Question

How will you bring out the reduction of the following metal oxide?

$\mathrm{ZnO}$, $\mathrm{HgO}$, ${\mathrm{Ag}}_2\mathrm{O}$ and ${\mathrm{MnO}}_2$

Answer 1

Reduction of metal oxides

Carbon as a reducing agent:

• The commercial preparation of some metals involves the reduction of metal oxide by carbon$\left(\mathrm{C}\right)$ at high temperatures.
• This process is known as smelting.
• Metal in the middle of the reactivity series, such as $\mathrm{Zn},\mathrm{Fe},\mathrm{Pb}$ and $\mathrm{Cu}$ which are electropositive in nature are reduced to metals by using Carbon as a reducing agent.
• The reduction reaction of Zinc oxide$\mathrm{ZnO}$ is as follows:
• $\mathrm{ZnO}\left(\mathrm{s}\right)+\mathrm{C}\left(\mathrm{s}\right)\to \mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{CO}\left(\mathrm{g}\right)$
• Hence, $\mathrm{ZnO}$ is reduced by Carbon$\left(\mathrm{C}\right)$.

Aluminum as a reducing agent:

• Aluminum is used to reduce Manganese$\left(\mathrm{Mn}\right)$, Iron$\left(\mathrm{Fe}\right)$ and Chromium$\left(\mathrm{Cr}\right)$ metal oxides to free metals.
• Aluminum$\left(\mathrm{Al}\right)$ is a good reducing agent due to its high affinity for Oxygen$\left({\mathrm{O}}_2\right)$.
• The reduction reaction of Manganese dioxide$\left({\mathrm{MnO}}_2\right)$ is as follows:
• $3{\mathrm{MnO}}_2\left(\mathrm{s}\right)+4\mathrm{Al}\left(\mathrm{s}\right)\to 3\mathrm{Mn}\left(\mathrm{s}\right)+2{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)$
• Hence, ${\mathrm{MnO}}_2$ is reduced by Aluminum$\left(\mathrm{Al}\right)$.

Thermal decomposition:

• Oxides of metals that are low in reactivity series are least stable and can be reduced to metal by heating alone.
• Mercury$\left(\mathrm{Hg}\right)$ and Silver$\left(\mathrm{Ag}\right)$ are present in the lower part of reactivity series.
• The thermal decomposition reaction of Mercuric oxide$\left(\mathrm{HgO}\right)$ and Silver oxide$\left({\mathrm{Ag}}_2\mathrm{O}\right)$ is as follows:
• $2\mathrm{HgO}\left(\mathrm{s}\right)\stackrel{∆}{\to }2\mathrm{Hg}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$
• $2{\mathrm{Ag}}_2\mathrm{O}\left(\mathrm{s}\right)\stackrel{∆}{\to }4\mathrm{Ag}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$
• Hence, $\mathrm{HgO}$ and ${\mathrm{Ag}}_2\mathrm{O}$ are reduced by Thermal decomposition.