Question

Comment on the feasibility of titrating pyridine in water and suggest other solvents that would be satisfactory for the titration of pyridine.

Answer 1

Pyridine being a weak base it is hard to titrate in water with no sharp endpoint.

Instead we should use Acetic acid as a solvent for pyridine, acetic acid exerts its levelling effect and enhances the basic properties of the pyridine.It is possible, therefore, to titrate a solution of a weak base in acetic acid with perchloric acid in acetic acid, and obtain a sharp endpoint when attempts to carry out the titration in aqueous solution are unsuccessful.

Example:

HClO₄ + CH₃COOH ⇌ CH₃COOH₂⁺ + ClO₄⁻

C₅H₅N + CH₃COOH ⇌ C₅H₅NH⁺ + CH₃COO⁻

CH₃COOH₂⁺ + CH₃COO⁻ ⇌ 2CH₃COOH

Adding HClO₄ + C₅H₅N ⇌ C₅H₅NH⁺ + ClO₄⁻