Draw a z-diagram.


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III.Interstitial sites and coordination number (CN)a. If the spheres are assumed to be ions, which of the spheres is most likely to be the anion and which

the cation, the colorless spheres or the colored spheres? Why?

b. Consider interstitial sites created by spheres of the same size. Rank the interstitial sites, as identi�edby their coordination numbers, in order of increasing size (for example, which is biggest, the site withcoordination number 4, 6 or 8?).

c. Using basic principles of geometry and assuming that the colorless spheres are the same anion withradius r A in all three cases, calculate in terms of rA the maximum radius, rC, of the cation that will �tinside a hole of CN 4, CN 6 and CN 8. Do this by calculating the ratio of the radius of to cation to theradius of the anion: rC/rA.

d. What terms are used to describe the shapes (coordination) of the interstitial sites of CN 4, CN 6 andCN 8?

CN 4: ________________CN 6: _______________CN 8: ________________

8.5.5 IV.Ionic Solids

A. Cesium Chloride1. Fill the table below for Cesium Chloride

Colorless spheres Green spheres

Type of cubic structure

Atom represented

Table 8.8

2. Using the simplest unit cell described by the colorless spheres, how many net colorless and net greenspheres are contained within that unit cell?

3. Do the same for a unit cell bounded by green spheres as you did for the colorless spheres in question4.

4. What is the ion-to-ion ratio of cesium to chloride in the simplest unit cell which contains both? (Doesit make sense? Do the charges agree?)

B. Calcium Fluoride1. Draw the z diagrams for the layers (include both colorless and green spheres).

2. Fill the table below for Calcium Fluoride



Colorless spheres Green spheres

Type of cubic structure

Atom represented

Table 8.9

3. What is the formula for �uorite (calcium �uoride)?

C. Lithium Nitride1. Draw the z diagrams for the atom layers which you have constructed.

2. What is the stoichiometric ratio of green to blue spheres?

3. Now consider that one sphere represents lithium and the other nitrogen. What is the formula?4. How does this formula correspond to what might be predicted by the Periodic Table?

D. Zinc Blende and WurtziteFill in the table below:

Zinc Blende Wurtzite

Stoichiometric ratio of colorless to pink spheres

Formula unit (one sphere represents and the other the sul�de ion)

Compare to predicted from periodic table

Type of unit cell

Table 8.10


Chapter 9

Organic Reactions1

9.1 Organic Reactions

9.1.1 Objectives

• Synthesis of some important esters.• Oxidation of a primary alcohol �rst to an aldehyde and then a carboxylic acid.• To saponify a typical vegetable oil.

9.1.2 Grading

You will be assessed on

• detailed answers required in the lab report.• the correctness and thoroughness of your observations.

9.1.3 Introduction

Esters are an important class of organic compounds commonly prepared from the esteri�cation reaction ofan organic acid with an alcohol in the presence of a strong mineral acid (usually H2SO4). They are chie�yresponsible for the pleasant aromas associated with various fruits, and as such are used in perfumes and�avorings. Some esters also have useful physiological e�ects. The best known example is the analgesic("pain killing") and anti-pyretic ("fever reducing") drug acetylsalicylic acid, otherwise known by its tradename aspirin.

Liniments used for topical relief of sore muscles contain the ester methyl salicylate ("oil of wintergreen"),which is prepared from the reaction of methyl alcohol with the acid group of salicylic acid. Methyl salicylateacts as an analgesic and is absorbed through the skin; however, methyl salicylate is also a skin irritant(like many organic substances), which in this instance provides the bene�cial side e�ect of the sensation ofwarming in the area of the skin where the liniment is applied.

Oxidation of a primary alcohol may yield either an aldehyde or a carboxylic acid, depending on thereaction conditions. For example, mild oxidation of ethanol produces acetaldehyde, which under morevigorous conditions may be further oxidised to acetic acid. The oxidation of ethanol to acetic acid isresponsible for causing wine to turn sour, producing vinegar.

A number of oxidising agents may be used. Acidi�ed sodium dichromate (VI) solution at room temper-ature will oxidise primary alcohols to aldehydes and secondary alcohols to ketones. At higher temperaturesprimary alcohols are oxides further to acids.



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86 CHAPTER 9. ORGANIC REACTIONS

Figure 9.1

The dichromate solution turns from the orange color of the Cr2O2−7 (aq) to the blue color of the Cr3+

(aq). This color change is the basis for the "breathalyser test". The police can ask a motorist to exhalethrough a tube containing some orange crystals. If the crystals turn blue, it shows that the breath containsa considerable amount of ethanol vapor.

