What is prescribed practical C1 in Single Award science?

What are the key learning points about practical C1?

Neutralisation between an acid and an alkali produces salt and water, and the pH rises as alkali is added.
Universal indicator can be used to track pH changes as small volumes of alkali are added until the mixture reaches pH 7.
A pH probe gives more accurate, objective pH readings than colour‑matching with indicator.

The purpose of this practical is to follow a neutralisation reaction by monitoring pH.

In this reaction we are going to react an acid with an alkali and measure the pH change during the reaction.

The acid will react with the alkali to produce a salt and water – no gas is produced.

Also, in this reaction there is no colour change.

However, the pH will change.

Carefully measure 15 cm³ of hydrochloric acid using the measuring cylinder and place it in the beaker.
Add a few drops of universal indicator solution.
Record the colour the universal indicator has changed to and use the colour chart to record the pH in the results table.
Then measure 1 cm³ of sodium hydroxide solution using the dropping pipette.
Add the sodium hydroxide solution to the acid, mix with the stirring rod, measure and record the colour and pH of the reaction mixture.
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.