The K_a of hypochlorous acid (HClO)is 3.0 × 10^-8 at 25.0°C. Calculate the pH of a 0.0335 M hypochlorous acid solution.

Question

Quizplus · Accepted Answer

The Ka expression for HClO is:

Ka = [H+][ClO-]/[HClO]

HClO is a weak acid, so we can assume that its dissociation is small compared to its initial concentration [HClO]. In other words, we can assume that [HClO] ≈ 0.0335 M.

Let x be the concentration of H+ ions that are formed from the dissociation of HClO. Then, the concentration of ClO- ions formed is also x.

Using the equilibrium expression to solve for x, we have:

Ka = (x)(x)/(0.0335-x) = 3.0 × 10^-8

Solving for x using the quadratic formula gives:

x = 1.3 × 10^-4 M

The pH is defined as the negative logarithm of the H+ concentration:

pH = -log[H+] = -log(1.3 × 10^-4) = 3.02

Therefore, the answer is C.

The Ka of Hypochlorous Acid (HClO)is 3

The K_a of Hypochlorous Acid (HClO)is 3