A student prepares an acetic acid / acetate buffer at pH = 4.74 (pKa of CH3COOH = 4.74). Available stock solutions are 0.500 M CH3COOH and 0.500 M CH3COONa. The student combines 25.0 mL of acetic acid with 25.0 mL of sodium acetate to a total of 50.0 mL. The measured pH is 4.74.
What is the buffer ratio [A-]/[HA] in the prepared solution?
- A
0.5
- B
10
- Ccheck_circle
1.0
- D
2.0
Explanation
Henderson-Hasselbalch: pH = pKa + log([A-]/[HA]). Since pH = pKa, log ratio = 0 and [A-]/[HA] = 1.