You have a 250.0-mL sample of 1.00 M acetic acid (K_a = 1.8 $\times$10^-⁵).Calculate the pH after adding 0.0040 mol HCl to 1.0 liter of the best buffer.

Question

Quizplus · Accepted Answer

The best buffer is created when the concentration of acetic acid (weak acid) is equal to its conjugate base (acetate ion), which occurs at the pKa of acetic acid. The addition of HCl, a strong acid, will slightly shift the equilibrium, but the buffer's capacity should maintain the pH close to the pKa of acetic acid. The pKa of acetic acid is approximately 4.75 (derived from the given Ka = 1.8 x 10^-5), so the closest answer is 4.72.

You Have a 250 ×\times× 10-5)

You Have a 250 $\times$ 10^-⁵)