Cyanides, solubility-product constant

Numerical values for solubility-product constants, dissociation constants, and formation constants are conveniently evaluated through the measurement of cell potentials. One important virtue of this technique is that the measurement can be made without appreciably affecting any equilibria that may be present in the solution. For example, the potential of a silver electrode in a solution containing silver ion, cyanide ion, and the complex formed between them depends on the activities of the thiee species. It is possible to measure this potential with negligible current. 

Polarographic studies on the reduction of the Ni(CN)4" ion have been performed. The results confirmed the irreversibility of the reduction, and indicated a minimum formation constant of about 10. Polarograms of saturated solutions of Ni(CN)2 showed waves due to the aquonickel(II) ion and the Ni(CN)4 complex, but no free cyanide ions could be detected. This indicates that the solid is actually Nipvli(CN)4] (see also [51 LON]. The solubility product of Ni[Ni(CN)4] in 0.1 M NaCl solution was reported to be log,oX =-8.77. 

Earlier we pointed out that when cyanide ions encounter silver ions, a precipitate forms. There are relatively few cations that precipitate cyanide, but other anions such as phosphate or carbonate precipitate readily with a wide range of cations. Eor the engineers and chemists who design industrial processes, solubility often is vital in both the isolation of desired products and the treatment of waste streams. Because industrial processes are often carried out at high temperatures, the characteristics of solubility must be viewed within the context of the equilibrium (and the equilibrium constant) of the reactions at those temperatures. 

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