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Method

1. Carefully measure 15 cm³ of hydrochloric acid using the measuring cylinder and place it in the beaker.
2. Add a few drops of universal indicator solution.
3. Record the colour the universal indicator has changed to and use the colour chart to record the pH in the results table.
4. Then measure 1 cm³ of sodium hydroxide solution using the dropping pipette.
5. Add the sodium hydroxide solution to the acid, mix with the stirring rod, measure and record the colour and pH of the reaction mixture.
6. Continue to add the sodium hydroxide solution 1cm³ at a time until all 15cm³ have been added, record the colour and pH each time.

During this reaction the alkali neutralises the acid.

As the alkali is added the solution will increase in pH.

When equal volumes of both acid and alkali are present the solution should be pH 7 (the universal indicator should be green).

A more accurate way of following the change in pH would be to use a pH probe/meter.

This would directly measure the pH of the reaction mixture to 1 decimal place.

This also removes human error in judging and matching colours to the indicator colour chart.