Topic 33: Carboxylic Acids and Derivatives

Question 1

Definitions I:
(a) Carboxylic acid
(b) Acyl chloride
(c) Ester

Answer 1

Definitions I:
(a) Compound with -COOH group, e.g., CH₃COOH.
(b) Compound with -COCl group, e.g., CH₃COCl.
(c) Compound from acid and alcohol, e.g., CH₃COOCH₃.

Question 2

Write equations for:
(a) C₆H₅CH₃ → benzoic acid [1 Mark]
(b) CH₃COOH + PCl₅ → acyl chloride [1 Mark]

Answer 2

(a) C₆H₅CH₃ + 4[O] → C₆H₅COOH + H₂O (KMnO₄, OH⁻, heat, then H⁺) (1 mark)
(b) CH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl (1 mark)

Question 3

In a lab, HCOOH reacts with Tollens’ reagent. Write the equation and observations. [2 Marks]

Answer 3

HCOOH + 2Ag⁺ + H₂O → CO₂ + 2Ag + 2H⁺ (Tollens’) (1 mark)
Silver mirror forms (1 mark)

Question 3

Predict the product of CH₃CH₂OH + CH₃COCl and name it. [2 Marks]

Answer 3

CH₃CH₂OH + CH₃COCl → CH₃COOCH₂CH₃ + HCl (1 mark)
Ethyl ethanoate (1 mark)

Question 4

Compare the acidities of CH₃COOH, C₆H₅OH, and CH₃CH₂OH. [3 Marks]

Answer 4

CH₃COOH > C₆H₅OH > CH₃CH₂OH (1 mark)
-COOH stabilises anion via resonance (1 mark)
Phenol delocalises, ethanol +I effect (1 mark)

Question 5

Describe the hydrolysis of CH₃COCl with H₂O and name the products. [2 Marks]

Answer 5

CH₃COCl + H₂O → CH₃COOH + HCl (room temp) (1 mark)
Ethanoic acid, hydrogen chloride (1 mark)

Question 6

In a test, ClCH₂COOH is more acidic than CH₃COOH. Explain why. [2 Marks]

Answer 6

Cl withdraws electrons, stabilises ClCH₂COO⁻ (1 mark)
Increases acidity over CH₃COOH (1 mark)

Question 6

Show the mechanism for CH₃COCl + NH₃ forming an amide. [3 Marks]

Answer 6

NH₃ attacks C=O, forms CH₃C(OH)ClNH₂ intermediate (1 mark)
Cl⁻ leaves, H⁺ lost (1 mark)
CH₃CONH₂ + HCl forms (1 mark)

Question 7

Why does CH₃COCl hydrolyse faster than CH₃CH₂Cl? [2 Marks]

Answer 7

CH₃COCl: C=O polar, reactive to H₂O (1 mark)
CH₃CH₂Cl: C-Cl less polar, slower SN (1 mark)

Question 7

Predict the product of C₆H₅OH + C₆H₅COCl and write the equation. [2 Marks]

Answer 7

C₆H₅OH + C₆H₅COCl → C₆H₅COOC₆H₅ + HCl (room temp) (1 mark)
Phenyl benzoate (1 mark)

Question 7

Describe the oxidation of HOOCCOOH with warm acidified KMnO₄. [2 Marks]

Answer 7

HOOCCOOH + [O] → 2CO₂ + H₂O (KMnO₄/H⁺, warm) (1 mark)
Oxidises both -COOH groups (1 mark)

Question 8

Explain why C₆H₅COCl resists hydrolysis compared to CH₃COCl. [2 Marks]

Answer 8

C₆H₅COCl: aromatic stabilisation, less reactive (1 mark)
CH₃COCl: no resonance, hydrolyses faster (1 mark)