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_2O hArr Cod H^(+) + OH^(-)`
pH=9.95 , pOH=14-9.95=4.05
`therefore` -log `[OH^-]` =4.05
log `[OH^-]=-4.05` or =`bar(5).95`
`therefore [OH^-]=8.913xx10^(-5)`
`K_b=(["Cod" H^+][OH^-])/"[Cod]"=[OH^-]^2/"[Cod]"`
`=((8.913xx10^(-5))^2)/(5xx10^(-3))=1.588xx10^(-6)`
`pK_b =-log (1.588xx10^(-6))=-(-6+0.200)`
=5.8