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Chapter 12Chapter 12

Chemical QuantitiesChemical Quantities

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How do you measure How do you measure things?things?

We measure mass in grams.We measure mass in grams. We measure We measure volumevolume in in

liters.liters. We count atoms or We count atoms or

compounds in compounds in MOLES.MOLES.

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MolesMoles Defined as the number of Defined as the number of

carbon atoms in exactly 12 carbon atoms in exactly 12 grams of carbon-12.grams of carbon-12.

1 mole is 6.02 x 101 mole is 6.02 x 102323 particles.particles.

6.02 x 106.02 x 102323 is called is called Avogadro’s number.Avogadro’s number.

MEMORIZE this number!MEMORIZE this number!

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Types of questionsTypes of questions How many molecules of COHow many molecules of CO22 are in are in

4.56 moles of CO4.56 moles of CO22 ? ?

How many moles of water is 5.87 x How many moles of water is 5.87 x 10102222 molecules? molecules?

How many atoms of carbon are there How many atoms of carbon are there in 1.23 moles of Cin 1.23 moles of C66HH1212OO66 ? ?

How many moles is 7.78 x 10How many moles is 7.78 x 102424 formula units of MgClformula units of MgCl22??

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Measuring MolesMeasuring Moles The decimal number on the The decimal number on the

periodic table is also the periodic table is also the mass of 1 mole of those mass of 1 mole of those atoms in grams.atoms in grams.

Called Called molar massmolar mass # on PT = 1 mole# on PT = 1 mole

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ExamplesExamples How much would 2.34 moles of How much would 2.34 moles of

carbon weigh?carbon weigh? How many moles of magnesium How many moles of magnesium

in 24.31 g of Mg?in 24.31 g of Mg? How many atoms of lithium in How many atoms of lithium in

1.00 g of Li?1.00 g of Li? How much would 3.45 x 10How much would 3.45 x 102222

atoms of U weigh?atoms of U weigh?

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What About Compounds?What About Compounds? in 1 mole of Hin 1 mole of H22O molecules there are O molecules there are

two moles of H atoms and 1 mole of O two moles of H atoms and 1 mole of O atomsatoms

To find the mass of one mole of a To find the mass of one mole of a compound compound – determine the moles of the elements determine the moles of the elements

they havethey have– Find out how much they would weighFind out how much they would weigh– add them upadd them up

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What is the mass of one mole of What is the mass of one mole of CHCH44??

1 mole of C = 12.01 g1 mole of C = 12.01 g 4 mole of H x 1.01 g = 4.04g4 mole of H x 1.01 g = 4.04g 1 mole CH1 mole CH44 = 12.01 + 4.04 = = 12.01 + 4.04 =

16.05g16.05g The The molar mass molar mass of CHof CH44 is 16.05g is 16.05g

What About Compounds?What About Compounds?

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Molar MassMolar Mass The mass of one mole of a The mass of one mole of a

compound.compound. What is the molar mass of FeWhat is the molar mass of Fe22OO33??

2 moles of Fe x 55.85 g = 111.70 g2 moles of Fe x 55.85 g = 111.70 g 3 moles of O x 16.00 g = 48.00 g3 moles of O x 16.00 g = 48.00 g The molar mass = 111.70 g + 48.00 The molar mass = 111.70 g + 48.00

g = 159.70gg = 159.70g

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ExamplesExamplesCalculate the molar mass of the Calculate the molar mass of the

following:following:

1.1. NaNa22SS

2.2. NN22OO44

3.3. CC6060

4.4. Ca(NOCa(NO33))22

5.5. CC66HH1212OO66

6.6. (NH(NH44))33POPO44

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Using Molar MassUsing Molar Mass

Finding moles of Finding moles of compoundscompounds

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Molar MassMolar Mass The number of grams of 1 The number of grams of 1

mole of atoms, ions, or mole of atoms, ions, or molecules.molecules.

Make conversion factorsMake conversion factors Change grams of a Change grams of a

compound to moles of a compound to moles of a compound.compound.

