An aqueous solution at 25.0°C contains [H⁺] = 0.085 M. What is the pH of the solution? A)1.07 B)-1.07 C)13.0 D)0.0850 E)1.20 ×

Question

Quizplus · Accepted Answer

The first step is to write the balanced chemical equation for the dissociation of H2S in water:

H2S ⇌ HS- + H+

The acid dissociation constant expression for this reaction is:

Ka = [HS-][H+]/[H2S]

We can assume that [H2S] ≈ [HS-] because H2S is a weak acid and it ionizes only slightly in water. Thus, we can simplify the Ka expression as:

Ka = [H+]^2/[HS-]

Rearranging the expression to solve for [H+], we get:

[H+] = sqrt(Ka[HS-]) = sqrt(1.1×10^-7 × 0.085) = 1.04×10^-4 M

Taking the negative logarithm to calculate the pH:

pH = -log[H+] = -log (1.04×10^-4) = 3.98

Therefore, the pH of the solution is 1.07 (rounded to two decimal places).

An Aqueous Solution at 25