Stoichiometry: The Mole and Molar Mass

Converting Between Number and Mass: The Mole Concept

The Definition of a Mole and Avogadro's Number

• The mole is a unit that allows conversion between the number of something and its mass.

• Definition: A mole is defined as the number of atoms in exactly $12$ grams of carbon-12 (isotope).

• This specific number of atoms is called Avogadro's number, which is approximately $6.022 \times 10^{23}$. For example, exactly $12$ grams of carbon-12 contains $6.022 \times 10^{23}$ atoms of carbon-12.

• Relationship: Anything that has a mass number in atomic mass units (AMU) will have the same mass in grams per mole.

  • Example 1: One mole of carbon-12, with an atomic mass of $12$ AMU, will weigh $12$ grams.

  • Example 2: One mole of lithium, with an atomic mass of $6.941$ AMU, will weigh $6.941$ grams.

  • Example 3: One mole of carbon (elemental, average isotopic mass) with an atomic mass of $12.011$ AMU, will weigh $12.011$ grams.

• This relationship of