Buffer pH Calculator Formula
Understand the math behind the buffer ph calculator. Each variable explained with a worked example.
Formulas Used
Buffer pH
ph = pka + log10(conc_base / conc_acid)Base/Acid Ratio
ratio = conc_base / conc_acidVariables
| Variable | Description | Default |
|---|---|---|
pka | pKa of Weak Acid | 4.76 |
conc_base | Concentration of Conjugate Base [A⁻](M) | 0.1 |
conc_acid | Concentration of Weak Acid [HA](M) | 0.1 |
How It Works
Henderson-Hasselbalch Equation
Formula
pH = pKa + log₁₀([A⁻] / [HA])
Where:
When [A⁻] = [HA], pH = pKa. Buffers resist pH changes best within ±1 of the pKa.
Worked Example
An acetate buffer with pKa = 4.76, [CH₃COO⁻] = 0.1 M, [CH₃COOH] = 0.1 M.
- 01pH = pKa + log₁₀([A⁻]/[HA])
- 02pH = 4.76 + log₁₀(0.1/0.1)
- 03pH = 4.76 + log₁₀(1)
- 04pH = 4.76 + 0
- 05pH = 4.76
Frequently Asked Questions
What is the Henderson-Hasselbalch equation?
It relates the pH of a buffer solution to the pKa of the acid and the ratio of conjugate base to acid concentrations. It is derived from the Ka expression by taking logarithms.
When is this equation most accurate?
It works best when the buffer ratio [A⁻]/[HA] is between 0.1 and 10, i.e., within ±1 pH unit of the pKa.
Can I use this for basic buffers?
Yes. Use pKa of the conjugate acid, [A⁻] as the base form, and [HA] as the acid form of the buffer pair.
Learn More
Guide
pH and pOH Guide
Understand pH, pOH, and the pH scale. Learn how to calculate pH from hydrogen ion concentration, the relationship between pH and pOH, buffers, and real-world applications.
Ready to run the numbers?
Open Buffer pH Calculator