`K_(a)` for the ionisation of `Fe^(3+)` to `Fe(OH)^(2+)` and `H^(o+)` is `6.5 xx 10^(-3)`, what is the maximum `pH` value which could be used so that at least `95%` of the total `Fe^(3+)` in a dilute solution exists as `Fe^(3+)`?

Explanation

`{:(Fe^(3+)+,H_(2)OhArr,Fe(OH)^(2+)+,H^(+),,K_(h)=6.5xx10^(-3)),((1-h),,h,h,):}`
`[H^(o+)] = Ch`
and `K_(h) = (C.h^(2))/(1-h)` and `h = (5)/(100)`
Thus, `6.5 xx 10^(-3) = (C xx5xx5xx100)/(100xx100xx95)`
`:. C = 2.47 M :. [H^(o+)] = 2.47 xx (5)/(100)`
`:. pH = 0.9083`