Soaps are produced by the reaction of metallic hydroxides with animal fats and vegetable oils. The majorcomponents of these fats and oils are triglycerides. Triglycerides are esters of the trihydroxy alcohol calledglycerol and various long-chain fatty acids. Tristearin is a typical triglyceride. Upon reaction with sodiumhydroxide, the ester bonds of tristearin are broken. The products of the reaction are the soap, sodiumstearate, and glycerol. This type of reaction is called saponi�cation (Greek: sapon, soap) and it is depictedbelow.

Figure 9.2

Soap is made commercially by heating beef tallow in large kettles with an excess of sodium hydroxide.When sodium chloride is added to this mixture (called the "saponi�ed" mixture), the sodium salts of thefatty acids separate as a thick curd of crude soap. Glycerol is an important by-product of the reaction. It is


87

recovered by evaporating the water layer. The crude soap is puri�ed, and coloring agents and perfumes areadded to meet market demands.

9.1.3.1 EXPERIMENTAL PROCEDURE

CAUTION WEAR EYE PROTECTION!

CAUTION - Concentrated sulfuric acid will burn and stain the skin as well as damage clothing. In caseof skin or clothing contact, wash the area immediately with large amounts of water.

9.1.3.2 Synthesis of esters

1. Place approximately 2 g (or 2 mL if the substance is a liquid) of the organic acid and 2 mL of thealcohol in a large test tube.

2. Add 5 - 7 drops of concentrated (18 M) sulfuric acid, mix the solution well with a glass stirring rodand then place the test tube in a hot water bath (largest beaker in your drawer) (∼ 80 ◦C) for 5 - 10minutes.

3. Remove the test tube from the hot water bath and cautiously pour the mixture into about 15 mL ofsaturated sodium bicarbonate contained in a small beaker. The sodium bicarbonate will destroy anyunreacted acid.

4. Observe the aroma produced from each of the following esteri�cation reactions. Write the structure ofthe esters produced, and the balanced equations for the esteri�cation and the acid/sodium bicarbonatereactions:

Complete the following reactions using the procedure above and record your observations.

(1) C7H6O3 + CH3OH→salicylic acid + methyl alcohol(2) CH3CH2CH2CH2CH2CH2CH2CH2OH+ CH3COOH→1 - octanol + glacial acetic acid(3) CH3CH2CH2CH2CH2OH+ CH3COOH→amyl alcohol + glacial acetic acid(4) C2H5OH+ CH3COOH→ethanol + acetic acid

9.1.3.3 Oxidation of an alcohol with acidi�ed potassium dichromate(VI) solution

• Add 10 drops of dilute sulfuric acid (6M) and 5 drops of potassium dichromate(VI) solution (0.01M)to 5 drops of ethanol. The oxidising agent is added slowly to the alcohol so that the temperature iskept below that of the alcohol and above that of the carbonyl compound. (Carbonyl compounds aremore volatile than the corresponding alcohols). Usually the alcohol is in excess of the oxidant and thealdehyde is distilled o� to avoid further oxidation.

• Note the color and smell cautiously (Royal Wave).• Warm the mixture and smell cautiously (Royal Wave).• Repeat the experiment using �rst methanol and then propan-2-ol in place of ethanol.

Describe what happens and explain the color changes.What conditions and techniques would favour the oxidation of ethanol toa. ethanal rather than ethanoic acid.b. ethanoic acid rather than ethanal?



9.1.3.4 Oxidation of an alcohol with acidi�ed potassium permanganate (VII) solution

• Add 10 drops of dilute sulfuric acid and 5 drops of potassium permanganate (VII) solution (0.01M) to5 drops of ethanol. Note the color and smell cautiously.

• Warm the mixture and smell cautiously (Royal Wave).• Repeat the experiment using �rst methanol and then propan-2-ol in place of ethanol.• Take the pH of your �nal mixture using Universal indicator paper

Describe what happens and explain the color changes.What is your �nal product?

9.1.3.5 Saponi�cation of a vegetable oil

CAUTION - Sodium hydroxide is a very caustic material that can cause severe skin burns. Eye burns causedby sodium hydroxide are progressive: what at �rst appears to be a minor irritation can develop into a severeinjury unless the chemical is completely �ushed from the eye. If sodium hydroxide comes in contact withthe eye, �ush the eye with running water continuously for at least 20 minutes. Notify your TA immediately.If sodium hydroxide is spilled on some other parts of the body, �ush the a�ected area with running watercontinuously for at least 2-3 minutes. Notify your TA immediately.

Never handle sodium hydroxide pellets with your �ngers. Use weighing paper and a scoopula. Solidsodium hydroxide will absorb water from the atmosphere. It is hygroscopic. Do not leave the container ofsodium hydroxide open.

Keep ethanol and ethanol-water mixtures away from open �ames.Aqueous iron chloride will stain clothes permanently and is irritating to the skin. Avoid contact with this

material.

