• The Mole Concept

• Conversions Using Avogadro’s Number

• Molar Mass

• Conversions Using Molar Mass

3.2 Introducing the Mole: The Central Unit of Chemistry

The Mole Concept

Since an oxygen atom weighs 16 times as much as a hydrogen atom, it requires 16 g O to have the same number of atoms as 1 g H. This reasoning can be extended to all the elements therefore 1.0 g H, 12.0 g C, 16.0 g O etc. all have the same number of atoms.

text pages 115-116

3.2 Introducing the Mole: The Central Unit of Chemistry

text pages 115-116

3.2 Introducing the Mole: The Central Unit of Chemistry

A mole is a quantity equal to the number of atoms in the atomic mass of any element expressed in grams, e.g. the number of atoms in 16 grams of oxygen.

The number of things in a mole is also called Avogadro’s number.

One mole equals approximately 6.02 x 1023 items.

The Mole Concept

Conversions Using Avogadro’s Number

text pages 116-117

3.2 Introducing the Mole: The Central Unit of Chemistry

3 mol O x 6.02 x 1023 atoms O = 2 x 1024 atoms O 1 mol O

Examples:

2 x 1024 atoms O x 1 mol O = 3 mol O 6.02 x 1023 atoms O

Molar Mass

text pages 118-119

3.2 Introducing the Mole: The Central Unit of Chemistry

The mass of one mole of anything is that thing’s molar mass.

The molecular mass or formula mass of a compound is the sum of its constituent atomic masses, e.g. for H2O 1 u + 1 u + 16 u = 18 u.

It follows from the definition of a mole that the molar mass of a substance is its atomic, molecular or formula mass expressed in grams, e.g. the molar mass of H2O is 18 g.

Conversions Using Molar Mass

3.2 Introducing the Mole: The Central Unit of Chemistry

3.0 mol H2O x 16.0 g H2O = 48 g H2O 1 mol H2O

Examples:

48 g H2O x 1 mol H2O = 3.0 mol H2O 16.0 g H2O

text pages 119-120