Question

In an acidified aqueous solution of $M{n^{2 + }}$, $N{i^{2 + }}$, $C{u^{2 + }}$ and $H{g^{2 + }}$ ions. ${H_2}S$ gas was passed. Precipitates are:
A. $MnS$ and $CuS$
B. $NiS$ and $HgS$
C. $MnS$ and $NiS$
D. $CuS$ and $HgS$

Answer 1

Hint: We know that in double displacement reactions, when the cations and the anions switch between two reactants, new products are formed. In order for the reaction to occur, one of the products is usually a solid precipitate, a gas or a molecular compound.

Complete step by step answer:
The term “Precipitation” refers to a chemical reaction, which occurs in aqueous solution when two ions attach together to form an insoluble salt that is called as the precipitate.
We call a reaction a precipitation reaction when two solutions containing different salts are combined, and the cation/anion pair in the resulting mixed solution forms an insoluble salt; this salt later precipitates out of solution.
A precipitate is an insoluble solid that comes from liquid solution and emergence of the insoluble solid from solution is known as precipitation.
The liquid which causes the formation of solid is called as precipitant.
We can say precipitation is a diffusion of a solid, and creation of a solid in a solution.
We have to know that in cationic estimation group, $C{u^{2 + }}$ and $H{g^{2 + }}$ are present in group II, where as $M{n^{2 + }}$, and $N{i^{2 + }}$ are present in group IV.
The reagent of group II is ${H_2}S$ gas in the presence of dilute hydrochloric acid and for group IV, we use the reagent as ${H_2}S$ gas in the presence of ammonium hydroxide. SO when we pass ${H_2}S$ gas in acidified solution of given cations, we get the precipitates as $CuS$ and $HgS$

Therefore, the option (D) is correct .

Note:
We must remember that the precipitation reaction helps in determining a specific element present in the given solution. These reactions monitor the formation of a precipitate when a certain chemical is added to solutions. We can use precipitation reactions for the extraction of magnesium from the seawater. We can also use precipitation reactions in the treatment of wastewater. Precipitation reactions depend on concentration of the solution, buffer solution, temperature etc.