Hydrolysis of Iron(III)
This example is related to Example 6.1 in Aquatic Chemistry 2nd ed., W. Stumm and J. J.
Morgan, Wiley-Interscience, 1981. They consider iron(II) solutions with the possible precipitation
of amorphous ferric hydroxide. They give the following data:
Fe3 + H2O = FeOH2+ + H+;
log10(K1) = -3.05
Fe3 + 2H2O = Fe(OH)2+ + 2H+;
log10(K1) = -6.31
2Fe3 +2H2O = Fe2(OH)24+ + 2H+;
log10(K1) = -2.91
Fe(OH)3(s) + 3H2O = Fe3+ + 3H+;
log10(K1) = 3.96
Fe(OH)3(s) + H2O = Fe(OH)4- + H+;
log10(K1) = -18.7
As is typical for problems in this field, they manipulate the above equations into a single polynomical equation. Another typical feature is that they address the possible precipitation of Fe(OH)3(s) only indirectly, in that they assume its presence or absence in advance.
EQS4WIN can efficiently solve this type of problem, and furthermore can directly address the solid precipitation aspect. For example, EQS4WIN can directly determine whether or not the solid phase forms for a given starting composition. Also, by using the special Equilibrium Constraint option, the solubilty and the resulting equilibrium species distribution can be simultaneously calculated. Finally, this example illustrates the use of Reaction Input Data in EQS4WIN. This feature is illustrated in several example problems included in all versions of EQS4WIN.
Click on image to enlarge (17K)