Introduction

Complexes and preipitates of nickel (II) are formed by adding ammonium hydroxide, ethylenediamine, and dimethylglyoxime to dilute solutions of Ni2+ in beakers.

      Ni(H2O)62+ (aq) + 6 NH3 (aq) “ Ni(NH3)62+ (aq) + 6 H2O

      Ni(H2O)62+ (aq) + en (aq) “ Ni(H2O)4(en)2+ (aq) + 2 H2O

      Ni(H2O)62+ (aq) + 2 en (aq) “ Ni(H2O)2(en)22+ (aq) + 4 H2O

      Ni(H2O)62+ (aq) + 3 en (aq) “ Ni(en)32+ (aq) + 6 H2O

      Ni(H2O)62+ (aq) + 2 dmg- (aq) “ Ni(dmg)2 (aq) + 6 H2O

 Solutions with Nickel

Supplies

Short List

  •   Gloves
  •   goggles
  •   6 (or 7) 50-mL beakers
  •   10-mL graduated cylinders with pre-measured amounts of reagents

Chemicals

  •   2 M NiSO4 (263 g NiSO4(6H2O/L) or NiCl2 (238 g NiCl2(6 H2O/L)
  •   6 M NH3
  •   25% ethylenediamine (dilute 250 mL en to 1 L)
  •   1% dimethylglyoxime (8 g dmg/L ethanol)

Prior to Lecture  (prep time ~10 min.)

1.  Assemble the following chemicals:

  1.   2 M NiSO4 (263 g NiSO4(6H2O/L) or NiCl2 (238 g NiCl2(6 H2O/L)
  2. 6 M NH3
  3. 25% ethylenediamine (dilute 250 mL  to 1 L)
  4. 1% dimethylglyoxime (8 g dmg/L ethanol)

2.  Assemble the following equipment:

  1.  6 (or 7) 50-mL beakers
  2.  gloves
  3.  goggles
  4.  10-mL graduated cylinders with pre-measured amounts of reagents

To Conduct Demonstration

  1.   Leave one beaker of six (or seven, if CN- is being used) filled with NiCl2 or NiSO4 solution as a control.
  2.  Add approximately 3 mL of 6M NH3 to the second beaker.
  3.   Add approximately 0.5 mL of 25% ethylenediamine to the third beaker.
  4. Add approximately 1 mL of 25% ethylenediamine to the fourth beaker.
  5.  Add approximately 1.5 mL of 25% ethylenediamine to the fifth beaker.
  6. Add approximately 2.5 mL of 1% dimethylglyoxime to the sixth beaker.

Safety and Disposal

Cyanide salts and solutions are extremely poisonous.  Reaction with acid liberates hydrogen cyanide gas, one of the most toxic and rapidly acting poisons.  Solutions must be kept basic (pH>8).  Gloves are necessary to prevent absorption through the skin.

Nickel salts are poisonous if ingested.  Ammonia and ethylenediamine are caustic and irritating to skin, eyes, and the respiratory system.

Disposal 

A separate waste container for this demo is available since no other demo uses ethylenediamine.