1. Vocabulary average atomic mass molar mass
Mona Lisa, Fernando Botero, Colombian.

2. What does “mole” mean?
A mole is a number. It is 6.02x1023. A mole of anything is 6.02x1023 units of that thing.

3. Comparison
So if you have a mole of mice, how many mice do you have? 6.02 x 1023 mice!!! If you have a mole of elephants, how many elephants do you have? 6.02x1023 elephants!!!

4. A mole is a mole!
A mole of mice and a mole of elephants have the same number of animals: 6.02 x But do they have the same mass?

5. NO!!! A mole of elephants weighs substantially more than a mole of mice!
The same is true with atoms. A mole of a light element like hydrogen will have much less mass than a mole of a heavy element like gold.
hydrogen atom gold atom

6. Molar Mass to the rescue
The mass of one mole of every element is on the periodic table. The average atomic mass is the mass of one atom of an element in amu, but that number is also called the molar mass and is the mass of one mole of an element in grams.
Average atomic mass = mass of one atom in amu
Same number!!
Molar mass = mass of one mole in grams

7. Try these: What is the molar mass of carbon?
12.01 g/mol meaning g C = mol C
What is the molar mass of gold?
g/mol meaning g Au = mol Au
What is the molar mass of tungsten?
g/mol meaning g W = mol W

8. What about compounds?
So how do you think we can determine the molar mass of a compound like carbon dioxide, CO2?
Simply add the molar masses of each atom making up the compound. In this case, that means 1 carbon atom and 2 oxygen atoms.

9. What about compounds? To find the molar mass of CO2:
Element
Molar mass
x Number of atoms
Total
carbon
12.01 g/mol
x 1
oxygen
16.00 g/mol
x 2
32.00 g/mol
44.01 g/mol
So the molar mass of CO2 is g/mol, meaning 1 mol of CO2 has a mass of g.

10. You try: What is the molar mass of calcium chloride?
Calcium chloride is CaCl2
Element
Molar mass
x Number of atoms
Total
calcium
40.08 g/mol
x 1
chlorine
35.45 g/mol
x 2
70.90 g/mol
g/mol

11. The use of molar mass
Molar mass is important because it allows us to convert between the mass of a substance and the moles of a substance.

12. Let’s try using molar mass in a dimensional analysis problem
What is the mass of 4.5 moles of gold? (Remember: the molar mass of gold from the periodic table is g/mol.)
4.5 mol Au
g Au
1 mol Au x =
890 g Au
Start with given amount you are trying to convert.
Use appropriate conversion factor.
Write answer with units and rounded to proper sig figs.

13. Let’s try another problem
How many moles of Li2O will have a mass of 392 g? (Remember: find the molar mass of Li2O.
392 g Li2O
1 mol Li2O
29.88 g Li2O x =
13.1 mol Li2O
Start with given amount you are trying to convert.
Use appropriate conversion factor.
Write answer with units and rounded to proper sig figs.