Colors of Nickel Coordination Complexes

Materials

• 1.5 liter Erlenmeyer Flask with Stir Bar and Rubber Stopper
• Magnetic Stir Plate
• DI Water
• Gloves and Goggles
• Premeasured solutions:

                                  40 mL Nickle Nitrate

                                  80 mL 5M Ammonium Hydroxide

                                  40 mL 25% Ethylene Diamine Solution

                                  50 mL 1% Dimethylglyoxime Solution

                                 400 mL 1M Potassium Cyanide

Procedure

1. Place a 1500ml flask containing about 500ml distilled water and a stirring bar on a magnetic stirrer and adjust stirring rate.     
   

        

   Add solutions in sequence and listen for oohs and aahs from the audience.

2. Add  1M Ni(NO₃)₂ , turns green.
3. Add  5M NH₃, turns blue.
4. Add  25% ethylenediamene solution, turns purple.
5. Add  1% dimethylglyoxime solution, turns red.
6. Add  1M KCN, turns orange.
7. Wait for applause

Reactions

Ni(H₂O)₆²⁺ (aq) + 6NH₃ (aq) -> Ni(NH₃)₆²⁺ (aq) + 6H₂O

                        K(eq) = 1.2 x 10⁹

Ni(NH₃)₆²⁺ (aq) + 2etdm(aq) -> Ni(etdm)₃²⁺ (aq) + 6NH₃ (aq)

                 K(eq) = 1.1 x 10⁹

Ni(etdm)₃²⁺ (aq) + 2dmg(aq) -> Ni(dmg)₂ (aq) + 3etdm(aq) + 2H⁺ (aq)

                          K(eq) = 1.3 x 10^-1

Ni(etdm)₃²⁺ (aq) + 2dmg(aq) -> Ni(dmg)₂ (s) + 3etdm(aq) + 2H⁺ (aq)

                   K(eq) = 1.35 x 10⁵

Ni(dmg)₂ (s) + 4 CN^- (aq) -> Ni(CN)₄^-2 (aq) + 2 dmg^- (aq)

                   K(eq) = 6.3 x 10⁷