Answer
$CH_3COOH$ and $NaCH_3COO$ are not the best combination for a buffer with $pH \approx 9$, because the $pKa$ for acetic acid is not close to 9.
Work Step by Step
1. Identify the acid:
$CH_3COOH$.
2. Calculate its pKa:
$pKa = -log(Ka)$
$pKa = -log( 1.8 \times 10^{- 5})$
$pKa = 4.75$
3. Compare this number to 9.
- It is not approximately 9, therefore, these compounds are not the best combination for a buffer with a pH $\approx$ 9.
