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How to compute Henderson-Hasselbalch pKa in Python using UliEngineering

You can easily compute the acid dissociation constant (pKa) from pH and concentration ratio using the UliEngineering Python library:

henderson_hasselbalch_pKa.py
from UliEngineering.Chemistry.Henderson import henderson_hasselbalch_pKa

# Compute pKa for pH 7.4 with ratio 10:1
pka = henderson_hasselbalch_pKa(7.4, 10.0)
print(f"pKa (pH 7.4, ratio 10:1): {pka:.2f}")

# Compute pKa for pH 5.0 with ratio 1:1
pka = henderson_hasselbalch_pKa(5.0, 1.0)
print(f"pKa (pH 5.0, ratio 1:1): {pka:.2f}")

# Compute pKa for pH 8.5 with ratio 100:1
pka = henderson_hasselbalch_pKa(8.5, 100.0)
print(f"pKa (pH 8.5, ratio 100:1): {pka:.2f}")

Example output

henderson_hasselbalch_pKa_output.txt
pKa (pH 7.4, ratio 10:1): 6.40
pKa (pH 5.0, ratio 1:1): 5.00
pKa (pH 8.5, ratio 100:1): 6.50

The Henderson-Hasselbalch pKa calculation determines the acid dissociation constant from the measured pH of a buffer solution and the ratio of conjugate base to acid. This is essential for characterizing buffer systems, determining acid strength, and understanding the behavior of weak acids and bases in solution. It’s the inverse operation of computing pH from pKa and ratio.

The pKa is computed using the rearranged Henderson-Hasselbalch equation: $\text{p}K_a = \text{pH} - \log_{10}\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$, where $\text{pH}$ is the measured solution pH, and $\frac{[\text{A}^-]}{[\text{HA}]}$ is the ratio of conjugate base concentration to acid concentration. This allows determination of acid strength from buffer measurements.

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