CHAPTER 10The Mole

10.1 MEASURING MATTER Matter can be measured in 3 ways:

Counting particles Mass Volume

MOLE SI unit, measures the amount of substance 602,213,670,000,000,000,000,000

A mole of pennies would be $6,022,136,700,000,000,000,000

six sextillion, twenty-two quintillion, one hundred thirty-six quadrillion, seven hundred trillion dollars

6.02 x 1023

AVOGADRO’S NUMBER 6.02 x 1023

The number of representative particles in one mole of a pure substance

REPRESENTATIVE PARTICLES Atoms

Right off periodic table 7 elements exist only as diatomic

molecules (H2 N2 O2 F2 Cl2 Br2 I2)

Molecules Covalently bonded

Formula Units Ionic Compounds

ONE MOLE OF Fe = 6.02 x 1023 atoms

H2O = 6.02 x 1023 molecules

CaCl2 = 6.02 x 1023 formula units

MOLES REPRESENTATIVE PARTICLES

Conversion factor = 6.02 x 1023 particles

1 mole

How many atoms are in 2.00 mol of argon?

How many molecules are in 7.25 mol of carbon dioxide?

How many formula units are in 3.15 mol of sodium oxide?

REPRESENTATIVE PARTICLES MOLES

How many moles are in 1.62 x 1023 atoms of argon?

How many moles are in 4.35 x 1024 molecules of dinitrogen triflouride?

MOLAR MASS Mass of one mole of a substance

g/mol Mass of atoms is found on the periodic

table K =

Mass of compounds must be calculated H20 CO2

CALCULATING MOLAR MASS What is the molar mass of barium

acetate?

What is the molar mass of ammonium sulfate?

MASS MOLES How many moles are in 12.5 g of

Carbon dioxide?

How many moles are in 83.2 g of H2SO4?

MOLES MASS What is the mass in grams of 1.5 mol of

sodium chloride?

What is the mass in grams of 0.774 mol of oxygen?

MOLAR VOLUME STP

Standard temperature and pressure T = 0 oC P = 1 atmosphere (atm)

At STP 1 mole of gas occupies a volume of 22.4L

22.4L = molar volume of a gas

22.4L of a gas contains 6.02 x 1023 particles of that gas.

MOLES VOLUME What is the volume of 1.50 mol of

nitrogen at STP?

What is the volume of 3.75 mol of helium at STP

VOLUME MOLES How many moles are in 75.3 L of water

vapor at STP?

How many moles are in 250 L of nitrogen dioxide at STP?

CONVERTING BETWEEN UNITS Must ALWAYS go to moles first

Moles

Particles

Volume

Mass

Particles

Volume

Mass

How many atoms are in a 44.3 g piece of iron?

What is the volume of 5.24 x 1022 molecules of iodine?

What is the volume of 68.4 g of fluorine gas at STP?

How many molecules are in 0.75 L of nitrogen gas at STP?

What is the mass in grams of 2.301 L of sodium phosphate?

What is the volume of 17.3 g of NH3 gas at STP?

PERCENT COMPOSITION The percent by

mass of each element in a compound

The percents of all the elements should add up to 100

CALCULATING PERCENT COMPOSITION1. Find the total molar mass of each

element in the compound.2. Find the molar mass of the entire

compound.3. Divide the total molar mass of each

element by the molar mass of the compound then multiply by 100

4. Check that all your percentages add up to 100

EXAMPLE: C3F6

1. Total mass of C = total mass of F =

2. Mass of compound C3F6 =

3. % of C = % of F =

4. Check your work!

What is the percent composition of H2SO4?

10.2 EMPIRICAL AND MOLECULAR FORMULAS

Empirical formula – shows the smallest whole-number ration of atoms in a compound

Molecular formula – gives the actual number of each kind of atom in a molecule

C6H12O6

CALCULATING EMPIRICAL FORMULA1. Change % to g (assume 100 g of

compound so 30% = 30 g)2. Convert each element from g to moles3. Divide each mole amount by the

smallest number from step 24. Change to a whole number = subscript

in empirical formula

EXAMPLE: 30.5% N AND 69.5% O1. g of N = g of O =

2. Convert to moles

3. Divide

4. Formula =

EXAMPLE: 43.7 % P AND 56.3 % O

8.7 MOLECULAR FORMULAS To find the molecular formula you must

know Empirical formula Molar mass of compound

Can be the same as the empirical formula but often is not

CALCULATING MOLECULAR FORMULA1. Calculate the mass of the empirical

formula

2. Divide molar mass of compound by mass of empirical formula

3. Multiply each subscript in the empirical formula by the answer from step 2

EMPIRICAL = NO2, MOLAR MASS = 92 G/MOL

1. Mass of NO2 =

2.

3. Molecular formula =

An unknown compound contains 58.5% carbon, 9.8% hydrogen, and 31.4% oxygen. Its molar mass is 102 g/mol. What are its empirical and molecular formulas?