The Halogens
6 marks · NormalA teacher wants to compare the reactivity of chlorine, bromine and iodine using displacement reactions with metal halide solutions.
Chlorine is bubbled into a solution of potassium bromide. The solution turns orange. Explain why this colour change occurs. Include what is formed.
A student adds bromine water to a solution of potassium chloride. No visible change is seen. Explain this observation, referring to relative reactivity.
State and explain which halogen is the least reactive out of chlorine, bromine and iodine.
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.
Show answer
(a) Chlorine is more reactive than bromine and displaces bromine from potassium bromide, forming orange bromine solution.
(b) No reaction occurs because bromine is less reactive than chlorine and cannot displace it from potassium chloride.
(c) Iodine is the least reactive halogen of the three because reactivity decreases down the group.
Common mistakes: Not mentioning relative reactivity; Not stating the new substance formed or produced; Incorrectly identifying the least reactive halogen
Show mark scheme and worked solution
Marking points
E1 (a) · 1 mark · Recognises that chlorine is more reactive than bromine and displaces it.
E2 (a) · 1 mark · Correctly links orange colour to formation of bromine.
E3 (b) · 1 mark · Correctly states that no reaction occurs because bromine is less reactive than chlorine.
E4 (b) · 1 mark · Explains that bromine cannot displace chlorine from potassium chloride.
E5 (c) · 1 mark · Correctly identifies iodine as the least reactive halogen.
E6 (c) · 1 mark · States that reactivity decreases down the group.
Worked solution
a) The colour change occurs because chlorine is more reactive than bromine. Chlorine displaces bromine from potassium bromide, forming bromine, which dissolves to give an orange colour.
b) There is no visible change because bromine is less reactive than chlorine. It cannot displace chlorine from potassium chloride, so no new substance or colour is formed.
c) Iodine is the least reactive halogen of chlorine, bromine, and iodine, because reactivity in Group 17 decreases as you move down the group.