How to use this calculator
- Enter pKa and the initial weak-acid and conjugate-base amounts.
- Select the added strong acid or strong base.
- Enter the added amount and calculate.
- Review the post-reaction buffer amounts before you use the pH result.
Formula and variables
pH = pKa + log10(nbase/ nacid) after stoichiometry
| Symbol | Meaning | Unit |
|---|---|---|
| nbase | post-reaction base amount | mol |
| nacid | post-reaction acid amount | mol |
Worked example
Adding 0.10 mol strong acid to 1.0 mol each of acid and base changes them to 1.10 and 0.90 mol before pH is calculated.
Interpretation
The result shows the post-addition composition; exhausted buffer components are rejected rather than sent into a logarithm.
Common mistakes
- Apply strong-addition stoichiometry before equilibrium.
- Do not continue the buffer equation after a component is exhausted.
Frequently asked questions
Why does the calculator apply stoichiometry first?
A strong acid or base reacts with a buffer component before the remaining pair reaches equilibrium.
What happens when one buffer component is exhausted?
The buffer equation no longer applies. The calculator rejects that result.
Can I enter concentrations instead of moles?
Convert each component and the added reagent to moles before you use this calculator.
Can I use scientific notation?
Yes. Enter values such as 6.022e23 or 1.0e-6 in a numeric field.
How should I round the result?
Keep extra digits during the calculation. Round the final result to the precision required by your data.