O-LevelChemistryAtomic Structure5070/22 · Oct/Nov 2020 · Q910 Marks

Lead is a metal in Group IV of the Periodic Table.

(a)An ion of lead has the symbol 207 Pb2+ 82 Deduce the number of electrons and neutrons in this ion. number of electrons number of neutrons[2]
(b)(i)Lead(IV) oxide, PbO2, is an oxidising agent. Describe a test for oxidising agents. test observations[2]
(b)(ii)Lead(IV) oxide reacts with concentrated hydrochloric acid to form lead(IV) chloride, PbCl4, and water. Construct the equation for this reaction.[1]
(c)(i)When lead(IV) chloride is warmed in a closed container an equilibrium mixture is formed. The forward reaction is exothermic. PbCl4(l) ⇌ PbCl2(s) + Cl2(g) lead(IV) chloride lead(II) chloride Describe and explain the effect, if any, on the position of equilibrium when the concentration of chlorine is increased.[2]
(c)(ii)Describe and explain the effect, if any, on the position of equilibrium when the temperature is increased.[2]
(d)Name a lead 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.

[1] 9(a) electrons = 80 (1)
[1] 9(a) neutrons = 125 (1)
[1] 9(b)(i) add (aqueous) potassium iodide (1)
[1] 9(b)(i) (colour change) from colourless to brown (1)
[1] 9(b)(ii) PbO2 + 4HCl → PbCl4 + 2H2O
[1] 9(c)(i) equilibrium moves to the left / more reactant formed (1)
[1] 9(c)(i) lead(II) chloride combines with chlorine to reduce the concentration of added chlorine (1)
[1] 9(c)(ii) equilibrium moves to the left / more reactant formed (1)
[1] 9(c)(ii) (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) lead nitrate

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