basic

pH of a Buffer After Strong-Acid Addition Calculator

pH = pKa + log10((n_A − n_HCl) / (n_HA + n_HCl)).

Compute the new pH of a Henderson-Hasselbalch buffer after adding moles of a strong acid (HCl). The strong acid converts conjugate base A⁻ to weak acid HA mol-for-mol: pH = pKa + log₁₀((n_A − n_HCl) / (n_HA + n_HCl)). The calculator also flags whether the buffer has been overwhelmed (n_HCl ≥ n_A).

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

mol
mol
mol

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

pH = pKa + log₁₀((n_A⁻ − n_HCl) / (n_HA + n_HCl)).

In depth

Compute the new pH of a Henderson-Hasselbalch buffer after adding moles of a strong acid (HCl). The strong acid converts conjugate base A⁻ to weak acid HA mol-for-mol: pH = pKa + log₁₀((n_A − n_HCl) / (n_HA + n_HCl)). The calculator also flags whether the buffer has been overwhelmed (n_HCl ≥ n_A).