250+ TOP MCQs on Preparation Method of Diazonium Salts and Answers

Chemistry Multiple Choice Questions on “Preparation Method of Diazonium Salts”.

1. What is the most suitable temperature for the diazotisation reaction to take place?
a) 0°C
b) 10°C
c) 22°C
d) 30°C
Answer: a
Clarification: Benzene diazonium salts are prepared by the reaction of aniline with nitrous acid at very low temperatures (273-278K). If the temperature was to cross 278K, phenol will be formed instead.

2. Identify the diazonium group in the diazonium salt ArN₂⁺Br-.
a) ArN₂⁺
b) N₂⁺Br^–
c) N₂⁺
d) ArN₂Br
Answer: c
Clarification: The Ar represents the aromatic ring and Br^– is the negative ion that forms the salt by combining with the diazonium group, N₂⁺.

3. What is the correct name of the compound C₆H₅N₂⁺HSO₄^–?
a) Benzenediazonium hydrogensulphate
b) Benzenehygrogensulphate diazonium
c) Diazonium benzenehydrogensulphate
d) Hydrogensulphate diazoniumbenzene
Answer: a
Clarification: Diazonium salts are named by suffixing diazonium to the parent hydrocarbon (benzene) from which they are formed, followed by the name of the anion (HSO₄^–).

4. Identify the reagent ‘X’ in the following reaction.

a) HNO₃
b) NaNO₂ and HCl
c) NaCl and HNO₃
d) NaNO₂ and H₂SO₄
Answer: b
Clarification: Aniline actually reacts with HNO₂ (nitrous acid) at 273K to form Benzenediazonium chloride. But this nitrous acid in produced in situ, by a mixture of NaNO₂ and HCl.

5. Why is the reason for the stability of aromatic diazonium salts?
a) Dispersal of negative charge over the benzene ring
b) Dispersal of positive charge over benzene ring
c) Bond between diazonium group and anion
d) High electronegativity of anion compared to the N atom
View Answer

Answer: b
Clarification: The stability of benzenediazonium salt is due to its resonance structures. In three of the resonance structures, the positive charge is dispersed over the benzene ring at ortho and para positions.

6. Aliphatic diazonium salts are highly unstable.
a) True
b) False
View Answer

Answer: a
Clarification: Alkyldiazonium salts are highly unstable as they readily decompose at low temperatures forming a carbocation and nitrogen gas.

7. The preparation of diazonium salts from primary aromatic amines is known as ______
a) acylation
b) alkylation
c) benzonation
d) diazotisation
View Answer

Answer: d
Clarification: This is a method of preparation of diazonium salts. This occurs by the formation of nitrosonium ion followed by diazohydroxide, which on protonation gives diazonium ion. This takes up the acid anion to form diazonium salt.

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