Equilibrium - Result Question 49

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

[2004]

(a) log[In][HIn]=pKInpH

(b) log[HIn][In]=pKInpH

(c) log[HIn][In]=pHpKIn 

(d) log[In][HIn]=pHpKIn 

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Solution:

  1. (d) For an acid-base indicator

HInH++In

KIn=[H+][In][HIn] or [H+]=KIn×[HIn][In]

or logH+=logKIn +log[HIn][In]

Taking negative on both sides

\begin{bmatrix} ended with \end{matrix}

or we can write pH=pKIn +log[In][HIn]

 or log[In][HIn]=pHpKIn 



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