Topic 18: Carboxylic Acids and Derivatives

Question 1

Definitions I:
(a) Carboxylic acid
(b) Ester
(c) Esterification

Answer 1

Definitions I:
(a) Organic compound with a -COOH group, e.g., CH₃COOH.
(b) Compound from alcohol and carboxylic acid, e.g., RCOOR’.
(c) Condensation forming an ester from acid and alcohol.

Question 2

Write equations for producing CH₃COOH:
(a) From ethanol [1 Mark]
(b) From CH₃CN [1 Mark]

Answer 2

(a) CH₃CH₂OH + 2[O] → CH₃COOH + H₂O (KMnO₄/H⁺, reflux) (1 mark)
(b) CH₃CN + 2H₂O → CH₃CONH₂ → CH₃COOH + NH₃ (HCl, then H⁺) (1 mark)

Question 3

Describe the reaction of CH₃CH₂COOH with:
(a) Mg [1 Mark]
(b) Na₂CO₃ [1 Mark]

Answer 3

(a) 2CH₃CH₂COOH + Mg → (CH₃CH₂COO)₂Mg + H₂ (1 mark)
(b) 2CH₃CH₂COOH + Na₂CO₃ → 2CH₃CH₂COONa + H₂O + CO₂ (1 mark)

Question 4

In a lab, ethanoic acid reacts with ethanol. Write the equation and name the ester. [2 Marks]

Answer 4

CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O (H₂SO₄) (1 mark)
Ethyl ethanoate (1 mark)

Question 5

How does CH₃CH₂COOH reduce to an alcohol with LiAlH₄? [2 Marks]

Answer 5

CH₃CH₂COOH + 4[H] → CH₃CH₂CH₂OH + H₂O (LiAlH₄) (1 mark)
Propan-1-ol forms (1 mark)

Question 6

In a test tube, CH₃COOCH₃ is hydrolysed with dilute HCl. Write the equation. [2 Marks]

Answer 6

CH₃COOCH₃ + H₂O → CH₃COOH + CH₃OH (HCl, heat) (1 mark)
Acid hydrolysis reverses esterification (1 mark)

Question 7

Compare the hydrolysis of CH₃COOCH₂CH₃ with dilute NaOH vs. dilute H₂SO₄, heat. [3 Marks]

Answer 7

NaOH: CH₃COOCH₂CH₃ + OH⁻ → CH₃COO⁻ + CH₃CH₂OH (1 mark)
H₂SO₄: CH₃COOCH₂CH₃ + H₂O → CH₃COOH + CH₃CH₂OH (1 mark)
Base forms salt, acid forms acid (1 mark)

Question 8

Why does CH₃COOH react with NaOH to form a salt and water? [2 Marks]

Answer 8

CH₃COOH + NaOH → CH₃COONa + H₂O (1 mark)
Acid-base neutralisation, H⁺ + OH⁻ (1 mark)

Question 9

In a classroom demo, propanoic acid fizzes with CaCO₃. Write the equation. [2 Marks]

Answer 9

2CH₃CH₂COOH + CaCO₃ → (CH₃CH₂COO)₂Ca + H₂O + CO₂ (1 mark)
CO₂ gas causes fizzing (1 mark)

Question 10

Predict the product when CH₃CH₂CH₂COOH reacts with methanol (H₂SO₄ catalyst). [2 Marks]

Answer 10

CH₃CH₂CH₂COOH + CH₃OH → CH₃CH₂CH₂COOCH₃ + H₂O (H₂SO₄) (1 mark)
Methyl butanoate (1 mark)

Question 11

Write equations for CH₃COOH production from:
(a) CH₃CHO oxidation [1 Mark]
(b) CH₃COOCH₃ hydrolysis [1 Mark]

Answer 11

(a) CH₃CHO + [O] → CH₃COOH (K₂Cr₂O₇/H⁺, reflux) (1 mark)
(b) CH₃COOCH₃ + H₂O → CH₃COOH + CH₃OH (NaOH, then H⁺) (1 mark)

Question 12

Describe the reaction of CH₃CH₂COOH with Zn, including observations and products. [3 Marks]

Answer 12

2CH₃CH₂COOH + Zn → (CH₃CH₂COO)₂Zn + H₂ (1 mark)
H₂ bubbles observed (1 mark)
White zinc propanoate forms (1 mark)