AP Chemistry Chapter 3
Chemical
Quantities
(The Mole)
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
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.
Avogadro’s Number
6.02 x 1023 is called “Avogadro’s Number” in
honor of the Italian chemist Amedeo Avogadro
(1776-1855).
I didn’t discover it. Its
just named after me!
Amadeo Avogadro
The Mole (Quantities)
Mass:
1 mole =
Molar mass (periodic table)
Volume:
1 mole = 22.4 L for a gas @STP
Representative Particles:
1 mole = 6.02 x 1023
atoms
molecules
formula units
(elements) (nonmetals) (cation-anion)
1. Convert 3.00 moles of ammonia, NH3, to
grams of ammonia.
1. Convert 3.00 moles of ammonia, NH3, to
grams of ammonia.
Conversion factor:
1 mole NH3 =
3.00 mol NH3 x
g NH3
mol NH3
??
=
You have to find
molar mass.
(Use Periodic Table)
g NH3
g NH3
Molar mass of ammonia.
NH3
7
N
14.01
14.01 g
x
1
14.01 g
1
H
1.01
1.01 g
x
3
+
3.03 g = 17.04 g NH3
1 mole NH3 = 17.04 g NH3
1. Convert 3.00 moles of ammonia, NH3, to
grams of ammonia.
Conversion factor:
1 mole NH3 =
3.00 mol NH3 x
NH3
g NH3
mol NH3
=
17.04 g NH3
g NH3
51.1 g NH
3
On calculator: 3.00 x 17.04 = 51.12
Round to 3 sig. figs.
14.01
1.01
x 1
x3
14.01 g+ 3.03 g = 17.04 g/mol
Ch. 7 (Calculating Chemical Quantities)
1.
3.00 mol NH3  17.04 g NH3 = 51.1 g NH3
1 mol NH3
14.01
1.01
x 1
x3
14.01 g + 3.03 g = 17.04 g/mol
2.
3.
2. How many molecules of carbon dioxide are in
2.00 moles of CO2?
2. How many molecules of carbon dioxide are in
2.00 moles of CO2?
Conversion factor:
1 mole CO2 = 6.02 x 1023 molecules CO2
2.00 mol CO2 x
molec. CO2
mol CO2
=
molec. CO2
1 mole = 6.02 x 1023 representative
particles
CO2 is made of all nonmetals so
rep. particles are “molecules”
2. How many molecules of carbon dioxide are in
2.00 moles of CO2?
Conversion factor:
1 mole CO2 = 6.02 x 1023 molecules CO2
2.00 mol CO2 x
molec. CO2
mol CO2
=
molec. CO
CO22
1.20 x 1024 molec.
On calculator: 2.00 x (6.02 x 1023) = 1.204 x 1024
Round to 3 sig. figs.
Ch. 7 (Calculating Chemical Quantities)
1.
3.00 mol NH3  17.04 g NH3 = 51.1 g NH3
1 mol NH3
14.01
1.01
x 1
x3
14.01 g + 3.03 g = 17.04 g/mol
2.
6.02 x 1023 molec. CO 2
2.00 mol CO 2 
 1.20 x 1024
1 mol CO 2
molec. CO2
3.
3. How many moles of oxygen are in
44.8 L of oxygen, O2?
Conversion factor:
1 mole O2 = 22.4 L O2
44.8 L O2
x
mol O2
L O2
O 2 O2
= 2.00 molesmoles
On calculator: 44.8 ÷ 22.4 = 2
Show to 3 sig. figs.
1 mole = 22.4 L (for any gas @ STP)
Ch. 7 (Calculating Chemical Quantities)
1.
3.00 mol NH3  17.04 g NH3 = 51.1 g NH3
1 mol NH3
14.01
1.01
x 1
x3
14.01 g + 3.03 g = 17.04 g/mol
2.
6.02 x 1023 molec. CO 2
2.00 mol CO 2 
 1.20 x 1024
1 mol CO 2
molec. CO2
3.
1 mole O 2
44.8 L O 2 
 2.00 mol O2
22.4 L O 2
4. How many grams of lithium are in 3.50
moles of lithium?
