O-LevelChemistryAtomic Structure5070/21 · May/June 2018 · Q210 Marks

The elements in Group VII of the Periodic Table are called the halogens.

(a)Explain why the elements in Group VII have similar chemical properties.[1]
(b)(i)A redox reaction happens when chlorine gas is bubbled through aqueous potassium iodide. Cl2(g) + 2I-(aq) → I2(aq) + 2Cl-(aq) Describe what is observed during this reaction.[1]
(b)(ii)Use the equation to explain that oxidation takes place in this reaction.[1]
(b)(iii)Use the equation to explain that reduction takes place in this reaction.[1]
(c)Describe the chemical test for chlorine gas. test observation[2]
(d)(i)Chlorine reacts with iron to form iron(III) chloride in a closed container. The pressure of chlorine is increased. Describe and explain what happens to the rate of this reaction.[2]
(d)(ii)Iron(III) chloride can act as a catalyst for some reactions. Explain how a catalyst increases the rate of a reaction.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] 2(a) all have 7 electrons in their outer shell
[1] 2(b)(i) (colourless) to brown (solution)
[1] 2(b)(ii) iodide (ion) loses electrons
[1] 2(b)(iii) chlorine (molecule) gains electrons
[2] 2(c) test - (moist red or blue) litmus paper (1) observation - bleached / goes white (1)
[2] 2(d)(i) rate increases particles are more crowded / more particles in the same volume / increased number of particles per unit volume (1) more collisions per second / increased collision frequency (1)
[2] 2(d)(ii) alternative reaction pathway (1) has lower activation energy (1)

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