Question

Which compound is insoluble in dilute $ HN{{O}_{3}} $ and dissolved in aqua regia?

• A. $ HgS $
• B. $ CuS $
• C. $ B{{i}_{2}}{{S}_{3}} $
• D. $ PbS $

Answer 1

Answer: (A)

Except $ HgS, $ all other sulphides of second (IIA) group of qualitative analysis are soluble in dilute $ HN{{O}_{3}} $ but $ HgS $ is soluble only in aqua regia (a mixture of 3 part $ HCl $ and 1 part $ HN{{O}_{3}} $ ). $ 3HgS+\underbrace{2HN{{O}_{3}}+6HCl}_{aqua\,\,regia}\xrightarrow{{}}3HgC{{l}_{2}}+3S $ $ +2NO+4{{H}_{2}}O $