Question

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?    [1]

(b) Write a reaction in which Aluminium is used as a reducing agent to obtain metal from its oxide.    [1]

(c) (i) How is copper obtained from its ore (Cu₂S)? Give equations of the reactions.    [2]

OR

(c) (ii) (I) Why highly reactive metals cannot be obtained from their oxides by using carbon as a reducing agent?    [1]

(II) Why solder, an alloy of lead and tin, is used for welding electrical wires together?    [1]

Answer 1

(a) Reducing a metal oxide to obtain the free metal is much easier than reducing a metal carbonate or metal sulphide. Therefore, we first convert ores into oxides through calcination (for carbonates) or roasting (for sulphides).

(b) Aluminium is used as a reducing agent in highly exothermic reactions known as Thermite reactions. For example, obtaining Iron from Iron (III) oxide:

\[\ce{Fe2O3_{(s)} + 2Al_{(s)} -> 2Fe_{(l)} + Al2O3_{(s)} + Heat}\]

(c) (i) Copper occurs as copper glance (Cu₂S). It is obtained by simply heating the ore in air.

Roasting: Some sulphide is converted to oxide.

\[\ce{2Cu2S + 3O2 ->[\Delta] 2Cu2O + 2SO2}\]

Self-reduction: When oxygen supply is stopped, the formed oxide reacts with the remaining sulphide.

\[\ce{2Cu2O + Cu2S ->[\Delta] 6Cu + SO2}\]

OR

(c) (ii) (I) Highly reactive metals (like Na, Mg, Al) have a very high affinity for oxygen. Carbon is a weaker reducing agent and cannot pull oxygen away from these metals. Therefore, they cannot be obtained from their oxides by using carbon as a reducing agent.

(II) Solder has a significantly lower melting point than the pure metals (lead and tin) it is made from. This allows it to melt quickly and bond electrical components without damaging them.