Chemical Concepts Demonstrated: Complex formation and solubility chemistry of nickel
Demonstration:
The following solutions are added to a beaker containing nickel (II) sulfate hexahydrate (NiSO4 * H2O).
| Solution | Chemical Equation |
Observations: |
| HCl | Ni 2+ (aq) + 4 Cl -(aq) <=> NiCl4 2-(aq) | A yellow solution of the NiCl4 2- complex ion is produced. |
| H2O | NiCl4 2-(aq) <=> Ni 2+ (aq) + 4 Cl -(aq) | The solution turns green as the NiCl4 2- complex dissociates. |
| Na2CO3 | Ni 2+ (aq) + CO3 2-(aq) <=> NiCO3 (s) | The green- yellow carbonate precipates out of the solution. |
| HNO3 | NiCO3 (s) + 2 H + (aq) ---> Ni 2+ (aq) + H2O (l) + CO2 (g) | The HNO3 destroys the carbonate ion to produce a green solution of the Ni 2+ ion. |
| NaOH | Ni 2+ (aq) + 2 OH -(aq) <=> Ni(OH)2 (s) | A gelatinous, light green precipate is produced. |
| NH3 | Ni(OH)2 (s) + 6 NH3 (aq) <=> Ni(NH3)6 2+(aq) + 2 OH -(aq) | The nickel (II) hydroxide precipitate is dissolved to form the hexaminenickel (II) complex ion. |
| NaBr | Ni(NH3)6 2+(aq) + 2 Br -(aq) <=> Ni(NH3)6 Br2 (s) | A lavendar precipitate is formed. |
| NaOH | Ni(NH3)6 Br2 (s) + 2 OH -(aq) <=> Ni(OH)2 (s) + 2 Br -(aq) + 6 NH3 (aq) | The precipitate changes color from lavendar to gray-blue. |
| HNO3 | Ni(OH)2 (s) + 2 H + (aq) <=> Ni 2+ (aq) + 2 H2O (l) | HNO3 dissolves the precipitate to form a green solution of Ni 2+ ion. |
| 25% ethylenediamine sol. | Ni 2+ (aq) + 3 en (aq) <=> Ni(en)3 2+(aq) | A soluable purple colored complex is formed. |
| 1% dimethylgloxime sol. | Ni(en)3 2+(aq) + 2 DMG - (aq) <=> Ni(DMG)2 (s) + 3 en (aq) | The bright red Ni(DMG)2 precipitate is formed. |
| Na2S | Ni(DMG)2 (s) + S 2- (aq) <=> NiS (s) + 2 DMG - (aq) | The black sulfide precipitate is formed. |