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2025 H2 Chem P2 Q1: Period 3 Chlorides Solution

Period 3 Chlorides 2025 A-Level H2 Chemistry · Paper 2 · Q1 · 12 marks

Question

Aluminium and phosphorus react separately with chlorine gas to form solid chlorides.

(a)(i)[1]

A beaker containing \(AlCl_3\) is placed next to some concentrated \(NH_3\). When drops of water are added to the \(AlCl_3\), white fumes containing \(NH_4Cl\) are observed.

Write an equation for the reaction of water and \(AlCl_3\).

(a)(ii)[1]

Name the type of reaction that occurs when water is added to \(AlCl_3\).

(b)[2]

\(NH_4Cl\) can be formed by adding the base \(NH_3(g)\) to \(HCl(g)\).

Identify the type of base present in this reaction. Explain your reasoning.

(c)[2]

When solid aluminium chloride, \(AlCl_3\), is heated under pressure, it melts and \(Al_2Cl_6\) is produced.

Draw a 'dot-and-cross' diagram of one molecule of \(Al_2Cl_6\) to show the arrangement of outer shell electrons.

Represent electrons from aluminium as \(\times\). Represent electrons from chlorine as \(\bullet\).

(d)(i)[3]

When \(Al_2Cl_6(l)\) is heated, it vapourises and both \(Al_2Cl_6(g)\) and \(AlCl_3(g)\) are produced.

An equilibrium between \(Al_2Cl_6(g)\) and \(AlCl_3(g)\) is set up in a closed system at a temperature of \(T\,°C\).

\(Al_2Cl_6(g) \rightleftharpoons 2AlCl_3(g)\)

Suggest the effect, if any, on the amount of \(AlCl_3\) present in the equilibrium mixture when the temperature is increased. Explain your answer.

(d)(ii)[1]

Suggest the effect, if any, on the equilibrium constant, \(K_p\), when the pressure is increased and the temperature of the mixture remains at \(T\,°C\).

(e)(i)[1]

Phosphorus(V) chloride exists as a solid that contains \(PCl_4^+\) and \(PCl_6^-\) at room temperature and pressure.

Predict the shape of \(PCl_4^+\).

(e)(ii)[1]

Predict the bond angle of \(PCl_6^-\).

Video Solution

Overview

Question 1 works through the Period 3 chlorides aluminium chloride and phosphorus(V) chloride. It opens with the reaction of AlCl₃ with water, the equation and the name of that reaction, then the type of base involved when ammonia reacts with hydrogen chloride to form ammonium chloride. Next comes a dot-and-cross diagram of the Al₂Cl₆ dimer, showing the dative bonds that hold the two halves together. The question then sets up the Al₂Cl₆ to AlCl₃ gas equilibrium and asks how the amount of product and the equilibrium constant Kp respond to a change in pressure. It closes with the shape of PCl₄⁺ and the bond angle in PCl₆⁻, the two ions that make up solid PCl₅.

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