GSI notes:

Week 1S1b: take pictures of students to remember names; get into groups for check-in; one drawer per group of three at a lab bench; safety lecture; collect group contract for ICP

S1c: Icebreakers; Great chance to go around to groups and make sure that they are in their roles (speak only with reporter); facilitate discussion/summary at end; really build on scientific method. Collect ICP-S1c

Week 2S2a: Demonstrate use of the balanceWrite the two questions (1a,b,c) up on the board.Between 1962 and 1982, pennies were 95% copper and 5% zinc (mass 3.1g). During1982, the composition was switched to 97.6% zinc, and 2.4% copper.(mass 2.5g) Diameter: 19.mm, Thickness:1.25 mm

There are 8 groups of pennies (2 random, 1960s, 1970s, 2-1980s, 1990s, 2000s) as students get done taking data and graphing it; then begin data collection discussion.

Start with hypothesis. Take a survey.Then goto the data collected to answer the first question. Start with the random groups and get them to show both of their graphs. Analogy to Battleship (take systematically random approach until you find a target.) Then create a new hypothesis and a new plan for “collecting data.” (What data would you want to have?) Then you can go through decades systematically by decade or zoom in on the 80s and then go through the other decades. Remember that you need to confirm that the composition didn’t change through 2006. Look at both graphs from each group if possible.

Have students collect all of the data in an Excel file (S2a_pennies) which they e-mail you. Collect all of the data and e-mail it back out. Then put them to work on the rest of the questions and problems.

Last fall, the classes did not get to do the problems. Tell the students that the are good practice problems and you may return to them later.

Collect ICP-S2a

S2b pretty much runs on its own; students should be self sufficient but worth going around and asking questions. Make sure they are taking on their group roles; discussion to wrap things up at the end. No ICP today

S2c

Foiled Again (30 minutes)

ObjectivesStudents will identify alternate forms of measurement for very small objects (weighing).Students will solve problems by analyzing and using conversion factors.Students will evaluate the soundness of their answers.Students will be able to explain why we use the mole.

MisconceptionsStudents feel they cannot measure the thickness accurately.

Student DifficultiesStudents may find it hard to relate mass and moles to a form of measurement.Relating the macroscopic measurements to microscopic measurements.Incomprehensible size of atoms. Finding a conversion factor for atoms/cm.

Task Reason Notes

Place a large jar of candy in front of classroom and have students guess how many pieces of candy are in the jar. Winner gets the jar.

Grabs attention of students. Only collect the guesses.

Ask students to devise a method of determining the number of candy pieces without counting them.

Requires problem solving. Students should end up wanting the mass of the candy and dividing by the mass of one piece of candy.

After students solve the problem announce a winner.

Ask students to measure the thickness of a square piece of aluminum foil in centimeters.

Students will see the need for alternate methods of measurement.

Instruct students that only accurate measurements will be considered.

When students cannot determine the thickness ask them to determine the number of atoms in the aluminum foil.

The students will have to relate it to mass (like the candy problem) and Avogadro’s number.

The approximate mass is 0.045 g for a one-inch square piece of aluminum foil.

Give students density of aluminum to determine the volume of their aluminum foil in centimeters.

Using conversion factors. Density = 2.70 g/cm3 at 25oC

Ask students to determine thickness in centimeters. Using conversion factors.  

Ask students to determine the thickness in terms of atoms.Hint: They need a conversion

Shows that atoms are very small and relates atoms to a measurement.

Must convert density to atoms/cm3 and then take the cube root. This is very difficult for

factor for atoms/cm. students.

Have students evaluate the soundness of their answers. To visualize size of atom. Foil should be approx. 1 x 105

atoms thick.

Ask students to compare the candy problem with what they did with aluminum foil and to comment on the importance of the mole (put it in writing).

Students have to relate macroscopic candy to microscopic atoms to determine why the mole is useful.

Students will have to realize that counting in chemistry is done by weighing.

Discuss the results. To relate mass, moles, dimensional analysis.

The size of atoms and the importance of Avogadro’s number should be realized.

