Now, suppose we add some oxalic acid (H2C2O4) to the original solution. Oxalic acid ionizes in water to form the oxalate ion, C2O42-, which binds strongly to the Fe3+ ions. The formation of the stable yellow ion Fe(C2O4)33- removes free Fe3+ ions in solution. Consequently, more FeSCN2+ units dissociate and the equilibrium shifts from left to right:
|
FeSCN2+ (aq) |
® Fe3+ (aq) |
+ SCN-(aq) |