WBBSE Class 10 Physical Science Notes Chapter 8.5 Metallurgy

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 8.5 Metallurgy can help students make connections between concepts.

Metallurgy Class 10 WBBSE Notes

Occurrence of metals : A few metals particularly noble metals (Au, Pt, Ag etc.) having least electropositive charader occur in free state. About 75% of the known elements are metals. Most of the metals are found in the combined state in nature as their compounds.

Minerals : The natural materials containing metals and their compounds associated with earthy and other impurities found under earth’s crust are called minarals.

Ores : The minerals from which the metals can be extracted conveniently and profitably. All ores are minerals but all minerals are not ores.

Metallurgy : It is a process of extracting metals from their ores.

Gangue or Matrix: They are the rocky and earthy impurities associated with the minerals.

Concentration of ore : It is the process of removal of gangue from the ore.

Flux: It is the substance which combines with gangue to form light and easiÍilusible material called slag.

Slag : It is the light and fusible material obtained by the combination of flux with gangue.

Calcination : It is the process of heating an ore in a limited supply of air or in absence of air at a temperature just below its melting point.

Roasting : It is the process of heating an ore in a limited supply of air or in absence of air at a temperature just below its melting point.

Extraction of metal : Different processes that are used for the extraction of pure metals from ores are called extraction of meials;

Alumimium (AI)

Symbol: Al; Valency : 3;
Atomic weight: 26-78
Atomic Number: 13,

Position in Periodic Table:
Period: 3, Group IIIA (13);
Electronic configuration : ls²2s²2p⁶3s²3p¹

Occurrence: Aluminium is not found in pure state. It occurs to the extent of 8% in earth’s crust in many silicate rocks and clays. It is the third most abundant element in the earth’s crust.

Important aluminium minerals are :

• Chief ore of aluminium : Chief ore of aluminium is bauxite (Al₂O₃-2H₂O).
• Mines : In India, large quantities of bauxite are available in Bihar, Jharkhand, Orissa, Andhra Pradesh, Madhya Pradesh, Rajasthan, Tamilnadu, Gujarat and Jammu-Kashmir. But large deposit of quality grade bauxite are found in Andhra Pradesh.
• Extraction of aluminium : Initially alumina is prepared from bauxite then after mixing with cryolite and fluosper aluminium is extracted by electrolysis at about 950°C
  
• The ore of aluminium (bauxite) is purified by Baeyer’s process, Hall’s process or Serpeck’s process depending upon the type of impurities present in it. Baeyer’s process or Hall’s process is used for ores containing oxides of iron as main impurity while Serpeck’s process is used for ores containing silica as main impurity.

Physical properties of Aluminium :

• It is silvery white metal and is very light, (sp.gr. = 21)
• It melts at 660°C and boils at 2270°C.
• It is a good conductor of heat and electricity.
• It is malleable and ductile.
• Atomic radius of aluminium is 125 pm.
• The ionisation enthalpies of Aluminium are 600 KJ mol^-1, 2427 KJ mol^-1 and 3568 KJ mol^-1
• Sum of the first three ionisation enthalpies being very high, aluminium forms covalent compounds.

Chemical Properties :

(i) Action on

• Dry air has no action on aluminium. In moist air, it forms a thin film of oxide on its surface.
• When heated strongly, it burns with a brilliant white light, producing aluminium oxide and little nitride.

(ii) Action of water : Pure water has no effect on the metal due to the presence film on the surface. Amalgamation with mercury prevents the protective oxide film. Amalgamated metal, therefore, can decompose even cold water. Commercial aluminium can be readily attacked by sea water. It decomposes boiling water, liberating hydrogen. 2Al + 6H₂O = 2Al(OH)₃ + 3H₂

(iii) Action of chlorine : when aluminium is heated gently with chlorine, it forms aluminium chloride.
2Al + 3Cl₂ = 2AlCl₃
A mixture of aluminium powder and iodine catches fire when a drop of water is added on it.

