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

Explanation

`Cod +H_(2)O hArr Cod H^(+) +OH^(-)`
`("Base")`
`pH = 9.95 , pOH =14 -9.95 = 4.05 , - log [OH^(-)] =4.05`
`log [OH^(-)] =- 4.05 = bar(5).95 , [OH^(-)] = " Antilog " bar(5).95 =8.913 xx 10^(-5)`
`K_(b) =[[Cod H^(+)][OH^(-)]]/[[Cod]] =[[OH^(-)]^(2)]/[[Cod]] =((8.91 xx 10^(-5))^(2))/((5xx 10^(-3)))= 1.588 xx 10^(-6)`
`pK_(b) =- log K_(b) =- log (1.588xx 10^(-6)) =(6 -log 1.588) =6 -0.1987 =5.8`