Acetylsalicylic acid (aspirin), HC9H7O4, is the most widely used pain reliever and fever reducer. Find the pH of 0.035 M aqueous aspirin at body temperature (Ka at 37°C = 3.6 × 10−4.)

The pH of 0.035 M aqueous aspirin is 2.48

Explanation:

We are given:

Concentration of aspirin = 0.035 M

The chemical equation for the dissociation of aspirin (acetylsalicylic acid) follows:

Initial:         0.035

At eqllm:    0.035-x        x         x

The expression of for above equation follows:

We are given:

Putting values in above expression, we get:

Neglecting the value of x = -0.0037 because concentration cannot be negative

So, concentration of = x = 0.0033 M

We are given:

= 0.0033 M

Putting values in above equation, we get:

Hence, the pH of 0.035 M aqueous aspirin is 2.48