In this experiment, you will saponify a vegetable oil

1. Pour 5 mL (5.0 g) of vegetable oil into a 250-mL beaker.2. Slowly dissolve 2.5 g of NaOH pellets in 15 mL of the 50% ethanol/water mixture in a 50-mL beaker.3. Add 2-3 mL of the NaOH solution to the beaker containing the oil. Heat the mixture over a hot plate

with stirring. CAUTION: Keep your face away from the beaker and work at arm's length. Stirringis required to prevent spattering. Every few minutes, for the next 20 minutes, add portions of theethanol/water mixture while continuing to stir to prevent spattering. After about 10 more minutes ofheating and stirring, the oil should be dissolved and a homogenous solution should be obtained.

4. Add 25 mL of water to the hot solution. Using the hot grips, pour this solution into a 250 mL beakercontaining 150 mL of saturated NaCl solution. Stir this mixture gently and permit it to cool for a fewminutes.

5. Skim the soap layer o� the top of the solution and place it in a 50-mL beaker.6. Into a test tube, place a pea-sized lump of your soap. Place a similar amount of laundry detergent in a

second tube and a similar amount of laundry detergent in a second tube and a similar amount of handsoap in a third tube. Add 10 mL of water to each tube. Stopper each tube and shake thoroughly.

7. Estimate the pH of the solution using wide-range indicator solution or wide-range test paper. Recordthe results. Pour the contents of the test tubes into the sink and rinse the tubes with water.

Figure 9.3


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9.2 Pre-Lab: Introductory Organic Reactions



will not be allowed to begin the lab until you have completed this assignment.For questions 1-4, draw the structural formulae of:1) 2,2 - dimethylbutane

2) 3-ethyl-2,4-dimethylpentane

3) 2,3,4-trimethylhexane

4) 3-ethyl-2-methylheptane

For questions 5-8, give the names of5) CH3CH2CH2CH2CH = CH2

6) CH3CH = C = CH2

7) CH3CH = CHCH3

8) (CH3)2 C = CHCH3

For questions 9-11, give the structural formulae for:9) hex-3-ene

10) 3-methylhex-1-ene

11) 2,5- dimethylhex-2-ene

For questions 12-14, give the names of:12)

2http://cnx.org/content/m15483/latest/PreLabOR07.doc



Figure 9.4

13)

Figure 9.5

14)

Figure 9.6

For questions 15-19, give the stuctural formulae of:15) trans-1,2-dibromoethene

16) trans-1-chloroprop-1-ene

17) cis- hex-2-ene

18) pent-1-yne

19) 3-methylbut-1-yne

For questions 20-25, name the following compounds:20)

Figure 9.7

21)


91

Figure 9.8

22)

Figure 9.9

23)

Figure 9.10

24)

Figure 9.11

25)

Figure 9.12



9.4 Report: Organic Reactions




9.4.1 Observations:

9.4.1.1 Synthesis of esters

Reagents Product Observations

C7H6O3(salicylic acid ) +CH3OH(methyl alcohol)

CH3CH2CH2CH2CH2CH2CH2CH2OH(1 - octanol ) +CH3COOH(glacial acetic acid)

CH3CH2CH2CH2CH2OH(amylalcohol) +CH3COOH (glacialacetic acid)

C2H5OH (ethanol) +CH3COOH(acetic acid)

Table 9.1

9.4.2 Oxidation of an alcohol with acidi�ed potassium dichromate(VI) solution.

Remember to describe what happens and explain the color changes.What conditions and techniques would favour the oxidation of ethanol toa. ethanal rather than ethanoic acid.b. ethanoic acid rather than ethanal?

Add 10 drops of dil. H2SO4 to 5drops of K2Cr2O7 to the follow-ing alcohols

Observations: color/smellSmellcautiously!

Observations: color/smell onwarmingSmell cautiously!

Ethanol

Methanol


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93

Propan-2-ol

Table 9.2

9.4.3 Oxidation of an alcohol with acidi�ed potassium permanganate (VII) solu-tion

Remember to describe what happens and explain the color changes.What is your �nal product?

Add 10 drops of dil. H2SO4 to 5drops of KMnO4 to the followingalcohols

Observations: color/smellSmellcautiously!

Observations: color/smell onwarmingSmell cautiously!

Ethanol

Methanol

Propan-2-ol

Table 9.3

9.4.4

9.4.5 Saponi�cation of a vegetable oil

Reagent pH from indicator paper

Your soap

Laundry Detergent

Hand Soap

Table 9.4

w from the File menu, and then double-click your template.


Chapter 10

Transition Metals1

10.1 Transitions Metals: Synthesis of an Inorganic Compound (trans-dinitrobis(ethylenediamine)cobalt(III) nitrate)

10.1.1 Objectives

• To synthesize a transition metal complex of cobalt three, Co(III), and ethylenediamine.• To characterize the resulting metal complex spectroscopically.• To understand concept of limiting reactant.

