Aldehydes and ketonesAQA A-Level Chemistry: Topic test

20 questions, 54 marks

AQA A-Level Chemistry

Aldehydes and ketones topic test

Total 54 marks

Name

Class

Date

1
A teacher demonstrates the silver mirror test by warming ethanal, CH₃CHO, with Tollens' reagent in a clean test tube. In a separate demonstration she warms ethanal with Fehling's solution.
(a)
What is observed when ethanal is warmed with Tollens' reagent?
[1 mark]
AThe solution turns from orange to green
BA blue precipitate forms
CA silver mirror forms on the inside of the test tube
DThe colourless solution stays unchanged
(b)
Which compound is the organic product when ethanal is oxidised?
[1 mark]
AEthanoic acid
BEthanol
CPropanone
DEthane-1,2-diol
(c)
State the observation when ethanal is warmed with Fehling's solution and state the change in oxidation state of copper that causes it.
[2 marks]
Total for question 1: 4 marks
2
Cyclohexanone, C₆H₁₀O, is a cyclic ketone used in the manufacture of nylon intermediates. It is reduced to cyclohexanol, C₆H₁₁OH, using NaBH₄ in aqueous solution at room temperature.
(a)
What is the role of NaBH₄ in this reaction?
[1 mark]
AAn electrophile that attacks the carbon of the C=O group
BA source of hydride ions, which act as a nucleophile
CAn oxidising agent that adds oxygen to the ring
DA free-radical initiator
(b)
What type of compound is cyclohexanol?
[1 mark]
AA primary alcohol
BA tertiary alcohol
CA carboxylic acid
DA secondary alcohol
(c)
Write an overall equation for the reduction of cyclohexanone using [H] to represent the reducing agent, and name the type of reaction.
[2 marks]
Total for question 2: 4 marks
3
Compound E has molecular formula C₅H₁₀O and is one of the three ketones pentan-2-one, pentan-3-one and 3-methylbutan-2-one. It has a branched carbon chain and does not react with Fehling's solution. When E is reduced with NaBH₄ in aqueous solution it forms compound F, which shows optical isomerism.
(a)
Identify E. Use the information to justify your answer and give the structural formula of F.
[3 marks]
(b)
Write an overall equation for the reduction of E to F using [H], and outline the mechanism of the reaction.
[4 marks]
Total for question 3: 7 marks
4
Octanal, CH₃(CH₂)₆CHO, is used in perfumery. A chemist carries out three experiments on octanal: warming it with Fehling's solution, reducing it with NaBH₄ in aqueous solution, and reacting it with KCN followed by dilute acid.
(a)
Describe what happens when octanal is warmed with Fehling's solution and when it is reduced with NaBH₄. Include the organic products and outline the mechanism of the reduction.
[6 marks]
(b)
Octanal reacts with KCN followed by dilute acid to form 2-hydroxynonanenitrile. Explain why the product shows no net rotation of plane-polarised light even though its molecule is chiral. Outline the mechanism of the first step and state a hazard of using KCN.
[6 marks]
Total for question 4: 12 marks
5
3-Methylbutanal, (CH₃)₂CHCH₂CHO, reacts with KCN followed by dilute acid to give 2-hydroxy-4-methylpentanenitrile, (CH₃)₂CHCH₂CH(OH)CN.
(a)
What is the role of the cyanide ion in this reaction?
[1 mark]
AElectrophile
BFree radical
COxidising agent
DNucleophile
(b)
Which species is formed when cyanide ions attack the carbonyl carbon, before any acid is added?
[1 mark]
AA positively charged intermediate with an OH₂⁺ group
BA negatively charged intermediate with an O⁻ group
CA pair of free radicals
DThe hydroxynitrile itself
(c)
Write an overall equation for the formation of 2-hydroxy-4-methylpentanenitrile from 3-methylbutanal using HCN, and state the role of the dilute acid in the reaction using KCN.
[2 marks]
Total for question 5: 4 marks
6
A technician warms 1.44 g of 2-methylpropanal, (CH₃)₂CHCHO (M_r = 72.0), with excess Tollens' reagent. The reduction half-equation for the reagent is [Ag(NH₃)₂]⁺ + e⁻ → Ag + 2NH₃. In a separate experiment, 2-methylpropanal is reduced using NaBH₄ in aqueous solution. The relative atomic mass of silver is 107.9.
(a)
What is the organic product of the reduction of 2-methylpropanal by NaBH₄?
[1 mark]
A2-Methylpropan-1-ol
B2-Methylpropan-2-ol
C2-Methylpropanoic acid
DButan-2-ol
(b)
How many moles of silver are formed from one mole of 2-methylpropanal in the Tollens' reaction?
[1 mark]
A1
B3
C2
D4
(c)
Calculate the maximum mass of silver formed in the Tollens' reaction. Give your answer to three significant figures.
[2 marks]
Total for question 6: 4 marks
7
A technician prepares 2-hydroxy-2-methylpropanenitrile, (CH₃)₂C(OH)CN, by adding propanone to a solution of KCN and then adding dilute sulfuric acid. The product shows no optical isomerism.
(a)
Outline the mechanism for the first step of this reaction, in which the cyanide ion reacts with propanone, and describe how the second step forms the product.
[3 marks]
(b)
Explain why 2-hydroxy-2-methylpropanenitrile shows no optical isomerism, and state two hazards or precautions linked to the use of KCN and acid in this preparation.
[4 marks]
Total for question 7: 7 marks
8
Compound K is an aldehyde. It contains 69.8% carbon, 11.6% hydrogen and 18.6% oxygen by mass, and its relative molecular mass is 86.0. K gives a silver mirror with Tollens' reagent. Reduction of K with NaBH₄ in aqueous solution gives compound L, a primary alcohol that shows optical isomerism. The relative atomic masses are C = 12.0, H = 1.0 and O = 16.0.
(a)
Deduce the structural formula of K. Show your working.
[6 marks]
(b)
Describe the mechanism for the reduction of K to L by NaBH₄, give the overall equation using [H], and state what is observed when L is warmed with Fehling's solution.
[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).