Question

A 500 ml solution of 0.10 m acetic acid (pka 4.76) is at ph 4.94. What is the ratio of conjugate base to acid or a–/ha?

Answer 1

Answer : The ratio of the conjugate base to acid
`(\left [ A^(-) \right ])/(\left [ HA \right ])` is 1.513.

Solution :

Given data,

pH = 4.94

pKa = 4.76

The Henderson-Hasselbalch equation is used as follows:

`pH=pKa+\log (\left [ A^(-) \right ])/(\left [ HA \right ])` .........(1)

Substitute the given values in equation (1) , we get the ratio of conjugated base to acid :

`4.94=4.76+\log (\left [ A^(-) \right ])/(\left [ HA \right ])`

`4.94-4.76=\log (\left [ A^(-) \right ])/(\left [ HA \right ])`

`0.18=\log (\left [ A^(-) \right ])/(\left [ HA \right ])`

`(\left [ A^(-) \right ])/(\left [ HA \right ])=10^(0.18)`

`(\left [ A^(-) \right ])/(\left [ HA \right ])=1.513`

Thus , the answer is 1.513.