In the separation of Cu2+ and Cd2+ in II group qualitative analysis of cations tetrammine copper (II — Qualitative and Quantitative Analysis Chemistry Question
Question
In the separation of Cu2+ and Cd2+ in II group qualitative analysis of cations tetrammine copper (II) sulphate and tetrammine cadmium (II) sulphate react with KCN to form the corresponding cyano complexes. Which one of the following pairs of the complexes and their relative stability enables the separation of Cu2+ and Cd2+ ?
💡 Solution & Explanation
Step 1: In systematic qualitative analysis, Group II sulfides are divided into Group IIA (copper group) and Group IIB (arsenic group) using yellow ammonium sulfide (YAS). Step 2: Group IIB sulfides (As2S3, Sb2S3, SnS) dissolve in yellow ammonium sulfide by forming soluble thiosalts (e.g., [AsS4]3-, [SbS4]3-, [SnS3]2-). Step 3: Group IIA sulfides, including copper(II) sulfide (CuS), are completely insoluble in yellow ammonium sulfide, matching option (a).