20 values, each with its units, its uncertainty, and where it came from.
All 361 constants →
kg/molThe standard atomic weight of calcium, 40.078 g/mol — the ion that dominates water hardness and the scale it leaves behind.
kg/molThe equivalent weight of caustic soda, 39.997 g/eq — identical to NaOH's formula mass, because each unit supplies exactly one hydroxide.
kg/molThe equivalent weight of citric acid, 64.041 g/eq — a third of the 192.123 g/mol molar mass, counting all three carboxylic protons.
kg/molThe equivalent weight of hydrated lime, 37.046 g/eq — half of Ca(OH)₂'s 74.092 g/mol, two hydroxides per formula unit of slaked lime.
kg/molThe equivalent weight of hydrochloric acid, 36.458 g/eq — equal to its molar mass, since the molecule has exactly one proton to give.
kg/molThe equivalent weight of nitric acid, 63.012 g/eq — identical to the molar mass because HNO₃ is monoprotic, one proton per molecule.
kg/molThe equivalent weight of phosphoric acid for alkalinity work, 97.994 g/eq — one proton counted, since only the first titrates by pH 4.5.
kg/molThe equivalent weight of soda ash, 52.994 g/eq — half of Na₂CO₃'s 105.988 g/mol, since carbonate accepts two protons on the way to CO₂.
kg/molThe equivalent weight of sodium bicarbonate, 84.006 g/eq — the whole formula mass, one proton accepted, the gentlest alkalinity feed.
kg/molThe equivalent weight of sodium bisulfate, 120.054 g/eq — the full formula mass, one acidic proton, the workhorse of dry acid dosing.
kg/molThe equivalent weight of sulfuric acid, 49.036 g/eq — half the 98.072 g/mol molar mass, because each H₂SO₄ delivers two protons.
dimensionlessThe first acid dissociation constant of carbonic acid at 25 °C, Kₐ₁ = 4.45 × 10⁻⁷, governing the CO₂-bicarbonate equilibrium in natural water.
dimensionlessThe first pKₐ of carbonic acid at 25 °C, 6.352 — the pH at which dissolved CO₂ and bicarbonate are present in equal concentrations.
dimensionlessThe autoionisation constant of pure water at 25 °C, [H⁺][OH⁻] = 1.0 × 10⁻¹⁴, the equilibrium behind the whole 0–14 pH scale.
kg/molThe formula mass of calcium carbonate, 100.086 g/mol — the reference substance for reporting hardness and alkalinity as mg/L as CaCO₃.
dimensionlessThe negative logarithm of water's ionic product at 25 °C, pKw = 13.995, universally rounded to 14.00 for the pH + pOH identity.
dimensionlessThe second acid dissociation constant of carbonic acid at 25 °C, Kₐ₂ = 4.69 × 10⁻¹¹, the bicarbonate-to-carbonate step that drives scaling.
dimensionlessThe second pKₐ of carbonic acid at 25 °C, 10.329 — the pH at which bicarbonate and carbonate ions are present in equal concentrations.
dimensionlessThe solubility product of calcite at 25 °C, K_sp = 3.36 × 10⁻⁹ — the number that decides whether a water scales or corrodes.
dimensionlessThe solubility product of anhydrous calcium sulfate at 25 °C, K_sp = 4.93 × 10⁻⁵ — the gypsum scale that acid cleaning cannot remove.
