Buffer pH Calculator Formula

Understand the math behind the buffer ph calculator. Each variable explained with a worked example.

Use the Buffer pH Calculator

Formulas Used

Buffer pH

ph = pka + log10(conc_base / conc_acid)

Base/Acid Ratio

ratio = conc_base / conc_acid

Variables

VariableDescriptionDefault
pkapKa of Weak Acid4.76
conc_baseConcentration of Conjugate Base [A⁻](M)0.1
conc_acidConcentration of Weak Acid [HA](M)0.1

How It Works

Henderson-Hasselbalch Equation

Formula

pH = pKa + log₁₀([A⁻] / [HA])

Where:

  • pH = hydrogen ion activity
  • pKa = acid dissociation constant (log scale)
  • [A⁻] = concentration of conjugate base
  • [HA] = concentration of weak acid

    • 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.

    pka = 4.76conc_base = 0.1conc_acid = 0.1
    1. 01pH = pKa + log₁₀([A⁻]/[HA])
    2. 02pH = 4.76 + log₁₀(0.1/0.1)
    3. 03pH = 4.76 + log₁₀(1)
    4. 04pH = 4.76 + 0
    5. 05pH = 4.76

    Ready to run the numbers?

    Open Buffer pH Calculator