 What is a Mole?
 What is the mass of a NaCl molecule?

Chapter 7.1b

Common counting units:
 shoes by the pair (pair = 2)
 eggs by the dozen (dozen = 12)
 paper by the ream (ream = 500 sheets).

Counting With Moles o Chemical reactions usually involve very large numbers of tiny particles o We use a counting unit called the mole to measure amounts of a substance.
o Mole (mol) = amount of any substance that contains approximately 6.02 × 10 23 particles.
o This amount is known as Avogadro’s number .
o Ex: 1 mole of iron = 6.02 × 10 23 atoms of iron.

Molar Mass:
 mass of one mole of a substance
 same as atomic mass, in grams.
Examples:
 Carbon:
 Atomic mass = 12.0 amu
 Molar mass = 12.0 grams.
 Sulfur:
 Atomic mass = 32.1 amu
 Molar mass = 32.1 grams.

Counting With Moles o Molar Mass of a compound = o o sum of atomic masses of all its atoms, expressed in grams.
Tells us the total grams in one mole of the compound
•
•
•
•
Example: Carbon dioxide (CO
2
)
1 carbon atom = 12.0 amu
2 oxygen atoms = (2 × 16.0 amu) = 32.0 amu
•
CO
2 atomic mass = (12.0 + 32.0) = 44.0
CO
2 molar mass = 44.0 grams
44.0g CO
2 in 1 mol CO
2 amu

Mole-Mass Conversions


Knowing the molar mass of a substance lets you easily convert between moles and mass
“ converting” means you can calculate one from the other
Example:
 Molar mass of CO
2 is 44.0 grams
1.0 mole of CO
2
= 44.0 grams
 Conversion factors 
OR

Converting Example: Chocolate
Cake Recipe
Recipe calls for 4 eggs per cake and you plan to make
3 cakes. Eggs can only be bought by the dozen (i.e. groups of 12). How may dozen eggs do you need to buy?
Conversion factors: 4 eggs 1 cake
1 cake 4 eggs
12 eggs 1 doz. eggs
1 doz. eggs 12 eggs
Calc: 3 cakes x 4 eggs x 1 doz eggs = 1 doz eggs
1 cake 12 eggs

Counting With Moles o o
You have 55.0 grams of CO
2
. How many moles?
To calculate how many moles of CO
2 you have, multiply the mass by a conversion factor.
o You can check your answer.

Chemical Calculations o In chemical reactions, the mass of a reactant or product can be calculated.
o Use a balanced chemical equation and the molar masses of the reactants and products.

Chemical Calculations o In a balanced chemical equation, the number of atoms of each element on the left equals the number of atoms of each element on the right.

Chemical Calculations o The Coefficient tells us the # of moles of each reactant and product involved the reaction

Chemical Calculations o Molar Mass = the # of grams per mole of each reactant and product

Chemical Calculations o o
Mass (of a reactant or product) = the # of moles in the balanced equation
(Coefficient) x the molar mass.

Chemical Calculations - Stoichiometry
Converting Mass to Moles
To calculate how much oxygen is required to make 144 grams of water, begin with a balanced chemical equation for the reaction.
•
2H
2
+ O
2

2H
2
O
Determine how many moles of water you are trying to make.
• Convert the given mass (144g) of water into moles.

Chemical Calculations
Using Mole Ratios
 Write the conversion factors, or mole ratios.
 2H
2
+ O
2

2H
2
O
 Calculate how many moles of oxygen are required to produce eight moles of water.

Chemical Calculations
Converting Moles to Mass
 Convert moles of O
2 to grams of O
2 using the molar mass of O conversion factor.
2 as a by
 To produce 144 grams of H
2
O, you must supply 128 grams of O
2
.

Assessment Questions
1.
Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? a.
b.
c.
d.
Al + NH
4
ClO
4
4Al + 3NH
4
ClO
4
8Al + NH
4
ClO
4
—› 4Al
2
O
—› 4Al
2
O
3
3
+ 3NH
+ NH
4
Cl
4
Cl
8Al + 3NH
4
—› Al
2
O
3
ClO
4
+ NH
4
Cl
—› 4Al
2
O
3
+ 3NH
4
Cl

Assessment Questions
1.
Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? a.
b.
c.
d.
Al + NH
4
ClO
4
4Al + 3NH
4
ClO
4
8Al + NH
4
ClO
4
—› 4Al
2
O
—› 4Al
2
O
3
3
+ 3NH
+ NH
4
Cl
4
Cl
8Al + 3NH
4
—› Al
2
O
3
ClO
4
+ NH
4
Cl
—› 4Al
2
O
3
+ 3NH
4
Cl
ANS: D

Assessment Questions
2.
How many moles of NaCl (molar mass
= 58.5) are there in a 5.85-gram sample?
a.
58.5 mol b.
5.85 mol c.
0.10 mol d.
0.28 mol

Assessment Questions
2.
How many moles of NaCl (molar mass
= 58.5) are there in a 5.85-gram sample?
a.
58.5 mol b.
5.85 mol c.
0.10 mol d.
0.28 mol
ANS: C

Assessment Questions
3.
In the reaction shown below, how many grams of hydrogen are produced when 10 moles of potassium react with water?
2K + 2H
2
O —› 2KOH + H
2 a.
2.5 g b.
5 g c.
d.
10 g
20 g

Assessment Questions
3.
In the reaction shown below, how many grams of hydrogen are produced when 10 moles of potassium react with water?
2K + 2H
2
O —› 2KOH + H
2 a.
2.5 g b.
5 g c.
d.
10 g
20 g
ANS: C

Assessment Questions
1.
In the chemical equation below, the reactants are carbon dioxide and water.
CH
4
+ 2O
2
—› CO2 +2H
2
O
True <or> False?
ANS: False, products