1. Using Moles to Count Atoms
Chapter 3 Section 4 Notes
Using Moles to Count Atoms

2. What is a mole?
The SI base unit that describes the amount of a substance; a collection of a very large number of particles.

3. What is a mole useful for?
Counting small particles

4. Avogadro’s Constant
Avogadro’s Constant: the number of particles in 1 mol
Equals x 1023 particles/ mol
602,213,670,000,000,000,000,000 particles
How does Avogadro’s constant relate to a mole of something?
It is the number of particles in one mole of anything.

5. Moles and Grams are related
Molar Mass: the mass in grams of 1 mol of a substance
How do you find molar mass?
The average atomic mass is equal to molar mass.
Simply look on the Periodic Table!

6. Practice
Determine the molar mass of the following elements: (Round to the nearest hundredth)
Manganese, Mn
54.94 g/mol
Cadmium, Cd
g/mol
Arsenic, As
74.92 g/mol
Strontium, Sr
87.62 g/mol

7. More Practice Determine the mass, in grams of each of the following:
0.48 mol of platinum
2.50 mol of sulfur
0.48 mol x g =
94 g
1 mol
2.50 mol x
32.07 g =
80.2 g
1 mol

8. Even More Practice
Determine how many moles are present in each of the following:
620 g of mercury
11 g of silicon
620 g x
1 mol
= 3.09 mol g
11 g x
1 mol
= 0.39 mol
28.09 g

9. Compounds also have molar mass
To find the molar mass of a compound, add up the molar masses of all the atoms in a molecule of the compound.
Example: H2O
Molar Mass of Hydrogen: 1.01 x 2 = 2.02 g/mol
Molar Mass of Oxygen: 16 g/mol
Total Mass of H2O: 2.02 g + 16 g = g/mol