The mole

The gram formula mass (GFM) of a substance is known as the mass of one mole.

Relative atomic masses of selected elements can be found in the SQA Data Booklet.These can be used to calculate the gram formula mass of a substance.

Example

What is the mass of one mole of calcium chloride?

To calculate this, work out the formula of calcium chloride then add all the mass numbers together.

Calcium has a valency of 2. Chlorine has a valency of 1. The formula is CaCl2. The mass number of calcium is 40. The mass number of chlorine is 35.5. Two times 35.5 is 71. 71 plus 40 is 111.

One mole of calcium chloride has a mass of 111 g.

Chemists predict the weight of chemical substances using a unit called 'the mole'