Cyanide recovered from the refining of gold ore
can be determined indirectly by EDTA titration. A known
excess of Ni2 is added to the cyanide to formtetracyanonickelate(
II):
4CN + Ni ---> Ni(CN)4
When the excess Ni2 is titrated with standard EDTA,
Ni(CN)4 does not react. In a cyanide analysis, 12.7 mL of
cyanide solution were treated with 25.0 mL of standardsolution
containing excess Ni to form tetracyanonickelate. The excess
Ni required 10.1 mL of 0.013 0 M EDTA for complete
reaction. In a separate experiment, 39.3 mL of 0.013 0 M EDTA
were required to react with 30.0 mL of the standard Ni
solution. Calculate the molarity of CN in the 12.7-mL sample
of unknown.