Ask students to determine how much money their aluminum would be worth if each atom were a penny and how long would it take for them to spend it if they spent it at a rate of $100 billion a day.

Concluding activity to stress the incomprehensible size of atoms. Practice with conversion factors.

Their answer should be of the magnitude of 105 years.

New Element (15 min)

ObjectivesStudents will determine the "atomic mass" of M&Ms.Students will use Avogadro's number.

MisconceptionsAtomic mass is the mass of an atom of an element

Task Reason

Ask students "If M&M's were to be added to the periodic chart as a new element what atomic weight would be used?"

To evaluate the students' knowledge of how to use Avogadro's number and understanding of what atomic mass is.

Have students explain how they determine their answers. To evaluate their method.

Give students other questions to practice using the mole. To review.

Notes: This activity will clearly show any misconception students have about the mole and atomic weight. Many students will report the mass of one M&M as the atomic weight. Asking students if one atom of hydrogen weighs more than ONE M&M can clear up some confusion. Other students may try to determine a "molecular" weight by using ingredients in an M&M, thus

missing the definition of "element" altogether. Others may probe deeper and will want to know how many protons and neutrons are in an M&M. These students are trying to use the formal definition of atomic mass. Finally, some students may bring up the fact that there are many different types of M&M's (plain, peanut, peanut butter, almond, etc.). This fact can be used to discuss isotopes.

Collect ICP-S2c

Week 3

S1a Atomic Hotel (30 minutes)

ObjectivesStudents will be able to define Aufbau principle, Pauli Exclusion Principle, and Hund's Rule.Students will be able to distinguish between ground and excited states.Students will be able to determine when these quantum mechanical rules are broken or not.Students will be able to list and describe the four quantum numbers.Students will be able to explain the "order of evacuation" of electrons from an atom.

Misconceptions

An electron in the excited state breaks Hund's Rule.

DifficultiesUnderstanding why a 3d level can fall between 4s and 4p

Task Reason

Allow students to work through the provided worksheet.

To introduce a simple analogy to help students understand quantum mechanical rules.

Summarize all the rules and definitions covered on the worksheet.

To give the rules in a chemistry setting rather than a "hotel" setting.

There is a PP to guide this studio. The atomic hotel is a great analogy; then you get to help make the connection to real atoms.

S3b Students should do most of this work on their own. Walk around to help groups with questions and keep them on task. At the end, hold a review/discussion. Have each of the groups tell you the general direction of one of the trends by drawing directional arrows as shown for atomic number on the first page of the studio.

Collect ICP-S3b

S3c

Collect their penny lab reports at the beginning of the studio. Mark anyone whose is late (+/- five minutes as 10% off.)

There are three things going on today1) They create their own periodic table from “fictional” elements2) They learn about periodic trends in LEDs3) They tackle a periodic trend problem Doubleelectron

ICP points should be awarded for periodic table presentations; LEDs is a mini-lecture, please prepare accordingly. Double electron will throw them for a loop. Insist that they can do it and that it is a good check of their understanding of the rules associated with electrons and atoms

Week 4

S4a Lewis Structures. Students should work in groups. Again, move around to answer questions and ask questions to keep the students moving along. May want to do a discussion/wrap up at the end

For ICP today do a one-minute paper. ~ 3 minutes before the end of class ask the students to individually write on a sheet of paper what they found to be the most confusing and what questions they still have.

S4b: VSEPR This will be a challenging day for students, but they will learn a lot. Note: we don’t talk about hybridization in class.

You might do a little intro to the rules; you might not.

Have students work through 3 & 4. Assign one table to present “3” showing off their Lewis structures, models, angles, and names for geometries. Ask the students which should be the same for each of these molecules the electron pair geometry or the molecular geometry. Verify correct angle measurements. (120o and ~115o) Tell the students the actual electron pair geometry and molecular geometry names. (The book uses triangular planar and angular (as opposed to trigonal planar and bent).

