Verified Solution • 2025–26 Session moderate

QAIPMT-2004-Ch-2585: NEET 2004 Chemistry - Class 11 AIPMT-2004-Ch-2585 Solution: The rapid change of pH near the stoichiometric point of an…

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−In^-) forms of the indicator by the expression

Multiple Choice Options

  • A log⁡[In−][HIn]=pKIn−pH\log\frac{[In^-]}{[HIn]}=pK_{In}-pH
  • B log⁡[HIn][In−]=pKIn−pH\log\frac{[HIn]}{[In^-]}=pK_{In}-pH
  • C log⁡[HIn][In−]=pH−pKIn\log\frac{[HIn]}{[In^-]}=pH-pK_{In}
  • D log⁡[In−][HIn]=pH−pKIn\log\frac{[In^-]}{[HIn]}=pH-pK_{In}

Step-by-Step Verified Solution

For an acid-base indicator H In _ H + + In - K in = [ H + ] [ I n _ ] [ H i n ] _ [ H + ] = K i n [ I n _ ] [ H i n ] Take � log on both sides _ log _ [ H + ] = _ log _ ( K i n [ I n _ ] [ H i n ] ) _ pH = �log K In + log _ [ I n _ ] [ H i n ] _ pH = pK In + log _ [ I n _ ] [ H i n ] _ log _ [ I n _ ] [ H i n ] = pH - pK In

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