1. AP Chemistry Chapter 3
Chemical Quantities
(The Mole)

2. Amedeo Avogadro
Hypothesis: Equal volumes of different gases at the same temperature and pressure contain equal numbers of particles. H2
hydrogen
CH4
methane
Amadeo Avogadro

3. The Mole 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023
There are exactly 12 grams of carbon-12 in one mole of carbon-12.

4. I didn’t discover it. Its just named after me!
Avogadro’s Number
6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amedeo Avogadro ( ).
I didn’t discover it. Its just named after me!
Amadeo Avogadro

5. The Mole (Quantities) Mass: 1 mole = Molar mass (periodic table)
Volume:
1 mole =
22.4 L for a
Representative Particles:
1 mole =
6.02 x 1023
atoms molecules formula units
(elements) (nonmetals) (cation-anion)

6. 1. Convert 3.00 moles of ammonia, NH3, to grams of ammonia.

7. You have to find molar mass.
1. Convert 3.00 moles of ammonia, NH3, to grams of ammonia.
Conversion factor:
1 mole NH3 = ?? g NH3
g NH3
3.00 mol NH3 x =
g NH3
mol NH3
You have to find molar mass.
(Use Periodic Table)

8. NH3 Molar mass of ammonia. N H 1 mole NH3 = 17.04 g NH3 14.01 g 1.01 g
x 1
x 3
14.01 g
g =
17.04 g NH3
1 mole NH3 = g NH3

9. 1. Convert 3.00 moles of ammonia, NH3, to grams of ammonia.
Conversion factor:
1 mole NH3 = g NH3 1
17.04
g NH3
3.00 mol NH3
51.1 g NH3 x =
g NH3
mol NH3
NH3
On calculator: 3.00 x = 51.12
x x 3
14.01 g g = g/mol
Round to 3 sig. figs.

10. Ch. 7 (Calculating Chemical Quantities)
17.04 g NH3
1 mol NH3 1.
= 51.1 g NH3
x 1 x 3
14.01 g g = g/mol 2. 3.

11. 2. How many molecules of carbon dioxide are in 2.00 moles of CO2?

12. 1 mole = 6.02 x 1023 representative particles
How many molecules of carbon dioxide are in
2.00 moles of CO2?
Conversion factor:
1 mole CO2 = 6.02 x 1023 molecules CO2
molec. CO2
2.00 mol CO2 x =
molec. CO2
mol CO2
1 mole = 6.02 x 1023 representative particles
CO2 is made of all nonmetals so
rep. particles are “molecules”

13. How many molecules of carbon dioxide are in 2.00 moles of CO2?
Conversion factor: 1
1 mole CO2 = 6.02 x 1023 molecules CO2
6.02 x 1023
molec. CO2
2.00 mol CO2 x =
1.20 x 1024 molec. CO2
molec. CO2
mol CO2
On calculator: 2.00 x (6.02 x 1023) = x 1024
Round to 3 sig. figs.

14. Ch. 7 (Calculating Chemical Quantities)
17.04 g NH3
1 mol NH3 1.
= 51.1 g NH3
x 1 x 3
14.01 g g = g/mol 2.
1.20 x 1024
molec. CO2 3.

15. 1 mole = 22.4 L (for any gas @ STP)
3. How many moles of oxygen are in
44.8 L of oxygen, O2?
Conversion factor: 1
1 mole O2 = L O2
22.4
mol O2
44.8 L O2 x =
2.00 moles O2
moles O2
L O2
On calculator: 44.8 ÷ 22.4 = 2
Show to 3 sig. figs.
1 mole = 22.4 L (for any STP)

16. Ch. 7 (Calculating Chemical Quantities)
17.04 g NH3
1 mol NH3 1.
= 51.1 g NH3
x 1 x 3
14.01 g g = g/mol 2.
1.20 x 1024
molec. CO2 3.
2.00 mol O2

17. 24.3 g Li 4. How many grams of lithium are in 3.50 moles of lithium?
Conversion factor: 1
1 mole Li = g Li
6.94
g Li
3.50 mol Li x =
24.3 g Li
g Li
mol Li
On calculator: 3.50 x 6.94 = 24.29
Round to 3 sig. figs.

18. The Mole (Quantities) Mass: 1 mole = Molar mass (periodic table)
Volume:
1 mole =
22.4 L for a
Representative Particles:
1 mole =
6.02 x 1023
atoms molecules formula units
(elements) (nonmetals) (cation-anion)

19. 2.62 mol Li 5. How many moles of lithium are in 18.2 grams of lithium?
Conversion factor: 1
1 mole Li = g Li
6.94
mol Li
18.2 g Li x =
2.62 mol Li
mol Li
g Li
On calculator: 18.2 ÷ 6.94 =
Round to 3 sig. figs.