Then have each of the other three tables present one of group of “4,” including their Lewis structure, model, angles, and geometry names. Students will have a very hard time coming up with the tetrahedral shape! You will probably see mostly a 2-D structure with all of the hydrogen atoms in the same plane. If no one gets a tetrahedral structure, ask them about the bond angles and if it is possible to spread the atoms out more evenly? Ask them to think 3-D and start by moving one hydrogen out of the plane. Give them a minute or two to work on their structure. Then see if any are close. Show them the shape and give them the bond angles

(109.5o) for methane. Then ask them to adjust their work with this knowledge. Collect all of the answers and provide the actual geometries and angles (Tetrahedral, triangular pyramidal, angular and 109.5o, 107.5o, and 104.5o)

Once everyone is set on the “3” and “4” geometries, let them move onto the “5” and “6” geometries. Have each group present one of the 5 or 6 molecules. Collect ideas for geometries and the supply the correct geometries and angles.

5: Triangular bipyramidal (90o/120o/180o), seesaw (~<90o/<120o/<180o), T-shaped (even smaller angles than the seesaw), linear (180o) 6: octahedral (90o/180o), square pyramidal(~<90o), square planar (90o).

Collect ICP-S4b.

S4c Food brief. Student presentations to be evaluated by you and the course instructors. Try to end a few minutes early so we can discuss grades.

Week 5

S5a Students will work on their own initially. This is again a challenging topic for students to see the net polarity of a molecule. I usually think in terms of a net vector analogy, but this often goes over their heads. Tug-of-war is more familiar. One fun way to demonstrate polarity is to have a person sit on a chair and be the central atom. Then students stand around this person who is holding the appropriate number of strings/bungee cords and pulls on their string with their assigned electronegativity difference (greater differences pull harder.) Make sure not to always give the stronger pulling to males

Collect ICP-S5a

S5b

Like dissolves like (25 minutes)Objectives

Students will be able to collect data in an organized fashion.Students will identify intermolecular forcesStudents will classify polar and non-polar solvents.

Misconceptions:If oil floats on water and ethanol in one tube then it should in both tubes.

Student difficultiesExplaining the difference in density when different amounts of water and ethanol are mixed.

  Task Reason Notes

1

Give students oil, water, and ethanol and ask them to find out which ones mix and collect observations.

To develop skills of experimental design and data collection.

Urge students to use drops of the substances (small test tubes)

2Give them the instructions. Have them make observations before and after shaking the test tubes.

To see how water, oil, and ethanol mix.

The densities of ethanol, water, and vegetable oil are important here.

3

Give the structures of water, oil and ethanol, and have students make a list of similarities and differences in the structures.

To identify intermolecular forces and distinguish between polar and non-polar molecules.

 

4

Have students explain their observations in terms of intermolecular forces, solubility, and polarity.

To determine how structure and intermolecular forces affect solubility in polar and non-polar solvents.

The difference in densities may not be obvious.

5

Discuss the results and bring up important concepts (ie like dissolves like, intermolecular forces, density).

To review previously learned concepts like intermolecular forces and relate them to solubility.

 

The Structures

*Vegetable oil consists primarily of Soybean Oil.According to the Merck Index, Soybean Oil has the following components:Triglycerides of oleic acid (26%), of linoleic acid (49%), of linolenic acid (11%), of saturated fats (14%), free fatty acids (<1%), lecithin (1.5-4%), stigmasterol, sitosterols, and tocopherols (0.8%). Lecithin, stigmasterol, sitosterols, and tocopherols are removed when the oil is processed. The structure for the triglyceride of linoleic acid is provided because that is the largest component of vegetable oil.

SimilaritiesAll structures contain hydrogen and oxygen.

DifferencesEthanol and vegetable oil contain carbon and water does not.Vegetable oil contains long carbon chains.Vegetable oil is a much larger structure.

The Explanation

Water is a polar molecule and ethanol is only slightly polar due to its short carbon chain. Ethanol is soluble in water because like dissolves like. Neither water nor ethanol is soluble in vegetable oil because the oil is not polar due to its long hydrophobic carbon chains.

The Results

The colored solutions of the chemicals will allow students to see that blue water and red ethanol will mix to give a purple combination, while the oil remains separated. In Test Tube #1, the vegetable oil will float on top of the water and ethanol mixture. In Test Tube #2, the vegetable oil will sink below the mixture. The resulting density of the water/ethanol mixture explains these observations. When more water is used then the density of the mixture is greater than that of the oil. When more ethanol is used then the density is less than that of the oil..

