Question

An unknown monoprotic acid HA with a concentration of 0.050 M has a pH of 2.3. Which of the following can we conclude?

A) It must be a strong acid.
B) It must be a weak acid.
C) A salt of its conjugate base would have no pH effect in solution.
D) Both A and C
E) None of the above

Answer 1

B) It must be a weak acid.

Step-by-step explanation:

If HA is a strong acid

`HA\rightleftharpoons H^++A^-`

Now the pH value can be written as follows

`pH=-log[H^+]\\pH=-log(5* 10^(-2))\\pH=2* log5\\pH=1.4`

But given that acid HA has 2.3 pH value.

Therefore we can say that HA is weak acid.

Thus the answer will be option (B).

B) It must be a weak acid.