20. Representative Particles: Using Avogadro’s Number
Use 6.02 x 1023 when looking for atoms, molecules, or formula units
6. How many atoms of lithium are in 3.50 moles of lithium?
6.02 x 1023 atoms Li
3.50 mol Li x
= atoms Li
2.11 x 1024
1 mol Li

21. Representative Particles: Two-part problem
7. How many atoms of lithium are in 18.2 g of
lithium?
6.02 x 1023 atoms Li
1 mol Li
18.2 g Li x x
6.94 g Li
1 mol Li
(18.2)/6.94 x (6.02 x 1023)
= atoms Li
1.58 x 1024

22. 8. A sample of sodium chloride, (NaCl) commonly called table salt contains 7.86 g of sodium and g of chlorine. Find the % composition.
Find total mass of NaCl
7.86 g g
Total mass = g
Take the mass of the element divided by total mass.
7.86 g
%Na =
X 100 =
30.23 % Na
26.00 g
18.14 g
%Cl =
X 100 =
69.77 % Cl
26.00 g

23. C3H8 C H = = 9. Find the % composition of propane, (C3H8). 12.01 g6 C
12.01 1 H
1.01
12.01 g
1.01 g
x 3
x 8
36.03 g
g =
44.11 g C3H8
36.03 g %C =
X 100 =
81.68 % C
44.11 g
8.08 g %H =
X 100 =
18.32 % H
44.11 g

24. 10. A 12. 8 g sample of a gas contains 6. 4 grams of sulfur and 6
10. A 12.8 g sample of a gas contains 6.4 grams of sulfur and 6.4 grams of oxygen. What is the empirical formula for this gas?

25. Formulas empirical formula = CH
Empirical formula: the lowest whole number ratio of atoms in a compound.
Molecular formula: the true number of atoms of each element in the formula of a compound.
molecular formula = (empirical formula)n where n = integer
molecular formula = C6H6 = (CH)6
empirical formula = CH

26. Formulas (continued)
Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio).
Molecular:
H2O
C6H12O6
C12H22O11
Empirical:
H2O
CH2O
C12H22O11
All can be divided by 6

27. Empirical Formula Determination
Convert grams values to moles for each element.
Divide by lowest moles.
If necessary: Multiply each number by an integer to obtain all whole numbers.

28. S O SO2 Empirical Formula S O x x
10. A 12.8 g sample of a gas contains 6.4 grams of sulfur and 6.4 grams of oxygen. What is the empirical formula for this gas?
1. Convert to moles. 16 S
32.07 8 O
16.00
2. Divide by lowest moles.
1 mol S x
6.4 g S =
mol S = 0.20 mol S 1
32.07 g S
0.20 mol
1 mol O
6.4 g O x
= 0.4 = 0.40 mol O 2
16.00 g O
0.20 mol
S O
SO2
Empirical Formula

29. H C O H2CO3 Empirical Formula H C O Assume 100 g sample = 3.16 mol H
11. An unknown clear colorless liquid with no odor is analyzed and found to contain the following.
Determine the empirical formula.
3.2 % Hydrogen
19.4% Carbon
77.4% Oxygen
= 3.2 g H
= 19.4 g C
= 77.4 g O
1. Convert to moles.
2. Divide by lowest moles. 1 H
1.01 6 C
12.01 8 O
16.00
Assume 100 g sample
1 mol H
3.2 g H =
3.16 mol H
= 3.2 mol H x 2
1.01 g H
1.6 mol
1 mol C
19.4 g C x
= 1.62
= 1.6 mol C 1
12.01 g C
1.6 mol
1 mol O
77.4 g O x
= 4.84
= 4.8 mol O 3
16.00 g O
1.6 mol
H C O
H2CO3
Empirical Formula

30. 8. A sample of sodium chloride, (NaCl) commonly called table salt contains 7.86 g of sodium and g of chlorine. Find the % composition.
NaCl 11 Na
22.99 17 Cl
35.45
22.99 g
35.45 g
x 1
x 1
22.99 g
g =
58.44 g NaCl
22.99 g
%Na =
X 100 =
39.34 % Na
58.44 g
35.45 g %O =
X 100 =
60.66 % Cl
58.44 g

31. The Mole (Quantities) Mass: 1 mole = Molar mass (periodic table)
Volume:
1 mole =
22.4 L for a
Representative Particles:
1 mole =
6.02 x 1023
atoms molecules formula units
(elements) (nonmetals) (cation-anion)