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Colors of Nickel Coordination Complexes

Procedure

1. Place a 1500ml flask containing 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 40ml 1M Ni(NO₃)₂ , turns green.
3. Add 80ml 5M NH₃, turns blue.
4. Add 40ml 25% ethylenediamene solution, turns purple.
5. Add 50ml 1% dimethylglyoxime solution, turns red.
6. Add 400ml 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