What is the pH of a 0.00200 M HClO₄ solution?

Question

Quizplus · Accepted Answer

HClO is a weak acid, with a Ka value of 3.0 x 10^-8. Using an ICE table, we can find that the concentration of H+ ions in a 0.00200 M solution of HClO is:

Ka = [H+][ClO-]/[HClO]
[H+] = sqrt(Ka*[HClO]) = sqrt(3.0 x 10^-8 * 0.00200) = 2.699 x 10^-4 M

Taking the negative logarithm of this value gives us the pH:

pH = -log[H+] = -log(2.699 x 10^-4) = 3.568

However, we must consider the dissociation of HClO into H+ and ClO-:

HClO + H2O <--> H3O+ + ClO-

Since the concentration of HClO is much greater than the concentration of H3O+, we can safely assume that the amount of H3O+ formed is negligible compared to the amount of HClO. This means that the concentration of H3O+ is approximately equal to the concentration of H+ ions:

[H3O+] = [H+] = 2.699 x 10^-4 M

Taking the negative logarithm of this value gives us the pH:

pH = -log[H+] = -log(2.699 x 10^-4) = 2.699

Therefore, the pH of a 0.00200 M HClO solution is 2.699, which is choice C.

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