O-LevelChemistryBonding & Structure5070/22 · May/June 2021 · Q48 Marks

Zinc bromide and zinc carbonate are both ionic compounds.

(a)Predict two physical properties, other than electrical conductivity, of zinc bromide. 1. 2.[2]
(b)Zinc reacts with bromine to make zinc bromide. Zn + Br₂ → ZnBr₂ Zinc bromide contains Zn²⁺ and Br⁻ ions. Explain, in terms of the movement of electrons, how ZnBr₂ is formed from zinc atoms and bromine molecules.[2]
(c)(i)Use the equation to explain that oxidation takes place.[1]
(c)(ii)Use the equation to explain that reduction takes place.[1]
(d)(i)Zinc carbonate can be prepared by reacting aqueous zinc bromide with CO₃²⁻(aq) ions in a precipitation reaction. Name a suitable aqueous solution that can provide CO₃²⁻(aq) ions.[1]
(d)(ii)A sample of zinc carbonate is heated strongly. Name the products of this reaction.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[2] Any two from: soluble in water (1) insoluble in organic solvents (1) high melting point/ solid at room temperature (1) white (1)
[1] zinc loses electrons and bromine gains electrons (1)
[1] reference to (transfer of) two electrons (1)
[1] magnesium (atom) loses electrons
[1] Zn²⁺ (ion) gains electrons / zinc ions gain electrons
[1] sodium carbonate / potassium carbonate / ammonium carbonate
[1] zinc oxide AND carbon dioxide

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