Explain autoionisation of water. Derive a relation for ionic product o

1.	Explain autoionisation of water. Derive a relation for ionic product of water.
Answer» Pure water ionises to a very less extent. The ionisation equilibrium is represented as follows, H₂O₍₁₎ + H₂O₍₁₎ ⇋ H₃O⁺_(aq) + OH^-_(aq) The equilibrium constant K for the above equilibrium is represented as, K = \(\frac{[H_3O^+][OH^-]}{[H_2O]^2}\) ∴ K × [H₂O]² = = [H₃O⁺] × [OH^-] Since K and active mass of pure water [H₂O] are constant we can write, K x [H₂O] = K_w' ∴ K_w = [H₃O⁺] x [OH^-] Where K_w is called ionic product of water. At 25 °C, K_w = 1 × 10^-14.

Explain autoionisation of water. Derive a relation for ionic product of water.

Answer»

Pure water ionises to a very less extent.

The ionisation equilibrium is represented as follows,

H₂O₍₁₎ + H₂O₍₁₎ ⇋ H₃O⁺_(aq) + OH^-_(aq)

The equilibrium constant K for the above equilibrium is represented as,

K = \(\frac{[H_3O^+][OH^-]}{[H_2O]^2}\)

∴ K × [H₂O]² = = [H₃O⁺] × [OH^-]

Since K and active mass of pure water [H₂O] are constant we can write,

K x [H₂O] = K_w'

∴ K_w = [H₃O⁺] x [OH^-]

Where K_w is called ionic product of water.

At 25 °C,

K_w = 1 × 10^-14.