pH Meters & Universal Indicator (DP IB Chemistry: SL)

• The most accurate way to determine the pH is by reading it off a pH meter
• The pH meter is connected to the pH electrode which shows the pH value of the solution

The diagram shows a digital pH meter that measures the pH of a solution using a pH electrode

• A less accurate method is to measure the pH using universal indicator paper
• The universal indicator paper is dipped into a solution of acid upon which the paper changes colour
• The colour is then compared to those on a chart which shows the colours corresponding to different pH values

The diagram shows the change in colour of the universal indicator paper when dipped in a strong (HCl) and weak (CH₃COOH) acid. The colour chart is used to read off the corresponding pH values which are between 1-2 for HCl and 3-4 for CH₃COOH