1. The Mole, Mass & Formulas
Dr. Ron Rusay
Fall 2001
© Copyright 2001 R.J. Rusay

2. The Mole
Definition: The number of carbon atoms in exactly 12 grams of pure 12C. The number equals  atoms.
1 mole = 6.02  units
6.02  “units” of anything: atoms, people, stars, $s, etc., etc. = 1 mole
There are about 6.2 billion people in the world.
How many moles of people are there?

3. Avogadro’s number equals 1 mole ….which equals
Avogadro’s number equals 1 mole ….which equals
6.022  1023 “units”
How many molecules are there in 0.5 moles of oxygen?

4. Counting by Weighing 12 red marbles @ 7g each = 84g
12 yellow each=48g
55.85g Fe = x 1023 atoms Fe
32.07g S = x 1023 atoms S
Consult the Periodic Table

5. Relative Masses of 1 Mole
CaCO3 Name? g
Oxygen
32.00 g
Copper
63.55 g
Water
18.02 g
1 mole of a gas
equals
22.4 Liters.
(A balloon diameter
of 35 cm.)
What is the volume of
1 mole of water?

6. Atomic and Molecular Weights Mass Measurements
1H weighs x g and 16O x g.
DEFINITION: mass of 12C = exactly 12 amu.
Using atomic mass units:
1 amu = x g
1 g = x 1023 amu

7. Atomic and Molecular Weights
Formula Weight a.k.a. Molecular Weight
Formula weights (FW): sum of Atomic Weights (AW) for atoms in formula.
FW (H2SO4) = 2AW(H) + AW(S) + 4AW(O)
= 2(1.0 amu) + (32.0 amu) + 4(16.0)
= amu

8. Atomic and Molecular Weights
Molecular weight (MW) is the weight of the molecular formula in amu.
MW of sugar (C6H12O6 ) = ?
MW = 6(12.0 amu) + 12(1.0 amu) + 6(16.0 amu)
= 180 amu

9. Molar Mass
A substance’s molar mass is the mass in grams of one mole of the element or compound. (Equals the formula weight: atomic or molecular weight in grams)
Molar Mass CO2 = ?
C = grams per mole (g/mol)
O = grams per mole (g/mol)
CO 2 = grams per mole (g/mol) (16.00) = 44.01

11. Percent Composition Mass percent of an element:
For iron in (Fe2O3), iron (III) oxide = ?

12. Formulas: Dalton’s Law
Dalton’s law of multiple proportions:
When two elements form different compounds, the mass ratio of the elements in one compound is related to the mass ratio in the other by a small whole number.

13. Formulas: Multiple Proportions

14. Formulas & Multiple Proportions Components of acid rain, SO2(g) and SO3(g)
Compound A contains:
1.000 g Sulfur & g Oxygen
Compound B contains:
1.000 g Sulfur & g Oxygen
Mass ratio A: 1 to 1.5; Mass ratio B: 1 to 1
MUST adjust for atomic mass differences: AW sulfur is 2x the AW oxygen; therefore the oxygen ratios are 2x sulfur.
S1O3 and S1O2 respectively

15. Formulas & Molecular Representations
molecular formula = C6H6 Benzene
empirical formula = CH = C6/6H6/6
molecular formula = (empirical formula)n
[n = integer] (CH)6
Other representations: Lewis Dot formulas, structural formulas, 2-D, 3-D

16. Formulas & Molecular Representations

17. Empirical Formulas from Analyses

18. Empirical Formula Determination
1. Use percent analysis.
Let 100 % = 100 grams of compound.
2. Determine the moles of each element.
(Element % = grams of element.)
3. Divide each value of moles by the smallest of the mole values.
4. Multiply each number by an integer to obtain all whole numbers.

19. Empirical & Molecular Formula Determination
Quinine:
C 74.05%, H 7.46%, N 8.63%, O 9.86%
74.05/12.01, 7.46/1.008, 8.63/14.01, 9.86/16.00
C6.166 H7.40 N0.616 O0.616
Empirical Formula: C10 H12 N1 O1
Empirical Formula Weight = ?
Molecular Weight =
Molecular Formula = 2x empirical formula
Molecular Formula = C20 H24 N2 O2

20. Structural Representations of Quinine