10.1.2 Grading

Your will be determined according to the following:

• prelab (10%)• lab report form (80%)• TA points (10%)

10.1.3 Introduction

The transition metals are the largest �group� (classi�cation) of elements from the periodic table. These canbe found in nature as ores or in its elemental form, such as gold. All transition metals have more thanone oxidation state. Most transition metals (TMs) can complex with other species (called ligands in �TMComplex� jargon) by giving their electrons to them, forming a complex. These ligands, which are the nearestneighbor atoms to the metal center, constitute the inner (or �rst) coordination sphere. Complexes may beeither neutral or charged and have distinctive properties that may be quite unlike those associated with theirconstituent molecules and ions, each of which is capable of independent existence. An example of a chargedcomplex is ferricyanide, [Fe (CN)6 ]−3

. The Fe+3 and CN− ions found in the ferricyanide complex ion existas independent species and in other compounds. The transition metals are well known for forming a largenumber of complex ions. In this experiment we will synthesize a transition metal complex containing cobalt,Co(III), and ethylenediamine.



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96 CHAPTER 10. TRANSITION METALS

10.1.3.1 Stereochemistry

The most common coordination numbers (the number of individual ligands bound) are two, four, and six,with geometries illustrated in Fig 1:

Figure 10.1

Fig 1. Common geometries for complex ions. (A) linear, (B) square planar, (C) tetrahedral, and (D)octahedral

Complexes of Cu(I), Ag(I), Au(I) and some of Hg(II) form linear structures (A) such as Cu (CN)−2 ,Ag (NH3)

+2 , etc. Four-fold coordination (C) is not too common with transition metals, and the square

planar geometry (B) occurs in complexes of Pd(II), Pt(II), Ni(II), Cu(II), and Au(III). Six-fold coordination(D) is the most common and in fact the one we will study in this laboratory exercise.

A ligand that is capable of occupying only one position in the inner coordination sphere by forming onlyone bond to the central atom is called a monodentate (�one tooth�) ligand. Examples are F−, Cl−, OH−,H2O, NH3 and CN−. If the ligand has two groups that are capable of bonding to the central atom, it iscalled a bidentate ("two teeth") ligand, and so forth. An example of a bidentate ligand is ethylenediamine


97

(CH2NH2CH2NH2), which is commonly abbreviated "en". Both nitrogen atoms in "en" can bond to thecentral atom in a complex at the same time.

Complex ion salts with the same chemical formulas often behave di�erently because the same number ofatoms can be arranged into di�erent forms called isomers. Hydrate isomerism is illustrated by the followingexample: There are three distinct compounds with the formula Cr (H2O)6 Cl3. One of these, violet in color,reacts immediately with AgNO3 to precipitate all of the chlorines as AgCl. The second is light green butonly 2/3 of the chlorine is precipitated as AgCl. The third compound is dark green and only 1/3 of thechlorine is precipitated as AgCl. The last compound has only one reactive Cl, so apparently two chlorinesin this compound are bonded tightly to the Cr and are not available for reaction. We might thus write thiscompound as [CrCl2 (H2O)4] · (H2O)2, where the species within the brackets are regarded as ligands bondedfairly strongly to the central chromium, and this species would behave as a single ion in solution. i.e., inaqueous solution,

[CrCl2 (H2O)4]Cl · (H2O)2 → [CrCl2 (H2O)4 ]+ + Cl− + waterThe light green compound with two reactive chlorines is apparently [CrCl (H2O)5]Cl2 ·H2O, while the

violet compound with three reactive chlorines is Cr (H2O)6 Cl3.Closely related to hydrate isomerism is ionization isomerism, where an ion takes the place of water.

Consider two di�erent compounds with the formula Co (NH3)5 SO4Br. One of these, [Co (NH3)5 (SO4)]Br,appears red, whereas the other, [Co (NH3)5 Br] SO4, appears violet.

In addition to these coordination sphere isomers there are geometrical isomers, which have coordinationspheres of the same composition but di�erent geometrical arrangement. Geometrical isomers are distinctcompounds and can have di�erent physical properties (although often not too di�erent) such as color, crystalstructure, melting point, and so on. For example, dichlorodiamine platinum (II) occurs in the square planargeometry (B) so the chlorine ligands can be either next to one another (cis) or opposite from one another(trans). The compound you will synthesize has an octahedral geometry with two (bidentate) "en" ligands,and two nitro (NO2) ligands. The geometrical isomer you will make is the trans form, in which the NO2

ligands are not adjacent to one another. This di�erence between cis and trans octahedral isomers is shownin Fig 2.

