Question

Oswalds dilution law is applicable for electrolytes.

• A. weak
• B. strong
• C. non

Answer 1

The correct option is A weak

For a particular temperature, consider an aqueous solution of a weak electrolyte HA. In aqueous solution, HA remains in equilibrium with its ions.

HA+ $H_{2}O$ $\leftrightharpoons$ $H^{+}$+ $A^{-}$

$K_{eq}$ = $\frac{\left[H^{+}\right]\left[A\right]}{\left[HA\right]\left[H_{2}O\right]}$

$K_a$ = $K_{eq}$ [$H_{2}O$] = $\frac{\left[H^{+}\right]\left[A\right]}{\left[H_{2}O\right]}$

If the initial concentration of HA is c M, and the degree of dissociation be $\alpha$, then at equilibrium,

$K_a$ = c $\alpha$ . $\frac{c\alpha }{c(1-\alpha )}$ = $\frac{c{\alpha }^2}{1-\alpha }$

Whenever weak electrolytes are used, the value of α is very small, approximated as 1- $\alpha$ $\approx$ 1

Hence K $\alpha$ = c ${\alpha }^2$ or $\alpha$ = $\sqrt{\frac{K\alpha }{c}}$

This is known as the Oswald's dilution law. It is strictly applicable only for weak electrolytes. This is not applicable for strong electrolytes as their value of dissociation is not negligible.

At infinite dilution, c $\to$ 0 and 1 - $\alpha$ $\to$ 0 or $\alpha$ $\to$ 1

At infinite dilution, weak electrolytes also behave as like strong ones - dissociating almost completely.