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.)