Free Aldehydes and Ketones MCQs with Answers
679 Aldehydes and Ketones MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Aldehydes and ketones contain the polar carbonyl group, but aldehydes are generally more readily oxidised and more reactive than ketones. Coverage includes preparation by oxidation or reduction routes, nucleophilic addition of reagents such as hydrogen cyanide and bisulfite, and tests that distinguish aldehydes from ketones.
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- A. it carries a partial positive charge, oxygen being more electronegative
- B. it carries a partial negative charge
- C. it has a lone pair of electrons
- D. it is bonded to hydrogen
Explanation: The carbon to oxygen double bond is strongly polarised towards oxygen, leaving the carbon electron deficient and open to attack by a…
Correct answer: it carries a partial positive charge, oxygen being more electronegative- A. the carbonyl group is absent
- B. two alkyl groups release electron density towards the carbonyl carbon and also hinder attack
- C. the carbonyl carbon carries a full positive charge
- D. the carbon to oxygen bond is much longer
Explanation: Alkyl groups push electron density towards the carbonyl carbon, reducing its positive character, and their bulk physically blocks the…
Correct answer: two alkyl groups release electron density towards the carbonyl carbon and also hinder attack- A. ketones only
- B. both aldehydes and ketones
- C. aldehydes only
- D. neither aldehydes nor ketones
Explanation: An aldehyde still has a hydrogen on the carbonyl carbon, so it is easily oxidised to a carboxylic acid while the silver ions are reduced…
Correct answer: aldehydes only- A. propanone
- B. benzaldehyde
- C. ethanol
- D. ethanal
Explanation: Aliphatic aldehydes such as ethanal reduce the blue copper two complex to a brick red precipitate, whereas ketones do not react at all.
Correct answer: ethanal- A. ethanoic acid
- B. 2-hydroxypropanenitrile
- C. ethanol
- D. propanone
Explanation: The cyanide ion attacks the carbonyl carbon and the resulting alkoxide picks up a proton, giving a hydroxynitrile with one more carbon…
Correct answer: 2-hydroxypropanenitrile- A. a primary alcohol
- B. a carboxylic acid
- C. a secondary alcohol
- D. an alkane
Explanation: The hydride ion adds to the carbonyl carbon, which then carries two alkyl groups and a hydroxyl, so the product is a secondary alcohol.
Correct answer: a secondary alcohol- A. a silver mirror
- B. a colourless solution
- C. carbon dioxide
- D. an orange crystalline precipitate
Explanation: This reagent, often called Brady's reagent, condenses with any carbonyl group to give a bright orange or yellow solid, so it detects the…
Correct answer: an orange crystalline precipitate- A. ethanol
- B. ethanoic acid
- C. ethene with hydrogen
- D. propanone
Explanation: Oxidising the primary alcohol ethanol with acidified dichromate, distilling off the product as it forms, gives ethanal, and the same…
Correct answer: ethanol- A. propan-1-ol
- B. propane
- C. propan-2-ol
- D. propanoic acid
Explanation: Propan-2-ol is a secondary alcohol, so removing the hydrogen from the carbinol carbon leaves a ketone, and the reaction stops there…
Correct answer: propan-2-ol- A. Propanal
- B. Propanone
- C. Benzaldehyde
- D. Methanal
Explanation: The test requires a methyl group attached directly to the carbonyl carbon, and propanone is the simplest methyl ketone, giving the pale…
Correct answer: Propanone- A. they have smaller molecules
- B. they are non polar
- C. they are ionic
- D. they cannot hydrogen bond to one another, having no hydrogen attached to oxygen
Explanation: Carbonyl compounds are polar and attract one another by dipole to dipole forces, which lifts their boiling points above those of alkanes…
Correct answer: they cannot hydrogen bond to one another, having no hydrogen attached to oxygen- A. measuring the pH of the compound
- B. separating and purifying the carbonyl compound, since the adduct can be decomposed to regenerate it
- C. converting the compound into an alkane
- D. detecting the presence of a benzene ring
Explanation: The bisulphite adduct crystallises out and can be filtered off, and treating it with dilute acid or alkali releases the original aldehyde…
Correct answer: separating and purifying the carbonyl compound, since the adduct can be decomposed to regenerate it- A. sp3 to sp2
- B. sp to sp2
- C. sp2 to sp3
- D. sp3 to sp
Explanation: The carbonyl carbon starts as trigonal planar sp2 with a bond angle of 120 degrees, and when the nucleophile adds it acquires a fourth…
Correct answer: sp2 to sp3- A. preserving biological specimens
- B. flavouring food
- C. treating drinking water
- D. use as a fuel
Explanation: Methanal cross links the proteins of tissue, hardening it and killing microorganisms, which is why formalin preserves specimens and is…
Correct answer: preserving biological specimens- A. CH3CHO
- B. CH3COCH3
- C. CH3COOH
- D. CH3CH2OH
Explanation: In propanone the carbonyl group lies between two carbon atoms, which is the defining feature of a ketone, while CH3CHO is the aldehyde…
Correct answer: CH3COCH3- A. a primary alcohol
- B. a ketone
- C. a carboxylic acid with the same number of carbon atoms
- D. carbon dioxide only
Explanation: The hydrogen on the carbonyl carbon is replaced by a hydroxyl group, so ethanal becomes ethanoic acid with no change in the length of the…
Correct answer: a carboxylic acid with the same number of carbon atoms17. The compound formed when ethanal reacts with a Grignard reagent, followed by acid hydrolysis, is
- A. a primary alcohol
- B. a secondary alcohol
- C. a tertiary alcohol
- D. a carboxylic acid
Explanation: The alkyl group of the Grignard reagent adds to the carbonyl carbon, which then carries that new group, the original methyl group, a…
Correct answer: a secondary alcohol- A. benzaldehyde is a ketone
- B. benzaldehyde contains no carbonyl group
- C. Fehling's solution reacts only with aromatic compounds
- D. aromatic aldehydes are oxidised less readily than aliphatic aldehydes
Explanation: Fehling's solution is the milder oxidising agent of the two, so it fails with aromatic aldehydes whose carbonyl group is stabilised by…
Correct answer: aromatic aldehydes are oxidised less readily than aliphatic aldehydes- A. oximes
- B. esters
- C. alcohols
- D. amines
Explanation: The nitrogen of hydroxylamine attacks the carbonyl carbon and water is then eliminated, so the product contains a carbon to nitrogen…
Correct answer: oximes- A. a solvent, because it dissolves both polar and non polar substances and evaporates quickly
- B. an oxidising agent
- C. a fuel for vehicles
- D. a food preservative
Explanation: Its polar carbonyl group and small hydrocarbon portion let propanone dissolve a wide range of materials, and its low boiling point of 56…
Correct answer: a solvent, because it dissolves both polar and non polar substances and evaporates quicklyAldehydes and Ketones MCQs: common questions
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