(iv) Action of acids: (a) With dilute sulphuric acid, hydrogen gas is evolved at a slow rate. In hot concentrated sulphuric acid, metal dissolves with the evolution of
2Al + 3H₂SO₄ (dilute) = Al₂(SO₄)₃ + 3H₂
2Al + 6H₂SO₄ (cone) = Al₂(SO₄)₃ + 3SO₂ + 6H₂O

(b) With dilute nitric acid, aluminium nitrate and ammonium nitrate are produced.
Action with carbon Sulphur :
8Al + 3OHNO₃ = 8Al(NO₃)₃ + 9H₂O + 3NH₄NO₃

(v) Action with carbon and sulphur :
Aluminium reacts with boiling caustic soda or caustic potash forming sodium aluminate or potassium aluminate respectively with the evolution of hydrogen gas.

(vi) Action of alkalls: Aluminium reacts with boiling caustic soda or caustic potash forming sodium aluminate or potassium aluminate respectively with the evolution of hydrogen gas.
2Al + 2NaOH + 2H₂O = 2NaAlO₂ + 3H₂↑
2M + 2KOH + 2H₂O = 2KAlO₂ + 3H₂↑
That is why, caustic soda is not boiled in aluminium pot.

(vii) Displacement reactions: Aluminium is strongly electropositve. Hence, it readily displaces less electropositive metals, such as-murcury, silver, gold etc.
2Al + 3HgCl₂ = 2AlCl₃ + 3Hg.

(viii) Peducing property: Due to its strong affinity of oxgen it acts as a strong reducing agent. It readily reduces certain metallic oxides to the metal.

These reactions are highly exothermic and they can be utlised for welding (Thermite welding) of metals.

Uses of Aluminium:
At present, use of aluminium is just after iron.

• Being a light material as also stable and resistance to water vapour it is used to prepare external structures of air-ships and motor cars.
• It is used in electric wire and electric equipments as it is a very good conductor of electricity.
• It forms many useful alloys used for different purposes. Alloys like dural­umin, magnelium bronze etc. and also in flash bub used in photography aluminium metals are used.
• Aluminium is used in thermit process. Due to its strong affinity for oxygen, it is used for the extraction of metals like Cr and Mn from their ores.
• Mixed with linseed oil, powdered aluminium is used as paint.
• Ammonal, a mixture of ammonium nitrate and aluminium powder, is used in explosive bombs.
• Aluminium power has the use in fireworks.
• Aluminum is used in the preparation of different utensils, chair, table and the packing over a cigarette, coffee, chocolate etc.

Artificial gem are produced by dropping powdered alumina mixed with little of other metallic oxides to obtain desired colour (e.g. 2-5% chromic oxide for artificial ruby). Sapphire is similary produced from alumina with addition of a little magnetic iron oxide and titanium oxide.

Foods having sour taste should not be preserved in aluminium foil, since fatty acid present in those types of foods react with aluminium foil producing salts which are very harmful to health.

Magnesium (Mg)

Symbol: Mg ; Valency: 2 ; Atomic weight: 24
Atomic Number: 12 :
Position in Periodic Table :
Period: 3; Group: IIA (2) :
Electronic Configuration : Is²2s²2p⁶3s²
Occurrence: Magnesium is not found in free state in nature.

Important magnesium minerals are :

Nature	Minerals
1. As carbonates	Magnesite : MgCO3 Dolomite : MgCO, CaCO
2. As chloride	Carnallite : MgCl2 . KCl . 6H2O
3. As sulphate	Kieserte : MgSO4 . H2O Kainite : MgSO4 – KCl- 3H2O Epsom Salt : MgSO4– 7H2O
4. As silicate	Asbestos: CaMg3 (SiO3)4

Chief ore: Magnesium is extracted from the ores magnesite and carnallite. Magnesium metal is also found in sea-water, chlorophyll and also in sping.

Mines : The chief ore of magnesium is carnallite. But carnallite is not available in India. It is imported from Germany, where it exists as deposits at stassfurt. Other important ores of magnesium are magnesite and dolomite which are abundantly available in Tamilnadu, Karnataka and in many parts of Bihar, Jharkhand, Orissa, West Bengal and Sikkim.

Extraction: Magnesium is prepared by:

• Electrolytic reduction of the fused magnesium chloride.
• Chemical reduction of MgO by carbon or ferro-silicon.

