Free Reactivity of Aldehydes and Ketones MCQs with Answers
83 Reactivity of 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.
The polar carbonyl group makes aldehydes and ketones undergo nucleophilic addition, reduction and condensation reactions. Aldehydes are generally more reactive and oxidise readily to carboxylic acids, whereas ketones resist mild oxidation; reactions with hydrogen cyanide, sodium bisulfite and 2,4-DNP help identify their behaviour.
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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. 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. 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. 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 atoms- 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. HI
- B. LiAlH4
- C. K2Cr2O7
- D. NaBH4
Explanation: Acidified potassium dichromate is the standard oxidising agent for converting an aldehyde to a carboxylic acid, turning from orange to…
Correct answer: K2Cr2O7- A. sp3 hybridised
- B. sp2 hybridised
- C. sp hybridised
- D. Unhybridised
Explanation: The carbonyl carbon forms three sigma bonds in a trigonal planar arrangement and has an unhybridised p orbital for the pi bond, so it is…
Correct answer: sp2 hybridised- A. White colour
- B. Yellow colour
- C. Red colour
- D. Blue colour
Explanation: HCHO reduces Fehling solution, converting blue Cu2+ ions into brick-red Cu2O precipitate while the aldehyde is oxidised to formate or…
Correct answer: Red colour- A. Aldehydes
- B. Thio alcohols
- C. Amines
- D. Ethers
Explanation: In Tollens' test, aldehydes reduce diamminesilver(I) ions to metallic silver, producing a silver mirror, while the aldehyde is oxidised to…
Correct answer: Aldehydes- A. Tollen's reagent
- B. Iodoform test
- C. Schiff's test
- D. Benedict's reagent
Explanation: A dimethyl ketone is acetone, CH3COCH3, which contains the CH3CO- group required for the iodoform test.
Correct answer: Iodoform test- A. Ethanol
- B. Ethanal
- C. Propane
- D. Propanol
Explanation: Clemmensen reduction uses zinc amalgam and concentrated HCl to replace the carbonyl oxygen of a ketone with two hydrogen atoms.
Correct answer: Propane- A. Iodoform test
- B. Lucas test
- C. Benedict's test
- D. Tollen's test
Explanation: Acetaldehyde gives the iodoform test because it contains the CH3CO- equivalent, and it gives Benedict's and Tollens' tests because it is…
Correct answer: Lucas test- A. Acetone
- B. Acetaldehyde
- C. Acetic acid
- D. Methyl acetate
Explanation: Schiff's reagent is decolorized by sulphurous acid and develops a pink or magenta colour with aldehydes, such as acetaldehyde.
Correct answer: Acetaldehyde- A. Acetone
- B. Acetic acid
- C. Acetophenone
- D. Phenyl acetate
Explanation: The structure C6H5-CO-CH3 has a carbonyl group bonded to a phenyl group and a methyl group, so it is acetophenone, an aromatic ketone.
Correct answer: Acetophenone- A. Ether
- B. Ketone
- C. Aldehyde
- D. Ester
Explanation: Acetophenone has the structure C6H5COCH3, in which the carbonyl carbon is bonded to two carbon groups, phenyl and methyl.
Correct answer: KetoneReactivity of Aldehydes and Ketones MCQs: common questions
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