# pH from Concentration pH directly from concentration: strong solutes fully dissociate, weak solutes solve the exact quadratic with α and the 5% rule. > Canonical page: https://elysiatools.com/en/tools/ph-from-concentration - **Category:** Science & Education - **Keywords:** ph calculation, ph from concentration, strong acid ph, strong base ph, weak acid ka, degree of dissociation, 5 percent rule ## Overview The pH from Concentration calculator determines the exact pH, pOH, and ion concentrations of aqueous solutions. It handles complete dissociation for strong monoprotic and polyprotic acids and bases, and solves the exact equilibrium quadratic equation for weak acids and bases with Ka or Kb inputs, degree of dissociation (α), and a 5% rule validation. ## Inputs - **Solute type** (select) - **Concentration c** (number): e.g. 0.01 - **Concentration unit** (select) - **Protons or hydroxides per formula unit (strong only)** (number): e.g. 2 for H₂SO₄ or Ba(OH)₂ - **Ka or Kb (required for weak solutes)** (number): e.g. 1.8e-5 for acetic acid ## When to use - Calculating the exact pH of strong acid or base solutions across molar, millimolar, or micromolar concentration ranges. - Evaluating weak acid or weak base equilibria without relying on inaccurate simplification approximations. - Checking the degree of dissociation (α) and testing whether the 5% approximation rule holds for weak electrolytes. ## How it works - Select the solute category: strong acid, strong base, weak acid, or weak base. - Enter the analytical concentration and choose the unit (mol/L, mmol/L, or µmol/L). - Specify the number of protons/hydroxides per formula unit for strong electrolytes, or enter the Ka/Kb value for weak electrolytes. - Review the resulting pH, pOH, equilibrium ion concentrations, dissociation degree (α), and mathematical breakdown. ## Use cases - Laboratory reagent preparation: Verifying target pH values for standard volumetric titrants and buffer precursors. - Chemistry coursework and teaching: Demonstrating differences between complete dissociation and weak equilibrium quadratics. - Industrial quality control: Calculating acidity and hydroxide ion concentrations in chemical treatment baths. ## Frequently asked questions ### How does the tool calculate pH for strong acids and bases? It assumes complete dissociation where [H⁺] or [OH⁻] equals the analytical concentration multiplied by the proton or hydroxide factor (n), with pH derived as −log₁₀[H⁺]. ### How are weak acids and bases solved? The calculator solves the exact quadratic equilibrium equation Ka = x²/(c − x) or Kb = x²/(c − x) using the quadratic formula, avoiding shortcut errors. ### What is the 5% rule evaluation in the result? It checks whether the degree of dissociation α is below 5%, showing whether the standard approximation √(Ka·c) would have been valid. ### What temperature and Kw value are assumed? Calculations assume standard aqueous conditions at 25 °C with an autoionization constant of water Kw = 1.0 × 10⁻¹⁴. ### Can I calculate polyprotic strong acids like H₂SO₄ or bases like Ba(OH)₂? 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