The rapid change of pH near the stoichiometric point of an acid-base titration is the basic of indicator detection. pH of the solution is related to the ratio of the concentration of conjugate acid (H∈) and base (In−) forms of the indicator by the expression

Question

Filo · Accepted Answer

Acid indicatiors are generally weak acid. The dissociation of indicator Hin takes place as floows

H I n \Leftrightarrow H^{+} + I n^{-}

∴ K_{I n} = \frac{[ H ^{+} ] [ I n ^{-} ]}{[ H I n ]}

or

[H^{+}] = K_{I n} . \frac{[ H I n ]}{[ I n ^{-} ]}

….(i)

∵ p H = - lo g [H^{+}]

...(ii)
From eq. (i) and (ii) we get,

∴ p H = - lo g (K_{I n} . \frac{[ H I n ]}{[ I n ^{-} ]})

= - lo g K_{I n} + lo g . \frac{[ I n ^{-} ]}{[ H I n ]} = p K_{I n} + lo g . \frac{[ I n ^{-} ]}{[ H I n ]}

or

lo g . \frac{[ I n ^{-} ]}{[ H I n ]} = p H - p K_{I n}

Question Text	The rapid change of $p H$ near the stoichiometric point of an acid-base titration is the basic of indicator detection. $p H$ of the solution is related to the ratio of the concentration of conjugate acid $(H \in)$ and base $(I n^{-})$ forms of the indicator by the expression
Answer Type	Text solution:1
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The rapid change of $p H$ near the stoichiometric point of an acid-base titration is the basic of indicator detection. $p H$ of the solution is related to the ratio of the concentration of conjugate acid $(H \in)$ and base $(I n^{-})$ forms of the indicator by the expression

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