Question

In the extraction of nickel by Mond's process, the metal is obtained by:
A) Electrochemical reduction
B) Thermal decomposition
C) Chemical reduction by aluminium
D) Reduction by carbon

Answer 1

Hint:Nickel is refined by mond’s process. Nickel easily forms a volatile compound with available reagent. This volatile compound can then be readily decomposed to facilitate the recovery of metal.

Complete answer:
Some of the methods that can be used for the refining of metals are distillation, liquation, poling, electrolysis, zone refining and vapour phase refining. Nickel is refined by mond’s process. Impure nickel reacts with carbon monoxide at around 330-350 K to form nickel tetracarbonyl. Nickel tetracarbonyl is a volatile compound and is obtained as a vapour. The impurities are left behind. At a high temperature of around 450-470 K, nickel tetracarbonyl is decomposed to regenerate pure nickel.

Let us write the balanced chemical equations for the process.
\[\begin{array}{l}
{\rm{Ni + 4 CO }} \to {\rm{ Ni}}{\left( {{\rm{CO}}} \right)_4}\\
{\rm{Ni}}{\left( {{\rm{CO}}} \right)_4} \to {\rm{ Ni + 4 CO}}
\end{array}\]

In the first reaction, one nickel atom combines with four carbon monoxide molecules to form nickel tetracarbonyl. In the next step, one molecule of nickel tetrachloride decomposes to give one nickel atom and four carbon monoxide ligands. Thus, in the extraction of nickel by Mond's process, the metal is obtained by thermal decomposition.

Hence, the correct answer is option’ B’ i.e, thermal decomposition.

Note: In the vapour phase refining technique, metal to be purified, is converted into a volatile compound by reaction with suitable reagent. In the next step, this volatile compound of metal is decomposed to obtain pure metal. The vapour phase refining technique is used for the refining of nickel, titanium and zirconium metals.