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. HCHO
- B. C6H5CHO
- C. Cl3CCHO
- D. CH3COCH3
Explanation: Aldol condensation requires a carbonyl compound with at least one alpha hydrogen, which allows enolate formation.
Correct answer: CH3COCH322. On heating aldehydes with Fehlings solution we get a precipitate whose colour is_________________?
- A. pink
- B. black
- C. yellow
- D. brick red
Explanation: Aldehydes reduce the blue Cu2+ ions in Fehling's solution to insoluble Cu2O, which forms a brick-red precipitate, while the aldehyde is…
Correct answer: brick red- A. HCOX
- B. CX4
- C. CHX3
- D. CH3X
Explanation: A haloform has one hydrogen and three halogen atoms attached to the same carbon, so its general formula is CHX3, where X may be Cl, Br or…
Correct answer: CHX3- A. formaldehyde
- B. acetaldehyde
- C. diemthyl ketone
- D. propionaldehyde
Explanation: Aldol condensation requires an alpha hydrogen to form an enolate or enol, but formaldehyde has no alpha carbon and therefore cannot…
Correct answer: formaldehyde- A. nucleophile addition
- B. polymerization
- C. oxidation
- D. all of the above
Explanation: Aldehydes and ketones can undergo nucleophilic addition at the carbonyl group, and some carbonyl compounds can polymerize; oxidation is…
Correct answer: all of the above- A. sp hybridized
- B. sp2 hybridized
- C. cp3 hybridized
- D. dsp2 hybridized
Explanation: The carbonyl carbon forms three sigma bonds and has no lone pair involved in its hybrid orbitals, giving it trigonal planar geometry and…
Correct answer: sp2 hybridized- A. methanol
- B. ethanal
- C. propanal
- D. hexanone
Explanation: Hexanone has the largest carbon skeleton and molar mass among the choices, so its stronger dispersion forces give it the highest boiling…
Correct answer: hexanone- A. ethanol and methanol
- B. acetaldehyde and methanal
- C. acetone and diethyl ketone
- D. all of the above
Explanation: The iodoform test is positive for ethanol and compounds containing the CH3CO- or CH3CH(OH)- group, including acetaldehyde and acetone.
Correct answer: all of the above29. Cannizaros reaction takes place through the transfer of ____________________ from complex anion?
- A. hydrogen ion
- B. hydride ion
- C. oxide ion
- D. methoxide ion
Explanation: In the Cannizzaro reaction, one aldehyde molecule is oxidized while another is reduced through transfer of a hydride ion, H-, from an…
Correct answer: hydride ion- A. proton
- B. H+
- C. both A & amp; B
- D. H-
Explanation: The tetrahydroborate ion, BH4-, supplies hydride, H-, which attacks the carbonyl carbon and reduces aldehydes or ketones to alcohols.
Correct answer: H-- A. formation of phenolic resins
- B. formation of mirror
- C. antiseptic inhalant
- D. formation of throat lozenges
Explanation: Acetaldehyde is used for silvering mirrors because it reduces silver ions to metallic silver, and it is also associated with…
Correct answer: formation of throat lozenges- A. in silvery mirror
- B. in making medicine urotropine
- C. in making throat lozenges
- D. in making acetic acid
Explanation: Formaldehyde can be used in silvering mirrors and in preparing urotropine, while its antiseptic action supports some medicinal uses such…
Correct answer: in making acetic acid- A. alkyl groups are electron donating
- B. steric hindrance
- C. Both A and B
- D. none
Explanation: Ketones are less reactive because two alkyl groups donate electron density toward the carbonyl carbon, reducing its positive character…
Correct answer: Both A and B- A. formaldehyde
- B. acetaldehyde
- C. benzaldehyde
- D. trimethyl acetaldehyde
Explanation: Cannizzaro reaction is shown by aldehydes that do not have an alpha hydrogen.
Correct answer: acetaldehyde- A. CH3-CHO
- B. CH3-CH-CH3
- C. CH3-COOH
- D. CH3-CO-CH2-CH3
Explanation: Tollens reagent oxidizes aldehydes to carboxylate ions while Ag+ is reduced to metallic silver, producing the characteristic silver…
Correct answer: CH3-CHO- A. acetaldehyde
- B. ethyl alcohol
- C. methyl alcohol
- D. acetone
Explanation: The iodoform test is positive for compounds containing the CH3CO group, and ethanol is oxidized under the test conditions to ethanal…
Correct answer: methyl alcohol- A. reaction with HCN
- B. reaction with NaHSO3
- C. reaction with 2 4 dinitrophenyl hydrazine
- D. reaction with Fehling solution
Explanation: Ketones form addition products with HCN and NaHSO3 and condensation products with 2,4-dinitrophenylhydrazine because their carbonyl group…
Correct answer: reaction with Fehling solution- A. Ethanal
- B. Acetone
- C. Benzaldehyde
- D. Butanone
Explanation: Aldol condensation requires at least one alpha hydrogen so that an enolate can form.
Correct answer: Benzaldehyde- A. alkaline aquenous iodine
- B. aqueous bromine
- C. Fehling solution
- D. aqueous NaOH
Explanation: Acetone contains the CH3CO- group and gives the iodoform test with alkaline aqueous iodine, producing yellow iodoform, CHI3.
Correct answer: alkaline aquenous iodine- A. Aqueous Bromine
- B. Fehling's reagent
- C. Tollen's reagent
- D. Alkaline aqueous iodine
Explanation: Propanone (also known as acetone) is a ketone that is often produced in the breath of diabetic patients.
Correct answer: Alkaline aqueous iodine