Which of the following heavy metal sulphides, obtained during systematic qualitative analysis, are p — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

In qualitative analysis, copper sulphide ($CuS$) is separated from mercury sulphide ($HgS$) because $CuS$ dissolves in hot 50% $HNO_3$, whereas $HgS$ is unaffected and requires aqua regia to dissolve. Similarly, in Group IV, both nickel sulphide ($NiS$) and cobalt sulphide ($CoS$) are exceptional in that, once precipitated, they become highly crystalline and insoluble in concentrated $HCl$ and 50% $HNO_3$, thus requiring an oxidizing mixture like aqua regia to dissolve them into their respective chlorides.