Metals are required for a variety of purposes. For this we need their extraction from their ores. Ores mined from the earth are usually contaminated with many impurities which must be removed prior to the extraction of metals. The extraction of pure metal involves the following steps: (1) Concentration of ore (2) Extraction of the metal from the concentrated ore (3) Refining of the metal (a) Name an ore of Mercury and state the form in which Mercury is present in it. (b) What happens to zinc carbonate when it is heated strongly in a limited supply of air? (c) The reaction of a metal A with $\mathrm{Fe}_2\mathrm{O}_3$ is highly exothermic and is used to join railway tracks. (I) Identify the metal A and name the reaction taking place. (II) Write the chemical equation for the reaction of metal A with $\mathrm{Fe}_2\mathrm{O}_3$. OR (c) We cannot use carbon to obtain sodium from sodium oxide. Why? State the reactions taking place at cathode and anode during electrolytic reduction of sodium chloride.

(a) The ore of Mercury is Cinnabar. Mercury is present in it in the form of Mercury(II) sulphide ($\text{HgS}$).

(b) When zinc carbonate is heated strongly in a limited supply of air, it undergoes calcination to decompose into zinc oxide and carbon dioxide gas.

$$\text{ZnCO}_3\text{(s)} \xrightarrow{\text{Heat}} \text{ZnO(s)} + \text{CO}_2\text{(g)}$$

(c) (I) Metal A is Aluminium ($\text{Al}$). The reaction taking place is the Thermite reaction.

(II) The balanced chemical equation is:

$$\text{Fe}_2\text{O}_3\text{(s)} + 2\text{Al(s)} \rightarrow 2\text{Fe(l)} + \text{Al}_2\text{O}_3\text{(s)} + \text{Heat}$$

OR

(c) Sodium is a highly reactive metal and has a much higher affinity for oxygen than carbon does. Therefore, carbon cannot reduce sodium oxide to sodium metal.

During the electrolytic reduction of molten sodium chloride ($\text{NaCl}$), the reactions are:

• At Cathode (negative electrode):

$$\text{Na}^+ + \text{e}^- \rightarrow \text{Na(s)}$$

• At Anode (positive electrode):

$$2\text{Cl}^- \rightarrow \text{Cl}_2\text{(g)} + 2\text{e}^-$$