Chemistry

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Buffer pH Calculator.

Calculate buffer pH from pKa and conjugate base and acid amounts.

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Set your values

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pH: 4.76

pH

4.7600
Base/acid ratio: 1

Base/acid ratio

1.000000

Educational chemistry arithmetic only. Keep units consistent and verify assumptions against your laboratory or course specification.

Use Cases

Preparing buffer solutions in the lab

Quickly determine the pH of a buffer you plan to make by entering the pKa and the mole amounts of the conjugate base and weak acid you intend to mix.

Example: For an acetic acid buffer with pKa 4.76, 0.1 mol acetate, and 0.1 mol acetic acid, the pH is 4.76.

Checking buffer pH after adding components

Verify the pH of a buffer solution after adding specific amounts of conjugate base and weak acid, ensuring it meets experimental requirements.

Example: If you add 0.05 mol base and 0.02 mol acid to a buffer with pKa 7.2, the pH becomes 7.6.

Frequently Asked Questions

How do I calculate buffer pH using this calculator?
Enter the pKa of the weak acid, the amount of conjugate base in moles, and the amount of weak acid in moles. The calculator applies the Henderson-Hasselbalch equation: pH = pKa + log([base]/[acid]).
What is the Henderson-Hasselbalch equation?
It is pH = pKa + log([A-]/[HA]), where [A-] is the concentration of conjugate base and [HA] is the concentration of weak acid. This calculator uses the mole amounts directly, assuming equal volumes, so the ratio of moles is used.
Can I use this calculator for any buffer system?
Yes, as long as you know the pKa of the weak acid and the mole amounts of the conjugate base and weak acid. It works for any weak acid/conjugate base pair, such as acetic acid/acetate or ammonium/ammonia.

Tips & Common Mistakes

Tips

  • Ensure the pKa value matches the specific weak acid you are using, as pKa varies with temperature and ionic strength.
  • Use the same units for both conjugate base and weak acid amounts (moles) to get an accurate ratio.
  • For precise pH, consider activity coefficients if working with concentrated solutions, but this calculator assumes ideal dilute conditions.
  • If you have concentrations instead of moles, multiply by volume (in liters) to get moles before entering.

Common Mistakes to Avoid

  • Forgetting to convert concentrations to moles when using volumes; this calculator expects mole amounts, not molarity.
  • Using the pKa of the conjugate acid instead of the weak acid; ensure you have the correct pKa for the acid in your buffer pair.
  • Assuming the calculator accounts for volume changes; it assumes equal volumes for base and acid, so the ratio of moles is used directly.

Last updated: August 13, 2026