1. The Mole
By Mr. M

2. What is the mole?
It is a word that represents a number just like how a dozen represents 12
A mole represents
It is easier to use scientific notation and write it as x1023
Established by Amedeo Avogadro, a lawyer and professor

3. How big is this? 1 mole of pennies would cover the Earth 1/4 mile deep
A mole of paper placed end to end would go beyond pluto
It would take 10 billion chickens laying 10 eggs per day more than 10 billion years to lay a mole of eggs

4. So why use it? Atoms are small
A drop of water the size of a period in size 12 font would contain ten trillion molecules which is thirty trillion atoms.
A mole of atoms of any element can be held in your hands (assuming it was stable)

5. How to use it
A mole of an element has a unique mass called a molar mass.
The molar mass just so happens to be the same number as the atomic mass, but the unit is grams/mole which can be abbreviated g/mol

6. Molar Mass Examples 12.01 g/mol 26.98 g/mol 65.39 g/mol carbon
aluminum
zinc
12.01 g/mol
26.98 g/mol
65.39 g/mol

7. Molar Mass Examples H2O 2(1.01) + 16.00 = 18.02 g/mol NaCl
water
sodium chloride
H2O
2(1.01) = g/mol
NaCl
= g/mol

8. Moles
Avogadro’s number = NA = x 10 23

9. Molar Conversion Examples
How many moles of carbon are in 26 g of carbon?
26 g C
1 mol C
12.01 g C
= 2.2 mol C

10. Molar Conversion Examples
How many molecules are in 2.50 moles of C12H22O11?
6.02  1023
molecules
1 mol
2.50 mol
= 1.51  1024
molecules
C12H22O11

11. Molar Conversion Examples
Find the mass of 2.1  1024 molecules of NaHCO3.
2.1  1024
molecules
1 mol
6.02  1023
molecules
84.01 g
1 mol
= 290 g NaHCO3

12. (mass of part ÷ mass of the whole) × 100
Percent Composition
(mass of part ÷ mass of the whole) × 100

13. Simple version…
the percentage by mass of each element in a compound

14. Percentage Composition
Find the % composition of Cu2S.
g Cu
g Cu2S
%Cu =
 100 =
79.852% Cu
32.07 g S
g Cu2S
%S =
 100 =
20.15% S

15. Percentage Composition
Find the percentage composition of a sample that is 28 g Fe and 8.0 g O.
28 g
36 g
%Fe =
 100 =
78% Fe
8.0 g
36 g
%O =
 100 =
22% O

16. Percentage Composition
How many grams of copper are in a 38.0-gram sample of Cu2S?
Cu2S is % Cu
(38.0 g Cu2S)( ) = 30.3 g Cu

17. C2H6 CH3 Empirical Formula
Smallest whole number ratio of atoms in a compound
C2H6
reduce subscripts
CH3

18. Empirical Formula 1. Find mass (or %) of each element.
2. Find moles of each element.
3. Divide moles by the smallest # to find subscripts.
4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

19. Empirical Formula
Find the empirical formula for a sample of 25.9% N and 74.1% O.
25.9 g
1 mol
14.01 g
= 1.85 mol N
= 1 N
1.85 mol
74.1 g
1 mol
16.00 g
= 4.63 mol O
= 2.5 O

20. N2O5 N1O2.5 Empirical Formula
Need to make the subscripts whole numbers
 multiply by 2
N2O5

21. (CH2)2  C2H4 Molecular Formula empirical mass = 14.03 g/mol
The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is g/mol?
empirical mass = g/mol
28.1 g/mol
14.03 g/mol
= 2.00
(CH2)2  C2H4