17.5.2 - Acid-base reactions of amines

Question 1

What is the general reaction of an amine with water and with an acid?
RNH2

Answer 1

RNH2 + H2O = RNH3^+ + OH-

RNH2 + H^+ = RNH3^+

Question 2

What is a dative covalent bond?

Answer 2

When the shared pair of electrons in a covalent bond come from one atom.

Question 3

What happens to basicity of amines as the carbon chain length increases and explain why.

Answer 3

Bacisity increases.
The alkyl groups exert a positive inductive effect and they push electrons towards the nitrogen on ammonia. This means the nitrogen is more electron-rich and so can form dative bonds with hydrogen ions.

Question 4

Why is phenylamine much less basic than other amines?

Answer 4

The lone pairs on the nitrogen atom interact with electrons in the delocalised pi system.
This makes the ammonia less electron-rich.
Meaning that the lone pair of electrons is less available to form a dative bond with hydrogen atoms.

Question 5

Predict whether dimethylamine has a higher or lower basicity than methylamine.

Answer 5

Higher basicity.
The 2 methyl groups will have a greater positive inductive effect so the nitrogen will be more electron-rich. This means it will form dative bonds with hydrogen atoms more readily.

Question 6

What is the name of the salt formed when methylamine reacts with nitric acid.

Answer 6

methylammonium nitrate