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g mole

g

need to change grams to moles

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g mole

g

need to change grams to moles for NaOH:

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g mole

g

need to change grams to moles for NaOH: 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g mole

g

need to change grams to moles for NaOH: 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g 1 mole

40.00 g

need to change grams to moles for NaOH: 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

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For exampleFor example

How many moles is 5.69 g of How many moles is 5.69 g of NaOH?NaOH?

5 69. g 1 mole

40.00 = 0.142 mol NaOH

g

need to change grams to moles Need molar mass for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g

1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

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ExamplesExamples1.1. How many moles is 4.56 g of COHow many moles is 4.56 g of CO22

??

2.2. How many grams is 9.87 moles How many grams is 9.87 moles of Hof H22O?O?

3.3. How many molecules in 6.8 g of How many molecules in 6.8 g of CHCH44??

4.4. 49 molecules of C49 molecules of C66HH1212OO66 weighs weighs

how much?how much?

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Gases and the MoleGases and the Mole

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GasesGasesMany of the chemicals Many of the chemicals we deal with are gases.we deal with are gases.

Difficult to weighDifficult to weighHow do we know how How do we know how many moles of gas we many moles of gas we have?have?

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GasesGasesTwo things effect the Two things effect the

volume of a gas:volume of a gas:1.1. TemperatureTemperature2.2. PressurePressureCompare at the same Compare at the same

temperature and temperature and pressure.pressure.

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Standard Temperature Standard Temperature and Pressureand Pressure

STP is 0ºC and 1 atm STP is 0ºC and 1 atm pressurepressure

At STP 1 mole of gas At STP 1 mole of gas occupies 22.4 Loccupies 22.4 L

This is called This is called molar molar volumevolume

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Avogadro’s HypothesisAvogadro’s Hypothesis

at the same temperature at the same temperature and pressure, equal and pressure, equal volumes of gas have volumes of gas have the same number of the same number of particles.particles.

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ExamplesExamplesWhat is the volume of 4.59 What is the volume of 4.59 mole of COmole of CO22 gas at STP? gas at STP?

How many moles is 5.67 L How many moles is 5.67 L of Oof O2 2 at STP?at STP?

What is the volume of 8.8g What is the volume of 8.8g of CHof CH44 gas at STP? gas at STP?

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Density of a GasDensity of a Gas The units will be The units will be g / L g / L We can determine the density We can determine the density

of any gas at STP if we know its of any gas at STP if we know its formula.formula.

If you assume you have 1 mole, If you assume you have 1 mole, then the mass is the molar mass then the mass is the molar mass (P.T.)(P.T.)

At STP the volume is 22.4 L.At STP the volume is 22.4 L.

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ExamplesExamples1.1. Find the density of COFind the density of CO22 at at

STP.STP.

2.2. Find the density of CHFind the density of CH44 at at

STP.STP.

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The other wayThe other way Given the density, we can find the Given the density, we can find the

molar mass of the gas.molar mass of the gas. Again, pretend you have a mole at Again, pretend you have a mole at

STP, so V = 22.4 L.STP, so V = 22.4 L. m is the mass of 1 mole, since you m is the mass of 1 mole, since you

have 22.4 L of a gas.have 22.4 L of a gas. What is the molar mass of a gas What is the molar mass of a gas

with a density of 1.964 g/L?with a density of 1.964 g/L? 2.86 g/L?2.86 g/L?

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All the things we can All the things we can changechange

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We have learned how We have learned how to changeto change

moles to gramsmoles to grams moles to atomsmoles to atoms moles to compoundsmoles to compounds moles to litersmoles to liters compounds to atomscompounds to atoms compounds to ionscompounds to ions

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Moles

Mass

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Moles

MassPT

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Moles

MassVolume PT

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Moles

MassVolume PT22.4 L

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Moles

MassVolume

Compounds

PT22.4 L

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6.02 x 1023

Moles

MassVolume

Compounds

PT22.4 L

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Moles

MassVolume

Compounds

6.02 x 1023

PT

Atoms

22.4 L

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Moles

MassVolume

Compounds

6.02 x 1023

PT

Atoms Ions

22.4 L

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Percent CompositionPercent Composition

Part x 100 %Part x 100 %

WholeWhole

Find the mass of each Find the mass of each component, then divide component, then divide by the total mass.by the total mass.

