This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Preparation Method of Diazonium Salts”.
1. What is the most suitable temperature for the diazotisation reaction to take place?
Explanation: 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-.
Explanation: 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
Explanation: 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–).
Explanation: 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
Explanation: 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.
Explanation: 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 ______
Explanation: 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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