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GCSE Chemistry · key term
A comparison used to check whether an observed change was caused by the factor being investigated.
Used by Edexcel and OCR
Paper 2
Revise: Suggested PracticalsA column receiving distilled water instead provides a control: it shows how the halogen solution looks after dilution without a halide being added. Wear eye protection and follow the teacher’s instructions for handling the halogen solutions and their fumes.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A comparison experiment used to show what happens when the variable being investigated is absent.
For a practical-method question, include the solutions tested, a suitable control, what is observed and how the pattern of results gives the reactivity order.
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Prepare reference wells by adding each halogen solution to the same volume of distilled water. These controls show the colour expected from dilution alone.