AlcoholsAQA A-Level Chemistry: Topic test

20 questions, 54 marks

AQA A-Level Chemistry

Alcohols topic test

Total 54 marks

Name

Class

Date

1
A school science club ferments a solution of glucose using yeast in a sealed flask fitted with an air lock, keeping the flask at 35 °C. After several days the liquid is filtered and then fractionally distilled to collect ethanol.
(a)
Why is air kept out of the flask?
[1 mark]
AOxygen would oxidise the ethanol formed to ethanoic acid
BOxygen would raise the pH and denature the yeast enzymes
COxygen would reduce the glucose to a polymer
DOxygen would prevent any carbon dioxide from forming
(b)
Which statement describes ethanol used as a biofuel?
[1 mark]
AA fuel obtained only from crude oil
BA fuel that does not release carbon dioxide on burning
CA fuel made from living or recently living biological material
DA fuel made by reacting ethene with steam
(c)
Write the equation for the fermentation of glucose and explain why the temperature is kept at 35 °C rather than at 60 °C.
[2 marks]
Total for question 1: 4 marks
2
Hexan-2-ol, CH₃CH(OH)CH₂CH₂CH₂CH₃, is heated under reflux with an excess of acidified potassium dichromate(VI) solution.
(a)
What is the organic product of this reaction?
[1 mark]
AHexanal
BHexanoic acid
CHex-2-ene
DHexan-2-one
(b)
What colour change is seen in the reaction mixture?
[1 mark]
AGreen to orange
BOrange to green
CColourless to orange
DPurple to colourless
(c)
State the observations when a sample of the organic product is warmed separately with Tollens' reagent and with Fehling's solution.
[2 marks]
Total for question 2: 4 marks
3
Butan-2-ol, CH₃CH(OH)CH₂CH₃, is heated with concentrated phosphoric acid. A mixture of three alkenes forms and the gases are collected over water.
(a)
Outline the mechanism for the formation of but-1-ene from butan-2-ol.
[3 marks]
(b)
Name the three alkenes and explain why a mixture forms rather than a single alkene.
[4 marks]
Total for question 3: 7 marks
4
Butan-2-ol, CH₃CH(OH)CH₂CH₃, is manufactured by reacting but-1-ene with steam in the presence of a phosphoric acid catalyst. Butan-2-ol is a secondary alcohol that can be oxidised or dehydrated. Its isomer 2-methylpropan-2-ol, (CH₃)₃COH, behaves differently.
(a)
State the conditions and outline the mechanism for the formation of butan-2-ol from but-1-ene, explaining why butan-2-ol is the major product.
[6 marks]
(b)
Compare the reactions of butan-2-ol with acidified potassium dichromate(VI) and with concentrated phosphoric acid. Include the organic products, the observation with dichromate(VI), a test that distinguishes the two organic products, and what happens to 2-methylpropan-2-ol with dichromate(VI).
[6 marks]
Total for question 4: 12 marks
5
Ethanol is made industrially by passing a mixture of ethene and steam over a solid phosphoric acid catalyst. The ethene used is obtained from crude oil.
(a)
Which statement about this process is correct?
[1 mark]
AIts atom economy is below 100% because water is a by-product
BIts atom economy is 100% because ethanol is the only product
CIt is a substitution reaction
DThe acid catalyst is used up in the reaction
(b)
What is the role of the phosphoric acid?
[1 mark]
AA catalyst that provides H⁺, which is regenerated in the final step
BA reactant that is used up forming phosphate by-products
CAn oxidising agent for ethene
DA dehydrating agent that removes water from ethanol
(c)
Explain why ethanol made by this process is not regarded as a renewable or carbon neutral fuel.
[2 marks]
Total for question 5: 4 marks
6
Four alcohols have the molecular formula C₅H₁₂O. P is 2-methylbutan-1-ol, Q is 3-methylbutan-2-ol, R is 2-methylbutan-2-ol and S is pentan-3-ol. Each is heated separately with acidified potassium dichromate(VI).
(a)
Which alcohol is not oxidised by acidified potassium dichromate(VI)?
[1 mark]
AP
BQ
CR
DS
(b)
Which pair of alcohols is oxidised to ketones?
[1 mark]
AP and Q
BP and R
CQ and R
DQ and S
(c)
State the conditions needed to oxidise P to a carboxylic acid and write an equation for the reaction, using [O] to represent the oxidising agent.
[2 marks]
Total for question 6: 4 marks
7
Glucose, C₆H₁₂O₆ (Mr = 180.0), is fermented by yeast to form ethanol (Mr = 46.0) and carbon dioxide (Mr = 44.0). A brewer ferments 90.0 g of glucose. The molar gas volume is 24.0 dm³ mol⁻¹ at room temperature and pressure.
(a)
Calculate the maximum mass of ethanol that can be formed from 90.0 g of glucose.
[3 marks]
(b)
Calculate the volume of carbon dioxide produced at room temperature and pressure, and the atom economy for the formation of ethanol in this fermentation.
[4 marks]
Total for question 7: 7 marks
8
Butan-1-ol, CH₃CH₂CH₂CH₂OH (boiling temperature 118 °C), can be oxidised by acidified potassium dichromate(VI) to butanal (boiling temperature 75 °C) or to butanoic acid (boiling temperature 164 °C). It can also be dehydrated by heating with concentrated phosphoric acid to form but-1-ene (boiling temperature −6 °C).
(a)
Outline the mechanism for the dehydration of butan-1-ol to but-1-ene and describe how a student can show that the gas collected is an alkene.
[6 marks]
(b)
Explain how the method used determines whether butanal or butanoic acid is obtained from butan-1-ol, and how a student can test the product from the first method to show that it is an aldehyde.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).