Question

Give an example of a double displacement reaction accompanied by evolution of a gas.

Answer 1

Double displacement reactions

Reactions in which one component each of both reactants are exchanged to form new compounds are called double displacement reactions. Neutralization reactions and precipitation reactions occur by double displacement.

The general form of a double displacement reaction is:

$AB+CD\to AD+CB$

Example for double displacement reaction

The reaction between Sodium sulphide (Na₂S) and Hydrochloric acid (HCl) produces Sodium chloride (NaCl) with the evolution of Hydrogen sulphide (H₂S) gas. In this reaction, the sulphide ion in Sodium sulphide is replaced with chloride ions and the sulphide ions form Hydrogen sulphide with hydrogen ions. Therefore, an exchange of ions takes place and this reaction is an example of a double displacement reaction forming a gas.

The chemical equation for the reaction is:

$N{a}_{2}S\left(aq\right)+2HCl\left(aq\right)\to 2NaCl\left(aq\right)+H_{2}S\left(g\right)$

(Sodium (Hydrochloric (Sodium (Hydrogen

Chloride) acid) chloride) sulphide)

Another example for a double displacement reaction involving evolution of a gas include the reaction of Potassium sulphide (K₂S) with Hydrochloric acid (HCl) to form Potassium chloride (KCl) with the evolution of Hydrogen sulphide (H₂S) gas.

$K_{2}S\left(aq\right)+2HCl\left(aq\right)\to 2KCl\left(aq\right)+H_{2}S\left(g\right)$

(Potassium (Hydrochloric (Potassium (Hydrogen

sulphide) acid) chloride) sulphide)