The rapid change of pH near the stoichiometri | vedclass

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Question

(B) An indicator $(HIn)$ is a weak acid that dissociates in solution as follows:$HIn \rightleftharpoons H^{+} + In^{-}$The equilibrium constant expres

Vedclass · Accepted Answer

$\log \frac{[In^{-}]}{[HIn]} = pH - pK_{In}$

Vedclass · Answer

(B) An indicator $(HIn)$ is a weak acid that dissociates in solution as follows:$HIn \rightleftharpoons H^{+} + In^{-}$The equilibrium constant expression is:$K_{In} = \frac{[H^{+}][In^{-}]}{[HIn]}$Taking the negative logarithm on both sides:$-\log K_{In} = -\log [H^{+}] - \log \frac{[In^{-}]}{[HIn]}$$pK_{In} = pH - \log \frac{[In^{-}]}{[HIn]}$Rearranging the terms,we get:$\log \frac{[In^{-}]}{[HIn]} = pH - pK_{In}$

The rapid change of $pH$ near the stoichiometric point of an acid-base titration is the basis of indicator detection. The $pH$ of the solution is related to the ratio of the concentrations of the conjugate acid $(HIn)$ and base $(In^{-})$ forms of the indicator by the expression:

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