O-LevelChemistryBonding & Structure5070/22 · Oct/Nov 2017 · Q213 Marks

Sodium chloride, NaCl, and magnesium chloride, MgCl2, are both ionic compounds.

(a)Describe the arrangement of the ions and the type of attractive forces between the ions in solid magnesium chloride. arrangement type of attractive forces[2]
(b)Explain why solid magnesium chloride does not conduct electricity but aqueous magnesium chloride does conduct.[2]
(c)State the electronic configuration of a magnesium ion and of a chloride ion. magnesium ion chloride ion[2]
(d)(i)Why are hydrogen ions and not sodium ions discharged at the negative electrode?[1]
(d)(ii)Construct the equation for the reaction at the negative electrode.[1]
(d)(iii)Describe a test for chlorine. test result[2]
(e)(i)Give the formulae of the four ions present in aqueous sodium chloride.[1]
(e)(ii)Suggest why the solution becomes alkaline as the electrolysis proceeds.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] Arrangement: ordered / lattice / regular / layers / uniformly arranged / repeated pattern
[1] Type of force: electrostatic
[1] Crystals: ions cannot move
[1] Aqueous: ions can move
[1] Magnesium ion 2,8
[1] Chloride ion 2,8,8
[1] Hydrogen is lower in the reactivity series (than sodium) / sodium more reactive (than hydrogen) / hydrogen ions are reduced more easily (than sodium ions)
[1] 2H+ + 2e¯ → H2
[1] Litmus paper / named indicator paper
[1] Bleaches / loses its colour
[1] All four of: H+, OH¯, Cl¯, Na⁺
[1] Hydrogen ions removed
[1] Idea of OH⁻ remaining (causing alkalinity)

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