The `pH` of `0.05M` aqueous solution of diethy`1` amine is `12.0` . Caluclate `K_(b)`.

Answer

`2.5 xx 10^(-3)`

Explanation

pH of solution =12.0
`pH +pOH =14.0 , :. " "pOH =14.0 -12.0 =2.0`
`" or "" "-log [OH^(-)] =2.0 " or " [OH^(-)] =10^(-2) M = 0.01 M`
the molar concentration of different species at the equilibrium point may be represented as follows :
`{:((C_(2)H_(5))_(2)NH +H_(2)O,hArr,(C_(2)H_(5))_(2)NH_(2)^(+),+,OH^(-)),((0.05 -0.01),,0.01M,,0.01M),(=0.04 M,,,,):}`
Applying Law of chemical equilibrium.
`K_(b) =[[(C_(2)H_(5))_(2)NH_(2)^(+)][OH^(-)]]/[[(C_(2)H_(5))_(2)NH]]=((0.01 M)(0.01M))/((0.04 M)) =2.5 xx 10^(-3) M`