1. Quantities in Chemistry
The Mole and Molar Mass

2. Mole Review
A Mole is a unit of measurement in chemistry. It represents 6.02 x 1023 of an entity. One mole of sodium is 6.02 x atoms of sodium. The symbol of mole is “mol”.
6.02 x 1023 is also known as Avogadro’s constant.

3. Molar Mass
Molar Mass (M) is the mass (in grams) of one mole of a chemical entity.
The formula for molar mass is:
Molar Mass (M) = mass (g) / mole (mol)
The molar mass of an element can be determined from the periodic table. It is the same number as the atomic mass.
For example Hydrogen’s molar mass is 1.01 g/mol

4. Molar Mass of Compounds
The molar mass of a compound is equal to the sum of the molar masses of the atoms in the molecules or ions in the compound.
For example, the molar mass of water is:
MH2O = 2(MH) + (MO)
= 2(1.01g/mol) + 1(16.0g/mol)
=18.02 g/mol

5. Example: Find the molar mass of H2CO2
M H2CO2 = 2(MH) + (MC) +2(MO)
= 2(1.01g/mol) + (12.00g/mol) + 2(16.0g/mol)
=46.02 g/mol

6. Calculations Involving Atoms, Moles, Mass & Molar Mass
It is often more convenient and practical to determine the number of atoms using mass instead of counting.
It is easier to determine mass by using number of moles

7. Atoms, Moles, Mass & Molar Mass Calculations
Example 1: Calculate the molar mass of magnesium if 0.330mol has a mass of 8.02g
M=m/n
= 8.02g/0.330mol
= 24.3g/mol

8. Atoms, Moles, Mass & Molar Mass Calculations
Example 2: Calculate the mass, in grams, of 2.00 mol of calcium atoms.
M=m/n
m = M x n
= 40.08g/mol x 2.0 mol
= 80.2g

9. Atoms, Moles, Mass & Molar Mass Calculations
Example 3: How many moles of gold are in 275.8g of pure gold?
M=m/n
n = m/M
= 275.8g / g/mol
= mol

10. Calculating Number of Atoms
If you have a mass of the number of moles of an item, you can determine the number of molecules in an amount of an element using Avogadro’s number.
Avogadro’s number = 6.02 x 1023 atoms/mol

11. Atom Calculations
Example 4: How many atoms of gold are in a 232.8g of pure gold?
Step 1: Determine the number of moles
n = m/M
= 232.8g / 197.0g/mol
= mol
Step 2: Using Avogadro’s number and the number of moles, determine the number of atoms.
N= n x NA
= mol x 6.02 x 1023 atoms/mol
= 7.12 x 1023 atoms

12. Atom Calculations
Example 5: How many atoms of sulfur are in a 230.0g of pure sulfur?
Step 1: Determine the number of moles
n = m/M
= 230.0g / 32.06g/mol
= mol
Step 2: Using Avogadro’s number and the number of moles, determine the number of atoms.
N= n x NA
= mol x 6.02 x 1023 atoms/mol
= x 1024 atoms