Physical properties of magnesium:

• Magnesium is a light, white metal with a bright lustre which tarnishes in moist air due to the deposition of a film of oxide.
• Soft, malleable, and ductile, it can be readily drawn into a wire of ribbon.

Chemical properties:
(i) Action with air: Mg does not react with dry air. If magnesium metal is left in moist air it gradually becomes dull and pale due to the formation of a layer of MgO. Magnesium metal when heated in presence of air it burns with bright white flame. Magnesium oxide and magnesium nitride are thus formed.
2Mg + O₂ = 2MgO ; 3Mg + N₂ = Mg₃N₂

(ii) Reaction with water (a) At ordinary temperature Mg metal does not react with water, (b) Heated Mg burns in presence of water vapour magnesium oxide and hydrogen are formed.
Mg + H₂O = MgO + H₂↑

(iii) Reaction with dilute nitric acid: It dissolves in dilute nitric acid, liberating hydrogen, but not in alkalis.
Mg + 2HNO₃ = Mg(NO₃)₂ + H₂↑

(iv) Mg acts as reducing agent. It is a powerful reducing agent; the heated metal reduces such stable oxides as silica, sodium oxide and potassium oxide. Ignited magnesium continues to burn in CO₂ depositing carbon.

(v) Reaction with chlorine Heated magnesium burns in chlorine and form magnesium chloride.
Mg + Cl₂ = MgCl₂

Uses of magnesium : It is used

• In flash light powders (magnesium powder mixed with potassium chlorate or barium peroxide) for photography, in military star shell, in light signals and in fire works.
• for the preparation of Grignerd reagent in organic chemistry and for reducing agent.
• In the production of light alloys, such as-duralumin, magnelium in the construction of airships and motor cars.
• In incendiary explosive (goop is an incendiary containing magnesium powder).
• In the extraction boron and silicon.

Zine (Zn)

Symbol : Zn ; Valency : 2; Atomic weight: 65.3
Atomic Number : 30;
Position in Periodic Table;
Period: 4, Group : IIB (12);
Electronic Configuration : ls²2s²2p⁶3s²3p⁶3d¹⁰4s²

Occurrence : Zinc does not occur free in nature. In the combined state, it occurs in the form of following minerals.

Nature	Minerals
1. As sulphide	Zinc blende : ZnS
2. As oxide Franklinite : ZnC	Zincite : ZnO,Fe2O3
3. As carbonate	Calamine : ZnCO3
4. As silicate	Willemite : Zn2SiO4

Chief ore: The most important source of zinc is zinc hiende, usually containing about 6% Zn.

Mines: Zinc blende is obtained from zawar at Udaipur (Rajasthan) in India. Calamine is obtained at smithsonite in the U.S.A.

Extraction: Zinc is extracted mostly from zinc blende. The zinc blende which invariably contains so me galena in concentrated by oil floating process. Zinc is obtained from the zinc concentrate either. (a) by the carbon reduction process (b) by the electrolytic process.

• Physical properties of zinc:
• It is a bluish white solid which melts at 420°C and boils at 920°C.
• Its density is 7-14 g/c.c.
• It is a good conductor of electricity.

Chemical properties of zinc :

(i) Action of air: It burns in air with a green flame, if strongly heated, forming white clouds of zinc oxide which settles in wooly flocks (philosopher’s wool) 2Zn + O₂ = ZnO

(ii) Action of water Pure zinc has no action of water. Impure zinc decomposes boiling water. Zn-Cu couple decomposes water producing hydrogen gas.
Zn + 2H₂O = ZnO + H₂↑

(iii) Action of chlorine and sulphur Zinc reacts with chlorine forming zinc choride with sulphur, zinc sulphide is formed.
Zn + Cl₂ = ZnCl₂
Zn + S = ZnS

(iv) Reactions with acids :
(a) With HCl : Zn + 2HCl (dilute) = ZnCl₂ + H₂↑
(b) With H₂SO₃ :
(i) Zn + H₂SO₄ (dilute) = ZnSO₄ + H₂↑
(ii) Zn + 2H₂SO₄ (cone.) = ZnSO₄ + SO₂ + 2H₂O
Action with alkalis:
Zinc dissolves in hot solutions of caustic soda and potash, yielding hydrogen and zincate.

