Explaining the trend in the reactivity of the halogens
2 marks · NormalState what you would observe if chlorine water is added to a solution of sodium iodide. Explain your answer.
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The solution turns brown, because iodine is formed.
Also accept: A brown colour appears due to the formation of iodine.
Common mistakes: Saying no reaction happens; Wrong colour (e.g., yellow or green)
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Marking points
B1 · 1 mark · Observation: Solution turns brown (or iodine formed)
B2 · 1 mark · Explanation: Because chlorine displaces iodine from iodide
Worked solution
You would see the solution turn brown. This is because chlorine is more reactive than iodine and displaces iodine from sodium iodide, forming iodine which is brown in solution.