Henderson-Hasselbalch equation Calculator

Formula first

Overview

The Henderson-Hasselbalch equation describes the relationship between the pH of a buffer solution and the equilibrium concentrations of a weak acid and its conjugate base. It is a logarithmic transformation of the acid dissociation constant expression, facilitating the calculation of acidity in complex biological and chemical systems.

Symbols

Variables

pK_a = Acid Dissociation Constant, [A^-] = Conjugate Base, [HA] = Acid, pH = Potential of Hydrogen

Apply it well

When To Use

When to use: Apply this equation when calculating the pH of a buffer solution consisting of a weak acid and its salt. It is most reliable when the ratio of acid to base is between 0.1 and 10 and the concentrations are high enough to ignore the self-ionization of water.

Why it matters: This formula is essential for understanding physiological buffering, such as the bicarbonate system that regulates human blood pH. It also enables scientists to design stable environments for enzyme assays and industrial fermentation processes.

Avoid these traps

Common Mistakes

• Swapping acid and base in the ratio.
• Using ln instead of log10.

One free problem

Practice Problem

An ethanoic acid / sodium ethanoate buffer is prepared. pKa of ethanoic acid = 4.76. [A-] = 0.08 mol/$d{m}^3$ and [HA] = 0.02 mol/$d{m}^3$. Calculate the pH.

Solve for: $pH$

Hint: pH = pKa + log10([A-]/[HA]).

The full worked solution stays in the interactive walkthrough.

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Related Formulas

References

Sources

1. Atkins' Physical Chemistry
2. IUPAC Gold Book
3. Wikipedia: Henderson-Hasselbalch equation
4. IUPAC Gold Book: pH
5. IUPAC Gold Book: acid dissociation constant, K_a
6. McQuarrie, Donald A. General Chemistry
7. Chemistry: The Central Science by Brown, LeMay, Bursten, Murphy, Woodward, and Stoltzfus
8. Analytical Chemistry by Gary D. Christian, Purnendu K. Dasgupta, and Kevin A. Schug