Maths for Diploma Studies

The mole is a specific number of elementary entities (a clever–sounding name for what is, for our purposes, atoms) of a chemical. The number of atoms in a mole is 6.022 10²³, which is called the Avogadro number. Avogadro was an Italian gentleman who established that the volume of a gas (at a given pressure and temperature) is proportional to the number of atoms or molecules regardless of the nature of the gas.

Because atoms have a known mass, a mole of a substance also has a known mass. This mass is based on the atomic mass, which is also the atomic number of the substance. The atomic mass of carbon is 12, so a mole of carbon has a mass of 12 g. For molecules, we add the atomic masses together. For example, the atomic mass of oxygen is 16, and molecular mass of an oxygen molecule (O₂) is 16 x 2 = 32, so one mole has a mass of 32 g.

So 100 g of oxygen is:

When we use mole in calculations, we drop the e so it is written as mol. Like g and m, the mole is an SI unit and can have prefixes for orders of magnitude above and below 10 (as we saw in the figure earlier). A kmol is 1,000 moles and is the mole equivalent to kg and km.