Addition of Chemicals (pH Calculator)

The reaction module (button Reac) allows the addition of chemicals to any aqueous solution (input water). In the simplest case the input water is “pure water” (H2O). In this way you get the pH of an acid, base, salt or another chemical compound.


The screenshots above are taken from this example. The addition of KOH (potasium hydroxide) enhances the pH from 7.90 to 9.03 (output 1). In this way, calcite becomes supersaturated and precipitates, again changing the pH to 7.83 (output 2).

Multi-Reactions. By activating the checkbox “more reactions” up to three additional reactants can be added. An example is given here.

Plot Titration Curve. Calculates the pH dependence of aqueous solutions by adding small portions of a given reactant. An example is given here.

List of Chemical Compounds (Reagents)

In total, aqion provides more than 300 chemicals 1 the user can add to the aqueous solution. The full list is arranged in alphabetical order, for example:


The addition/dosage can be performed in units of mmol/L or mg/L. Typical pH values of common acids and bases are displayed in the pH Table.

“Forced Mineral Dissolution”

The Reac module comprises also mineral phases denoted by the prefix “Mineral_”, such as

Mineral_Al(OH)3 Al(OH)3
Mineral_Brucite Mg(OH)2
Mineral_Calcite CaCO3
Mineral_Fe(OH)3 Fe(OH)3
Mineral_Gypsum CaSO4
Mineral_Hydroxyapatite Ca5(PO4)3OH
Mineral_Pyrochroite Mn(OH)2
Mineral_Rhodochrosite MnCO3
Mineral_Siderite FeCO3

and much more. Suppose one sets 0.5 mmol/L of “Mineral_Gypsum” then exactly 0.5 mmol/L CaSO4 will be added to the input water. This (kinetic) approach differs distinctly from the thermodynamics of mineral dissolution.

In thermodynamics (which is used here) the mineral dissolves only if the input solution is undersaturated with the mineral (SI < 0). The amount that dissolves is dictated by equilibrium thermodynamics and cannot be chosen arbitrary.

Conversely, the so-called “forced mineral dissolution” by-passes the equilibrium thermodynamics. The pre-selected amount to be added will dissolve completely, irrespective of whether SI > 0 or not. In this crude way we are able, say, to simulate strong supersaturated solutions.


  1. In addition, aqion PRO provides about 60 organic compounds (acids und their salts). 

[last modified: 2014-03-17]