2) Boiling away (50 minutes)

ObjectivesStudents will identify the intermolecular forces present in a liquid based its structure.Students will explain the relationship between intermolecular forces and evaporation.Students will determine the relative strengths of intermolecular forces.Students will relate intermolecular forces to other properties like boiling points.

MisconceptionsEvaporation is only related to temperature (heat).Any molecule containing hydrogen has hydrogen bonding.1

Shape of molecule is not important in determining intermolecular forces present.1

Boiling (or evaporation) breaks covalent bonds.1

Student DifficultiesDescribing the relationship between evaporation and intermolecular forces.

Describe why, at room temperature, propane is a gas, water is a liquid, and salt is a solid. The boiling point of propane is lower than room temp, the melting point of water is lower than room temp and the boiling point is higher than room temp, and the melting point of salt is higher than room temp. Melting point, boiling point, and evaporation are effected by the forces of attraction holding the compounds together. Salt has electrostatic forces, water has H-bonding and dipole-dipole, and propane has only dispersion.

Why do these substance have different magnitudes of temperature change? What factors affect evaporation?

The structures are different and have different forces holding them together. The ones with stronger intermolecular forces will take longer to evaporate and will have a small change in temp. Pentane has only dispersion; acetone has dipole-dipole, ethanol has small dipole-dipole and H-bonding, and 1-propanol has smaller dipole-dipole but larger dispersion than ethanol.

Based on the structures of the chemicals:a) How does the structure, which had the largest temperature change, differ from the others?

Many students said pentane does not have any oxygen, which is true. Since it does not have oxygen (or nitrogen or fluorine) it only has dispersion forces holding it together. The other molecules have dipole-dipole and H-bonding.

b) How does the structure, which had the smallest temperature change, differ from the others?

Many students said that 1-propanol has an -OH group and one more carbon and two more hydrogens than ethanol. 1-propanol has small dipole-dipole, small H-bonding, and larger dispersion than ethanol.

Table 3. Intermolecular Forces in the Liquids.

# Chemical StructureMolecular

Weight (g/mol)

Temperature Change

(oC)

Intermolecular Forces

1 Pentane 72.15 ~ 25 dispersion

2 Acetone 58.08 ~ 20 dipole-dipoledispersion

3 Ethanol 46.07 ~ 10 dipole-dipoleH-bondingdispersion

4 1-propanol 60.10 ~ 5 dipole-dipoleH-bondingdispersion

QuestionBased on what you have learned in this activity, predict the approximate temperature change associated with the evaporation of methanol, formaldehyde, and 2-propanol. The structures are provided below. Where would they fall among the 4 liquids you tested? You must provide reasoning for your answer in order to receive any credit.

Methanol Formaldehyde 2-propanol

SubstanceMolecular

Wt. (g/mol)ForcesPresent

Predicted Tempchange (oC) Reasoning

Methanol 32.04H-bonding

dipole-dipoledispersion

~ 15 it has the same forces as ethanol, but it is smaller so it has less dispersion and should evaporate quicker

Formaldehyde30.03 dipole-dipole

dispersion ~ 24 it has same forces as acetone, but it is smaller. (Actually, it should be >25 due to its small size and weak forces)

2-propanol 30.10 dipole-dipoledispersion

~ 9 - 10or< 5

it is your

it is just like 1-propanol, but the dipole is more centered in the molecule maybe making it more compact (less dispersion) but not quite as small as ethanol --Some actually argued that the

reasoning that counts

dipole forces would be stronger resulting in a smaller temp change.

3) Surface Tension (20 minutes)

ObjectivesStudents will identify the forces responsible for the phenomena of surface tension. Students will explain why surfactants break surface tension.Students will relate microscopic phenomena to macroscopic properties.

MisconceptionsPaper clips will not float on water because they are metal.

Student Difficulties

Activity

  Task Reason

1Ask students if different objects will float on water and why – weights, straw, wood, paper clips, sewing needles.

