Alcohol productionAQA A-Level Chemistry: Subtopic test

1. 1
   Ethanol is manufactured industrially in two ways: by the hydration of ethene using steam and an acid catalyst, and by the fermentation of glucose using yeast. The ethanol from fermentation is present in a dilute mixture with water and other substances.

   (a)

   Which equation represents the hydration of ethene?

   [1 mark]

   • AC₂H₄ + H₂ → C₂H₆
   • BC₂H₄ + H₂O → C₂H₅OH
   • CC₂H₄ + 2H₂O → C₂H₄(OH)₂ + H₂
   • DC₂H₅Br + OH⁻ → C₂H₅OH + Br⁻

   (b)

   Which method is used to separate ethanol from the dilute fermentation mixture?

   [1 mark]

   • AFractional distillation
   • BFiltration
   • CCrystallisation
   • DPaper chromatography

   (c)

   Write an equation for the fermentation of glucose to ethanol.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Bioethanol made from sugar cane is blended with petrol in some countries. Supporters of this fuel describe it as carbon neutral, so a student investigates the processes involved.

   (a)

   Which statement defines a biofuel?

   [1 mark]

   • AA fuel made from crude oil by fractional distillation
   • BA fuel that releases no carbon dioxide when burned
   • CA fuel obtained from coal
   • DA fuel made from plant or other biological material

   (b)

   What is the basis of the claim that bioethanol is carbon neutral?

   [1 mark]

   • ABurning ethanol does not produce carbon dioxide
   • BThe carbon dioxide released in fermentation is greater than the amount burned
   • CThe carbon dioxide released is balanced by that absorbed by photosynthesis as the crop grows
   • DEthanol absorbs carbon dioxide from the air as it burns

   (c)

   Write an equation for the photosynthesis that forms glucose and an equation for the complete combustion of ethanol.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A plant manager is comparing two routes to ethanol: fermentation of glucose by yeast, and the acid-catalysed hydration of ethene by steam. The staff must understand the conditions for the first route and the mechanism of the second.

   (a)

   Justify the conditions used for the fermentation of glucose: yeast, a temperature of about 35 °C, and the absence of air.

   [3 marks]

   (b)

   Outline the mechanism for the formation of ethanol from ethene and steam in the presence of an acid catalyst, referring to the movement of electron pairs.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A country is deciding whether to expand its production of bioethanol from sugar cane so that it can replace some of the petrol used in road transport.

   (a)

   Ethanol produced by fermentation is often described as a carbon neutral fuel. Use equations to support this statement and give reasons why it is not valid.

   [6 marks]

   (b)

   Discuss the environmental and ethical issues the country should consider in deciding whether to expand its use of biofuel.

   [6 marks]

   Total for question 4: 12 marks

End of questions