Testing for chlorine: damp litmus paper is bleached white
Definition
Chlorine
Chlorine is a gas identified by its ability to bleach damp litmus paper white.
Definition
Litmus paper
Litmus paper is paper containing a dye that changes appearance when exposed to certain chemicals.
- Hold a piece of damp litmus paper in the gas.
- If chlorine is present, the litmus paper is bleached white.
- The paper may turn red first because chlorine forms an acidic solution, and then it is bleached.
- The paper must be damp, because chlorine has to dissolve in the water to act.
Exam technique
- The marking point is bleached white with damp litmus paper.
- Turns red on its own is not enough, because that only shows the gas is acidic.
Why it works and common slips
- Chlorine is a bleach, so it removes the colour from the dye in the litmus paper.
- Chlorine is toxic, so the test is done with small amounts in a fume cupboard.
- Do not treat this as only an acid test; the defining change is bleaching to white.
Self review
- How do you test for chlorine?
- What is the positive result for chlorine?
- Why must the litmus paper be damp?
- Why might the paper turn red before it is bleached?
