The pH of an aqueous solution at 25.0 °C is 10.66. What is the molarity of H⁺in this solution?

Question

Quizplus · Accepted Answer

Using the pH value, we can calculate the concentration of H+ ions in the solution.

pH = -log[H+]
10^-pH = [H+]
10^-10.66 = [H+]
[H+] = 2.2 x 10^-11 M

In a neutral solution, the concentration of H+ and OH- ions are equal. Since this solution is basic, the concentration of OH- ions will be greater than the concentration of H+ ions. Let's assume the concentration of OH- ions is x.

Kw = [H+][OH-]
1.0 x 10^-14 = (2.2 x 10^-11)(x)
x = 4.5 x 10^-4 M

Now we can use the concentration of OH- ions to calculate the concentration of HS- ions in the solution using the Kb expression:

Kb = [HS-][OH-]/[S2-]
1.2 x 10^-14 = x^2/[HS-]
[HS-] = x^2/Kb
[HS-] = (4.5 x 10^-4)^2/1.2 x 10^-14
[HS-] = 1.7 x 10^-10 M

Therefore, the molarity of HS- ions in the solution is 1.7 x 10^-10 M, which is closest to choice C.

The PH of an Aqueous Solution at 25