MOLES

What is a mole?!?

6.022 X 6.022 X 10102323

The Mass of 1 mole of a substance (in grams)

Equal to the average atomic mass from

periodic table (round to the tenths place)

1 mole of C atoms = 12.0 g

1 mole of Mg atoms = 24.3 g

1 mole of Cu atoms = _____

Molar MassMolar Mass

Find the molar mass

(round to the tenths place)

Learning Check!Learning Check!

A.1 mole of Sn atomsB.1 mole of Br2 atoms

=____________

=____________

Formula Mass - Mass in grams of 1 mole equal to the sum of the atomic masses

1 mole of CaCl2

1 mole Ca x 40.1 g/mol = 40.1 g/mol

+ 2 moles Cl x 35.5 g/mol = 71.0 g/mol

111.1 g/mol CaCl2

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

How do we measure items?

You can measure mass, or volume, or you can count pieces. We measure mass in grams. We measure volume in liters. We count pieces in MOLES.

What is the mole?

We’re not talking about this kind of mole!

Moles (is abbreviated: mol)

A mole is defined as the number of carbon atoms in exactly 12 grams of carbon-12.

1 mole = 6.02 x 1023 particles.

Treat it like a very large dozen 6.02x 1023 is called: Avogadro’s

number.

Just How Big is a Mole?Just How Big is a Mole?

Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.

If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

Cue song!

The MoleThe Mole

1 dozen cookies = 12 cookies 1 mole of cookies = 6X1023

1 dozen cars =_12 cars 1 mole of cars= 6X1023 Cars

1 dozen Al atoms =________ atoms 1 mole of Al atoms =_______ atoms

Note that the NUMBER is always the same, but the MASS is very different!

Mole is abbreviated mol (gee, that’s a lot quicker to write, huh?)

= 6.022 x 1023 C atoms

= 6.022 x 1023 H2O molecules

= 6.022 x 1023 NaCl “molecules”

A Mole of ParticlesA Mole of Particles

Contains 6.02 x 1023 particles

1 mole C

1 mole H2O

1 mole NaCl

6.02 x 1023 particles 1 mol

or

1 mol

6.02 x 1023 particles

Note that a particle could be an atom OR a molecule!

Avogadro’s Number as Avogadro’s Number as Conversion FactorConversion Factor

So if one mole of C = 12 g How many moles is 24g? ____ What did you do?

Divided by Molar mass So to set up always Start with what you

are given then use dimensional analysis to get you to what you want.

24g C x 1mole C = 2 moles 12gCancel units!

Show in Dimensional analysis1. Number of grams in 0.500 mole of Al

2. Number of grams in 2.0 moles of CO2

Learning CheckLearning Check

Chalk Lab

Weigh a piece of ordinary chalk and write your name on the sidewalk. Weigh the chalk again, and determine the number of moles of calcium carbonate that were used. Show your work using dimensional analysis.

Weight of chalk before writing your name: _______________

Weight of chalk after writing your name: _______________

Grams of chalk required to write your name: _______________

EMPIRICAL AND MOLECULAR FORMULAS

Chemical Formulas of Chemical Formulas of CompoundsCompounds

Formulas give the relative numbers of atoms or Formulas give the relative numbers of atoms or moles of each element in a formula unit - always a moles of each element in a formula unit - always a whole number ratio (the law of definite whole number ratio (the law of definite proportions).proportions).

NONO22 2 atoms of O for every 1 atom of N 2 atoms of O for every 1 atom of N

1 mole of NO1 mole of NO22 : 2 moles of O atoms to : 2 moles of O atoms to every 1 mole of N atomsevery 1 mole of N atoms

If we know or can determine the relative number If we know or can determine the relative number of moles of each element in a compound, we can of moles of each element in a compound, we can determine a formula for the compound.determine a formula for the compound.

Types of FormulasTypes of Formulas Empirical FormulaEmpirical Formula

The formula of a compound that The formula of a compound that expresses the expresses the smallest whole number smallest whole number ratioratio of the atoms present. of the atoms present.

Ionic formula are always empirical formulaIonic formula are always empirical formula

Molecular FormulaMolecular FormulaThe formula that states the The formula that states the actualactual

number of each kind of atom found in number of each kind of atom found in one one moleculemolecule of the compound. of the compound.