Conversion factor:
1 mole Li =
3.50 mol Li
x
g Li
mol Li
=
6.94 g Li
g Li
24.3 g Li
On calculator: 3.50 x 6.94 = 24.29
Round to 3 sig. figs.
The Mole (Quantities)
Mass:
1 mole =
Molar mass (periodic table)
Volume:
1 mole = 22.4 L for a gas @STP
Representative Particles:
1 mole = 6.02 x 1023
atoms
molecules
formula units
(elements) (nonmetals) (cation-anion)
5. How many moles of lithium are in 18.2 grams
of lithium?
Conversion factor:
1 mole Li =
18.2 g Li
x
mol Li
g Li
=
6.94 g Li
2.62 molmolLiLi
On calculator: 18.2 ÷ 6.94 = 2.6225
Round to 3 sig. figs.
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?
3.50 mol Li x
6.02 x 1023 atoms Li
1 mol Li
= 2.11 x 1024 atoms Li
Representative Particles:
Two-part problem
7. How many atoms of lithium are in 18.2 g of
lithium?
18.2 g Li x
1 mol Li
6.94 g Li
x
6.02 x 1023 atoms Li
1 mol Li
(18.2)/6.94 x (6.02 x 1023)
=1.58 x 1024 atoms Li
8. A sample of sodium chloride, (NaCl) commonly
called table salt contains 7.86 g of sodium and
18.14 g of chlorine. Find the % composition.
7.86 g
+ 18.14 g
Total mass = 26.00 g
Find total mass of NaCl
Take the mass of the element divided by total mass.
7.86 g
%Na=
X 100 = 30.23 % Na
26.00 g
%Cl =
18.14 g
X 100 = 69.77 % Cl
26.00 g
9. Find the % composition of propane, (C3H8).
C3H8
12.01 g
x
3
36.03 g
1.01 g
x
8
+
6
1
C
H
12.01
1.01
8.08 g = 44.11 g C3H8
%C =
36.03 g
X 100 = 81.68 % C
44.11 g
%H =
8.08 g
X 100 = 18.32 % H
44.11 g
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?
Formulas
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
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
Empirical Formula Determination
1. Convert grams values to moles for each
element.
2. Divide by lowest moles.
3. If necessary: Multiply each number by an
integer to obtain all whole numbers.
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
8
2. Divide by lowest moles.
S
O
32.07
16.00
6.4 g S
6.4 g O
x
x
1 mol S
32.07 g S
= 0.1995 mol S = 0.20 mol S 1
0.20 mol
1 mol O
16.00 g
= 0.4 = 0.40 mol O 2
O
0.20 mol
Empirical Formula
SSO
O2
11. An unknown clear colorless liquid with no odor is
analyzed and found to contain the following.
Determine the empirical formula.
3.2 % Hydrogen = 3.2 g H
= 19.4 g C
19.4% Carbon
= 77.4 g O
77.4% Oxygen
1. Convert to moles.
2. Divide by lowest moles.
1
6
8
H
C
O
1.01
12.01
16.00
3.2 g H x
19.4 g C x
77.4 g O x
1 mol H
1.01 g H
1 mol C
12.01 g C
1 mol O
16.00 g O
Assume 100 g sample
= 3.16 mol H = 3.2 mol H
1.6 mol
= 1.62 = 1.6 mol C 1
1.6 mol
= 4.84 = 4.8 mol O 3
1.6 mol
Empirical Formula
2
H2CO
CO
H
3
8. A sample of sodium chloride, (NaCl) commonly
called table salt contains 7.86 g of sodium and
18.14 g of chlorine. Find the % composition.
NaCl
22.99 g
x
1
22.99 g
35.45 g
x
1
+
11
17
Na
Cl
22.99
35.45
35.45 g = 58.44 g NaCl
%Na=
22.99 g
X 100 = 39.34 % Na
58.44 g
%O =
35.45 g
X 100 = 60.66 % Cl
58.44 g
The Mole (Quantities)
Mass:
1 mole =
Molar mass (periodic table)
Volume:
1 mole = 22.4 L for a gas @STP
Representative Particles:
1 mole = 6.02 x 1023
atoms
molecules
formula units
(elements) (nonmetals) (cation-anion)