(vi) Displacement of less electropositive metals :
When zinc is added to the salt solution of a less electropositive metal like copper, silver, the metal is displaced.
CuSO₄ + Zn = ZnSO₄ +Cu ↓
2AgNO₃ + Zn = Zn(NO₃)₂ + 2Ag ↓

Uses of zinc : It is used:

• For galvanisation of iron sheets because zinc is resistant to atmospheric corrosion due to the formation of basic carbonate on its surface.
• In the extraction of silver and gold by cyanide process.
• as a cathode in dry cells.
• zinc is used for the preparation white paint zinc oxide (ZnO).
• for the preparation of hydrogen in the laboratory.
• in the preparation of alloys such as brass, german silver, etc.

Iron (Fe):

Symbol: Fe ; Valency : 2, 3; Atomic weight: 55-85
Atomic number: 26 ;
Position in Periodic Table :
Period : 4, Group VIII(8);
Electronic Configuration : 1s² 2s²2p⁶3s²3p⁶3d⁶4s²

Occurrence : Iron is not obtained in free state. Next to aluminium, iron is the most abundant metal in the earth’s crust. Compounds of iron occur in the soil, in green plants and in haemoglobin (0-336% Fe) the red colouring matter of blood.

Meteorites sometimes consist of iron with (3 -30)% of Ni; because of its nickel content meteoric iron does not rust readily.

The chief minerals of iron are given below :

Nature	Minerals
1. As oxide Brown Haematite: Magnetite: Fe3O4	Red Haematite: Fe2O3 2Fe2O3. 3H2O (Limonite)
2. As sulphide	Iron pyrites: FeS2
3. As carbonate (Siderite)	Spathic iron ore: FeCO3

• Chief ore : Iron is extracted mainly from the ore Haematite an<-’ magnetite may be used.
• Extraction : Iron is extracted from its oxide and carbonate ores (burnt pyrites which is chiefly ferric oxide, is sometimes used) by reduction with carbon in a blast furnace.
• Mines : Rich deposits of good quality haematite are available in many parts of India, such as in Orissa, Bihar, West Bengal, Tamilnadu, Karnataka, Andhra Pradesh and Madhya Pradesh.

Physical properties of iron :

• Pure iron is silvery white lustrous metal resembling platinum in appearance. It can take high polish.
• It is malleable and ductile and good conductor of heat and electricity.
• It is relatively soft and possesses high tensile strength.
• It is the most magnetic of all metals but loses this property above 760°C.
• Iron melts at 1525°C, boils at 2450°C and its density is 7-86 g cm^-3.

Chemical properties :

(i) Action of water : Iron decomposes steam to liberate hydrogen. This reaction is utilized for the manufacture of hydrogen. 3Fe + 4H₂O = Fe₃O₄ + 4H₂↑

(ii) Action of moisture : When exposed to moist air, iron gets covered with a reddish yellow film. This is known as rust and the phenomenon is called rusting. The composition of rust is 2Fe₂O₃. 3₂O. Rusting is formed when iron reacts with oxygen and water vapour.

(iii) Action of water : Iron decomposes steam to liberate hydrogen. This reaction is utilized for the manufacture of hydrogen. 3Fe + 4H₂O = Fe₃O₄ + 4H₂↑

(iv) Action of halogens and sulphur

(v) Displacement of less electropositive metals: It displaces less electropos­itive metals like copper from their salts. CuSO₄ + Fe = FeSO₄ + Cu₄↓

(vi) Reaction with alkalis : It has no reaction with alkalis.

(vii) Action of acids :
(a) Fe + H₂SO₄ (dilute) = FeSO₄ + H↑
(b) Fe + 2HCl (dilute) = FeCl₂ + H₂↑
(c) 4Fe + 10HNO₃ (dilute) = 4Fe(NO₃)₂ + NH₄NO₃ + 3H₂O
(d) (i) Fe + 2H₂SO₄ (cone.) = FeSO₄ + SO₂ + 2H₂O
(ii) 2FeSO₄ + 2H₂SO₄ (cone.) = Fe₂(SO₄)₃ + 2H₂O + SO₂

(viii) Passivity of iron: Fairly strong nitric acid gives ferric nitrate and a mixture of oxides of nitrogen. However, cone., nitric acid makes iron passive i.e. it becomes chemically inert and does not react further.