Formulas

•Example: molecular formula for benzene is C6H6 (note that everything is divisible by 6)

•Therefore, the empirical formula = CH (the lowest whole number ratio)

Formulas (continued)

Formulas for molecular compounds MIGHT be the same as empirical (lowest whole number ratio).

Molecular:

H2O

C6H12O6 C12H22O11

Empirical:

H2O

CH2O C12H22O11

(Correct formula)

(Lowest whole number ratio)

To obtain an Empirical To obtain an Empirical FormulaFormula

1.1. Determine the mass in grams Determine the mass in grams of each of each element present, if necessary.element present, if necessary.

2.2. Calculate the number of Calculate the number of molesmoles of of each each element.element.

3.3. Divide each by the smallest number of moles Divide each by the smallest number of moles to obtain the to obtain the simplest whole number ratio.simplest whole number ratio.

If whole numbers are not obtainedIf whole numbers are not obtained** in step 3), in step 3), multiply through by the smallest number multiply through by the smallest number that will give all whole numbersthat will give all whole numbers

** Be careful! Do not round off numbers prematurelyBe careful! Do not round off numbers prematurely

Ex) A sample of a brown gas, a major air pollutant, is Ex) A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a found to contain 2.34 g N and 5.34g O. Determine a formula for this substance.formula for this substance.

Convert grams to molesConvert grams to moles

moles of N = moles of N = 2.34g of N 2.34g of N = 0.167 moles of N= 0.167 moles of N 14.01 g/mol14.01 g/mol

moles of O = moles of O = 5.34 g5.34 g = 0.334 moles of O = 0.334 moles of O 16.00 g/mol16.00 g/mol

Formula:Formula: 0.334 0.167ON0.167 0.334 2

0.167 0.167

N O NO

Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and 45.11 %N.

Assume 100 g sample, so 38.67 g C x 1mol C = 3.22 mole C

12.0 g C 16.22 g H x 1mol H = 16.22 mole H

1.0 g H 45.11 g N x 1mol N = 3.22 mole N

14.0 g N

Now divide each value by the smallest value

Example

The ratio is 3.22 mol C = 1 mol C 3.22 mol N 1 mol

N The ratio is 16.22 mol H = 5 mol H

3.22 mol N 1 mol N

= C1H5N1 which is = CH5N

Practice

A compound is 43.64 % P and 56.36 % O. What is the empirical formula?

Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

= P2O5

= C4H5N2O

Empirical to molecular

1. add up the mass of the empirical formula.

2. Divide the mass of the molecular formula by the mass of the empirical formula.

3. Multiply the empirical formula by that number.

Calculation of the Molecular Calculation of the Molecular FormulaFormula

A compound has an empirical formula of NOA compound has an empirical formula of NO22. The . The

colorless liquid, used in rocket engines has a molar colorless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the mass of 92.0 g/mole. What is the molecular formula molecular formula of of this substance?this substance?

Molecular Formula is N2O4

Formula MassN = 14 g * 1 mol = 15 g/molO = 16 g * 2 mol = 32 g/molNO2 = 46 g/mol

= 92 g/mol 46 g/mol= 2

Molecular Formula Practice

The empirical formula for a compound is CH2O. Find the Molecular formula is the compounds Molecular Weight or Molar Mass is 180 g/mol?

CALCULATING WITH MOLES-STOICHIOMETRY

Chocolate Chip Cookies!!

1 cup butter

1/2 cup white sugar

1 cup packed brown sugar

1 teaspoon vanilla extract

2 eggs

2 1/2 cups all-purpose flour

1 teaspoon baking soda

1 teaspoon salt

2 cups semisweet chocolate chips

Makes 3 dozen

•How many eggs are needed to make 3 dozen cookies?

•How much butter is needed for the amount of chocolate chips used?

•How many eggs would we need to make 9 dozen cookies?

•How much brown sugar would I need if I had 1 ½ cups white sugar?

Stoichiometry

From the Greek words stoicheion meaning “element” and metron meaning “measure” . . . measurement of the elements

Stoichiometry deals with the mass relationships between chemical elements

Mole Ratio

A mole ratio is a conversion factor that relates the amounts of moles in any two substances involved in a chemical reaction

Because any balanced chemical equation shows us the relative numbers of moles of the reactants and products we can write mole ratios for all chemical species given Ex. 2HgO(s) 2 Hg (l) + O2(g) The

equation tells us there are 2 moles of Mercury (II) Oxide, 2 moles of Mercury, and 1 mole of Oxygen gas

Chemistry Recipes

Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe)

Be sure you have a balanced reaction before you start!

