Question

the ratio of dissociation constant of two weak acids HA and HB is 4.At what concentration ratio the wo acids will have the same Ph?

Answer 1

Answer : The concentration ratio the two acids will have the same pH will be in 4:1.

Explanation:

1) $HA\rightleftharpoons A^-+H^+$

Dissociation constant of two weak acids HA

$K_a=K'_a4$...(1)

$pH_{HA}=-\frac{1}{2}\log{k_a}+\frac{1}{2}\log{C}$..(2)

2) $HA\rightleftharpoons B^-+H^+$

Dissociation constant of two weak acids HB

$pH_{HB}=-\frac{1}{2}\log{k'_a}+\frac{1}{2}\log{C'}$..(3)

Both acids have the same pH, which means  that:

$pH_{HA}=pH_{HB}$

We get $\frac{C}{C'}=\frac{4}{1}$