Example 8. Calcite solubility
This is the same chemical system as in Example 5.
Data for the chemical system H+, Ca2+ and CO32−
was extracted using DATABASE. Then it was modified in
SPANA to exchange components for reactions,
in this case CO32− was exchanged for CO2(g)
and Ca2+ for CaCO3(cr).
In the diagram the calculated solubilities, that is, the total concentrations
of each chemical component in the aqueous phase, are plotted against the amount of added
CO2 (from 0 to 0.004M) in a closed system that
contains an excess (0.05M) of calcite (CaCO3).
The solubility of calcite in pure water (when both [CO2]tot
= 0 and [H+]tot = 0) may be
read as the
point where the solubility curve for CaCO3
crosses the Y-axis: about 10−3.95
≈ 0.11 mM.
See also:
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