Bismuthiol II as an analytical reagent

Summary

With copper, bismuthiol II forms both cuprous and cupric complexes which are stable in mineral acids, acetic, citric and tartaric acids and the cuprous complex compared to cupric is insoluble in EDTA solution as well in organic solvents. The melting points of both cupric and cuprous complexes are respectively 148° C and 198° C. As an insoluble cupric complex copper is estimated from solutions having a maximum acidity of 0.1 N in hydrochloric or sulphuric acid and of 0.5 N in acetic acid. Even at a lower acidity, up to a p_H of about 6.2, the precipitation of copper is quantitative but at a p_H higher than 6.2 the copper complex shows an increased solubility. By the proper control of p_H and by suitable masking agents, it is possible to separate copper from almost all the ions except palladium, cadmium, lead and thallous ions.

Cuprous complex, being more stable and insoluble and having practically the same tolerance to an acid solution or to a solution at a high p_H, helps towards a more complete separation of copper from all the ions stated except the thallous and bismuth.