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ExampleExample

Calculate the Calculate the percent composition percent composition of a compound that of a compound that is 29.0 g of Ag with is 29.0 g of Ag with 4.30 g of S.4.30 g of S.

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Getting percent Getting percent composition from the composition from the

formulaformula

If we know the If we know the formula, assume formula, assume you have 1 mole.you have 1 mole.

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ExamplesExamplesCalculate the percent Calculate the percent composition of Ccomposition of C22HH44

Calculate the percent Calculate the percent composition of composition of Aluminum carbonate.Aluminum carbonate.

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Empirical FormulaEmpirical Formula

From percentage to From percentage to formulaformula

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Empirical Formula Empirical Formula - The - The lowest whole number ratio lowest whole number ratio of elements in a compound.of elements in a compound.

Molecular FormulaMolecular Formula - the - the actual ratio of elements in a actual ratio of elements in a compound.compound.

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Empirical and Molecular Empirical and Molecular FormulaFormula

- The two - The two cancan be the same. be the same. CHCH22 empirical formula empirical formulaCC22HH44 molecular formula molecular formulaCC33HH66 molecular formula molecular formulaHH22O bothO both

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Calculating EmpiricalCalculating EmpiricalFind the lowest whole number ratioFind the lowest whole number ratio CC66HH1212OO66 CHCH44OO It is not just the ratio of atoms, it is It is not just the ratio of atoms, it is

also the ratio of moles of atoms.also the ratio of moles of atoms. In 1 mole of COIn 1 mole of CO22 there is 1 mole of there is 1 mole of

carbon and 2 moles of oxygen.carbon and 2 moles of oxygen. In one molecule of COIn one molecule of CO22 there is 1 there is 1

atom of C and 2 atoms of O. atom of C and 2 atoms of O.

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Calculating EmpiricalCalculating Empirical We can get ratios from percent We can get ratios from percent

composition by assuming you composition by assuming you have 100g.have 100g.

The percentages become The percentages become grams.grams.

Can turn grams to moles. Can turn grams to moles. Find lowest whole number ratio Find lowest whole number ratio

by dividing by the smallest.by dividing by the smallest.

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ExampleExample Calculate the empirical formula of a Calculate the empirical formula of a

compound composed of 38.67 % C, 16.22 % compound composed of 38.67 % C, 16.22 % H, and 45.11 %N.H, and 45.11 %N.

Assume 100 g soAssume 100 g so 38.67 g C x 1mol C = 3.220 mole C 38.67 g C x 1mol C = 3.220 mole C

12.01 gC 12.01 gC 16.22 g H x 1mol H = 16.09 mole H 16.22 g H x 1mol H = 16.09 mole H

1.01 gH 1.01 gH 45.11 g N x 1mol N = 3.219 mole N 45.11 g N x 1mol N = 3.219 mole N

14.01 gN 14.01 gN

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ExampleExample The ratio is…The ratio is…

3.220 mol C = 1 mol C3.220 mol C = 1 mol C 3.219 molN 1 mol N 3.219 molN 1 mol N

The ratio is…The ratio is…

16.09 mol H = 5 mol H16.09 mol H = 5 mol H 3.219 molN 1 mol N 3.219 molN 1 mol N

CC11HH55NN11

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

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Empirical to molecularEmpirical to molecular empirical formula =lowest ratioempirical formula =lowest ratio Actual molecule would weigh more Actual molecule would weigh more

by a by a whole numberwhole number multiple. multiple. Divide the actual molar mass by Divide the actual molar mass by

the mass of one mole of the the mass of one mole of the empirical formula.empirical formula.

Caffeine has a molar mass of 194 Caffeine has a molar mass of 194 g. what is its molecular formula?g. what is its molecular formula?