Concentrations and volumes

Concentrations

You will not be asked to calculate any concentrations of solutions in GCSE Additional Science, but you need to know certain things about concentration.

The concentration of a solution is measured in moles per cubic decimetre, mol/dm³. The greater the concentration, the more dissolved particles there are in the solution:

• Equal volumes of different solutions that have the same concentration contain the same number of particles of dissolved solute. For example, a solution at 2 mol/dm³ is twice as concentrated as a solution at 1 mol/dm³.

Volumes of gases

You will not be asked to calculate any volumes of gases in GCSE Additional Science, but you need to know certain things about them.

Equal volumes of gases at the same temperature and pressure contain the same number of molecules. For example:

• 50cm³ of hydrogen contains twice as many molecules as 25cm³ of oxygen at the same temperature and pressure.
• One mole of any gas at room temperature and normal pressure occupies about 24 dm³.