The removal of non-metallic impurities, rocky materials and siliceous matter (called as gangue) from the ores is known as concentration of ores.
In this method crushed ore is allowed to dissolve in a suitable solvent to form a soluble metal salt or complex leaving the gangue undissolved is called leaching.
Crushed ore containing nickel, copper and cobalt is treated with aqueous ammonia under suitable pressure.
Ammonia selectively leaches these metals by forming their soluble complexes namely
The gangue left behind are iron (III) oxides / hydroxides and alumino silicate.
Sulphide ores ZnS, PbS can be leached with hot aqueous sulphuric acid.
In this process the insoluble sulphide is converted into soluble sulphate and elemental sulphur.
1.Conversion of the ore into metal oxide either by roasting or calcination.
2.Reduction of the metal oxide into metal.
• In the concentrated ore the metal exists in positive oxidation state and hence it is to be reduced to elemental state.
• From the principles of thermodynamics, the reduction of oxide is easier compared to the reduction of other compounds of metal.
• Hence before reduction the ore is first converted into metal oxide.
7. Write about the extraction of metal by the process of reduction by hydrogen.
This method can be applied to the oxides of the metals (Fe, Pb, Cu) which are less electropositive than hydrogen.
Ag2O(s) + H2(g)→ Ag(s) + H2O(l)↑
Nickel oxide is reduced to nickel by a mixture of hydrogen and carbon monoxide(water gas)
2NiO(s) + CO(g) + H2(g) → 2Ni(s) + CO2(g) + H2O(l)↑
8. What is auto reduction of metallic ores?
Simple roasting of some of the metallic ores give the crude metal.
Use of reducing agent is not necessary because of low thermal stability (eg) Cinnabar is roasted to give mercury.
HgS(s) + O2(g) → Hg(l) + SO2(g)↑
9. Write the applications of copper.
1. Copper is the first metal used by humans and extended use of its alloy bronze resulted in a new era, ‘Bronze age’.
2.Used for making coins and ornaments along with gold and other metals.
3.Copper and its alloys are used for making wires, water pipes and other electrical parts.
10. Write the applications of gold.
1.Gold is one of the expensive and precious metals.
2.Used for coinage and has been used as standard for monetary systems in some countries.
3.Extensively used in jewellery in its alloy form with copper.
4. Used in electroplating to cover other metals with a thin layer of gold, which are used in watches, artificial limb joints, cheap jewellery, dental fillings and electrical connectors.
5.Gold nanoparticles are used for increasing the efficiency of solar cells.
6.Used as a catalyst.
11. Write about alumino thermite process.
• In this method a metal oxide such as Cr2O3 is reduced to metal by aluminium.
• Metal oxide (Cr2O3) is mixed with aluminium powder in a fire clay crucible.The reduction process is initiated by ignition mixture of Magnesium power and barium peroxide.
BaO2+ Mg→BaO + MgO
• It is an exothermic process where heat is liberated.
• Temperature = 2400oC Heat liberated = 852kJmol-1.This heat initiate the reduction of Cr2O3 by Al.

12. What is refining process of a metal?
Metals extracted from its ore contains impurities such as unreacted oxide ore, other metals, non metals etc,. Removal of such impurities from crude metal is known as refining
process of a metal.
13. Write about distillation process of refining a metal?
This method is used for low boiling volatile metals like zinc and mercury. In this method impure metal is heated to evaporate and the vapours are condensed to get pure metal.
14. Write about liquation process of refining a metal?
• This method is used to remove the impurities with high melting points from metals having relatively low melting points.(eg) Tin, lead, mercury, bismuth.
• The impure metal is placed on sloping hearth of a reverberatory furnace and it is heated just above the melting point of the metal in the absence of air, the molten metal flows
down and impurities are left behind .The molten metal is collected and solidified.
15. Give example for the following
1. Frothing agent 2. Collector 3. Depressing agent
Frothing agent :Pine oil , eucalyptus oil
Collector :Sodium ethyl xanthate
Depressing agent :Sodium cyanide , sodium carbonate
16. What is cementation ?
Gold can be recovered by reacting the deoxygenated leached solution with Zinc. In this process Gold is reduced to its elemental state ( zero oxidation state) and the process is
called cementation

17. Why Fe, Pb , Cu are reduced by hydrogen ?
The oxides of metal Fe ,Pb , Cu having less electropositive character than hydrogen , these metal oxide can be reduced by hydrogen.

