UET Lahore ECAT Chemistry: Aldehydes & Ketones MCQs

UET Lahore ECAT Chemistry: Aldehydes & Ketones MCQs — sample questions

1. Question 1

   Q1. Which of the following is the most reactive aldehyde towards nucleophilic addition?

   • A) HCHO
   • B) CH₃CHO
   • C) C₂H₅CHO
   • D) C₆H₅CHO

   Answer: HCHO

   Explanation: HCHO is most reactive due to least steric hindrance and high electrophilicity of carbonyl carbon.

2. Question 2

   Q2. The reaction of aldehydes with NaHSO₃ is an example of?

   • A) Nucleophilic substitution
   • B) Nucleophilic addition
   • C) Electrophilic addition
   • D) Electrophilic substitution

   Answer: Nucleophilic addition

   Explanation: NaHSO₃ adds to carbonyl group, characteristic of nucleophilic addition reactions.

3. Question 3

   Q3. Tollens' reagent is used to distinguish between?

   • A) Aldehydes and ketones
   • B) Alcohols and ethers
   • C) Alkanes and alkenes
   • D) Alkynes and alkadienes

   Answer: Aldehydes and ketones

   Explanation: Tollens' reagent oxidizes aldehydes to carboxylates, forming silver mirror, while ketones are not oxidized.

4. Question 4

   Q4. Which ketone is most reactive towards nucleophilic addition?

   • A) Acetone
   • B) Cyclohexanone
   • C) Cyclopentanone
   • D) Diethyl ketone

   Answer: Cyclopentanone

   Explanation: Cyclopentanone is more reactive due to angle strain relief on going from sp² to sp³.

5. Question 5

   Q5. The product of the reaction of acetone with HCN is?

   • A) Acetone cyanohydrin
   • B) Acetone oxime
   • C) Acetone hydrazone
   • D) Acetone semicarbazone

   Answer: Acetone cyanohydrin

   Explanation: CN⁻ adds to carbonyl carbon of acetone, forming acetone cyanohydrin.

6. Question 6

   Q6. The reaction of benzaldehyde with CH₃MgBr followed by hydrolysis gives?

   • A) Benzyl alcohol
   • B) 1-Phenylethanol
   • C) 2-Phenylethanol
   • D) Benzene

   Answer: 1-Phenylethanol

   Explanation: Grignard reagent adds to benzaldehyde, forming secondary alcohol after hydrolysis.

7. Question 7

   Q7. Fehling's solution is used to distinguish between?

   • A) Aliphatic and aromatic aldehydes
   • B) Aldehydes and ketones
   • C) Primary and secondary alcohols
   • D) Tertiary and secondary alcohols

   Answer: Aldehydes and ketones

   Explanation: Fehling's solution oxidizes aldehydes to carboxylates, while ketones are not oxidized.

8. Question 8

   Q8. The product of aldol condensation of acetaldehyde is?

   • A) Crotonaldehyde
   • B) But-2-enal
   • C) 3-Hydroxybutanal
   • D) Butanal

   Answer: 3-Hydroxybutanal

   Explanation: Aldol condensation involves nucleophilic addition of enolate to carbonyl group, forming β-hydroxy aldehyde.

9. Question 9

   Q9. Cannizzaro reaction is characteristic of?

   • A) Aldehydes having α-H
   • B) Aldehydes lacking α-H
   • C) Ketones
   • D) Esters

   Answer: Aldehydes lacking α-H

   Explanation: Aldehydes without α-H undergo disproportionation in presence of strong base, characteristic of Cannizzaro reaction.

10. Question 10

    Q10. The reaction of aldehydes with NH₂OH gives?

    • A) Oximes
    • B) Hydrazones
    • C) Semicarbazones
    • D) Cyanohydrins

    Answer: Oximes

    Explanation: NH₂OH reacts with carbonyl group, forming oximes.

11. Question 11

    Q11. Which of the following aldehydes does not undergo aldol condensation?

    • A) Acetaldehyde
    • B) Benzaldehyde
    • C) Propanal
    • D) Butanal

    Answer: Benzaldehyde

    Explanation: Benzaldehyde lacks α-H, hence cannot undergo aldol condensation.

12. Question 12

    Q12. The product of the reaction of acetone with NH₂NH₂ is?

    • A) Acetone hydrazone
    • B) Acetone oxime
    • C) Acetone semicarbazone
    • D) Diacetone amine

    Answer: Acetone hydrazone

    Explanation: NH₂NH₂ reacts with carbonyl group of acetone, forming acetone hydrazone.

13. Question 13

    Q13. Which of the following is a test for unsaturation?

    • A) Tollens' test
    • B) Fehling's test
    • C) Baeyer's test
    • D) 2,4-DNP test

    Answer: Baeyer's test

    Explanation: Baeyer's test involves reaction with cold, dilute KMnO₄, indicating unsaturation.

14. Question 14

    Q14. The reaction of benzaldehyde with NH₃ gives?

    • A) Benzaldehyde ammonia
    • B) Benzylamine
    • C) Benzonitrile
    • D) Benzylamide

    Answer: Benzaldehyde ammonia

    Explanation: Benzaldehyde reacts with NH₃, forming benzaldehyde ammonia.

15. Question 15

    Q15. The product of the reaction of formaldehyde with CH₃MgBr followed by hydrolysis is?

    • A) Methanol
    • B) Ethanol
    • C) Propan-1-ol
    • D) Propan-2-ol

    Answer: Propan-1-ol

    Explanation: Grignard reagent adds to formaldehyde, forming primary alcohol after hydrolysis.

16. Question 16

    Q16. The reaction of acetone with semicarbazide gives?

    • A) Acetone semicarbazone
    • B) Acetone oxime
    • C) Acetone hydrazone
    • D) Diacetone amine

    Answer: Acetone semicarbazone

    Explanation: Semicarbazide reacts with carbonyl group of acetone, forming acetone semicarbazone.

17. Question 17

    Q17. Which of the following compounds is used as a reagent to detect aldehydes?

    • A) Tollens' reagent
    • B) Fehling's solution
    • C) 2,4-DNP
    • D) All of the above

    Answer: All of the above

    Explanation: All these reagents are used to detect or distinguish aldehydes from other compounds.

18. Question 18

    Q18. The reaction of aldehydes with PCl₅ gives?

    • A) Geminal dichlorides
    • B) Vicinal dichlorides
    • C) Alkyl chlorides
    • D) Acid chlorides

    Answer: Geminal dichlorides

    Explanation: PCl₅ reacts with carbonyl group, replacing oxygen with two chlorine atoms, forming geminal dichlorides.

19. Question 19

    Q19. The product of the Wolff-Kishner reduction of acetone is?

    • A) Propan-2-ol
    • B) Propane
    • C) Isopropane
    • D) Propanone hydrazone

    Answer: Propane

    Explanation: Wolff-Kishner reduction involves conversion of carbonyl group to alkane, here forming propane.

20. Question 20

    Q20. The reaction of benzophenone with NH₂OH gives?

    • A) Benzophenone oxime
    • B) Benzophenone hydrazone
    • C) Benzophenone semicarbazone
    • D) No reaction

    Answer: Benzophenone oxime

    Explanation: NH₂OH reacts with carbonyl group of benzophenone, forming benzophenone oxime.