The acid-dissociation constant at 25.0°C for hypochlorous acid (HClO)is 3.0 × 10^-8. At equilibrium, the molarity of H₃O⁺ in a 0.010 M solution of HClO is __________. A)1.7 × 10^-5 B)0.010 C)5.8 × 10^-10 D)4.76 E)2.00

Question

Quizplus · Accepted Answer

The dissociation reaction of HClO is:

HClO ⇌ H+ + ClO-

The acid dissociation constant expression is:

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

At equilibrium, let the molarity of H+ be x, then the molarity of ClO- will also be x, and the molarity of HClO will be 0.010 - x. Substitute the equilibrium concentrations into the Ka expression and solve for x:

Ka = x2/(0.010 - x) = 3.0 × 10^-8

x = [H+] = [ClO-] = 1.7 × 10^-5 M

Therefore, the molarity of HClO at equilibrium is:

[HClO] = 0.010 - [H+] = 0.010 - 1.7 × 10^-5 = 0.009983

So the best choice is A, 1.7 × 10^-5.

The Acid-Dissociation Constant at 25