1.8 Tests for Gases

Question 1

How do you carry out the test for Chlorine? (3)

Answer 1

• You get a test tube full of your sample gas
• Get a piece of blue litmus paper and dampen it
• When you put the damp paper in the test tube, it will turn white if it contains chlorine. This is because chlorine bleaches the blue litmus paper. It may turn red for a moment first though - that’s because the chlorine dissolves in the water on the damp paper and forms hydrochloric acid, which because its acidic will turn the blue litmus paper red

Question 2

What precautions should you take when carrying out the chlorine gas test?

Answer 2

Chlorine is poisonous, so you should wear a mask or do it in a fume cupboard

Question 3

Why may the blue litmus paper turn red briefly when you are testing for chlorine?

Answer 3

This may happen because the chlorine dissolves in the water on the damp paper and forms hydrochloric acid, this is acidic which turns the paper red