pH Calculator
Calculate pH, pOH and ion concentrations from hydrogen ion concentration.
Results
pH measures the acidity of a solution on a logarithmic scale from 0 to 14. Each whole number change represents a 10-fold change in hydrogen ion concentration. Pure water has pH 7 (neutral), acids are below 7 and bases are above 7. This calculator converts between H+ concentration, pH, pOH and hydroxide concentration.
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Frequently asked questions
For a strong acid like HCl, [H⁺] = 0.01 M. pH = -log10(0.01) = 2.0. The pOH is 12.0 and [OH⁻] is 1 × 10⁻¹² M.
[H⁺] = 10^(-pH). At pH 3, [H⁺] = 10⁻³ = 0.001 M. At pH 7, [H⁺] = 10⁻⁷ = 0.0000001 M.
pH + pOH = 14 at 25°C. If pH = 4, then pOH = 10. This relationship comes from the water autoionization constant Kw = 10⁻¹⁴.
H⁺ concentrations range from about 10 M to 10⁻¹⁵ M. The log scale compresses this 16-order-of-magnitude range into a manageable 0-14 scale. Each pH unit is a 10x change.
Lemon juice: pH 2.0, vinegar: pH 2.5, coffee: pH 5.0, milk: pH 6.5, pure water: pH 7.0, baking soda: pH 8.3, bleach: pH 12.5.