Chapter 3 Section 4 Notes

Using Moles to Count Atoms

What is a mole?

The SI base unit that describes the amount of a substance; a collection of a very large number of particles.

What is a mole useful for?

Counting small particles

Avogadro’s Constant

Avogadro’s Constant: the number of particles in 1 molEquals 6.022 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.

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!

Practice

Determine the molar mass of the following elements: (Round to the nearest hundredth) Manganese, Mn

54.94 g/mol Cadmium, Cd

112.41 g/mol Arsenic, As

74.92 g/mol Strontium, Sr

87.62 g/mol

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 1 mol

195.08 g = 94 g

2.50 mol x1 mol32.07 g = 80.2 g

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

200.59 g

1 mol = 3.09 mol

11 g x28.09 g1 mol = 0.39 mol

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: H2OMolar 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 = 18.02 g/mol