Figure 10.2



Fig 2. The trans and cis geometrical isomers for octahedral complexes with two bidentate (�en�) andmonodentate (NO2) ligands speci�cally dinitrobis(ethylenediamine)Co(III). The two black balls representthe NO2 ligands and the two pairs of linked white balls represent the two ethylenediamine ligands. Cis andtrans describe the relationship (relative position) between the two NO2 ligands.

In the procedure that follows we start with a cobalt solution made from the salt hexaquacobalt(II) nitrate,

[Co (H2O)6] (NO3)2. When this salt dissolves it ionizes to form two ions of NO−3 and one of Co (H2O)2+6 . Wewish to prepare a Co(III) compound of ethylenediamine, so we must add ethylenediamine (en) and oxidizethe Co(II) to Co(III). Because Co(II) is more reactive than Co(III), we allow it to react with (en) �rst, andthen oxidize the resulting complex ion. In aqueous solution (en) reacts with water to produce OH− ionswhich can also bind to Co(II), so the pH is adjusted close to 7 �rst by adding HNO3. (Other acids wouldintroduce new ligands to compete for the Co.) NaNO2 is added to provide the ligands that will be trans inthe �nal compound. Lastly, Co(II) is oxidized to Co(III) by bubbling oxygen through the solution.


1. Use your 10 mL graduated cylinder to measure out 20 mL of the 20% by weight solution of ethylene-diamine in dilute HNO3.

2. Pour it into a clean 125 mL Erlenmeyer �ask. Rinse the graduated cylinder with about 5mL of deionisedwater (DI water from white handle faucet) and add the rinse water to the �ask. Set this aside for amoment and prepare the second set of reactants as described below.

3. Weigh out 9.0 g of hexaquacobalt(II) nitrate and 6.0 g sodium nitrite ( NaNO2) using a rough balance(Record mass on report form). Add these reactants to approximately 15 mL of DI water in an Erlen-meyer �ask. After they have dissolved, add the neutralized ethylenediamine solution prepared in steps1-2. Record your observations.

4. For the next set of instructions, refer to the diagram below. Fit a piece of rubber tubing over an inertgas "IG" tap (on benchtop) and open the valve slowly to obtain a gentle �ow of oxygen. Then insert aPasteur pipet into the other end of the rubber tubing. CAUTION: Too high a gas �ow might blow thepipet out of the tubing and cause serious injury. Always adjust the valve carefully while pointing yourpipet in a safe direction. Test the �ow by immersing the pipet tip in a beaker of water�it should bubblevigorously, but not enough to cause much splashing. When the �ow is set to your satisfaction, immersethe tip of the pipet in the Erlenmeyer �ask containing the reaction mixture. Secure the �ask to astand with a clamp because the reaction mixture may need about 10 minutes of moderately vigorousbubbling to reach completion. Record your observations.


99

Figure 10.3

Figure 3. The bubbling apparatus.

1. After about 10 minutes of bubbling, turn o� the gas �ow and immerse the �ask in ice water. This willcause further crystallization. After approximately 5 minutes in the ice bath, pour the �ask's contentsthrough the �lter crucible while it has suction applied using the setup shown below. Record yourobservations.



Figure 10.4

Figure 4. Schematic diagram showing sintered-glass �lter crucible mounted on suction �ask with rubber�lter adapter. Clamp the �lter �ask to a support post to prevent breakage.

1. The crystals will remain in the crucible while the solution passes through. Wash your crystals byslowly pouring approximately 5 mL of ethanol over them while suction is applied. Why do we washwith ethanol? Answer on lab report form.

2. The next step is recrystallization to obtain a more puri�ed product. Transfer the product crystals toa 250 mL beaker. Add about 80 mL of DI water and stir to dissolve the crystals. Gently heat thebeaker over a Bunsen burner (or on high on a hotplate if available), gradually bringing it to a `slight'boil. Allow the solution to boil gently until its volume has been reduced to about 50 mL. Then let thesolution cooled to near room temperature, place the beaker into an ice bath (DO NOT PLACE THEBEAKER IN THE ICE BATH WHILE HOT. IT WILL CRACK AND YOU WILL LOOSE YOURPRODUCT). Crystal growth should be immediately apparent. After a few minutes in the ice bath,transfer the crystals into the �lter crucible. To help with this transfer you may use a rubber policemanon the end of a stirring rod. Remember that your crystals are water-soluble so if you use water in thetransfer you will lose the product. Apply suction and rinse the crystals three times with separate 5mL portions of ethanol. Scrape the crystals onto a watch glass and place in your drawer to dry.

In terms of the materials used, the overall reaction is:4{[Co (H2O)6] (NO3)2}+ 8NaNO2 + 8C2H4 (NH2)2 + 4HNO3 +O2 (g)→ 4trans−[Co (en)2 (NO2)2]NO3 + 8NaNO3 + 26H2OHowever, the actual reaction in solution involves ions and the en species exists partially in the form of


101

NH2CH2CH2NH+3 . From the reaction and quantities used, calculate the theoretical yield and your

percentage yield.



