BUFFER SOLUTION pH

Question

A buffer solution of pH 4.62 is to be prepared from acetic acid (with Ka = 1.80 x 10-5, sodium acetate and water. What must be the molar ratio of acetate ion to acetic acid in this solution to obtain this pH? Give your answer to 2 decimal places.

Answer 1

For this problem, we can use the Henderson Hasselbalch equation:

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

We are essentially being asked for solve for the ratio of [salt]/[acid]

The pKa will be -log Ka = -log 180x10-5 = 4.74

4.62 = 4.74 + log [salt]/[acid]

-0.12 = log [salt]/[acid]

[salt]/[acid] = 0.759

So, the salt to acid ratio will be 0.76 to 1