Titration

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Titrations

Titration is a technique that measures the volumes of acid and alkali solutions that are needed in a neutralisation reaction.

If, for example, we were neutralising an alkali with an acid, titration could be used to calculate the concentration of the alkali if we knew:
1. The concentration of the acid to be added.
2. The volume of the alkali.

Indicators show the end point of titrations by suddenly changing colour when the solution turns from acidic to alkaline, or alkaline to acidic.

When choosing an indicator, the strength of the acid and alkali must be considered.
If both the acid and alkali are strong, suitable indicators would be:
- Methyl orange (yellow in alkali → red in acid).
- Phenolphthalein (pink in alkali → colourless in acid).

The experiment for determining the reacting volumes of a strong alkali and a strong acid by performing a titration is:

Using a pipette, add a set volume of a strong alkali to a conical flask.
Add a few drops of a suitable indicator.
Place a strong acid (sulfuric, hydrochloric or nitric acid) of known concentration in a burette.
Take an initial reading of the volume of acid in the burette.
Gradually add the acid to the alkali. Make sure that you are regularly swirling the conical flask as you add the acid. As you get closer to the end point, start to add the acid at a slower rate.

As soon as the indicator changes colour, stop adding acid.
Take a final reading of the volume of acid in the burette.
Subtract the final reading from the initial reading to calculate the volume of acid needed to neutralise the alkali.