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

1 Answer
Oct 4, 2017

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.....