Displacement reactions involving the halogens

2 marks · Normal

State what you would observe when chlorine water is added to a solution of potassium iodide. Write the chemical equation for the reaction.

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Also accept: Observation: solution turns brown/orange-brown/yellow-brown; Equation written with full state symbols

Common mistakes: Saying no reaction occurs; Wrong colour (e.g. orange for bromine); Incorrectly writing bromine in the equation

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Marking points

B1 · 1 mark · Correct observation: brown (or orange-brown) colour.

B2 · 1 mark · Correct equation: 2KI(aq) + Cl2(aq) -> 2KCl(aq) + I2(aq). Must show displacement and products correctly.

Worked solution

When chlorine water is added to potassium iodide solution, the solution turns brown because iodine is formed.