1. 1
   A perfume manufacturer reacts two starting chemicals under controlled conditions to produce a fragrant ester used in a new product line, but finds that not all of the theoretical maximum mass of ester is recovered after purification.

   (a)

   A perfume manufacturer reacts two starting chemicals to produce a fragrant ester, with a theoretical maximum yield of 50 g predicted from the balanced equation. After the reaction and purification, the manufacturer actually collects 40 g of the ester. What is the percentage yield of this reaction?

   [1 mark]

   • A80%
   • B50%
   • C40%
   • D125%

   (b)

   The perfume manufacturer's chemist explains that the actual yield of the ester was lower than the theoretical maximum. Which of these is a genuine reason why percentage yield is often less than 100% in a real reaction, according to the specification?

   [1 mark]

   • AAtoms are destroyed during the reaction, reducing the total mass of product formed
   • BThe law of conservation of mass does not apply to reactions producing esters
   • CPercentage yield is always exactly 100% if the correct apparatus is used
   • DSome of the reversible reaction may not go to completion, and some product may be lost during separation

   (c)

   Suggest two practical reasons, other than the reaction being reversible, why the perfume manufacturer might have obtained less than the theoretical maximum mass of ester from this reaction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pharmaceutical company is comparing two possible reaction pathways for producing the same drug, in order to choose the pathway that wastes the least raw material as unwanted by-products.

   (a)

   A pharmaceutical company produces a drug via a reaction where the desired product has a relative formula mass of 90, and the sum of the relative formula masses of all the reactants used in the balanced equation is 150. What is the atom economy of this reaction?

   [1 mark]

   • A90%
   • B60%
   • C150%
   • D40%

   (b)

   An alternative reaction pathway for the same drug has an atom economy of 85%, compared with the 60% pathway described earlier. Which statement correctly interprets what a higher atom economy means for the company's choice of reaction pathway?

   [1 mark]

   • AAtom economy has no relationship to how much of the reactant mass ends up as useful product
   • BA higher atom economy means the reaction produces a lower percentage yield of the desired product
   • CA higher atom economy means a greater proportion of the mass of reactants is converted into the desired product, producing less waste by-product
   • DA higher atom economy means more of the reactant atoms are destroyed during the reaction

   (c)

   Explain why the pharmaceutical company might choose the 85% atom economy pathway over the 60% atom economy pathway, even if both pathways give a similar percentage yield of the desired drug.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A brewery ferments sugar to produce ethanol on an industrial scale, then compares the efficiency of this process with a second, smaller batch produced using slightly different fermentation conditions, to decide which method to use going forward.

   (a)

   A brewery ferments sugar to produce ethanol, with a theoretical maximum yield of 230 kg of ethanol predicted from a large batch of sugar. After fermentation and distillation, the brewery collects 184 kg of ethanol. Calculate the percentage yield of ethanol from this fermentation batch, showing your working.

   [3 marks]

   (b)

   In a second, smaller fermentation batch using different conditions, the brewery predicts a theoretical maximum yield of 92 kg of ethanol, but only collects 64.4 kg after distillation. Calculate the percentage yield of this second batch, and explain which of the two fermentation batches described was more efficient in terms of percentage yield.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemical engineer at a plastics factory is choosing between two possible industrial routes for manufacturing the same polymer from crude oil feedstock, weighing up efficiency, cost and environmental impact before recommending which route the factory should adopt at full scale.

   (a)

   Route A has a high atom economy but a low percentage yield, while Route B has a lower atom economy but a very high percentage yield. Explain fully the difference between atom economy and percentage yield as measures of a reaction's efficiency, and discuss why a chemical engineer might need to consider both measures together, rather than relying on just one, when deciding which industrial route is more sustainable and cost-effective overall.

   [6 marks]

   (b)

   The chemical engineer is given the following data: Route A has an atom economy of 90% and a percentage yield of 50%, while Route B has an atom economy of 55% and a percentage yield of 95%. Using this data, evaluate which route is likely to result in more raw material being wasted overall per tonne of polymer eventually produced, and recommend which route the factory should adopt, justifying your answer using both atom economy and percentage yield.

   [6 marks]

   Total for question 4: 12 marks

End of questions