Question

The `pH` of 0.05M aqueous solution of diethylamine is 12. What will be it's `K_b`? Thank you:)

Answer 1

`K_b=2.5xx10^-3`.....

Explanation:

We assess the reaction.....

`HN(C_2H_5)_2(aq) + H_2O(l) rightleftharpoons H_2""^+N(C_2H_5)_2 +HO^-`

And `K_b=([H_2N^+(C_2H_5)_2][HO^-])/([HN(C_2H_5)_2])`

Now initially `[HN(C_2H_5)_2]=0.05*mol*L^-1`....and we are given that the `pH=12`, and thus `pOH=14-12=2`, and thus `[HO^-]=10^-2*mol*L^-1`

And thus `[HO^-]=10^-2*mol*L^-1`; and so `H_2stackrel(+)N(C_2H_5)_2=10^-2*mol*L^-1`, and `[HN(C_2H_5)]=(0.05-0.01)*mol*L^-1=0.04*mol*L^-1`.

`K_b=(0.01xx0.01)/(0.04)=0.01^2/0.04=2.5xx10^-3`.....