A gardener uses universal indicator to measure the pH of soil drainage water.
Why should the result be treated as an estimate?
The indicator colour shows only whether the water is acidic or alkaline.
The indicator gives a decimal value which must be rounded to a whole number.
The indicator colour depends on the volume of water tested, not its pH.
The indicator colour is matched by eye with colours on a chart.
88 exam-style questions on AQA GCSE Chemistry 4.2 Reactions of acids, covering 4.2.1a Reactions of acids with metals, 4.2.1b Redox in acid-metal reactions, 4.2.2 Neutralisation of acids and salt production, 4.2.3 Soluble salts, 4.2.4 The pH scale and neutralisation, 4.2.5a Titrations, 4.2.5b Calculating quantities in titrations, and 4.2.6 Strong and weak acids. Each one has a worked solution and a mark scheme showing where the marks go.