Read the following passage and answer the questions given below: Most of metals occur in combined state in form of ores. Carbonate ores are converted into oxides by calcination and sulphide ores by roasting. Oxides are reduced with suitable reducing agent like carbon to get free metal. Highly reactive metals like Al, Mg are also used as reducing agents to obtain metal from their oxides. Most reactive metals are obtained by electrolytic reduction of their molten ores. Alloying is a very good method of improving the properties of a metal. We can get desired properties by this method. The electrical conductivity and melting point of an alloy is less than that of pure metals. (a) Why carbonate or sulphide ores are converted to oxides before extraction of metal from it? (b) Write a reaction in which Aluminium is used as a reducing agent to obtain metal from its oxide. (c) (i) How is copper obtained from its ore ($\mathrm{Cu_2S}$)? Give equations of the reactions. OR (c) (ii) (I) Why highly reactive metals cannot be obtained from their oxides by using carbon as a reducing agent? (II) Why solder, an alloy of lead and tin, is used for welding electrical wires together?

(a) Why carbonate/sulphide ores are converted to oxides before extraction:

It is easier to obtain a metal from its oxide than from its sulphide or carbonate ore. Sulphide ores are converted to oxides by roasting (heating strongly in excess air), and carbonate ores by calcination (heating strongly in limited air). The resulting oxides can then be reduced to the free metal using a suitable reducing agent such as carbon.

(b) Aluminium as a reducing agent (thermit reaction):

$$\mathrm{Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + Heat}$$

This highly exothermic displacement reaction (the thermit reaction) produces molten iron and is used to join railway tracks or cracked machine parts.

(c)(i) Extraction of copper from $\mathrm{Cu_2S}$:

Copper is low in the reactivity series, so its sulphide ore can be converted directly to the metal by heating in air (self-reduction):

$$\mathrm{2Cu_2S + 3O_2(g) \xrightarrow{Heat} 2Cu_2O(s) + 2SO_2(g)}$$

$$\mathrm{2Cu_2O + Cu_2S \xrightarrow{Heat} 6Cu(s) + SO_2(g)}$$

In the first step, some $\mathrm{Cu_2S}$ is oxidised to $\mathrm{Cu_2O}$ by heating in air; in the second step, the remaining $\mathrm{Cu_2S}$ reduces this $\mathrm{Cu_2O}$ to give metallic copper along with $\mathrm{SO_2}$.

OR (c)(ii):

(I) Highly reactive metals (like Na, Mg, Ca, Al) cannot be obtained from their oxides using carbon as the reducing agent because these metals have a greater affinity for oxygen than carbon does — carbon cannot displace them from their oxides. Such metals are instead obtained by electrolytic reduction of their molten compounds (e.g., molten chlorides or, for aluminium, molten oxide).

(II) Solder (an alloy of lead and tin) is used for welding electrical wires together because it has a low melting point. This allows it to melt easily at temperatures that do not damage the wire's insulation, flow into and bond the joint, and then solidify to form a strong electrical and mechanical connection.