This calls upon the experience of the students.

2 Allow the students to try to float paper clips on water.

Presents a challenge to some students. How many can they get to float?

3Once students are successful with the paper clips, give them paper clips that have been rubbed in dish detergent.

The students are presented with a problem when these paper clips will not float.

4 Show pictures of the microscopic diagram of surface tension and surfactant chemistry.

To identify forces creating surface tension and explain why surfactants break surface tension.

5Have students define surface tension and explain why the first set of paper clips would float and the second set would not.

To relate macroscopic properties to microscopic properties.

6 Review objectives and discuss student results.

To describe surfactant chemistry in terms of intermolecular forces.

Let the students work with the paperclips and answer the questions. Review the answers to the intermolecular forces and then ask why the second set of paperclips would not float. Create a

diagram to explain. (The surfactant collects at the water surface and creates a ion-dipole interaction at the water’s surface. The tails stick up in the air. The result is that the water molecules now have intermolecular interactions with other water molecules as well as with the surfactant molecules at the surface creating a more balanced pull on the surface water molecules and much less net tension in a single direction. NOTE: ion-dipole will be a “new” intermolecular force for the students. In lecture only dispersion, dipole-dipole, and H-bond were introduced.

Collect ICP_S5b

S5c

This is a classic lab. It works! The surrounding materials keep getting rewritten. Last year students had a really hard time with the diagrams. I would let them get started and they should be able to make it to the data collection and through the data collection with relatively little problem. Make sure that they collect all of their data and get it sent out to the entire class. If a group has an extra person I might suggest putting him/her in charge of collecting and sending all of the data out in an Excel sheet. The students need all of the data from all groups (mass/volume water used, mass salt and change in temp.)

After the data is collected, the students may struggle a bit with the follow up questions. Please help as needed and do a 5-10 wrap us discussion at the end. T

Collect ICP-S5c

______________________________________________________________________________

Week 6

S6a

You may need to revisit the hot pack studio if it was not finished in time.

Nutty time: Caution, students will be playing with fire!!! This is new (but pretty well published). Advise students to dispose of matches properly (soak in water and put in the solid wasted buckets.)

Each group will determine the caloric content of two nuts or a nut and a cheese puff. Assign their task.

Collect ICP-S6a

S6b

This is just a day in class to work problems and ensure that students have good handle on thermochemistry. The first half is a demo (computer interactive.) The second half is problems. This ran tight last year, so please work to keep students on pace.

Some of the first half may be redundant from lecture…it depends on how far we get.

Collect ICP-S6b

Week 7

S7b Group Change today! This will take a little bit of time. These are new groups for the rest of the semester.

The thermo section will complete this topic in the course and hopefully get them warmed back up from Fall break.

The solution section is just to introduce solution chemistry. Q7 How many differences in cooking recipe and electrochemical cell recipe (English vs. metric; solids given in dimensions; chemical glassware (beakers); solutions used Some of the solution problems will be a challenge. Please help students along as needed; mostly they will just need to be shown that it is all about dimensional analysis. They need to leave some time for the ICP problem (another challenge, but a good group problem.)

Collect ICP-S7a and new group contracts

S7c There is a lot of reading at the beginning. The two goals of this studio are to 1) get the diagram filled out and ensure that the students understand what is going on; 2) get students prepped for the next lab since time will be tight.

The students will need to do two sets of calculations: 1) conversion of ammonium to nitrate and 2) volumes for their nitrate standards.

Collect ICP-S7c

Week 8

S8a The experiment will take the students a while. Problems that you can anticipates: 1) getting the students to think about and find a good wavelength2) Steps 1&2 they must have left over zinc to filter out; otherwise they won’t have converted all nitrate to the salt and their data will be messed up

Try to get them through calculations by the end. If not, you can pick up with them next studio.

Collect ICP-S8a

S8bTwo goals: 1) progress with the case study so that students will be ready to find Cl- concentration at septic tank next studio2) Have students learn solubility rules

For solubility tests

Objectives:Students will design an experimental procedure.Students will be able to identify precipitation reactions.Students will draw conclusions based on observations.Students will develop general rules for solubility based on charge.

