12. Nitrogen and sulfur
A section of Chemistry, 9701
Listing 10 of 350 questions
Sulfuric acid is an important chemical with a variety of uses. It is manufactured by the Contact process, the fi rst stage of which involves the conversion of sulfur or a sulfi de ore, such as galena, PbS, into sulfur dioxide, SO2. Write an equation for the reaction between galena and oxygen to form sulfur dioxide and lead(oxide. Identify the oxidation number changes that take place during this reaction. The second stage of the Contact process involves the production of sulfur trioxide, SO3, from sulfur dioxide. 2SO2+ O22SO3∆H = –197 kJ mol–1 State the temperature usually chosen for this conversion and explain this in terms of reaction rates and Le Chatelier’s principle. temperature explanation 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. In the third stage of the process the sulfur trioxide is dissolved in 98% sulfuric acid followed by carefully controlled addition of water. Explain why the sulfur trioxide is not dissolved directly in water to produce sulfuric acid. Write equations for the reaction of sulfur trioxide with sulfuric acid and for the subsequent reaction with water. Explain why sulfur dioxide is used as an additive in some foods and wines. 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+ I2+ 2H2O→ 2I –+ SO4 2–+ 4H+A 50.0 cm3 sample of wine required 12.35 cm3 of 0.010 mol dm–3 I2for complete reaction with the SO2. How many moles of SO2 are present in 50.0 cm3 of wine? moles of SO2 in 50.0 cm3 = How many moles of SO2 are present in 1 dm3 of wine? moles of SO2 in 1 dm3 = How many milligrams, mg, of SO2 are present in 1 dm3 of wine? Give your answer to three signifi cant fi gures. (1 g = 1000 mg) mass of SO2 in 1 dm3 = mg
9701_s15_qp_22
THEORY
2015
Paper 2, Variant 2
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Questions Discovered
350