A correctness test of the computation of chemical speciation for the main constituents of natural waters

The agreement between measurement and a speciation model-based computation of the pH and the electrolytic conductivity was investigated for the three test cases: standard buffers, artificial model waters and routine laboratory reports of water analysis. The standard deviation for the difference between experimental and computed pH was found to be ΔpH ⩽ 0.04 and for the electrolytic conductivity the analogous difference is less than 1%. This result was obtained considering complexes and using the extended Debye-Hückel equation for the activity coefficient, however other equations are not substantially worse. The constituents of the species system tested are the hydrogen ion, hydroxyl ion, sodium, potassium, calcium, magnesium, ammonia, carbonate, sulphate, chloride, nitrate, phosphate, borate and silicate. A set of equilibrium constants and their temperature dependency factors is presented.