A gas-monitoring card has a patch of litmus paper that detects chlorine. The card is stored in a sealed packet so that the patch stays moist. Why must the patch be moist to detect chlorine?
The water makes the litmus acidic so that the chlorine can then bleach it.
The chlorine has to dissolve in the water before it can bleach the litmus.
The water stops the air from bleaching the litmus before chlorine arrives.
The water stops the chlorine from turning the litmus red before bleaching it.
89 exam-style questions on AQA GCSE Chemistry 8.2 Identification of common gases, covering 8.2.1 Test for hydrogen, 8.2.2 Test for oxygen, 8.2.3 Test for carbon dioxide, and 8.2.4 Test for chlorine. Each one has a worked solution and a mark scheme showing where the marks go.