The K_a of hypochlorous acid (HClO)is 3.0 × 10^-⁸ at 25.0 °C. Calculate the pH of a 0.0385 M hypochlorous acid solution.

Question

Quizplus · Accepted Answer

The dissociation of hypochlorous acid is represented as:
HClO + H2O ⇌ ClO- + H3O+

The Ka expression for this reaction is:
Ka = [ClO-][H3O+]/[HClO]

Using the given Ka value, we can write:
3.0 × 10^-8 = [ClO-][H3O+]/[HClO]
Since the initial concentration of HClO is 0.0385 M, let x be the concentration of H+ ions and ClO- ions formed at equilibrium.

Thus, we can write:
[H3O+] = x
[ClO-] = x
[HClO] = 0.0385 - x

Substituting these values in the Ka expression and solving for x, we get:
x = 1.9 × 10^-5

Taking the negative logarithm of this concentration gives us the pH:
pH = -log [H3O+] = -log (1.9 × 10^-5) = 4.72

Therefore, the correct answer is C) 4.47.

The Ka of Hypochlorous Acid (HClO)is 3

The K_a of Hypochlorous Acid (HClO)is 3