1. 1
   A car airbag contains sodium azide, NaN₃, which decomposes rapidly when ignited: 2NaN₃(s) → 2Na(s) + 3N₂(g). The reactive sodium formed is removed by potassium nitrate: 10Na(s) + 2KNO₃(s) → K₂O(s) + 5Na₂O(s) + N₂(g). Relative atomic masses: Na 22.99, N 14.01. Molar volume of an ideal gas at STP = 22.7 dm³ mol⁻¹.

   (a)

   What volume of nitrogen, measured at STP, is produced by the decomposition of 65.0 g of sodium azide?

   [1 mark]

   • A22.7 dm³
   • B15.1 dm³
   • C68.1 dm³
   • D34.0 dm³

   (b)

   What amount of potassium nitrate is needed to react completely with 1.00 mol of sodium?

   [1 mark]

   • A0.100 mol
   • B2.00 mol
   • C0.200 mol
   • D5.00 mol

   (c)

   Calculate the mass of sodium azide needed to produce 60.0 dm³ of nitrogen at STP from the decomposition alone. Give your answer to three significant figures.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student dissolves 3.20 g of hydrated sodium carbonate, Na₂CO₃·xH₂O, in water and makes the solution up to 250.0 cm³. A 25.0 cm³ portion of this solution requires 22.40 cm³ of 0.100 mol dm⁻³ hydrochloric acid for complete reaction: Na₂CO₃(aq) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g). Molar masses, in g mol⁻¹: Na₂CO₃ 105.99, H₂O 18.02.

   (a)

   What amount of sodium carbonate is present in the 25.0 cm³ portion?

   [1 mark]

   • A2.24 × 10⁻³ mol
   • B1.12 × 10⁻³ mol
   • C4.48 × 10⁻³ mol
   • D1.12 mol

   (b)

   What is the concentration of sodium carbonate in the solution?

   [1 mark]

   • A0.0448 mol dm⁻³
   • B0.0896 mol dm⁻³
   • C0.00448 mol dm⁻³
   • D44.8 mol dm⁻³

   (c)

   Determine the value of x in Na₂CO₃·xH₂O.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Aspirin is made by reacting salicylic acid with ethanoic anhydride: C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + CH₃COOH. A student mixes 2.00 g of salicylic acid with 5.00 cm³ of ethanoic anhydride (density 1.08 g cm⁻³), heats the mixture, then recrystallises the product from hot water, obtaining 1.89 g of dry aspirin. Molar masses, in g mol⁻¹: salicylic acid 138.13; ethanoic anhydride 102.10; aspirin 180.17; ethanoic acid 60.06.

   (a)

   Identify the limiting reactant, showing your working.

   [3 marks]

   (b)

   Calculate the percentage yield of aspirin and evaluate the student's claim that using even more ethanoic anhydride would have raised the yield.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Ethanol can be manufactured by two routes. Route A, hydration: ethene from crude oil reacts with steam, C₂H₄(g) + H₂O(g) → C₂H₅OH(g), at 300 °C and 6 MPa with a phosphoric acid catalyst; only about 5% of the ethene is converted on each pass through the reactor, but unreacted ethene is recycled so that overall conversion reaches 95%. Route B, fermentation: yeast converts glucose, C₆H₁₂O₆, from sugar cane into ethanol and carbon dioxide at 35 °C, with a percentage yield of 90.0%. Molar masses, in g mol⁻¹: C₂H₄ 28.06; H₂O 18.02; C₂H₅OH 46.08; C₆H₁₂O₆ 180.16; CO₂ 44.01.

   (a)

   Deduce the equation for fermentation, calculate the atom economy of each route, and explain why a process with a high atom economy can still have a low percentage yield.

   [6 marks]

   (b)

   A plant must produce 1.00 tonne of ethanol. Determine the mass of glucose needed for Route B, and evaluate which route is more sustainable.

   [6 marks]

   Total for question 4: 12 marks

End of questions