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Nickel Complexes

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, NiSO
  • Conc. Ammonium hydroxide, NHOH
  • 25 % Ethylene diamine in ethanol
  • 1% Dimethylglyoxime in ethanol

Materials

  • Stirring rods
  • 5 hydrometer cylinders
  • Stirring rod
  • Beakers or crystallizing dishes

Procedure

  1. In a large hydrometer cylinder place 100 mL 0.1M NiSO (this is the reference solution).
  2. In a second large hydrometer place 200 mL 0.1M NiSO. Add 20 mL of conc. NHOH and stir to get the blue color of nickel ammine.
  3. Pour half the nickel ammine into another large hydrometer and add ethylene diamine solution dropwise to get purple/lavender color.
  4. 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) 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

\(\ce{$\underset{\text{green (octahedral)}}{\ce{Ni(H2O)6^{+2} + 6NH3_{(aq)}}}$->$\underset{\text{blue (octahedral)}}{\ce{Ni(NH3)6^{+2} + 6H2O}}$}\)

\(\ce{$\underset{\text{blue (octahedral)}}{\ce{Ni(NH3)6^{+2} + 3en}}$->$\underset{\text{purple (octahedral)}}{\ce{Ni(en)3^{+2} + 6NH3}}$}\)

\(\ce{$\underset{\text{purple (octahedral)}}{\ce{Ni(en)32+ + 2DMG}}$->$\underset{\text{red ppt. (square planar)}}{\ce{Ni(DMG)2}}$}\)

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