Chemistry Questions and Answers – Diazonium Salts Chemical Reactions – 3

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This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Diazonium Salts Chemical Reactions – 3”.

1. The reaction involving the conversion of diazonium salts to azo compounds is known as _______ reaction.
a) diazotisation
b) deamination
c) coupling
d) carbylamine
View Answer

Answer: c
Explanation: Benzenediazonium salts react with highly reactive electron rich aromatic compounds to form azo compounds of the form Ar-N=N-Ar, where Ar represents an aromatic group. This type of reaction is known as coupling reaction.
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2. The coupling reaction is a type of _________ reaction.
a) electrophilic addition
b) electrophilic substitution
c) nucleophilic addition
d) nucleophilic substitution
View Answer

Answer: b
Explanation: During a coupling reaction, the diazonium cation which has a positive charge on the terminal nitrogen acts as the electrophile, and the electron rich compounds act as nucleophiles.

3. The coupling reaction of benzenediazonium chloride with aniline occurs in a ______ medium.
a) strongly basic
b) weakly basic
c) neutral
d) weakly acidic
View Answer

Answer: d
Explanation: Aniline is a compound that is slightly basic in nature. To counter the basic effect of aniline during its coupling with diazonium salt, in is conducted in a slightly acidic medium of pH 4 to 5.
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4. The reaction between benzenediazonium chloride and phenol results in a ______ coloured compound.
a) yellow
b) orange
c) red
d) purple
View Answer

Answer: b
Explanation: Benzenediazonium chloride undergoes coupling with phenol to form an azo compound, p-hydroxyazobenzene. This compound is orange in colour.

5. The reaction between a diazonium salt and aniline in a slightly acidic medium gives _______
a) o-aminoazobenzene
b) m-aminoazobenzene
c) p-aminoazobenzene
d) no reaction
View Answer

Answer: c
Explanation: Diazonium salts undergo coupling with aniline to form p-aminoazobenzene. The coupling predominantly occurs at the para position to the amino group.
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6. What is the most suitable pH of the medium for the conduction of coupling reaction of benzenediazonium chloride with phenol?
a) 2
b) 4
c) 7
d) 10
View Answer

Answer: b
Explanation: The coupling reaction with phenol occurs in a basic medium of pH value approximately 9 to 10. This is to counter the acidic nature of phenol and as a result produce water (by the combination of OH and H+) during the reaction.

7. Identify the colour of the compound ‘A’ from the following reaction.
Colour of compound ‘A’ from reaction is Yellow when diazonium salts reaction with aniline
a) Yellow
b) Colourless
c) Green
d) Blue
View Answer

Answer: a
Explanation: Diazonium salts on reaction with aniline form azo compounds which are coloured. This is because of the complex system involving the N-N double bond between two aromatic rings. In this case, compound A is p-aminobenzene, which is yellow coloured.
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8. The reaction between benzenediazonium chloride and N,N-dimethylaniline, in an acidic medium at 273 K gives an orange coloured compound.
a) True
b) False
View Answer

Answer: b
Explanation: This reaction yields p-dimethylaminoazobenzene, which is a yellow solid commonly known as methyl yellow. However, in an aqueous solution at low pH, methyl yellow appears red in colour.

9. When a diazonium salt is treated with p-cresol, at which position with respect to the hydroxy group does the coupling occur?
a) ortho
b) meta
c) para
d) coupling does not take place
View Answer

Answer: a
Explanation: Coupling generally occurs para to the hydroxy group. However in this case, the para position is preoccupied by CH3 group (cresol), and as a result the coupling takes place at ortho position.
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10. What is the product of the following reaction?
The product of the reaction is 2-Amino-5-phenylazophenol occurs at para position
a) 2-Amino-4-phenylazophenol
b) 6-Amino-2-phenylazophenol
c) 2-Amino-5-phenylazophenol
d) 2-Amino-3-phenylazophenol
View Answer

Answer: c
Explanation: The reactant (o-aminophenol) consists of both hydroxy and amino groups. Since the reaction takes place in an acidic medium, the coupling occurs at para position (first preferred) with respect to the amino group. If the reaction was to take place in a basic medium, the coupling would have occurred at para position with respect to hydroxy group.

11. p-Aminophenol on coupling with benzenediazonium chloride in a basic medium gives 4-amino-3-phenylazophenol.
a) True
b) False
View Answer

Answer: b
Explanation: As the reaction takes place in a basic medium, the coupling will take place at the ortho position (since para position is already occupied by amino group) with respect to OH group. This results in the compound 4-amino-2-phenylazophenol.

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