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GCSE Combined Science · key term
Paper containing a coloured indicator that changes colour in acidic or alkaline conditions.
Used by AQA and Edexcel
Specification 5.8.2.4 · Paper 4
Revise: Chlorine Gas TestThe test for chlorine uses damp litmus paper. Litmus paper contains a coloured indicator. Chlorine removes this colour, leaving the paper white: this is called bleaching.
Specification Group 7 · Paper 3, Paper 4
Indicator paper that is red in acidic conditions and blue in alkaline conditions; damp litmus paper is bleached white by chlorine.
Revise: Halogen physical properties and identificationExpose damp blue litmus paper to the gas. If chlorine is present, the paper is bleached white. It may turn red briefly before becoming white, because chlorine produces acidic substances when it comes into contact with the water on the paper.
State both the method and the positive result: put damp litmus paper into the gas; chlorine bleaches it white.
Include ‘damp’: dry litmus paper is not the correct test.
For the chlorine test, state that the litmus paper is damp and is bleached white. Turning blue litmus red alone does not identify chlorine.
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