Question

Which of the following reaction is a double displacement reaction.

• A. ${\mathrm{FeCl}}_3+3\mathrm{NaOH}\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_3+3\mathrm{NaCl}$
• B. $\mathrm{Zn}+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{ZnSO}}_4+{\mathrm{H}}_2$
• C. $2\mathrm{CO}+{\mathrm{O}}_2\to 2{\mathrm{CO}}_2$
• D. ${\mathrm{N}}_2+{\mathrm{O}}_2\to 2\mathrm{NO}$

Answer 1

The correct option is A

${\mathrm{FeCl}}_3+3\mathrm{NaOH}\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_3+3\mathrm{NaCl}$

Explanation of correct answer:

Option (A) is the correct answer.

Double displacement reaction: a chemical reaction in which two compounds in their aqueous state exchange their ions or radicals to form new substances is known as a double displacement reaction.

$\underset{\mathrm{Ferric}\mathrm{chloride}}{{\mathrm{FeCl}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{sodium}\mathrm{hydroxide}}{3\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{ferric}\mathrm{hydroxide}}{\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{sodium}\mathrm{chloride}}{3\mathrm{NaCl}\left(\mathrm{aq}\right)}$

The above chemical reaction clearly shows that when an aqueous solution of ferric chloride reacts with aqueous sodium hydroxide and during the reaction they exchange their ions i.e chloride ions of ferric chloride are exchanged by hydroxide ion of sodium hydroxide forming a brown precipitate of ferric hydroxide and soluble salt sodium chloride. This is an example of a double displacement reaction.

Explanation of incorrect answer:

Option (B):

$\underset{\mathrm{zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{zinc}\mathrm{sulphate}}{{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$- this is an example of a displacement reaction.

Displacement reaction: a reaction in which a more active element displaces a less active element from a compound is known as a displacement reaction.

Zn being a more active metal displaces hydrogen from sulphuric acid and forms the zinc sulfate.

Option (C):

$\underset{\mathrm{carbon}\mathrm{monoxide}}{2\mathrm{CO}\left(\mathrm{g}\right)}+\underset{\mathrm{oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{carbon}\mathrm{dioxide}}{2{\mathrm{CO}}_2\left(\mathrm{g}\right)}$it is an example of a combination reaction.

Combination reaction: the reaction in which two or more than two substances combine to form a single compound.

Option (D):

$\underset{\mathrm{Nitrogen}}{{\text{N}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Nitrogen}\mathrm{oxide}}{2\mathrm{NO}\left(\mathrm{g}\right)}$ is an example of a combination reaction.

Thus Option (A) is the correct answer.