Question

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of:
A) a combination reaction.
B) a displacement reaction.
C) a decomposition reaction.
D) a double displacement reaction.

Answer 1

Hint: Identify each type of reaction. Identify the changes taking place in each type of reaction. There are four types of reactions: we have to identify the type of reaction by simply writing the chemical reaction.

Complete step by step answer:
In the combination reaction, two (or more) reactants combine to give a product.
For example, hydrogen gas combines with oxygen gas to form water molecules.
\[{{\text{H}}_2}{\text{ + }}\frac{1}{2}{{\text{O}}_{\text{2}}} \to {{\text{H}}_{\text{2}}}{\text{O}}\]
In a displacement reaction, one element displaces another element from its salt solution. For example, chlorine displaces bromine from sodium bromide solution.
\[{\text{C}}{{\text{l}}_2}{\text{ + 2NaBr}} \to {\text{B}}{{\text{r}}_{\text{2}}}{\text{ + 2NaCl}}\]
In a decomposition reaction, a substance decomposes into two or more products. For example, calcium carbonate decomposes to give calcium oxide and carbon dioxide.
\[{\text{CaC}}{{\text{l}}_2}{\text{ }} \to {\text{C}}{{\text{O}}_{\text{2}}}{\text{ + CaO}}\]
When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution.
Write the balanced chemical equation for the process:
\[{\text{CuS}}{{\text{O}}_4}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{S}} \to {\text{CuS}} \downarrow + {{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_4}\]
In this reaction, cupric ions (from copper sulphate) combine with sulphide ions (from hydrogen sulfide) to form cupric sulphide. Hydrogen ions (from hydrogen sulphide) combine with sulphate ions (from copper sulphate) to form sulphuric acid.
The reaction is a double displacement reaction.

Hence, the correct option is the option (D).

Note: In a double displacement reaction, two compounds exchange cations and anions with each other. After the double displacement reaction, two new compounds are formed.