10.2 Pre-Lab: Transition Metals


Hopefully here2 for the Pre-LabNote: In preparing this report you are free to use references and consult with others. However, you may



1. List and draw the common geometries transition metal complexes:2. What are the two types of structural isomers for complex ion salts?3. What are the two types of geometrical isomers for complex ion salts?4. Why do we use Co(II) and then convert to Co(III) when synthesizing 4− trans [Co (en)2 (NO2)2]NO3?5. List two common monodentate ligands and two common bidentate ligands:

10.4 Report: Transition Metals

On my honor, in preparing this report, I know that I am free to use references and consult with others.Hopefully here3 for the Report FormNote: In preparing this report you are free to use references and consult with others. However, you may



Date ________________ Lab Section___________Note: In preparing this report you are free to use references and consult with others. However, you may

not copy from other students' work (except to compile the group data set) or misrepresent your own data.

10.4.1 1. Synthesis

A. Volume of 20% ethylenediamine solution used ______ (r = 0.980 g/mL)

Compound Weight Moles (Molar weight and stoichiometric coe�cient)

ethylenediamine

[Co (H2O)6] (NO3)2NaNO2

[Co (en)2 (NO2)2]NO3

Table 10.1

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10.4.2

10.4.3 a. Observations

1. Record your observations after adding the neutralized ethylenediamine solution.

1. Record your observations after 10 minutes of moderately vigorous bubbling.2. Record your observations after pouring the �ask's contents through the �lter crucible while suction is

applied.

10.4.4

10.4.5 b. Questions

1. Why do we wash the crystals with ethanol?

1. Give the net chemical equation for the reaction, writing dissociated reactants as ions, the solid productas an undissociated salt, and including all other ionic and neutral species needed to balance chargeand mass. Omit any spectator ions that would appear in equally on both sides.

1. Which is the limiting reactant in your experiment?

1. Calculate the maximum weight of product you would have obtained if the limiting reactant had reactedfully. This is the theoretical yield. What is your percent yield (the actual yield divided by theoreticalyield)?

Theoretical yield _______g Actual yield _______ g

1. Is the yield less, same, or more than the theoretical yield? Give reasons for why the actual yield isdi�erent theoretical yield.


Chapter 11

Physical Properties of Gases1

11.1 Physical Properties of Gases

11.1.1 Objectives

• Learn and understand physical properties of gases and explain observations in terms of the kineticmolecular theory of gases.

• Plot and calculate the root mean square speed of the Carvone molecules. (Comparison with speed invacuum).

• Estimate volume and volume change of a balloon when it goes from room temperature (RT) to liquidnitrogen temperature.

• Observe and explain behavior of gas in: a soda can, a balloon in a �ask, Cartesian diver, etc., when achange in pressure or temperature is applied.

11.1.2 Grading

You grade will be determined according to the following:

• Pre-lab (10%)• Lab Report Form (80%)• TA points (10%)

11.1.3 Introduction

Expanding and contracting balloons, imploding soda cans, exploding marshmallows are just some of thedemonstrations that are often used to illustrate the empirical gas laws and the kinetic molecular theoryof gases. In this experiment, you will be performing these and other `demonstrations' and using yourunderstanding of the physical properties of gases to explain your observations.

There will be demonstrations laid out at seven di�erent stations (2 sets at each) around the room andyou will go in 2 groups of 4 people (two sets of lab partners) to each station (you don't need to start with#1). If your group is assigned or start with, for example 5, you should then follow the following order: 5, 6,7, 1, 2, etc. Your group should spend no more than 15 minutes at each station. Perform the experiment byfollowing the instructions placed at each station. Then discuss your observations with your group. For eachof the activities, it is important to ask yourself what is going on, "how can our observations be explained



105

106 CHAPTER 11. PHYSICAL PROPERTIES OF GASES

using the kinetic molecular theory of gases?" Remember that for some demonstrations calculations may berequired also. Be thorough and precise in your explanations.

CAUTION: Important Safety Notes:Remember to use tongs, hot grips as appropriate when dealing with hot liquids, vapors and containers.Liquid nitrogen is extremely cold, with a boiling point of -196[U+F0B0] C and if it comes into contact

with skin can result in severe frostbite.The vacuum dessicator should be regarded as a potential implosion hazard when evacuated. Handle it

carefully.When doing the egg experiment do not put hot �ask immediately in the water bath (let it for at least 3

minutes sitting on the bench) it will crack and you may have to pay for it if it breaks.Observe and record what happens in your laboratory report form.You are encouraged to discuss among yourselves possible explanations to your observations.


