Question

Example of electrical decomposition reaction:

• A. Electrolysis of water
• B. Zinc reacts with copper sulphate
• C. Heating sulphur
• D. Heating copper sulphate solution

Answer 1

The correct option is A

Electrolysis of water

The explanation for the correct options

A. Electrolysis of water

Decomposition reaction

• In a decomposition reaction, complex compound is broken down into two or more simpler compounds.
• A source of energy, such as heat, light, or electricity, is required for most of the decomposition reactions.
• Based on the source of energy, decomposition reactions are divided into 3 types-

1. Electric decomposition / Electrolysis
2. Photo decomposition
3. Thermal decomposition

Electric decomposition / Electrolysis

• When decomposition reactions take place in presence of electricity, it is called electrical decomposition reaction or Electrolysis.
• For example, Electrolysis of water
• $\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\stackrel{\mathrm{Electricity}}{\to }\underset{\mathrm{Hydrogen}}{2{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

The explanation for the incorrect options

B. Zinc reacts with copper sulphate

• When Zinc (Zn) reacts with Copper Sulphate (CuSO₄) , Zinc displaces Copper from the Copper Sulphate solution and forms zinc sulphate because Zinc is more reactive than Copper.
• So , it is the example of displacement reaction.

$\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{Copper}\mathrm{Sulphate}}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Zinc}\mathrm{Sulphate}}{{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}$

C. Heating sulphur

• When Sulphur is heated in presence of Oxygen it forms Sulphur dioxide.
• So, it is an example of an addition reaction.

$\underset{\mathrm{Sulphur}}{\mathrm{S}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Sulphur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}$

D. Heating copper sulphate solution

• When Copper Sulphate solution is heated in presence of oxygen, it will decompose into Copper oxide, Sulphur dioxide, and oxygen.
• So, it is an example of a thermal decomposition reaction.
• For example, $\underset{\mathrm{Copper}\mathrm{Sulphate}}{2{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}\stackrel{\mathrm{Heat}}{\to }\underset{\mathrm{Copper}\mathrm{oxide}}{2\mathrm{CuO}\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphur}\mathrm{dioxide}}{2{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

Hence option (A) is correct, Electrolysis of water is an example of an electrical decomposition reaction.