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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