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a) Froth floatation method

b) It is used for removing gangue from suiphide ores. The mineral particles become wet by oils while the gangue particles by water. Finely powdered ore is agitated with water containing little frothing agent (e.g. pine oil) and froth stabilizers (e.g. cresols) by passing a forceful current of air. Heavier gangue particles are left to the bottom. The froth is skimmed off and then dried.

c)

• Stainless steel (Fe-74%, Cr-18%, Ni-8%)
• Nickel steel (Fe-96%, Ni-4%)

1. Cast iron :

• It is a form of iron obtained from pig iron.
• lt has 3% carbon content.

2. Pig iron :

• It is the least pure form of iron obtained directly from the blast furnace.
• It contains about 4% carbon and many impurities in smaller amount.  

1. Aluminium.

2. The alumina is dissolved in a mixture of molten cryolite. It is then electrolysed in a rectangular steel tank, with carbon lining, which serves as cathode. Anode is a set of thick carbon rods suspended from top into the fused Al₂O₃ . The temperature is maintained as 1200 K and 1310 K. Oxygen is evolved at anode which reacts with carbon of anode producing CO and CO₂ . Aluminium formed at the cathode gets collected.

1. Coper – Electrolytic refining 

Germanium – Zone refining

2. The copper in the furnace that contains Cu₂S and FeS is called copper matte. It is formed when copper ore is heated in reverberatory furnace after mixing with silica.

1. The statement is true. Choice of reducing agents depends strongly on factors like ΔH, ΔS, ΔG and T for the formation of the oxide to be reduced.

2. Electropositive metals like Al, K etc. can be extracted using electricity. Whereas CO is used for reducing haematite in the extraction of iron.

Down’s process.

Silica, SiO₂ .

Generally, metal oxides are basic in nature. To remove basic impurities an acidic flux like SiO₂ is used.

The entropy is higher if the metal is in liquid state than in solid state. The value of (∆S) of the reduction process is +ve when the metal formed is in liquid state the metal oxide being reduced is in solid state. The value of ∆G^Θ becomes more on -ve side and the reduction becomes easier.

The process of removal of impurities from the crude metal is called refining. The methods are :

• Distillation 
• Liquation
• Electrolytic refining 
• Zone refining 
• Van Arkel process 
• Mond’s process 
• Chromatographic methods 

Carbon is a poor reducing agent for sulphide ores whereas it is good reducing agent for oxide ores.

Metals occupying low positions in the electrochemical series can be extracted by hydrometallurgy because the metal ions (Mn⁺) of such metals can be easily reduced by treatment with some more electropositive metal. The metals occupying higher positions in the electrochemical series cannot be extracted by hydrometallurgy because the metal ions of such metals are difficult to be reduced.

Copper can be extracted by hydrometallurgy because it occupies quite lower position in the electrochemical series. On the other hand, zinc cannot be extracted by hydrometallurgy because it occupies higher position in the series and has large negative reduction potential.

It is a graph showing the variation of ∆_rG° for the formation of oxides with temperature. It helps in the choice of reducing agent in the reduction of oxides.

(a) ∆_f G° vs T

a) Ti – van Arkel method
Ni – Monds process

b) The crude metal is heated in an evacuated vessel with iodine. The metal iodide is formed. The metal iodide is decomposed on a tungsten filament, at about 1800 K. The pure metal is ’ deposited on the filament.

Mond process: In this method impure Ni is heated in a stream of carbon monoxide forming a volatile complex, nickel tetracarbonyl.

The carbonyl is subjected to higher temperature so that it is decomposed to give pure metal.

a) Zirconium (Zr) or Titanium (Ti)

b) i – d;

ii – c;

iii – a;

iv – b

i) Lime stone is added to blast furnace morder to remove acidic impurities (gangue) like silica (SiO₂). At high temperature, lime stone decomposed to form calcium oxide, which acts as a basic flux and removes acidic silica gaunge as calcium silicate slag.

CaCO₃  \(\overset{Heat}{\longrightarrow}\) CaO + CO₂

CaO + SiO₂ → CaSiO₃

ii) The following reaction take place at the higher temperature range (900 K – 1500 K) in the blast furnace:

C+O₂→CO₂,FeO+CO→Fe+CO₂

OR

i) The principal ore of Al is Bauxite (Al₂O₃ 2H₂O). In Hall-Heroult process for the electrolytic extration of Al, purified Al₂O₃ mixed with Na₃ALF₆ or CaF₂ acts as the electrolyte, steel cathode and graphite anode. The following reactions take place during electrolysis:

At cathode: Al₃(melt) + 3e → 4 Al(l)

At anode : The oxygen liberated at anode reacts with the carbon of anode producing CO and CO₂.

C(s) + O² (melt) → CO(g) + 2e

C(s) + 2O²(melt) → CO_2(g) + 4e^-

The overall reaction is

2Al₂O₃+3C→4Al+3CO₂

1. The mineral from which metal can be easily and economically extracted is called ore.

2. Leaching

3. Two examples for ores and their purification methods

• Hematite → Magnetic separation 
• Cinnabar → Froath floatation

Bauxite usually contains silica (SiO₂), iron oxides and titanium oxide (TiO₂) as impurities. The powdered ore is digested with a concentrated solution of NaOH at 473 – 523 K and 35 – 36 bar pressure. Al₂O₃ is leached out as sodium aluminate leaving the impurities behind. (SiO₂ is also leached as sodium silicate).

Al₂O₃(s) + 2NaOH_(aq) + 3H₂O(l) → 2Na[Al(OH)₄](aq)

The aluminate in solution is neutralised by passing CO₂ gas and hydrated Al₂O₃ is precipitated. At this stage, the solution is seeded with freshly prepared samples of hydrated Al₂O₃ to induce the precipitation.

2Na[Al(OH)₄](aq) + CO₂(g) → Al₂O₃ xH₂O + 2NaHCO₃(aq)

The sodium silicate remains in the solution and hydrated alumina is filtered, dried and heated to give back pure Al₂O₃.

AI₂O₃⋅xH₂O \(\overset{1470K}{\longrightarrow}\) Al₂O₃( s)+xH₂O(g)