6.8 - Chemical test for chlorine

Testing for chlorine

Expose damp blue litmus paper to the gas. Chlorine bleaches the paper white, often after a brief red stage. The red stage may be too quick to see; bleaching is the essential positive observation.

[DIAGRAM: asset_name: chlorine_litmus_test: Damp blue litmus test for chlorine - diagram 1; asset_slug: 154_6_8_chemical_test_for_chlorine_diagram1; file: diagram_assets/154_6_8_chemical_test_for_chlorine_diagram1.png; recommended_method: deterministic_drawn; description: Exact monochrome apparatus-and-observation diagram for Edexcel GCSE Chemistry 1CH0 6.8. Shows a gas jar or test tube containing chlorine gas, damp blue litmus paper held in the gas, and a second panel showing the positive observation: the litmus paper is bleached white, with a note that a brief red stage may appear first. Labels must state "damp blue litmus paper", "chlorine gas, Cl2(g)" and "positive result: white / bleached". Deterministic drawing is required because the litmus type, gas identity and observation wording are assessed.]

Water on the damp paper allows chlorine to form substances that bleach the litmus dye. Dry paper is therefore unsuitable for this standard test.