A-LevelChemistryChemical energetics9701/42 · May/June 2024 · Q113 Marks

Describe the trend in the solubility of the sulfates of magnesium, calcium and strontium. Explain your answer. most soluble > > least soluble

(a)Describe the trend in the solubility of the sulfates of magnesium, calcium and strontium. Explain your answer. most soluble > > least soluble[4]
(b)Define lattice energy, ΔΗlatt·[2]
(c)State and explain the main factors that affect the magnitude of lattice energies.[2]
(d)(i)Table 1.1 shows some energy changes. Table 1.1 energy change value/kJmol⁻¹ standard enthalpy change of atomisation of potassium +89 first ionisation energy of potassium +419 second ionisation energy of potassium +3070 standard enthalpy change of atomisation of sulfur +279 S-S bond energy +265 first ionisation energy of sulfur +1000 second ionisation energy of sulfur +2260 first electron affinity of sulfur -200 second electron affinity of sulfur +640 standard enthalpy change of formation of potassium sulfide, K₂S(s) -381 Born-Haber cycles can be used to determine the lattice energies of ionic compounds. Complete the Born–Haber cycle in Fig. 1.1 for potassium sulfide, K₂S(s). Include state symbols for all of the species. [Figure 1.1][3]
(d)(ii)Calculate the lattice energy, ΔHlatt, of K₂S(s) using relevant data from Table 1.1. Show your working. ΔHlatt of K₂S(s) = ................................... kJ mol⁻¹ [2][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 (May/June 2024). The mark or mark type is shown in brackets.

[4] M1 magnesium > calcium > strontium
M2 ∆Hlatt and ∆Hhyd both become less exothermic / less negative
M3 ∆Hlatt changes less OR ∆Hhyd is dominant factor
M4 ∆Hsol becomes less exothermic / less negative / more positive / more endothermic
[2] M1 ΔΗ/energy change when 1 mole of an ionic solid / compound is formed
M2 from gaseous ions (under standard conditions)
[2] M1 as ionic radii increases AND AHlatt less exothermic
M2 as ionic charge increases AND ∆Hlatt increases/more exothermic
[3] 2K+(g) + S2-(g).
2K+(g) + S(g) + 2e-
2K+(g) + S-(g) + e-
2K(g) + S(g) OR 2K+(g) + S(s) + 2e-
2K(g) + S(s) OR 2K(s) + S(g)
any two [1] any three [2] all four [3]
[2] M1 selection of ONLY six correct values (-381, 89, 419, 279, –200, 640) AND use of × 2 as only multiplier with K
M2 correct evaluation of data used ecf
-381 = (89 × 2) + (419 × 2) + 279 + (−200) + 640 + ∆Η°latt
ΔΗ°latt = −2116 (kJ mol-1)

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.