A 25.0-mL sample of 0.150 M hydrocyanic acid is titrated with a 0.150 M NaOH solution.What is the pH before any base is added? The of hydrocyanic acid is 4.9 × 10^-10.

Question

Quizplus · Accepted Answer

First, we can use the expression for the acid dissociation constant (Ka) to calculate the concentration of H+ ions at equilibrium before any base is added:

Ka = [H+][CN-] / [HCN]

4.9 × 10^-10 = [H+]^2 / 0.150

[H+] = 9.31 × 10^-6 M

Then, we can use the pH formula to calculate the pH:

pH = -log[H+]

pH = -log(9.31 × 10^-6)

pH = 5.07

Therefore, the correct answer is A.

A 250-ML Sample of 0