Question

Name oxide of one metal which is reduced by (give equation).
(i) reduction with carbon.
(ii) electrolytic reduction.
(iii) reduction with heat alone.

Answer 1

(i) On heating, cupric oxide, ferric oxide, zinc oxide get reduced to copper, iron, zinc metals respectively, in the presence of carbon as a reducing agent.

$$\begin{gathered} 2\mathrm{CuO}+\mathrm{C}\stackrel{\mathrm{Heat}}{\to }2\mathrm{Cu}+{\mathrm{CO}}_2 \\ \mathrm{Cupric}\mathrm{oxide}\mathrm{Carbon}\mathrm{Copper}\mathrm{Carbon}\mathrm{dioxide} \\ {\mathrm{Fe}}_2{\mathrm{O}}_3+3\mathrm{C}\stackrel{\mathrm{Heat}}{\to }2\mathrm{Fe}+3\mathrm{CO} \\ \mathrm{Ferric}\mathrm{oxide}\mathrm{Carbon}\mathrm{Iron}\mathrm{Carbon}\mathrm{monoxide} \\ 2\mathrm{ZnO}+\mathrm{C}\stackrel{\mathrm{Heat}}{\to }2\mathrm{Zn}+{\mathrm{CO}}_2 \\ \mathrm{Zinc}\mathrm{oxide}\mathrm{Carbon}\mathrm{Zinc}\mathrm{Carbon}\mathrm{dioxide} \end{gathered}$$

(ii) Aluminium oxide undergoes electrolysis and forms aluminium at the cathode and oxygen at the anode.

$$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3\stackrel{\mathrm{Electrolysis}}{\to }2{\mathrm{Al}}^{3+}+3{\mathrm{O}}^{2-} \\ \mathrm{At}\hspace{0.17em}\mathrm{cathode}:{\mathrm{Al}}^{3+}+3{\mathrm{e}}^{-}\to \mathrm{Al}\left(\mathrm{reduction}\right) \\ \mathrm{At}\mathrm{anode}:2{\mathrm{O}}^{2-}\to {\mathrm{O}}_2+4{\mathrm{e}}^{-} \end{gathered}$$

(iii) When mercuric oxide is heated strongly, it decomposes to form mercury and liberates oxygen.

$$\begin{gathered} 2\mathrm{HgO}\underset{\mathrm{Decompose}}{\overset{\mathrm{Heat}}{\to }}\mathrm{Hg}+{\mathrm{O}}_2 \\ \mathrm{Mercuric}\mathrm{oxide}\mathrm{Mercury}\mathrm{Oxygen}\mathrm{gas} \end{gathered}$$ 2HgO −→−−−−DecomposeHeat 2Hg + 2