O-LevelChemistryAcids, Bases & Salts5070/22 · Oct/Nov 2015 · Q67 Marks

When one mole of sulfur burns, 247 kJ of energy is released. S(s) + O2(g) → SO2(g)

(a)Calculate the energy released when 9.60 g of sulfur is burnt.[2]
(b)When sulfur dioxide is passed through aqueous sodium hydroxide, sodium hydrogensulfite is formed. Sodium hydrogensulfite contains the hydrogensulfite ion, HSO3¯. Construct the ionic equation for this reaction.[1]
(c)The hydrogensulfite ion is a weaker acid than ethanoic acid. Samples of 0.1g of magnesium are added separately to 0.1mol/dm³ ethanoic acid and 0.1 mol/dm³ hydrogensulfite ions. Explain why the reaction is faster with ethanoic acid.[2]
(d)Calculate the volume of 0.10mol/dm³ sodium hydroxide which contains 3.2g of sodium hydroxide.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.

[2] (a) 9.60/32 or 0.3(0) mol S (1) (247 × 0.30) = 74.1 (kJ) or 74 (kJ) (1)
[1] (b) SO2 + OH¯ → HSO3¯ (1)
[2] (c) higher concentration of H⁺ ions in ethanoic acid/more crowded H⁺ ions in ethanoic acid (or reverse argument) (1) collision frequency greater in ethanoic acid (or reverse argument) (1)
[2] (d) 3.2 g NaOH = 3.2/40 or 0.08 mol (1) (0.08/0.1) = 0.8 dm³ or 800 (cm³) (1)

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