8.2.1 Acid-base Titrations

• The steps involved in performing a titration and titration calculation are outlined in Topic 1.2.9 Titrations
• Acid-base titrations follow the same steps and are used to find the unknown concentrations of solutions of acids and bases
• Acid-base indicators give information about the change in chemical environment
• They change colour reversibly depending on the concentration of H⁺ ions in the solution
• Indicators are weak acids and bases where the conjugate bases and acids have a different colour
• Many acid-base indicators are derived from plants, such as litmus

Common Indicators Table

• A good indicator gives a very sharp colour change at the equivalence point
• In titrations is it not always possible to use two colour indicators because of this limitation, so for example litmus cannot be used successfully in a titration
• When phenolphthalein is used, it is usually better to have the base in the burette because it is easier to see the sudden and permanent appearance of a colour (pink in this case) than the change from a coloured solution to a colourless one