A-LevelChemistryChemical periodicity9701/22 · Oct/Nov 2022 · Q221 Marks

The chlorides of some of the Period 3 elements are shown in Table 2.1. [Table 2.1]

(a)Complete Table 2.1. • Identify the bonding shown by each chloride under standard conditions. Use C = covalent, I = ionic, M = metallic. • Identify the structure shown by each chloride under standard conditions. Use G = giant, S = simple. • Deduce the oxidation state of the Period 3 element in each chloride.[4]
(b)Write equations for the reactions of NaCl and PCl5 with water. Include state symbols in both equations.[3]
(c)(i)In the gas phase, AlCl3(g) exists at equilibrium with Al₂Cl₆(g) as shown. equation 1 2AlCl3(g) ⇌ Al₂Cl₆(g) ΔH₁ = −63 kJ mol⁻¹ Complete the dot-and-cross diagram to show the bonding in Al₂Cl₆. [Diagram with Al and Cl atoms and empty spaces to draw dots and crosses][2]
(c)(ii)State the effect of an increase in temperature on the equilibrium mixture in equation 1. Explain your answer.[1]
(d)A 3.30 g sample of a Period 3 chloride is heated to 500K in a sealed flask. At this temperature, the chloride is a gas of volume 250 cm³ and the pressure in the flask is 323 kPa. Use the ideal gas equation pV = nRT to calculate the Mᵣ of the Period 3 chloride. Deduce its formula.[3]
(e)(i)An excess of Cl⁻(aq) is added to 1 cm³ of Br₂(aq). Describe what is observed. Explain your answer.[2]
(e)(ii)SCl₂ has Mᵣ = 103.1 and is a liquid at room temperature. SBr₂ has Mᵣ = 191.9 and is a gas at room temperature. Explain the difference in the physical state of SCl₂ and SBr₂. Give your answer in terms of intermolecular forces.[2]
(f)(i)Bismuth is a dense metal in the same group as phosphorus. Draw a labelled diagram to show the bonding in bismuth metal.[2]
(f)(ii)Bismuth reacts with chlorine to form BiCl₃. BiCl₃ is a solid at room temperature. It melts when heated gently. BiCl₃ reacts vigorously with water at room temperature to form an acidic solution. Suggest the type of bonding and structure shown by BiCl₃. Explain your answer.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] Bonding: NaCl = I, AlCl3 = I OR C, SiCl4 = C, PCl5 = C
[1] Structure: NaCl = G, AlCl3 = G, SiCl4 = S, PCl5 = S
[1] Oxidation state: NaCl = +1, AlCl3 = +3, SiCl4 = +4, PCl5 = +5
[1] Oxidation state: PCl3 = +3, SCl2 = +2
[1] M1 NaCl(s) → Na+(aq) + Cl-(aq)
[1] PCl5(s) + 4H2O(l) → H3PO4(aq) + 5HCl(aq) M2 balanced equation
[1] M3 all state symbols for PCl5 equation
[1] M1 correct number and connectivity of Cl and Al atoms
[1] M2 2 correct dative bonds (→) between Cl and Al of AlCl3 neighbour AND correct number of non-bonding electrons around each atom of Al2Cl6
[1] reaction is exothermic so equilibrium shifts to the LHS OR equilibrium shifts to LHS because forward reaction is exothermic OR equilibrium shifts to LHS because backward reaction is endothermic OR endothermic reaction is favoured so more reactants / are AlCl3 is made
[1] M1 value of n based on re-arranged equation for 'n' and substitution of correct values n = (3.23×10⁵ * 250 ×10⁻⁶) / (8.31 * 500) = 0.0194(34416)
[1] M2 calculated value of Mᵣ based on M1 Mᵣ = 3.30 ÷ n = 170
[1] M3 period 3 chloride which matches Mᵣ in M2 (formula) SiCl4
[1] M1 orange colour (of solution) remains / no visible reaction
[1] M2 bromine/Br₂ cannot oxidise chloride/Cl⁻ OR bromine/Br₂ is not a strong enough oxidising agent (to oxidise chloride/Cl⁻)
[1] M1 sum of instantaneous dipole – dipole attractions and permanent dipole attractions in SCl₂ is greater than those in SBr₂ OR permanent dipole-permanent dipole (forces) in SCl₂ are stronger OR intermolecular forces are stronger in SCl₂ ora
[1] M2 SCl₂ (molecule / bond) is more polar than SBr₂ OR Cl is more electronegative than Br so SCl₂ has stronger (permanent) dipoles ora
[1] M1 diagram showing minimum of 4 particles (in total in 2 rows) • circles containing Biⁿ⁺ do not have to be labelled • must be labelled as 'ion' OR empty circles / circles with Bi must be labelled + ion / positive ion / cation / Biⁿ⁺ AND • with the circles surrounded by electrons shown as e- / – OR little circles labelled electrons
[1] M2 label/legend showing delocalised electrons
[1] M1 (structure =) simple/molecular, because it has a low melting/boiling point owtte
[1] M2 (bonding =) covalent, because it is hydrolysed