Question

Which of the following substances are soluble in concentrated $HN{O_3}$ ?​
(A) $BaS{O_4}$
(B) $CuS$
(C) $PbS$
(D) $HgS$

Answer 1

Hint: $HN{O_3}$ , often known as nitric acid, is a very corrosive mineral acid. As it interacts with various chemicals, it displays various traits. Depending on the quantity of $HN{O_3}$ , several products can be produced in reactions involving this compound. When nitric acid concentrations are low, it behaves similarly to other common acids.

Complete Step by Step Solution:
A nitrogen oxoacid with the formula $HN{O_3}$ is nitric acid, in which the nitrogen atom is linked to a hydroxyl group and the other two oxygen atoms by analogous bonds. It serves as a reagent and a protic solvent. It is a nitrate's conjugate acid.
Citrus juice $\left( {HN{O_3}} \right)$ , a colourless liquid used in the production of nitrates and nitro compounds for fertilisers, intermediates in dyeing processes, explosives, and several other organic chemicals. Chemical pneumonitis and chronic bronchitis are both possible side effects of prolonged vapour exposure.
Now we know that $HN{O_3}$ dissociates into ${H^ + }$ and $N{O_3}^ - $ ions, and $BaS{O_4}$ dissociates into $B{a^{2 + }}$ and $S{O_4}^{2 - }$ . If we look at the given question we will find that because the ${H^ + }$ ions of the acid cannot dissolve the $S{O_4}^{2 - }$ ions from barium sulphate, $BaS{O_4}$ is insoluble in concentrated $HN{O_3}$ .
Whereas $CuS$ is soluble in concentrated $HN{O_3}$ , leaving a white precipitate of sulphur.
\[CuS + 8HN{O_3}\,\, \to \,\,CuS{O_4} + 8N{O_2} + 4{H_2}O\]
$PbS$ is also soluble in concentrated $HN{O_3}$ ​. The reaction is as follows:
\[3PbS + 8HN{O_3}\,\, \to \,\,3PbS{O_4} + 8NO + 4{H_2}O\]
Similary $HgS$ is also soluble in concentrated $HN{O_3}$ .
Hence, option B., C. and D. are correct.

Note: For answering such questions one must have knowledge of properties of various chemical compounds and how they react with other chemical compounds specially some a few main acids and bases. If we include any chemical reaction in our solution then balancing those equations is important.