11.1.4.1 Di�usion:

The goal of this experiment is to measure the rate of di�usion of Carvone, a major component of spearmintoil. Find an area where there are few drafts and the air does not already smell of spearmint. (You may goto the hallway to perform the experiment)

Stand in a line, with the �rst person in the group holding the bottle of Carvone and several paper towels.All four people should be 1 meter apart. You will need to know the distance each person is from the bottleof Carvone. The fourth person should act as the timekeeper. When the timekeeper gives the signal, the�rst person should place a few drops of Carvone on the paper towels. Record the time that it takes for eachperson to smell the Carvone. Seal the paper towel in a plastic bag when you are �nished.

After the odor has dissipated, repeat the experiment twice.Using Excel plot the data in distance traveled versus time. Obtain a least squares �t (R value) for this

data and determine from it the rate of di�usion of Carvone in meters per second. Create a graph for eachtrial. Calculate the average of the rates for the three trials. Calculate the root mean square speed of carvonemolecules at 25[U+F0B0]C. Your TA will help you with this equation. Compare the result with the di�usionrate you measured. If they are signi�cantly di�erent, o�er an explanation. Would the di�usion take placefaster in a vacuum?

Note: You should spend no more than one-half hour preparing the plots. Please stagger yourselves sothat everyone has an opportunity to get to the computer stations.

11.1.4.2 Gas Laws in a Soda Can:

Pour 15 mL of water into an aluminum soda can. Set the can on a hot plate and turn on to a high temperaturesetting. While the can water heats, �ll a 1000-mL beaker with cold water (You may have a metal tin set outfor this purpose). Continue heating the can until the water inside boils vigorously and until steam escapesfrom the mouth of the can for about 20 seconds.

Using the hot grips to grip the can near the bottom, quickly lift the can from the burner and invert (sowater covers the mouth of the can) it in the beaker of cold water. Describe what happens. Explain why ithappens. You may repeat this experiment using a second soda can if you wish. Why is it necessary to invertthe can in the water? What would happen if a rigid container were used?

11.1.4.3 Balloon in liquid nitrogen:

Review the safety notes above regarding the handling of liquid nitrogen.In�ate a balloon and tie the end (Several balloons may have already been in�ated and tied). Using tongs,

place the balloon in a Dewar �ask containing liquid nitrogen. After the balloon stops changing size, removeit from the Dewar and allow it to warm to room temperature. Observe and record the changes (you shouldbe able to measure the radius and estimate volume).


107

Estimate the size of the balloon in liters. What is the pressure inside the balloon before it is placed inthe liquid nitrogen? What is the pressure inside the balloon after it is placed in the liquid nitrogen? Use theideal gas law to calculate the percent change in volume expected on going from room temperature to liquidnitrogen temperature. Is the volume of the cold balloon consistent with what you calculated, or is it largeror smaller? Suggest an explanation for your observation. Explain all of your observations in detail using thekinetic molecular theory of gases. How does the liquid nitrogen cool the gas in the balloon?

11.1.4.4 Tygon tube in liquid nitrogen:

Review the safety notes above regarding the handling of liquid nitrogen. Place a 2 foot long tygon cleartube in a Dewar with liquid nitrogen. Observe what happens and explain.

11.1.4.5 Balloon in a �ask:

Place about 5 mL of water in a 125-mL Erlenmeyer �ask. Heat the �ask on a hot plate until the water boilsdown to a volume of about 1 mL. Meanwhile, in�ate a balloon and then let the air out (this may not benecessary if balloons on table have been previously used). Remove the �ask from the heat, hold it with atowel, and immediately place the open end of the balloon over the mouth of the �ask. Observe the e�ect asthe �ask cools. Can you get the balloon back out again? If you can, How?

11.1.4.6 Cartesian diver:

The Cartesian diver is named for Rene Descartes (1596-1650), noted French scientist and philosopher. Atthis station, you will �nd a plastic soda bottle containing a medicine dropper, water, and air. Squeeze thebottle.

What happens? Why?

11.1.4.7 The Egg:

Lightly grease the inside of the neck of a 1 L Erlenmeyer �ask with stopcock grease. Clamp the �ask ontothe stand. Place about 5 mL H2O in the �ask and gently warm it with a Bunsen burner until the watervaporizes. Do not boil the water to dryness. Meanwhile, prepare an ice water bath in an evaporating dish.While the �ask is warm, seat the egg, narrow end down, in the mouth of the �ask. Unclamp the �ask, allowto cool slightly sitting on the bench and then immerse it in the ice water. (Read the safety notes above toavoid breaking the �ask)

Can you get the egg back out again?Assuming that the �ask reaches the maximum vacuum (minimum pressure) possible before the egg is

drawn into the �ask, calculate the minimum pressure reached in the �ask.

