Sample 1
Suppose you want to know if iron(III) precipitates in a solution of 1 µM at a pH of 4 (no competing ligands). You run the program with the following settings:
- free activity of H is 1E-4;
- total concentration of Fe(III) is 1E-6;
The output is shown on the right. Click the figure for a larger version.
Sample 2
Suppose now you want to know the
concentration of the iron precipitate under equilibrium
conditions. You run the program with the same settings as in
example 1 but with saturation solids included.
After running the calculation, you open the Cations window
to check the speciation of Fe(III). CHEAQS calculated that
solid Fe(III) amounts to 99.99% of total Fe(III).
See the figure for a view of the output. (Using View-Options
from the output menu, species representing less than 0.1%
were omitted from the output.)
Click the figure for a larger version.
Sample 3
Suppose now you want to know if
adding 1 µM of NTA is sufficient to keep the iron in
solution. You add 1 µM of NTA to the input and re-run the
program.
After running the calculation, you open the Cations window
to check the speciation of Fe(III). CHEAQS calculated that
Fe(III)NTA-complexes amount to 26.10% of total Fe(III)
(4.33% for Fe(III)NTA (aq), 1.17% for Fe(III)NTA(OH)-
and 20.60% for Fe(III)2(NTA)2(OH)22-).
More than 73% of the iron is still in solid form under
equilibrium conditions, so adding 1 µM of NTA is not
sufficient to keep the iron in solution.
See the figure. (click it for a larger version.)