An indicator is a weak acid and pH range of its colour is 3.1 to 4.5. If the neutral point of the indicator lies in the centre of the hydrogen ion concentrations correspondin to the given pH range, calculate the ionisation constain of the indicator.

An indicator is a weak acid and pH range of its colour is 3.1 to 4.5.

1.	An indicator is a weak acid and pH range of its colour is 3.1 to 4.5. If the neutral point of the indicator lies in the centre of the hydrogen ion concentrations correspondin to the given pH range, calculate the ionisation constain of the indicator.
Answer» `4.13 xx 10^(-8)` `4.13 xx 10^(-4)` `2.13 xx 10^(-4)` `3.27 xx 10^(-4)` Solution :`PH = 3.1 , pH = 4.5` `[H^(+)]_(1) = 7.94 xx 10^(-4) , [H^(+)]_(2) = 3.16xx 10^(-5)` At naturalpoint `[H^(+)] = ([H^(+)]_(1) + [H^(+)]_(2))/(2)` `:. HIN + H_(2)O hArr H_(3)O^(+) + In^(-)` `K_("In") = ([H_(3)O^(+)]["In"^(-)])/(["HIn"])` At netural point `["In"^(-)] = [HIn]`