Question

Which of the following acids has the weakest conjugate base in aqueous solution?

A.Hbr

B.HF

C.HNO₂

D.CH₃COOH

E.HOCl

Answer 1

It is well known that strong acid has weak conjugate base or vice versa. Among all determination of strong acid is first step. Now, strong acid is one which is more prone to ionize it's proton in aqueous solution.

the standard Ka values are:

HBr : 1*10⁹

HF: 6.8*10^-4

HNO2: 7.2*10^-4

CH3COOH: 1.8*10^-5

HOCl: 3*10^-8

Higher is the value of Ka, higher is the acidic nature. Therefore, HBr is the strongest acid and it's conjugate base is weakest rather than HF. Though Fluorine is more electronegative, the bond bewteen H-F is strongest ( due to size match between F and H) and it can't easily ionizable.

The right answer is HBr.