Balanced equations, yield and atom economyAQA A-Level Chemistry: Subtopic test

1. 1
   Ethanol can be manufactured by two methods. In the hydration of ethene, C₂H₄ + H₂O → C₂H₅OH. In the fermentation of glucose, C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Relative formula masses: C₂H₄ = 28.0, H₂O = 18.0, C₂H₅OH = 46.0, C₆H₁₂O₆ = 180.0.

   (a)

   What is the percentage atom economy for making ethanol by the hydration of ethene?

   [1 mark]

   • A60.9%
   • B50.0%
   • C46.0%
   • D100%

   (b)

   What is the percentage atom economy for making ethanol by fermentation of glucose?

   [1 mark]

   • A25.6%
   • B48.9%
   • C51.1%
   • D100%

   (c)

   A company chooses the hydration method. Explain two advantages to society and the environment of using a process with a high atom economy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student titrates 25.0 cm³ portions of sodium hydroxide solution with 0.100 mol dm⁻³ hydrochloric acid, using an indicator. The mean titre is 22.40 cm³.

   (a)

   What amount, in mol, of hydrochloric acid is in the mean titre?

   [1 mark]

   • A2.24 mol
   • B2.24 × 10⁻³ mol
   • C4.46 × 10⁻³ mol
   • D2.24 × 10⁻² mol

   (b)

   Which is the ionic equation for the reaction in the conical flask?

   [1 mark]

   • AH⁺(aq) + OH⁻(aq) → H₂O(l)
   • BNaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
   • CNa⁺(aq) + Cl⁻(aq) → NaCl(aq)
   • D2H⁺(aq) + O²⁻(aq) → H₂O(l)

   (c)

   Calculate the concentration, in mol dm⁻³, of the sodium hydroxide solution.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student prepares a standard solution of sodium carbonate to use in a titration with hydrochloric acid. She needs 250 cm³ of a solution of concentration 0.0500 mol dm⁻³, made using anhydrous sodium carbonate, Na₂CO₃ (Mr = 106.0).

   (a)

   Calculate the mass of anhydrous sodium carbonate she should weigh out.

   [3 marks]

   (b)

   Describe how she should make up the 250 cm³ of solution from the weighed solid, so that the concentration is accurate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Aspirin is made by reacting salicylic acid with ethanoic anhydride: C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + CH₃COOH. Relative formula masses: salicylic acid = 138.0, ethanoic anhydride = 102.0, aspirin = 180.0, ethanoic acid = 60.0. In a trial, 5.00 g of salicylic acid was reacted with excess ethanoic anhydride and 5.20 g of aspirin was obtained. A company is also considering an alternative route, Route B, which has a percentage yield of 95% but a percentage atom economy of 52%. The reaction above is Route A.

   (a)

   Calculate the percentage yield of aspirin in the trial and the percentage atom economy of Route A.

   [6 marks]

   (b)

   The company must choose between Route A and Route B. Evaluate the two routes, using the yields and atom economies, and consider economic, ethical and environmental factors. Give a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions