Question

In order to prepare a buffer solution of pH 5.74, sodium acetate is added to acetic acid. If the concentration of acetic acid in the buffer is 1.0 M, the concentration of sodium acetate in the buffer is __________ M. (Round off to the Nearest Integer). [Given : pKa (acetic acid) = 4.74]

Hint:

If $pH = pK_a + 1$, then $[\text{Salt}] = 10 \times [\text{Acid}]$. If $pH = pK_a$, then $[\text{Salt}] = [\text{Acid}]$.

Answer 1

Correct Answer: 10

Step 1: Use Henderson-Hasselbalch equation: $pH = pK_a + \log \frac{[\text{Salt}]}{[\text{Acid}]}$.
Step 2: $5.74 = 4.74 + \log \frac{[\text{Salt}]}{1.0}$.
Step 3: $1.0 = \log [\text{Salt}] \implies [\text{Salt}] = 10^1 = 10$ M.