Example: 2 Na + Cl2 2 NaCl This reaction tells us that by mixing 2 moles of

sodium with 1 mole of chlorine we will get 2 moles of sodium chloride

What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

Mole RatioIn Moleville…the mole ratio is needed to pass the guards to

jump on the mole bridge to change from one substance to another

1. Always start with a Balanced equation!2. Write what you are given with the label 3. Your mole ratio should be the ratio of the moles of what you

want to what you are given.

Ex) Given 3 moles of H2 how many moles of water can be produced?

2H2 + O2 → 2H2O

Mole Ratios

Example: How many moles of chlorine are needed to react with 5 moles of sodium (without any sodium left over)?

2 Na + Cl2 2 NaCl

5 moles Na 1 mol Cl2

2 mol Na= 2.5 moles Cl2

Mole-Mass Conversions Most of the time in chemistry, the amounts

are given in grams instead of moles We still go through moles and use the mole

ratio, but now we also use molar mass to get to grams

Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to produce sodium chloride?

2 Na + Cl2 2 NaCl

5.00 moles Na 1 mol Cl2 70.90g Cl2

2 mol Na 1 mol Cl2

= 177g Cl2

Mass-Mole We can also start with mass and convert to

moles of product or another reactant We use molar mass and the mole ratio to get

to moles of the compound of interest Calculate the number of moles of ethane (C2H6)

needed to produce 10.0 g of water 2 C2H6 + 7 O2 4 CO2 + 6 H20

10.0 g H2O 1 mol H2O 2 mol C2H6

18.0 g H2O 6 mol H20

= 0.185 mol C2H6

Mass-Mass Conversions

Most often we are given a starting mass and want to find out the mass of a product we will get (called theoretical yield) or how much of another reactant we need to completely react with it.

1. Change grams to moles 2. Do your mole ratio to switch

substances 3. Change moles to grams of that

substance

Mass-Mass Conversion

Ex. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen.

N2 + 3 H2 2 NH3

2.00g N2 1 mol N2 2 mol NH3 17.06g NH3

28.02g N2 1 mol N2 1 mol NH3

= 2.4 g NH3

Practice

How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen? 3Ca + N2 → Ca3N2

LIMITING REACTANTS AND PERCENT YIELD

Limiting Reactants and Percent Yield In the lab as well as industry,

reactions are rarely carried out with exactly the required amount of each reactants. In most reactions, one or more reactants is in excess.

Limiting Reactants The substance that is used up first is the

limiting reactant. The substance that is left over after the

reaction is the excess reactant. If you have 50 bicycle frames and 80

bicycle wheels, how many bicycles can be made. What limits the number of bicycles?

Example Problem

The reaction between solid white phosphorus and oxygen produces solid tetraphosphorus decoxide. Determine the mass of tetraphosphorus decoxide formed if 25.0 g of phosphorus (P4) and

50.0 g of oxygen are combined.

P4 +O2 → P4O10

When given masses of 2 reactants you need to determine the limiting reactant so go to moles of the product first. The one that makes the least moles is limiting.

Then change the moles to grams of the product to determine number of grams produced.

Percent Yield Similar calculations are made to

determine the success of a chemical reaction because most reactions do not succeed in producing the predicted amount of product.

Reactions fail to go to completion Liquid adheres to containers or

evaporates Solids get stuck in filter paper or lost in

the purification process.

Percent Yield Theoretical yield- the maximum amount of

product that can be produced from a given amount of reactant. (stoichiometry)

Actual yield-the amount of product actually produced when the reaction is carried out. (experimental)

Percent yield-the ratio of the actual yield to the theoretical yield as a percent.

100 x yield ltheoretica

yield actual yieldpercent

Percent Yield From the previous problem, the theoretical

yield was calculated to be 57.3 g P4O10. When the reaction was conducted in the lab 52.5 g of product was collected.

The percent yield is:

% 91.6 100 x 0P g 57.3

0P g 52.5 yield %

104

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