The weak acid HA dissociates with K _a = 1.0×10^{- 4}. The pH of a 0.50 M solution of HA is:

Question

Quizplus · Accepted Answer

To find the pH, we need to first find the concentration of H+ ions present in the solution.

HA ⇌ H+ + A-

Let x be the concentration of H+ ions that dissociate from HA.

Ka = [H+][A-]/[HA] 
1.0×10^-4= x^2/0.50

Solving for x:

x = 3.16×10^-3 M

pH = -log[H+] 
pH = -log(3.16×10^-3) 
pH = 2.15

Therefore, the answer is E.

The Weak Acid HA Dissociates with K a = 1