Final answer:
The pH of the buffer solution prepared from mixing 0.2 L of 0.05 M Na2HPO4 and 0.16 L of 0.05 M NaH2PO4 is 7.2, as calculated using the Henderson-Hasselbalch equation with the given moles of each species and pKa value.
Step-by-step explanation:
To calculate the pH of a buffer solution prepared from mixing a 0.2 L solution of 0.05 M Na2HPO4 (dibasic sodium phosphate) with a 0.16 L solution of 0.05 M NaH2PO4 (monobasic sodium phosphate), we use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Firstly, we need to calculate the moles of each species. For Na2HPO4: 0.2 L × 0.05 M = 0.01 mol, and for NaH2PO4: 0.16 L × 0.05 M = 0.008 mol. The pKa for the NaH2PO4/Na2HPO4 equilibrium is approximately 7.2.
Next, we use the Henderson-Hasselbalch equation to calculate the pH:
pH = 7.2 + log([0.01 mol / 0.2 L]/[0.008 mol / 0.16 L])
pH = 7.2 + log(0.05/0.05)
pH = 7.2
The pH of the buffer solution is 7.2.