What is the pH of a 0.020 M HClO₄ solution? A)0.020 B)0.040 C)1.70 D)12.30

Question

Quizplus · Accepted Answer

HClO is a weak acid, and its conjugate base ClO- is a weak base. The pH of a solution of HClO depends on the extent to which it dissociates in water.

HClO + H2O ↔ H3O+ + ClO-

The acid dissociation constant (Ka) for HClO is 3.5 × 10^-8.

Ka = [H3O+][ClO-]/[HClO]

At equilibrium, [HClO] = [H3O+], so

Ka = [H3O+]^2/[HClO]

[H3O+]^2 = Ka[HClO]

[H3O+] = sqrt(Ka[HClO])

[H3O+] = sqrt(3.5 × 10^-8 × 0.020)

[H3O+] = 1.87 × 10^-4 M

pH = -log[H3O+] = 1.70

Therefore, the answer is C: 1.70.

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