During a test in a fume cupboard, a colour sensor records the colour of damp blue litmus paper held in chlorine from a gas cylinder. The sensor records red, followed by white. A researcher concludes that the cylinder must contain a second gas as well as chlorine, because the paper changed colour twice.
Why is the researcher's conclusion wrong?
Chlorine bleaches the blue dye red, and its acidic solution then changes the red dye to white.
Chlorine forms an acidic solution in the water, changing the paper red, and then bleaches the dye white.
Chlorine changes the blue dye red, and the water later removes the colour from the dye.
Water changes the blue dye red, and chlorine then reacts with the red dye to make it white.
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.