For a weak acid HA, Ostwald's dilution law is | vedclass

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Question

(B) For a weak acid $HA$ dissociating as $HA \rightleftharpoons H^+ + A^-,$ the initial concentration is $c$ and the degree of dissociation is $\alpha

Vedclass · Accepted Answer

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

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(B) For a weak acid $HA$ dissociating as $HA \rightleftharpoons H^+ + A^-,$ the initial concentration is $c$ and the degree of dissociation is $\alpha.$At equilibrium,the concentrations are $[HA] = c(1 - \alpha),$ $[H^+] = c\alpha,$ and $[A^-] = c\alpha.$The dissociation constant $K_a$ is given by $K_a = \frac{[H^+][A^-]}{[HA]} = \frac{(c\alpha)(c\alpha)}{c(1 - \alpha)} = \frac{c^2\alpha^2}{c(1 - \alpha)} = \frac{c\alpha^2}{1 - \alpha}.$Thus,the correct expression is $K_a = \frac{\alpha^2 c}{1 - \alpha}.$

For a weak acid $HA,$ Ostwald's dilution law is represented by the equation

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