11.1.4.8 Expanding balloon:

Partially in�ate a balloon. Place the balloon inside the vacuum chamber and close the chamber with theblack rubber circle and the top of the chamber carefully centered on the base (A partially in�ated balloonmay already be in the dessicator). Close the needle valve (at the bottom of the black rubber tubing) byturning it clockwise. Turn the stopcock to the up position to connect the chamber to the vacuum pump.What happens? To open the chamber, turn the stopcock to the left position and open the needle valve.

11.1.4.9 Bonus 2 points:

1pt to name a real life example of the physical properties of gases at work1pt for a good explanation of how and why it works according to what you have learned in the lab.



11.2 Pre-Lab: Physical Properties of Gases


Hopefully here2 for the Pre-LabNote: In preparing this report you are free to use references and consult with others. However, you may



1. De�ne di�usion and write down equation for di�usion rate:2. Write equation for ideal gas law and describe each term.3. De�ne Charles', Boyle's, and Avogadro's law:4. Fill the blanks (which law applies):5. When temperature increases in a close balloon the volume ________.

_______Law

• When pressure is applied to a close balloon the volume _________.

_______Law

• When temperature decreases in a close balloon the pressure _________.

_______Law

11.4 Report: Physical Properties of Gases


Hopefully here3 for the ReportNote: In preparing this report you are free to use references and consult with others. However, you may


1. Di�usion:At the end of your report attach the graphs of each trial.The average of the rates for the three trials is��-The root mean square speed of carvone molecules at 25[U+F0B0]C is��Compare the result with the di�usion rate you measured. If they are signi�cantly di�erent, o�er an

explanation.

Would the di�usion take place faster in a vacuum?

2. Gas Laws in a Soda Can:

2http://cnx.org/content/m15545/latest/PreLabPP07.doc3http://cnx.org/content/m15545/latest/ReportPP07.doc


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Describe what happens.Explain why it happens. You may repeat this experiment using a second soda can if you wish.Why is it necessary to invert the can in the water?

What would happen if a rigid container were used?

3. Balloon in liquid nitrogen:The estimated size of the balloon in liters is��What is the pressure inside the balloon before it is placed in the liquid nitrogen?

What is the pressure inside the balloon after it is placed in the liquid nitrogen?

Use the ideal gas law to calculate the percent change in volume expected on going from room temperatureto liquid nitrogen temperature.

Is the volume of the cold balloon consistent with what you calculated, or is it larger or smaller?

Suggest an explanation for your observation. Explain all of your observations in detail using the kineticmolecular theory of gases.

How does the liquid nitrogen cool the gas in the balloon?

4. Balloon in a �ask:What was the e�ect as the �ask cools?

Can you get the balloon back out again?

5. Kissell's tygon tube:What happens?

Why?6. Cartesian diver:What happens?

Why?

7. The Egg:What happens?

Why?



Can you get the egg back out again?

The minimum pressure reached in the �ask is ��-

8. Expanding balloon:What happens?

Moore's bonus 2 points:1pt to name a real life example of the physical properties of gases at work1pt for a good explanation of how and why it works according to what you have learned in the lab.


ATTRIBUTIONS 111

Attributions

Collection: Honors Chemistry Lab Fall

Edited by: Mary McHaleURL: http://cnx.org/content/col10456/1.16/License: http://creativecommons.org/licenses/by/2.0/

Module: "Initial Lab: Avogradro and All That"By: Mary McHaleURL: http://cnx.org/content/m15093/1.1/Pages: 1-8Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Stoichiometry: Laws to Moles to Molarity"By: Mary McHaleURL: http://cnx.org/content/m15095/1.14/Pages: 9-16Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "VSEPR: Molecular Shapes and Isomerism"By: Mary McHaleURL: http://cnx.org/content/m15100/1.8/Pages: 17-21Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Beer's Law and Data Analysis"By: Mary McHaleURL: http://cnx.org/content/m15131/1.3/Pages: 23-32Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Hydrogen and Fuel Cells"By: Mary McHaleURL: http://cnx.org/content/m15192/1.4/Pages: 33-47Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "The Best Table in the World"By: Mary McHaleURL: http://cnx.org/content/m15206/1.2/Pages: 49-55Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/


112 ATTRIBUTIONS

Module: "Bonding 07"By: Mary McHaleURL: http://cnx.org/content/m15205/1.4/Pages: 57-66Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Solid State and Superconductors"By: Mary McHaleURL: http://cnx.org/content/m15259/1.8/Pages: 67-84Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Organic Reactions"By: Mary McHaleURL: http://cnx.org/content/m15483/1.3/Pages: 85-93Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Transition Metals"By: Mary McHaleURL: http://cnx.org/content/m15503/1.4/Pages: 95-103Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/

Module: "Physical Properties of Gases"By: Mary McHaleURL: http://cnx.org/content/m15545/1.7/Pages: 105-110Copyright: Mary McHaleLicense: http://creativecommons.org/licenses/by/2.0/


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Honors Chemistry Lab Fall

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