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 $HN{O}_3$ ). $3HgS+\underset{aquaregia}{\underbrace{2HN{O}_3+6HCl}}\to 3HgC{l}_2+3S$ $+2NO+4H_{2}O$