The `pH` of `0.005 M` codenine `(C_(18)H_(21)NO_(3))` solution is `9.95`. Calculate its ionisation constant and `pK_(b)`.

Answer

`K_(b) = 1.6xx10^(-6), pK_(b) = 5.8`

Explanation

Codeine + water `hArr` codenium ion + `OH^(-)`
Form given pH, `[H^(+)] = 1.12xx10^(-10) M`
`:. [OH^(-)] = (K_(w))/([H^(+)]) = (10^(-14))/(1.12xx10^(-10))=8.93xx 10^(-5)M`
`K_(b) = ([B^(+)] [OH^(-)])/([BOH]) = ((8.93xx10^(-5))^(2))/(0.005)=1.6xx10^(-6)`.