Question

An acid (HA) dissociates as follows:

HA → H⁺ + A^-

The pH of the 0.23 M solution of HA is 4.74.

What is [A^-]?

Express your answer as a decimal, not an exponent.

Please include a proper (abbreviated) unit.

Answer 1

HA dissociates as:

HA        <—>   H+   +   A-

0.23               0       0

0.23-x           x       x

Given:

pH = 4.74

use:

pH = -log [H+]

4.74 = -log [H+]

[H+] = 1.82*10^-5 M

[H+] = 0.0000182 M

So, x = 0.0000182 M

[A-] = x = 0.0000182 M

Answer: 0.0000182 M