Reactions of the halogens
3 marks · NormalExplain, in terms of group trends, why iodine does not displace chlorine from a solution of sodium chloride. Include reference to reactivity and position in the group.
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Iodine is less reactive than chlorine, so it cannot displace chlorine from sodium chloride solution. This is because reactivity decreases down Group 17; chlorine is higher in the group and is more reactive.
Also accept: Iodine is below chlorine in Group 17, so it is less reactive and cannot displace chlorine from its salt.
Common mistakes: Writing 'iodine is more reactive than chlorine'; confusing group order
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Marking points
M1 · 1 mark · Identifies that iodine is less reactive than chlorine.
M2 · 1 mark · Recognises reactivity decreases down the group.
A1 · 1 mark · Explains position in the group (chlorine is higher/up, iodine is lower/down).
Worked solution
Iodine is less reactive than chlorine because reactivity of the halogens decreases going down Group 17. Since iodine is below chlorine in the group, iodine cannot displace chlorine from sodium chloride solution.