Buffer pH after Acid or Base Addition Calculator
Estimate a conjugate acid/base buffer’s pH before and after a specified strong-acid or strong-base addition.
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Result
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Calculation steps
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How to calculate
Perform the strong-acid/base neutralization stoichiometry first. Apply Henderson–Hasselbalch to the remaining positive conjugate-pair amounts.
After added base b: HA′=HA−b; A−′=A−+b; pH≈pKa+log10(A−′/HA′)
Worked example
A buffer with pKa 4.76 and 10 mmol each of HA and A− starts at pH 4.76. Adding 1 mmol strong base leaves 9 and 11 mmol, giving pH≈4.84715.
Assumptions and input details
One ideal weak monoprotic conjugate acid/base pair with a common final volume. Positive addition means strong base; negative means strong acid. Both components must remain positive, otherwise the buffer approximation is rejected rather than extrapolated through exhaustion. Activities, ionic strength, water autoionization, temperature changes and very dilute/extreme-ratio accuracy are not solved. This is a concentration-ratio approximation, not a preparation or handling procedure.
References: OpenStax: buffers
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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