18. Write about gravity separation or hydraulic wash?
• Ore with high specific gravity is separated from gaugue with low specific gravity by simply washing with running water.
• Finely powdered ore is treated with rapidly flowing current of water.
• Lighter gaugue particles are washed away by the running water.
• This method is used for concentrating native ore such as gold and oxide ores such as haematite(Fe2O3), tin stone(SnO2).
19. Write about magnetic separation.
• This method is applicable to ferromagnetic ores.
• It is based on the difference in the magnetic properties of the ore and the impurities.
• Non-magnetic tin stone can be separated from the magnetic impurities wolframite.
• Similarly magnetic ores chromite, pyrolusite can be removed from non magnetic siliceous impurities.
• The crushed ore is poured to an electromagnetic separator with a belt moving over two rollers of which one is magnetic.
• Magnetic part of the ore is attached towards the magnet and falls as a heap close to the magnetic region.
• Non- magnetic part falls away from it.

20. Write about calcination.
• Calcination is the process in which the concentrated ore is strongly heated in the absence of air.
• During this process water of crystallisation present in the hydrated oxide escapes as moisture.
• Any organic matter present also get expelled leaving the ore porous.
• This method can also be carried out with a limited supply of air.
• During calcination of carbonate ore is decomposed to metal oxide and carbon dioxide is liberated.
21. Write about Van – Arkel method for refining zirconium/titanium?
• This method is based on the thermal decomposition of gaseous metal compounds to metals.(eg) Titanium and Zirconium.
• Impure titanium is heated in an evacuated vessel with iodine at 550K to form volatiletitanium tetra iodide.
• The impurities do not react with iodine.
• Volatile titanium tetraiodide is passed over a tungsten filament at 1800K.
• Titanium tetraiodide is decomposed to pure titanium which is deposited over the filament.Iodine is reused.

22. Write the applications of aluminium.
1. Used for making heat exchangers/sinks.
2. Used for making our day to day cooking vessels.
3. Used for making aluminium foils for packing, food items.
4. Alloys of aluminium with copper, manganese, magnesium, silicon are light weight and strong hence used in design of aeroplanes and other forms of transport.
5. Due to its high resistance to corrosion, it is used in the design of chemical reactors, medical equipment’s, refrigeration units and gas pipelines.
5. It is a good electrical conductor and cheap, hence used in electrical over head cables with steel core for strength.
23. Write the applications of iron.
1.Iron is one the most useful metals and its alloys are used everywhere including bridges, electricity pylons, bicycle chains, cutting tools and rifle barrels.
2.Cast iron is used to make pipes, valves and pump stoves etc.
3.Magnets can be made from iron , its alloys and compounds.
4.Important alloy of iron is stainless steel which is very resistant to corrosion.
5.It is used in architecture, bearings, cutlery, surgical instruments and jewellery.
6.Nickel steel is used for making cables, automobiles, and aeroplane parts.
24. Explain froth floatation method.
• This is used to concentrate sulphide ores such as galena (PbS) Zinc blende (ZnS) etc.
• Metallic ore particles preferentially wetted by oil can be separated from gangue.
• Crushed ore is mixed with water and a frothing agent like pine oil or eucalyptus oil.
• A small amount of sodium ethyl xanthate is added as a collector.
• A froth is formed by blowing air through the mixture.
• The collector molecules attach to the ore particles and make them water repellent.
• As a result ore particles wetted by the oil rise to the surface along with the froth.
• The froth is skimmed off and dried to recover the concentrated ore.
• Gangue particles preferentially wetted by water settle at the bottom.
• When sulphide ore contains other metal sulphides as impurities, depressing agents such as sodium cyanide, sodium carbonate etc. are used to selectively prevent other from coming to the froth
• For example , When impurities such as ZnS is present in Galena (PbS) , Sodium cyanide NaCN is added to depresses the flotation property of ZnS) by forming a layer of zinc complex Na2 [Zn(CN)4] on the surface of ZnS.
