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 `(Hin)` and base `(In^(-))` forms of the indicator by the expression

Options

A. `log[([In^(-)])/([HIn])]=pK_(a)+pH`
B. `log[([HIn])/([In^(-)])]=K_(a)+pH`
C. `log[([HIn])/([In^(-)])]=pH+pK_(a)`
D. `log[([In^(-)])/([HIn])]=pH-pK_(a)`

Answer

D

Explanation

For `HI hArr H^(+)+ln^(-)`
`k_(a)=([H^(+)][ln^(-)])/([H ln]) :. pH=pK_(a)+"log"([ln^(-)])([Hln])`