THE REACTION OF CN- IONS WITH Ni(EDTA)" IONS Submitted by: Checked by:
D. G. Littlejohn and J. C. Fanning, Department of Chemistry and Geology, Clemson University, Clemson, South Carolina 29631 E. C. Kostansek, Hiram College, Hiram, Ohio 44234
PREPARATION
Prepare the following solutions Solution A 4 . 1 2 F Ni(NO& (3.49 g Ni(NOa)z.6Hz0 Der 100 ml sold solution ~ 4 . 1 2N' ~~ EDTA ~ K (4.47 ~ g NalH2EDTA. 2H,O and 1.12 g KOH per 100 mlsolnj Solution C 4 . 5 F KCN and 0.5 F KOH (8.15 g KCN and 14.02g KOH per 250 ml soln)
+ 4CN--
Ni(EDTA)Zblue
Ni(CN)P yellow
+ EDTA4-
REMARKS
is slow and demonstrates many aspects of complex ion chemistry. The reaction shows the influence of the ligands on the color of the metal ion in solution and the effect of ligand structure and charge of ions on the reaction rate. The color changes that occur during and prior to the reaction are striking. The green Ni(NO& solution (A) changes immediately to blue upon the addition of the EDTA solution (B). The color changes to a deep violet upon addition of the cyanide solution (C). Mixed EDTA-cyanide complexes are probably present. The color slowly fades, becoming colorless, and then changes to the yellow color of Ni(CN)a2-. Margerum, Bydalek, and Bishop' have made a kinetic study of this reaction and have proposed a mechanism for it.
The reaction of CN- ions with the (ethylenedinitri10)tetraacetate nickel (11) ion, or Ni(EDTA)%-,in aqueous solution
'MARGERUM, D. W., BYDALEK, T. J., Amer. Chem. Soe., 83, 1791 (1961).
DEMONSTRATION (a) Place 10 ml of A and 10 ml of B in a 250-ml Erlenmeyer flask. If 60 ml of water and then 20 ml of C are added, the reaction is complete in about 3 min. If 15 ml of Cis used, the reaction takes about 10 min. ( b ) For comparison, place 10 ml of A in a 250-ml flask. Add 70 ml of water and then 20 ml of C. The reaction occurs immediately.
AND
BISHOP, J. J., J.
Volume 49, Number 4, April 1972
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A267
