1. 3.2 Introducing the Mole: The Central Unit of Chemistry
The Mole Concept
Conversions Using Avogadro’s Number
Molar Mass
Conversions Using Molar Mass

2. 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.
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3. 3.2 Introducing the Mole: The Central Unit of Chemistry
The Mole Concept
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.
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4. Conversions Using Avogadro’s Number
3.2 Introducing the Mole: The Central Unit of Chemistry
Conversions Using Avogadro’s Number
Examples:
3 mol O x x 1023 atoms O = 2 x 1024 atoms O
mol O
2 x 1024 atoms O x mol O = 3 mol O
6.02 x 1023 atoms O
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5. 3.2 Introducing the Mole: The Central Unit of Chemistry
Molar Mass
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.
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6. Conversions Using Molar Mass
3.2 Introducing the Mole: The Central Unit of Chemistry
Conversions Using Molar Mass
Examples:
3.0 mol H2O x g H2O = 48 g H2O
1 mol H2O
48 g H2O x mol H2O = 3.0 mol H2O
g H2O
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