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Polyprotic Acid Step Dissociation pH Calculator

pH from Ka₁ dominance: [H⁺] ≈ √(Ka₁·C).

Estimates pH for a diprotic acid H₂A using Ka₁ (dominant) and Ka₂ (second). Calculates [H⁺] from each step and the intermediate pH at the amphiprotic form H₂A/HA⁻/A²⁻.

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

Inputs

mol/L

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

pH₁ ≈ ½(pKa₁ − log C); pH_amphiprotic ≈ ½(pKa₁ + pKa₂)

In depth

Estimates pH for a diprotic acid H₂A using Ka₁ (dominant) and Ka₂ (second). Calculates [H⁺] from each step and the intermediate pH at the amphiprotic form H₂A/HA⁻/A²⁻.