## Chemistry: The Molecular Science (5th Edition)

$NaH_2PO_4$ and $Na_2HP{O_4}$ are the best combination for this solution.
1. Identify the acid: $- H_2PO_4$: 2. Calculate its pKa: $pKa = -log(Ka)$ $pKa = -log( 6.3 \times 10^{- 8})$ $pKa = 7.20$ 3. Compare this number to 7. $7.20$ is very close to 7, therefore, this is the best combination for a pH neutral buffer.