O-LevelChemistryAtomic Structure5070/21 · Oct/Nov 2020 · Q910 Marks

Calcium is a metal in Group II of the Periodic Table.

(a)Calcium can be used as a reducing agent. Describe a test for reducing agents. test observations[2]
(b)An ion of calcium has the symbol ⁴⁴₂₀Ca²⁺ Deduce the number of electrons and neutrons in this ion. number of electrons number of neutrons[2]
(c)(i)When calcium carbonate is heated in a closed container, an equilibrium mixture is formed. CaCO₃(s) ⇌ CaO(s) + CO₂(g) The forward reaction is endothermic. Describe and explain the effect, if any, on the position of equilibrium when a hole is made in the container.[2]
(c)(ii)Describe and explain the effect, if any, on the position of equilibrium when the temperature is increased.[2]
(d)When heated, calcium oxide reacts with chlorine to form calcium chloride and a gas which relights a glowing splint. Complete the equation for this reaction. 2CaO + ........... → ...........CaCl₂ + ...........[1]
(e)Calcium chloride is soluble in water. Name one other calcium salt which is soluble in water.[1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[2] 9(a) Add (acidified) potassium manganate(VII) (1) goes from purple to colourless (1)
[2] 9(b) electrons: 18 (1) neutrons: 24 (1)
[2] 9(c)(i) equilibrium moves to the right/more products formed (1) concentration of carbon dioxide falls so more calcium carbonate decomposes to (try to) maintain equilibrium (1)
[2] 9(c)(ii) equilibrium moves to the right / more products formed (1) increasing temperature pushes the reaction in the direction of absorbing energy/increasing temperature pushes the reaction in the direction of the endothermic reaction (1)
[1] 9(d) 2CaO + 2Cl2→ 2CaCl2 + O2
[1] 9(e) any suitable soluble calcium salt other than calcium chloride e.g. calcium nitrate, calcium ethanoate

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