Chemical Concepts Demonstrated: Complex-formation and oxidation/reduction chemsitry of iron
Demonstration:
The following solutions are added to a beaker containing 0.10M FeSO4 solution.
| Solution: | Chemical Equation: | Observations: |
| Sodium Citrate | Fe2+ (aq) + C6H5O7 3- (aq) <=> Fe(C6H5O7) - (aq) | A light yellow complex forms. |
| NaOH | Fe(C6H5O7) - (aq) + 2 OH - (aq) <=> Fe(OH)2 (s) + C6H5O73- (aq) | A dark green precipate is produced. |
| 3% H2O2 | 2 Fe(OH)2 (s) + H2O2 (aq) ---> 2 Fe(OH)3 (s) | Iron (II) hydroxide is oxidized to rust colored iron (III) hydroxide. |
| HCl | Fe(OH)3 (s) + 3 H+ (aq) + 4 Cl - (aq) <=> FeCl4 - (aq) + 3 H2O (l) | Iron (III) hydroxide dissolves to form a yellow-colored solution of the FeCl4 - complex ion is produced. |
| Sodium Salicylate | FeCl4 - (aq) + C7H5O3- (aq) <=> Fe(C7H5O3)2+ (aq) + 4 Cl - (aq) | A translucent, deep purple solution of the iron (III) salicylate complex ion. |
| H2SO4 | Fe(C7H5O3)2+ (aq) + H+ (aq) <=> Fe 3+(aq) + C7H5O3- (aq) | The iron (III) salicylate complex is destroyed to give a yellow-brown colored aqueous solution of the Fe 3+ ion. |
| KSCN | Fe 3+ (aq) + SCN- (aq)
<=> Fe(SCN)2+ (aq) |
Blood red colored iron (III) thiocyanate complex ion is produced. |
| SnCl2 | 2 Fe(SCN)2+(aq) + Sn2+(aq) --> 2 Fe2+ (aq) + Sn 4+(aq) + 2 SCN- (aq) | The iron (III) thiocyanate complex is slowly destroyed by reducing the metal to Fe2+ to give an orange-red solution. |
| K4Fe(CN)6 | 2 Fe2+ (aq) + Fe(CN)6 4- (aq) <=> Fe2[Fe(CN)6] (s) | Prussian blue solid potassium ferrocyanide is formed. |
| 3% H2O2 | 2 Fe2+ (aq) + H2O2
(aq) + 2 H+ (aq) ---> 2 Fe3+ (aq) + H2O (l) 4 Fe3+ (aq) + 3 Fe(CN)6 4- (aq) <=> Fe4 [Fe(CN)6]3 (s) |
The solid is oxidized into a blue-black solid, which is used in a pigment know as Prussian blue. |
| NaOH | Fe3+ (aq) + 3 OH - (aq) <=> Fe(OH)3 (s) | The rust-colored iron (III) hydroxide reprecipates from the solution. |
| Na2S | Fe(OH)3 (s) + 3 S 2- (aq) --> 2 FeS (s) + S(s) 6 OH - (aq) | The precipiate is converted to a mixture of black iron (II) sulfide and elemental sulfur. |