CAIE A Level Chemistry 9701 · Group 17
A student adds separate samples of sodium chloride, sodium bromide and sodium iodide to three test tubes, each containing an equal volume of concentrated sulfuric acid. The student observes the colour of any gas produced, tests any gas with damp blue litmus paper, and looks for a solid residue.
Suggest how the observations would differ, and explain the trend in the reducing ability of the halide ions, using equations where relevant.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Suggest means: Apply what you know to an unfamiliar situation. There may be more than one acceptable answer. Reason from the principle you have learned to the new context, and say which principle you are using.
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