An aqueous solution at 25.0 °C contains [ ] = 0.085 mol L^-1.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

L^-1 is the formula for Hydrazoic acid (HN3). It is a weak acid and can be written as: HN3 ⇌ H+ + N3- The balance constant of this reaction at 25.0 °C is given by: Kb = [H+][N3-]/[HN3] Kb = (1.9 × 10^-5) Since HN3 is a weak acid, we can assume that the amount of H+ produced from its dissociation is negligible compared to the initial concentration, hence we can assume that [H+] = x. Therefore, Kb = x^2/[HN3] = x^2/(0.085 mol/L) Solving for x, we get: x = 1.07 × 10^-3 M pH = -log[H+] = -log(1.07 × 10^-3) = 1.07 Therefore, the pH of the solution is 1.07.

An Aqueous Solution at 25