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CIE Jun 2015 v2 Paper 2 Q2
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![Sulfuric acid is an important chemical with a variety of uses. It is manufactured by the Contact process, therst stage of which involves the conversion of sulfur or a sul de ore, such as galena, PbS, into sulfur dioxide, SO2. (a) (i) Write an equation for the reaction between galena and oxygen to form sulfur dioxide and lead(II) oxide.[2] (ii) Identify the oxidation number changes that take place during this reaction.[2] (b) The second stage of the Contact process involves the production of sulfur trioxide, SO3, from sulfur dioxide. 2SO2(g) + O2(g) 2SO3(g) H = 197 kJ mol1 (i) State the temperature usually chosen for this conversion and explain this in terms of reaction rates and Le Chateliers principle. temperatureexplanation[3] (ii) State and explain the pressure conditions that would give the best rate and best yield of sulfur trioxide. Explain why these conditions are not actually used.[3] (c) In the third stage of the process the sulfur trioxide is dissolved in 98% sulfuric acid followed by carefully controlled addition of water. (i) Explain why the sulfur trioxide is not dissolved directly in water to produce sulfuric acid.[1]UCLES 2015 9701/22/M/J/15<br />
(ii) Write equations for the reaction of sulfur trioxide with sulfuric acid and for the subsequent reaction with water.[2] (d) Explain why sulfur dioxide is used as an additive in some foods and wines.[2] (e) The sulfur dioxide content of wine is most commonly measured by the Ripper Method which involves titration with iodine in the presence of starch as an indicator. SO2(aq) + I2(aq) + 2H2O(l)2I (aq) + SO4 2(aq) + 4H+(aq) A 50.0 cm3 sample of wine required 12.35 cm3 of 0.010 mol dm3 I2(aq) for complete reaction with the SO2. (i) How many moles of SO2 are present in 50.0 cm3 of wine? (ii) How many moles of SO2 are present in 1 dm3 of wine? moles of SO2 in 50.0 cm3 =[1] (iii) How many milligrams, mg, of SO2 are present in 1 dm3 of wine? Give your answer to three signi cantgures. (1 g = 1000 mg) moles of SO2 in 1 dm3 =[1] mass of SO2 in 1 dm3 =mg [1] [Total: 18]UCLES 2015 9701/22/M/J/15 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_QP_-_Paper_2_CIE_Chemistry_A-level_2-0.jpg)
![Page 3 Question Cambridge International AS/A LevelMay/June 2015 9701 22 Mark Scheme Syllabus Paper Mark Scheme Mark Total [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [18] [2] [2] [3] [3] [1] [2] [2] [1] [1] [1] [18] [1] [1] [1] [1] [3] [1] (a) (i) 2PbS + 3O2 2PbO + 2SO2 reagents and formulae balancing (ii) S (is oxidised) 2 to (+)4 O (is reduced) 0 to 2 (b) (i) T = 400600 C (chosen as a compromise because) High T increases rate ora High T decreases yield / moves eqm left / makes less SO3 as forward reaction exothermic ora (ii) High pressure increases rate as collision frequency increases ora High pressure moves eqm right / favours forward reaction as more moles on left ora Uneconomic to use high pressures / high yield at low pressure (c) (i) Reaction (too) exothermic / acid spray produced (ii) SO3 + H2SO4 H2S2O7 H2S2O7 + H2O 2H2SO4 (d) Preservative owtte antimicrobial / antioxidant / reducing agent (e) (i) 12.350.01 / 1000 = 1.23510 4 (ii) 1.23510 41000 / 50 = 2.4710 3 (iii) 2.4710 364.1 = 0.158327 g = 158 (3 sf only) (a) (i) Bond breaking = Cl-Cl = 242 C-H = 410 = 652 kJ Bond forming = C-Cl = 340 Enthalpy change = 652771 = 119 H-Cl = 431 = 771 kJ (ii) UV / High T / sunlightCambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_MS_-_Paper_2_CIE_Chemistry_A-level_2.jpg)