Using the Henderson-Hasselbalch equation with bicarbonate 24 mEq/L, carbonic acid 1.2 mEq/L, pK = 6.1, calculate pH.

Using the Henderson-Hasselbalch equation with bicarbonate 24 mEq/L, carbonic acid 1.2 mEq/L, pK = 6.1, calculate pH.

• A. 7.28
• B. 7.38
• C. 7.40
• D. 7.42

Answer: (C)

The Henderson-Hasselbalch equation for the bicarbonate buffer relates pH to the ratio of base to acid: pH = pK + log([HCO3-]/[H2CO3]). With pK 6.1, [HCO3-] = 24 and [H2CO3] = 1.2, the ratio is 24/1.2 = 20. The base- to acid-log is log10(20) ≈ 1.301. Adding to 6.1 gives pH ≈ 7.401, which rounds to 7.40. This shows how changing the bicarbonate to carbonic acid ratio shifts pH; here the ratio yields a pH around 7.40.

The Henderson-Hasselbalch equation for the bicarbonate buffer relates pH to the ratio of base to acid: pH = pK + log([HCO3-]/[H2CO3]). With pK 6.1, [HCO3-] = 24 and [H2CO3] = 1.2, the ratio is 24/1.2 = 20. The base- to acid-log is log10(20) ≈ 1.301. Adding to 6.1 gives pH ≈ 7.401, which rounds to 7.40. This shows how changing the bicarbonate to carbonic acid ratio shifts pH; here the ratio yields a pH around 7.40.