Question

What is displacement reaction? Give one example.

Answer 1

1. Definition

Displacement reaction: Reaction in which one of the higher reactive element displaces a less reactive element from its solution. $\mathrm{A}+\mathrm{BC}\to \mathrm{AC}+\mathrm{B}$ ( Here A is more reactive than B)

2. Example

When iron nails are dipped in ${\mathrm{CuSO}}_4$ solution, displacement reaction takes place and formation of ferrous sulphate takes place which is a green colour solution and on iron nail deposition of copper takes place which turns grey iron nail to brown in colour.

Reaction

$\mathrm{CuSO}{}_4(\mathrm{aq})+\mathrm{Fe}(\mathrm{s})\to \mathrm{FeSO}{}_4(\mathrm{aq})+\mathrm{Cu}\left(\mathrm{s}\right)$

Copper(II)sulphate Iron Iron sulphate Copper

(Blue ) (Grey) (Green) (Brown)

Since $\mathrm{Fe}$ is more reactive than $\mathrm{Cu}$ displacement takes place.

Reactivity series

$\mathrm{K}>\mathrm{Na}>\mathrm{Ca}>\mathrm{Mg}>\mathrm{Al}>\mathrm{Zn}>\mathrm{Fe}>\mathrm{Ni}>\mathrm{Sn}>\mathrm{Pb}>\mathrm{H}>\mathrm{Cu}>\mathrm{Hg}>\mathrm{Ag}>\mathrm{Au}>\mathrm{Pt}$

Here potassium is the most reactive metal and platinum is the least reactive metal in this series.

So, from the reactivity series, we can see $\mathrm{Fe}$ is more reactive than $\mathrm{Cu}$ so it can displace copper from its solution and therefore the blue colour is destroyed.
This is a displacement reaction.