Topic 19: Nitrogen Compounds

Question 1

Definitions I:
(a) Amine
(b) Nitrile
(c) Hydroxynitrile

Answer 1

Definitions I:
(a) Organic compound with -NH₂ group, e.g., CH₃NH₂.
(b) Organic compound with -CN group, e.g., CH₃CN.
(c) Compound with -OH and -CN on same carbon, e.g., RCH(OH)CN.

Question 2

In a lab, propanal reacts with HCN (KCN, heat). Write the equation and name the product. [2 Marks]

Answer 2

CH₃CH₂CHO + HCN → CH₃CH₂CH(OH)CN (KCN, heat) (1 mark)
2-Hydroxybutanenitrile (1 mark)

Question 2

Definitions II:
(a) Nucleophile
(b) Hydrolysis
(c) Halogenoalkane

Answer 2

Definitions II:
(a) Electron-pair donor, e.g., NH₃ in amine synthesis.
(b) Reaction with water to break bonds, e.g., nitrile to acid.
(c) Alkane with a halogen atom, e.g., CH₃CH₂Cl.

Question 3

Write equations for producing:
(a) CH₃CH₂NH₂ from CH₃CH₂Cl [1 Mark]
(b) CH₃CH₂CN from CH₃CH₂Br [1 Mark]

Answer 3

(a) CH₃CH₂Cl + NH₃ → CH₃CH₂NH₂ + HCl (ethanol, pressure, heat) (1 mark)
(b) CH₃CH₂Br + KCN → CH₃CH₂CN + KBr (ethanol, heat) (1 mark)

Question 4

Describe the hydrolysis of CH₃CN with dilute HCl, including the final product. [2 Marks]

Answer 4

CH₃CN + 2H₂O → CH₃CONH₂ → CH₃COOH + NH₃ (HCl, heat) (1 mark)
Ethanoic acid after acidification (1 mark)

Question 5

How is CH₃CH₂CH₂NH₂ synthesised from a halogenoalkane in a sealed vessel? [2 Marks]

Answer 5

CH₃CH₂CH₂Cl + NH₃ → CH₃CH₂CH₂NH₂ + HCl (1 mark)
Ethanol, sealed, heated under pressure (1 mark)

Question 6

In a classroom demo, CH₃COCH₃ forms a hydroxynitrile with HCN. Write the equation. [2 Marks]

Answer 6

CH₃COCH₃ + HCN → CH₃C(OH)(CN)CH₃ (KCN, heat) (1 mark)
2-Hydroxy-2-methylpropanenitrile forms (1 mark)

Question 7

Compare the hydrolysis of CH₃CH₂CN with dilute NaOH vs. dilute H₂SO₄, heat. [3 Marks]

Answer 7

NaOH: CH₃CH₂CN + OH⁻ → CH₃CH₂COO⁻ + NH₃, then H⁺ → CH₃CH₂COOH (1 mark)
H₂SO₄: CH₃CH₂CN + 2H₂O → CH₃CH₂COOH + NH₃ (1 mark)
Base forms salt first, acid direct (1 mark)

Question 8

Predict the product when CH₃CH₂CH₂Br reacts with KCN in ethanol, heat. [2 Marks]

Answer 8

CH₃CH₂CH₂Br + KCN → CH₃CH₂CH₂CN + KBr (ethanol, heat) (1 mark)
Butanenitrile (1 mark)

Question 9

Why does CH₃CHO + HCN need KCN as a catalyst to form CH₃CH(OH)CN? [2 Marks]

Answer 9

KCN provides CN⁻ nucleophile (1 mark)
Enhances attack on C=O, forms hydroxynitrile (1 mark)

Question 10

In an experiment, CH₃CH₂CN is hydrolysed to a carboxylic acid. Show the process with dilute alkali. [3 Marks]

Answer 10

CH₃CH₂CN + OH⁻ → CH₃CH₂COO⁻ + NH₃ (NaOH, heat) (1 mark)
Acidify: CH₃CH₂COO⁻ + H⁺ → CH₃CH₂COOH (1 mark)
Propanoic acid produced (1 mark)

Question 11

What’s the product when CH₃CHBrCH₃ reacts with NH₃ (ethanol, pressure, heat)? [2 Marks]

Answer 11

CH₃CHBrCH₃ + NH₃ → CH₃CH(NH₂)CH₃ + HBr (ethanol, pressure, heat) (1 mark)
Propan-2-amine (1 mark)