MisconceptionsThere are never exceptions to rules.

Student DifficultiesDistinguishing between precipitation reactions and color changes.

Intro:

Previously, the dissolution of salt, or solution chemistry has been reviewed. Although, you have seen that many salts dissolve in water, there are many more which are not soluble. As a consequence, when two or more soluble compounds are mixed in water, a new insoluble substance may form. This insoluble substance is called a precipitant and this type of reaction is called a precipitation reaction. For example, when solutions of AgNO3 and NaCl are mixed the following occurs:

Ag1+ (aq) + NO31- (aq) + Na1+ (aq) + Cl- (aq) --> Na1+ (aq) + NO3

1- (aq) + AgCl (s)

AgCl is an insoluble compound, a precipitant. Na1+ and NO31- are called spectator ions because

they do not participate in the reaction. Therefore, a net equation can be written:

Ag1+ (aq) + Cl- (aq) --> AgCl (s)Demo:Do demo on overhead: add x drops of AgNO3 to a small, clear evaporation dish. Then add the same number of drops of NaCl. You should get silver chloride precipitate.

In solution, ions of like charge will repel one another, while ions of opposite charge will attract one another. If the enthalpy of solvation is not enough to overcome solute enthalpy, then a precipitate may form. However, enthalpy of solvation is difficult to predict. Let’s consider Coulomb’s law

F = q1q2/Er2

where F is the force of attraction for oppositely charged particles and the force of repulsion for like charged particles, q1 and q2 are the charges of interacting ions, r is the distance separating the charged particles, and E is the dielectric constant and is related to the polarity of a solvent. When opposite charges come together the magnitude of the charges determines the force of attraction between them. Therefore, compounds containing highly charged ions tend to be less soluble than compounds containing +1 and –1 ions.

End the studio with a wrap up to make a class consensus on solubility.Why did we not see a precipitate when Ca2+ and SO4

2- were mixed?-CaSO4 is sometimes listed as soluble or slightly soluble rather than insoluble. It actually

depends on the concentration of the ions. The CRC Handbook lists the Ksp of CaSO4 as 2.45 x 10-5, which is close to the solubility limit.

Collect ICP-S8b

S8c

The goal is to wrap up the case study. Be very careful with the reagents used today.

Collect ICP-8c

Week 9

S9a

Ksp

Fe(OH)3 2.79 x10-39

CaSO4 4.93 x10-5

Ca(OH)2 5.02 x10-6

AgCl 1.77 x10-10

Ag2SO4 .20 x10-5

Students should try to precipitate silver with chloride, then calcium with sulfate, followed by iron with hydroxide. They do not need to save precipitates, just fill in the ICP.

Part 2: limiting reagents. More practice with solution calculations. Check to make sure that students are comparing moles; may need help with idea of stochiometrically. Also more practice with solubility rules.

Students will discover that their predictions are correct for reactions A and B, but for C they find both reactants. That sets you up for the short PP introduction to equilibrium.

Collect ICP-9a

S9a

Students use pennies and graphs to discover:1) that equilibrium means equal rates (not equal concentrations) 2) that equilibrium is dynamic3) starting at different concentrations/combinations leads to the same equilibrium

Collect ICP-9b

S9c

Watershed meetings will be taking place with the course instructors while students work on the concept of solubility products

The Ksp of CaCO3-2 is 8.3 x10-9

Week 10

S10a

Students see their first acid-base reaction trough Alka-Seltzer and practice concepts such as writing chemical reactions and limiting reagents.

They then use vinegar and Alka-Seltzer tables to evaluate a suggested protocol for determining the mass of sodium bicarbonate in an antacid tablet.

