Summary
Colorful aqueous complexes of nickel are made using ammonia, ethylene diamine and dimethylglyoxime ligands.
Hazards
Nickel compounds are considered cancer suspect agents. Use care.
Chemicals and Solutions
- 0.1M Nickel sulfate, NiSO₄
- Conc. Ammonium hydroxide, NH₄OH
- 25 % Ethylene diamine in ethanol
- 1% Dimethylglyoxime in ethanol
Materials
- Stirring rods
- 5 hydrometer cylinders
- Stirring rod
- Beakers or crystallizing dishes
Procedure
- In a large hydrometer cylinder place 100 mL 0.1M NiSO₄ (this is the reference solution).
- In a second large hydrometer place 200 mL 0.1M NiSO₄. Add 20 mL of conc. NH₄OH and stir to get the blue color of nickel ammine.
- Pour half the nickel ammine into another large hydrometer and add ethylene diamine solution dropwise to get purple/lavender color.
- Pour half the nickel ethylene diamine solution into a small hydrometer and add the DMG solution dropwise to form the red precipitate.
Hint: Any green precipitate formation is due to Ni(OH)₂ precipitate. (Add more ammonia to make it go away.) Make the ethylene diamine solution fresh if there are crystals present in the solution or if it's more than a year old. The ethylene diamine will oxidize with time. Test prior to class.
Discussion
\(\ce{$\underset{\text{green (octahedral)}}{\ce{Ni(H2O)6^{+2} + 6NH3_{(aq)}}}$->$\underset{\text{blue (octahedral)}}{\ce{Ni(NH3)6^{+2} + 6H2O}}$}\)
\(\ce{$\underset{\text{blue (octahedral)}}{\ce{Ni(NH3)6^{+2} + 3en}}$->$\underset{\text{purple (octahedral)}}{\ce{Ni(en)3^{+2} + 6NH3}}$}\)
\(\ce{$\underset{\text{purple (octahedral)}}{\ce{Ni(en)32+ + 2DMG}}$->$\underset{\text{red ppt. (square planar)}}{\ce{Ni(DMG)2}}$}\)