Oxidation and Reduction - UNSOLVED PRACTICE SET

Q7. Write the reaction of acetaldehyde with Tollens' reagent. What is observed?

Q8. Why do ketones not reduce Fehling's solution or Tollens' reagent? Explain.

Q9. Write the reaction of acetone with LiAlH₄ followed by hydrolysis. What is the product?

Q10. What is the Clemmensen reduction? Write the reaction for the reduction of acetophenone to ethylbenzene.

Q11. Distinguish between the products of reduction of aldehydes and ketones using NaBH₄.

Q12. Your teacher shows you that benzaldehyde does not reduce Fehling's solution. Explain why.

Q13. (a) Describe the oxidation of aldehydes using:

(i) Tollens' reagent

(ii) Fehling's solution

(iii) Benedict's solution

(iv) Acidified KMnO₄ or K₂Cr₂O₇

Write the reactions for each.

(b) Why do ketones not undergo oxidation by mild oxidizing agents?

(c) Under what conditions can ketones be oxidized?

Q14. (a) Describe the reduction of aldehydes and ketones using:

(i) Catalytic hydrogenation (H₂/Ni or Pt or Pd)

(ii) Metal hydrides (NaBH₄, LiAlH₄)

(iii) Clemmensen reduction

(iv) Wolff-Kishner reduction

Write the reactions and mention the conditions for each.

(b) Compare the mechanisms of reduction by NaBH₄ and LiAlH₄.

Q15. (a) Explain why:

(i) Aldehydes are easily oxidized while ketones are resistant to oxidation

(ii) Only α-hydroxy ketones reduce Tollens' reagent

(iii) α,β-unsaturated aldehydes are more easily oxidized than saturated aldehydes

(b) A compound with molecular formula C₅H₁₀O gives a positive Tollens' test but negative iodoform test. Identify the compound.

Q16. A student studies the oxidation and reduction of carbonyl compounds.

(a) Write the reaction of acetaldehyde with acidified K₂Cr₂O₇. What colour change is observed?

(b) Write the reaction of acetone with NaBH₄ followed by hydrolysis.

(c) If 29 g of acetone (molar mass = 58 g/mol) is reduced with NaBH₄, calculate the theoretical yield of propan-2-ol (molar mass = 60 g/mol).

(d) The Clemmensen reduction of acetophenone (C₆H₅COCH₃) gives ethylbenzene. If 60 g of acetophenone (molar mass = 120 g/mol) is used, calculate the theoretical yield of ethylbenzene (molar mass = 106 g/mol).

(e) Why is the Wolff-Kishner reduction preferred over Clemmensen reduction for compounds sensitive to acid?

Q17. The following reactions involve oxidation and reduction:

Reaction 1: CH₃CHO + [O] → CH₃COOH (Tollens' reagent)

Reaction 2: CH₃COCH₃ + H₂ → CH₃CH(OH)CH₃ (H₂/Ni)

Reaction 3: C₆H₅CHO + NaBH₄ → C₆H₅CH₂OH

Reaction 4: C₆H₅COCH₃ + Zn-Hg/HCl → C₆H₅CH₂CH₃

(a) Identify the type of reaction (oxidation or reduction) for each.

(b) For Reaction 1, calculate the mass of silver mirror formed from 11 g of acetaldehyde if the yield is 90%. (Ag = 108 g/mol)

(c) For Reaction 2, if 5.8 g of acetone is hydrogenated, calculate the volume of H₂ required at STP.

(d) For Reaction 3, explain why NaBH₄ reduces the aldehyde but does not reduce the benzene ring.

(e) For Reaction 4, why is Zn-Hg/HCl used instead of catalytic hydrogenation?

Q18. In a school chemistry lab, students perform various oxidation and reduction reactions.

(a) A student adds Fehling's solution to acetaldehyde and heats it. A red precipitate forms. Write the reaction and identify the red precipitate.

(b) Another student tries to oxidize acetone using Fehling's solution. No reaction occurs. Explain why. What reagent would oxidize acetone?

(c) A third student reduces benzaldehyde using NaBH₄. The product is tested with Lucas reagent. What observation is expected? Explain.

(d) The students learn that in the body, ethanol is oxidized to acetaldehyde by alcohol dehydrogenase, and then to acetic acid by aldehyde dehydrogenase. Write these reactions. Why is acetaldehyde more toxic than ethanol?

(e) The teacher asks: "If you were designing a breathalyser to detect drunk drivers, would you detect ethanol or acetaldehyde? Why?" Give your answer with reasoning.