(i) The extraction of metals from their oxides can be carried out by using different reducing agents.
(ii) Consider the following reaction
\(\frac{2}{\mathrm{y}} \mathrm{M}_{\mathrm{x}} \mathrm{O}_{\mathrm{y}(\mathrm{s})} \rightarrow \frac{2 \mathrm{x}}{\mathrm{y}} \mathrm{M}_{(s)}+\mathrm{O}_{ 2(\mathrm{~g})}\)            (1)
(iii) The above reduction may be carried out with carbon. In this case the reducing agent carbon may be oxidized to either CO or CO₂
\(\mathrm{C}+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2(\mathrm{~g})}  \)                  (2)
\(2 \mathrm{C}+\mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{(\mathrm{g})} \)                (3)
(iv) If CO is used as a reducing agent
\(2 \mathrm{CO}+\mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2(\mathrm{~g})}\)           (4)
(v) A suitable reducing agent is selected based on the thermodynamics considerations.
(vi) We know that for a spontaneous reaction, the change in free energy (\(\triangle\)G) should be negative.
(vii) Therefore, thermodynamically, the reduction of metal oxide with a given reducing agent can occur if the free energy change for the coupled reaction is negative.
(viii) Hence, the reducing agent is selected in such a way that it provides a large negative \(\triangle\)G value for the coupled reaction.

i) Silica is an acidic flux which is mixed with Copper pyrites ore and is heated in a reverberatory furnace. The ferrous oxide formed from the ore is basic in nature and it combines with silica to form ferrous silicate. It is removed as slag.
\(\mathrm{FeO}_{(s)}+\mathrm{SiO}_{2(s)} \overset { \Delta }{ \longrightarrow } \mathrm{FeSiO}_{3(s)}\\ gangue \quad flux \quad \quad slag\)
ii) Aluminium oxide does not dissolve in water, but it dissolves in molten cryolite. This is an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.
\(\mathrm{Al}_{2} \mathrm{O}_{3} \overset { \Delta }{ \longrightarrow } 2 \mathrm{Al}^{3+}+3 \mathrm{O}^{2-}\)
iii) Van-Arkel method is based on the thermal decomposition of metal compounds which lead to the formation of pure metals. Zirconium can be purified by using this method. Zirconium metal is heated with iodine at a temperature of 550 K to form zirconium tetraiodide. (ZrI₄). The impurities are left behind
\(\mathrm{Zr}_{(\mathrm{s})}+2 \mathrm{I}_{2(\mathrm{~s})} \frac{550 \mathrm{~K}}{\mathrm{D}} \mathrm{ZrI}_{\text {t(vapour })}\)
The volatile (ZrI₄) on further heating around 1800 K, it gives pure zirconium.
\(\mathrm{ZrI}_{4 \text { (vapour) }} \frac{1800 \mathrm{~K}}{\mathrm{D}} \mathrm{Zr}_{(\mathrm{s})}+2 \mathrm{I}_{2} \)    
iv) In the extraction of lead from galena (PbS) by froth flotation process, if ZnS is present as impurity, Sodium cyanide is added to depresses the flotation property of ZnS. It forms a complex. Na₂[Zn(CN)₄] on the surface of zinc sulphide.

(i) Ellingham diagram is constructed based only on thermodynamic considerations. It gives information about the thermodynamic feasibility of a reaction. It does not tell anything about the rate of the reaction. More over, it does not give any idea about the possibility of other reactions that might be taking place.
(ii) The interpretation of \(\triangle\)G is based on the assumption that the reactants are in equilibrium with the product which is not always true.

1. The crude metal is refined by electrolysis. It is carried out in an electrolytic cell
Anode : Impure metal to be refined with dilute acid.
Cathode : Thin strips of pure metal
Electrolyte : Aqueous solution of the salts of the metal with dilute acid.
2. The metal dissolves from the anode, pass into the solution.
3. At the same amount of metal ions from the solution will be deposited at the cathode.
4. During electrolysis, the less electropositive impurities in the anode, settle down at the bottom and are removed as anode mud.
Example: Electrolytic refining of silver.
Cathode: Pure silver
Anode: lmpure silver rods
Electrolyte: Acidified aqueous solution of silver nitrate
5. When a current is passed through the electrodes the following reactions will take place
(a) Reaction at anode: \({ Ag }_{ (s) }\longrightarrow { Ag }^{ + }_{ (aq) }+{ 1e }^{ - }\)
(b) Reaction at cathode: \({ Ag }^{ + }_{ (aq) }+{ 1e }^{ - }\longrightarrow { Ag }_{ (s) }\)
6. During electrolysis, at anode silver loses electrons and form silver ions and the silver ions migrate towards the cathode and get discharged and deposited on the cathode.
7. Copper, Zinc etc can also be refined by this process.

1. Reduction of oxides of active metals such as sodium, potassium etc., by carbon is thermodynamically not feasible.
2. Such metals are extracted from their ores by using electrochemical methods.
3. In this technique, the metal salts are taken in a fused form or in solution form.
4. The metal ion present can be reduced by some suitable reducing agent or by electrolysis.
5. Gibbs free energy for the electrolysis process is given by
Here,
 \(\Delta\)G^o = -nFE^o
 \(\Delta\)G^o - Standard Gibb's free energy change
n - number of electrons involved,
F - Faraday,
E^o - Standard electrode potential
6. If E^o is positive then the \(\Delta\)G^o is negative and the reduction is spontaneous
7. Hence a redox reaction is planned in such a way that the e.m.f of the net redox reaction is positive.
8. When a more reactive metal is added to less reactive metal salt solution, the more reactive metal will go into the solution.
Example:
\({ Cu }_{ (s) }+2{ Ag }^{ + }_{ (aq) }\longrightarrow { Cu }^{ 2+ }_{ (aq) }+2{ Ag }_{ (s) }\)
\({ Cu }^{ 2+ }_{ (aq) }+{ Zn }_{ (s) }\longrightarrow { Cu }_{ \left( s \right) } +{ Zn }^{ 2+ }_{ (aq) }\)