You wish to prepare a buffer containing CH₃COOH with a pH of 4.24.If the pK_a of acetic acid is 4.74,what ratio of [CH₃COO^-]/[CH₃COOH] must you use? A)0.10 B)0.50 C)0.32 D)2.0 E)2.8

Question

Quizplus · Accepted Answer

Using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
4.24 = 4.74 + log([A-]/[HA])
-0.5 = log([A-]/[HA])
10^-0.5 = [A-]/[HA]
0.32 = [A-]/[HA]

Since the buffer is made up of CH3COOH and its conjugate base CH3COO-, the ratio [A-]/[HA] refers to the ratio of the concentrations of these two species in the buffer solution. Therefore, the ratio of [CH3COO-]/[CH3COOH] in the buffer solution should be 0.32.

So, the best choice is C) 0.32.

You Wish to Prepare a Buffer Containing CH3COOH with a PH

You Wish to Prepare a Buffer Containing CH₃COOH with a PH