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GCSE Chemistry · key term
A substance that changes colour over a particular pH range and is used to detect the end point of an acid–alkali titration.
Used by Edexcel and OCR
Specification 3.3 · Paper 1
A substance that changes colour depending on whether a solution is acidic, neutral or alkaline.
Revise: IndicatorsAn indicator is a substance whose colour depends on whether a solution is acidic, neutral or alkaline. It provides a quick way to classify a solution: add the indicator and compare the observed colour with its known colours.
Specification C5.1b, PAG 2, PAG 6 · Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A dye that changes colour over a particular pH range and is used to detect the end-point of an acid–alkali titration.
Revise: Titration TechniquesA few drops of a suitable indicator are therefore added. Its colour change marks the end-point. The aim is to identify the first permanent colour change without adding an unnecessary excess of solution.
A substance that changes colour according to the pH of a solution.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A substance whose observable change, usually a colour change, is used to estimate pH or detect an end point.
Revise: Apparatus and techniquesIn OCR Practical Activity Group 6, titration is an example that brings these skills together: a reaction is monitored using a suitable pH indicator, accurate liquid volumes are measured, and the results can be used to determine the concentration of a strong acid or strong alkali.
Learn the colour in each condition, not merely that an indicator “changes colour”.
Do not claim that these indicators give an exact pH value; their colours help classify the conditions.
Do not say that an indicator makes neutralisation happen. It changes colour to show when the end-point has been reached.
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