A qualitative analysis mixture contains and ions. To separate them, excess potassium cyanide () is added to the solution until the initial precipitates dissolve, and then gas is passed. What is the re

Question

A qualitative analysis mixture contains $Cu^{2+}$ and $Cd^{2+}$ ions. To separate them, excess potassium cyanide ($KCN$) is added to the solution until the initial precipitates dissolve, and then $H_2S$ gas is passed. What is the resulting observation?

Prashant Kotian · Accepted Answer

Correct answer: B. Addition of excess forms soluble complexes for both: and . The copper complex is highly stable ( is very small), meaning the concentration of free is too low to exceed the of copper sulphide when is passed. Conversely, the cadmium complex is less stable, dissociating enough to provide a sufficient concentration to exceed the of , forming a yellow precipitate.

💡 Solution & Explanation

Practice 22,000+ questions like this