For a weak acid HCN at 25 , ^circ C,which of | vedclass

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(C) For a weak acid $HCN$,the dissociation equilibrium is $HCN \rightleftharpoons H^+ + CN^-$. The dissociation constant $K_a$ is given by $K_a = \fra

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Both $(A)$ and $(B)$

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(C) For a weak acid $HCN$,the dissociation equilibrium is $HCN ightleftharpoons H^+ + CN^-$. The dissociation constant $K_a$ is given by $K_a = \frac{[H^+][CN^-]}{[HCN]}$. For a weak acid,$[H^+] = [CN^-] = C\alpha$ and $[HCN] = C(1-\alpha) \approx C$. Thus,$K_a = C\alpha^2$,which implies $\alpha = \sqrt{\frac{K_a}{C}} = \frac{[H^+]}{C}$. From $K_w = [H^+][OH^-]$,we have $[H^+] = \frac{K_w}{[OH^-]}$. Substituting this into the expression for $\alpha$,we get $\alpha = \frac{K_a}{[H^+]} = \frac{K_a 	imes [OH^-]}{K_w}$. Therefore,both statements $(A)$ and $(B)$ are correct.

For a weak acid $HCN$ at $25 \, ^\circ C$,which of the following statements is correct?

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