1. Since the quantity of vinegar is not required in the calculation, the content of acetic acid in vinegar is not crucial. However, vinegar with a lower concentration will result in a later switch of the limiting reactant from the acid (H+) to NaHCO3 and vice versa.2. To improve the results for the early runs one might use a 10 mL graduated cylinder for the measurement of vinegar.3. The spattering of reaction mixture resulting from the bubbling of CO2 during the reaction may cause an extra weight loss. Therefore, the use of a tall type cup (or beaker) with volume around 250 mL is suggested.4. The cup containing reaction mixture is swirled during the experiment to ensure thorough mixing of the reaction mixture and complete release of the gas product (CO2).5. For a 10 min reaction period, there is a 35~70 mg of weight decrease in the blank vinegar-water solution depending on the temperature and the humidity in the room. The quantity of CO2 dissolved in 35 mL of reaction solution is approximately 46 mg (1). While the evaporation of water leads to too large a value of percent by mass of NaHCO3, the dissolving of CO2 in solution will affect the result in the opposite way.

Therefore, the combination of the two errors should only give a minimal effect on both the shape of the curve in the graph and the percent by mass of the NaHCO3.

Wrap up with a discussion of the merits and drawbacks to the experiment.

Collect ICP-10a

S10b

Students will spend the studio carrying out acid/base calculations with real-life scenarios. There are there challenges which get harder as they go along. They may need help with #3. These give them good practice with use of ICE tables and problem solving.

Collect ICP-10b

S10c

Equilibrium presentations today. You and an instructor will evaluate.

Week 11

S11a

Watershed day

S11b

1a) Preparation of the stock solution of bromocresol green (BCG)

Bromocresol green [76-60-8], ACS reagent, was used as received (Merck, Darmstadt, Germany).

The 1.8 x10-4 mol L-1 stock solution of BCG is prepared using no more than 12 mg of indicator, because it

has low solubility in water, weighed within 0.0001 g. The solid is transferred quantitatively to a 100 mL volumetric

flask and 90 mL of distilled water is added. In order to accelerate the dissolution of the indicator, the solution should

be sonnicated during 5 to 10 min. After complete dissolution, the solution is diluted to the mark.

Students should take aliquots of 0.50, 1.00, 1.50, 2.50, 4.50, 5.10, 6.00, 6.30 and 7.50 mL of stock solution

with an adjustable pipette. These aliquots should be diluted in separate 10 mL volumetric flasks. This is a good

range of concentration for this indicator to observe the color changes, as shown in Figure 1.

Figure 1 shows six cuvets containing the diluted aqueous solutions of BCG in decreasing order of

concentration. The color change can be clearly observed from the initial reddish color, which changes to blue for the

most diluted solution.

Figure 1: Aqueous BCG solutions at different concentrations: (1) 6.00, (2) 1.80, (3) 0.60,

(4) 0.30, (5) 0.18, (6) 0.059 x 10-4 mol L-1.

Try to get students to work through this one on their own. It is an exercise in observation,

models, spectroscopy, and finding Ka values.

Collect-ICP11b

Week 12

Finish up OxiClean (this only involves weighing and a few calculations; the remainder of the time is another opportunity to work on the Watershed project.Collect ICP-12a

Enjoy Thanksgiving break. No studio on Wednesday or Friday

Week 13

S13aBuffers: assign each group a pH: 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5 and then set up a system for rotating buffer solutions so that each group can check the pH and the buffer capacity.At the end do a group discussion of buffer capacity and see which group got the closest in their preparations. Note any trends and be sure that a consensus answer to the initial question, which pH buffer is best was reached.

Collect-ICP13a

S13b

Work on poster criteria for ~ 50 minutes. Collect Watershed poster criteria. Then move onto activity series. Get as much done as possible. This can spill a little bit over onto Friday if needed.

S13c

There will be a follow up to the watershed poster planning.

There is NOOOO! Way that the e-chem cell models should take up an entire two hours. But, they are very important. This will leave time for finishing up the activity series and a Q&A before the exam.

Week 14

S14a

Students make electrochemical cells. Then see affects of concentration and temperature.

Collect ICP-14a

S14bVitamin C and scurvy. Much fun with citrus fruit. No right answer, whatever the data best supports. Assign groups a fruit based on availability.

Collect ICP-14b

S14cFun with polymers and lab checkout. The polymers go quickly and they get souvenirs.

Week 15

S15a Students have their watershed posters due! Come ready to evaluate.

S15b Students will have an in class individual Chemical Scholarship exercise