Titration calculations

Titrations can give you an idea of which of the two solutions is more concentrated.

For example, if 20 cm3 of an acid is required to neutralise 20 cm3 of an alkali, it is likely that the concentrations are the same, provided the acid and alkali react in a 1:1 ratio.

However, if 25 cm3 of an acid is required to neutralise 20 cm3 of an alkali, the alkali is more concentrated because it has the same number of reactant particles as the acid in a smaller volume. To summarise, the reactant that requires the smaller volume has the higher concentration.

It is possible to work out the concentration of a solution in a titration provided that you know the concentration of the other solution. This can be done by comparison. If 20 cm3 of 0.1 mol/dm3 acid is neutralised by 10 cm3 of an alkali, the concentration of the alkali must be twice the concentration of the acid, as it only takes half the volume to neutralise the acid. This can be worked out using the following equation:

Concentration of unknown solution = (volume of known solution ÷ volume of unknown solution) × concentration of known solution

Concentration of alkali = (20 ÷ 10) × 0.1 = 2 × 0.1 = 0.2 mol/dm3