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For a polybasic acid, the dissociation constants have a different values for each step, e.g.,
\[
\begin{array}{l}
\mathbf{H}_{3} \mathrm{~A} \rightleftharpoons \mathbf{H}^{+}+\mathbf{H}_{2} \mathrm{~A}^{-} ; \mathrm{K}=\mathrm{K}_{\mathbf{a}_{1}} \\
\mathbf{H}_{2} \mathrm{~A}^{-} \rightleftharpoons \mathbf{H}^{+}+\mathbf{H A}^{2-} ; \mathrm{K}=\mathbf{K}_{\mathbf{a}_{2}} \\
\mathbf{H A}^{2-} \rightleftharpoons \mathbf{H}^{+}+\mathrm{A}^{3-} ; \mathrm{K}=\mathbf{K}_{\mathbf{a}_{3}}
\end{array}
\]
What is the observed trend of dissociation constants in successive stages?
(a) \( K_{a_{1}}K_{a_{2}}K_{a_{3}} \)
(b) \( \mathrm{K}_{\mathbf{a}_{1}}=\mathrm{K}_{\mathbf{a}_{2}}=\mathrm{K}_{\mathbf{a}_{3}} \)
(c) \( \mathrm{K}_{\mathbf{a}_{1}}\mathrm{K}_{\mathbf{a}_{2}}\mathrm{K}_{\mathbf{a}_{3}} \)
(d) \( \mathbf{K}_{\mathbf{a}_{1}}=\mathbf{K}_{\mathbf{a}_{2}}+\mathbf{K}_{\mathbf{a}_{3}} \)
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