What is the best buffer at pH = 5.0? Justify your answer.

a) Formic acid (pKa = 3.8)

b) acetic acid (pKa = 4.76)

c) ethylamine (pKa = 9.0)

b) acetic acid (pKa = 4.76)

Explanation:

Considering the Henderson - Hasselbalch equation for the calculation of the pH of the buffer solution as:

pH=pKa+log[base]/[acid]

The weak acid for making the buffer must have a pKa value near to the desired pH of the weak acid.

So, near to value, pH = 5, acetic acid is close which have of pKa of 4.76

Thus, option B is correct.