The Halogens
6 marks · NormalExplain, with the aid of a balanced equation, what happens when sodium reacts with bromine.
A student adds bromine water to a solution of potassium iodide in a test tube.
State what you would observe.
Write a balanced equation for the reaction.
Explain why bromine can displace iodine in this reaction but not chlorine.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Sodium reacts with bromine to form sodium bromide; e.g., 2Na(s) + Br2(l) \rightarrow 2NaBr(s).
(b(i)) Solution turns brown as iodine is formed.
(b(ii)) 2KI(aq) + Br2(aq) \rightarrow 2KBr(aq) + I2(aq)
(b(iii)) Bromine is more reactive than iodine, so it displaces iodine; but bromine is less reactive than chlorine, so it cannot displace chlorine.
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Marking points
M1 (a) · 1 mark · Describes sodium reacting with bromine to form sodium bromide.
A1 (a) · 1 mark · Correct balanced equation: 2Na(s) + Br2(l) → 2NaBr(s).
B1 (b(i)) · 1 mark · Brown color observed as iodine is formed.
M1 (b(ii)) · 1 mark · Correct reactants and products in equation.
A1 (b(ii)) · 1 mark · Equation balanced: 2KI(aq) + Br2(aq) → 2KBr(aq) + I2(aq).
B1 (b(iii)) · 1 mark · Explains bromine is more reactive than iodine (so displaces it), but less reactive than chlorine.
Worked solution
a) Sodium reacts with bromine to produce sodium bromide as follows:
b)(i) A brown color appears as iodine is produced.
b)(iii) Bromine is more reactive than iodine, so it displaces iodine, but cannot displace chlorine because chlorine is more reactive.