Organic Chemistry Multiple Choice Questions on “Physical Properties of Amines”.
1. Which of the following compound is expected to be most basic?
a) Aniline
b) Methylamine
c) Hydroxylamine
d) Ethylamine
Answer: d
Clarification: Alkyl groups are electron donating (EDG). So, the alkyl group stabilizes the positive charge on the attached nitrogen atom.
2. A solution of methyl amine shows which type of property with litmus paper?
a) Turns blue litmus red
b) Turns red litmus blue
c) Does not affect red or blue litmus
d) Bleaches litmus
Answer: b
Clarification: Methyl amine changes red litmus blue, this litmus paper test shows basic nature of methyl amine.
3. Which of the following statement is true about methyl amine?
a) Methyl amine is slightly acidic
b) Methyl amine is less basic than NH3
c) Methyl amine is stronger base than NH3
d) Methyl amine forms salts with alkali
Answer: c
Clarification: Presence of alkyl group increases electron density on nitrogen atom due to +I effect. Thus, basic nature increases.
4. By the presence of a halogen atom in the ring, what is the effect of this on basic properties of aniline?
a) Increased
b) Decreased
c) Unchanged
d) Doubled
Answer: a
Clarification: By the presence of a halogen atom in the ring, basic properties of aniline is increased because it is more electronegative so donation of electron will be easy, so basicity increases.
5. What is the characteristic smell of liquid amines?
a) Fish like smell
b) Rotten egg smell
c) Fruity smell
d) Bitter almond smell
Answer: a
Clarification: Amines possess a characteristic ammonia smell, liquid amines have a distinctive “fishy” smell.
6. Which of the following have less melting point than amine?
a) Alcohol
b) Phosphine
c) Carboxylic acid
d) Ether
Answer: b
Clarification: Hydrogen bonding significantly influences the properties of primary and secondary amines. Thus, the melting points and boiling points of amines are higher than those of the corresponding phosphines, but generally lower than those of the corresponding alcohols and carboxylic acids, ether.
7. Which of the following amine has highest boiling point?
a) Butyl amine
b) Diethylamine
c) Triethylamine
d) Dipropylamine
Answer: d
Clarification: Primary and secondary amines have higher boiling because they can engage in intermolecular hydrogen bonding. The boiling points of tertiary amines, which cannot engage in hydrogen bonding because they have no hydrogen atom on the nitrogen atom, and d is correct option because it has more molar mass than other primary, secondary and tertiary amine, more +I effect of propyl group.
8. What is the correct decreasing order of the basic character of the three amines and ammonia?
a) NH3 > CH3NH2 > C2H5NH2 > C6H5NH2
b) C2H5NH2 > CH3NH2 > NH3 > C6H5NH2
c) C6H5NH2 > C2H5NH2 > CH3NH2 > NH3
d) CH3NH2 > C2H5NH2 > C6H5NH2 > NH3
Answer: b
Clarification: All of the amines are more basic than ammonia, but primary and secondary amines are the most basic.
9. Unpleasant smelling carbylamines are formed by heating alkali and chloroform with which of the following?
a) Any amine
b) Any aliphatic amine
c) Any aromatic amine
d) Any primary amine
