Mathematics of ChemistryThe Mole

Mole = a specific Quantitylike 1 dozen = 12

1. 22.4L of any gas2. 6.02x1023 molecules3. GFM gram formula mass

H2O H 2 x 1 = 2 O 1 x 16 = 16 18g = 1 mole**GFM is the mass of a 1mole sample of any

substance.**All base on C12 as the standard so……H1 has a mass of 1 and = 1/12 of Carbon

Gas Amount Volume Molecules Mass

H2 1 Mole

O2 1 Mole

CO2 1 Mole

Volume

MoleMoleculeMolecule

MassMass

Volume

22.4L22.4L

6.02x1023

GFM

GFM

6.02x1023

÷ X

Doc’s Mole Bridge

What about atoms or particles?

Substance Quantity Volume(L)(L)(

Molecules Mass(grams)

AtomsOr

Particles

Mg 1 Mole 22.4L 6.02x1023 24g 6.02x1023

Atoms

H2 1 Mole 22.4L 6.02x1023 2g 1.02x1024

Particles

CO2 1 Mole 22.4L 6.02x1023 44g 1.86x1024

Particles

X 1

X 2

X 3

Mass to Mole and Mole to Mass

Volume to Mole and Mole to Volume

Volume to Mole and Mole to Volume

Determine percent compositionMass of the part x 100 = % comp.

Whole1. Determine the GFM

H2O H 2 x 1 = 2 O 1 x 16 = 16

18gpart x 100 =%

whole 2/18 x 100 = 11% for H16/18 x 100 = 89% for O

100%

Determine the molecular (True) formula from the empirical formula and molecular mass.

Empirical is NO2 and the molecular mass is 92g1. Determine the empirical mass

NO2 N 1 x 14 = 14 O 2 x 16 = 32

46g2. determine how many times this goes into the

molecular mass = quantity Molec Mass = quantity empirical mass

92/46 = 2

Molecular formula is N2O4

Determine Molecular (True) Formula from Empirical Formula.

The empirical formula of a compound is CH2. Its molecular mass is 70g/mole. What is its molecular formula?

A compound is found to be 40.0% Carbon, 6.7% Hydrogen and 53.5% Oxygen.Its molecular mass is 60. g/mole. What is its Molecular formula?

Determine the Empirical Formula from percent composition.

Steps1. Change percent to gram 75% C = .75g

25% H = .25 g

2. Go from gram to moleC .75/12 = .0625 moleH .25/1 = .25 mole

3. Determine mole ratio (divide each by the lowest).0625/.0625 = 1 C.25/ .0625 = 4 H

Empirical Formula is CH4

Percent Composition of a Hydrate1. Same as a % comp problem2. Hydrate is a crystal that contains water

CuSO4 . 5 H2O This says that 1 mole of Copper II Sulfate contains 5 moles of water

****Calculate the percent of Water in the Hydrate?Steps H2O

1. Calculate the gfm Cu 65, S 32 and 4 Oxy 64 + 5(18) = 251

part x 100 90 x 100 = 36% Whole 251

2. Determine percent of water in Na2S . 9 H20?

Stoichiometry made Simple

• Remember not to panic, just do ratios• Piece of cake