Uses of iron :

• Iron is widely used for making beams, rafters, rods for building and for con­structing ships, submarines, rails and rail-wagons.
• It is also used for preparing nuts, bolts, screws, wires, covers of drains, rain water pipes and pipes for conveying drinking water etc.
• It is also used to make ordinary steel and alloy-steels.

Iron is classified according to quantity of carbon present:

(i) Cast iron : (2-4)% carbon and small amount of silica, Mn, R S etc are present in iron. use: (t is used for the manufacture of railings, drain pipes, radiators, gutters.

(ii) Wrought iron : Smallest quantity of carbon is present in it. Iron of this type contains (01- 015)% of carbon. use: It is used for the manufacture of nails, chair, anchors, horse shoes.

Steel : In steel (0-15- 1-5)% and small quantities of silicon, Mn are mixed with iron. use: It is used for the manufacture of car wheel springs razor blades, ma­chine parts, ships, opera­tion equipments, building structures and arms.

Copper (Cu)

Symbol: Cu; valency : 1, 2; Atomic weight: 63-5
Atomic number : 29 ;
Position in Periodic Table :
Period : 4, Group IB(ll) ;
Electronic Configuration : ls²2s²2p⁶3s²3p⁶3d¹⁰4s¹

Occurrence : Copper occurs in minute quantities in plants, particularly in green peas. It is present in the haemocyanin of blood cuttlefish, which acts like haemoglobin as an oxygen carrier. Copper helps in the formation of haemoglobin in the body. Lower organisms are very sensitive to copper salts and hence their use as fungicide, copper exists in small amount in free state in nature. The chief minerals are :

Nature	Minerals
(i) As oxide	Cuprite : Cu2O Malaconite : CuO
(ii) As sulphide	Chalcocite (copper glance): Cu2S Chalcopyrite (copper pyrites): Cu2SFe2S3
(iii) As carbonate	Malachite : CuCO3–Cu(OH)2 Azurite : 2CuCO3 Cu(OH)2
(iv) As chloride	Attacamite : CuCl2 . 3Cu(OH)2

Chief ore: Copper is mainly extracted from copper pyrities.

Mines: The chief copper-producing regions are : Montana, Ariz una, Canada, Japan, Russia, Germany, Cango, Spain and Chile. India is not rich in copper ore. In India, copper pyrites is available in small amounts in Singhbhum, Bihar, Tamilnadu, Karnataka, Uttar Pradesh, Sikkim, Orissa.

Extraction of copper from copper pyrities :

• crushing
• concentration by froth floatation
• roasting
• smelting with coke and sand in a blast furnace
• best merization of molten matte obtained from blast furnace to get blister copper.
• purification by electrolytic process.

Physical properties of copper :

• It is a reddish brown metal.
• It is highly malleable and ductile.
• Copper melts at 1083°C and boils at 2323°C
• Copper is a quite heavy metal (density 8.94g/cc )
• It is an extremely good conductor of heat and electricity.
• It readily forms alloys.

Chemical properties of copper :

(i) Action of air: (a) Dry air has no effect on copper metal. However, when it is exposed to damp air for a long time, a green coating of basic copper carbonate. CaCO.Cu(OH)₂ is formed on its surface.

(b) When heated with air, copper forms cupric and cuprous oxides.

(ii) Action of Water (and even stearia) has no action on copper. How ever, at very 1 temperatures (at white heat), it is attacked by steam when slight oxidation takes place.

(iii) Action of acids on copper:

(iv) Reaction with chlorine and sulphur:

(v) Reducing properties:

Displacement reactions: Copper displaces less electropositive metal like silver, gold, platinum and mercury from their salts.
Cu + 2AgNO₃ = Cu(NO₃)₂ + 2Ag
3Cu + 2AuCl₃ = 2Au + 3CuCl₂

(vi) Action with cyanides: It also dissolves in an aqueous solution of potassium cyanide yielding the complex, [Cu(CN)₄]^2-

(vii) Formation of colloidal copper : On striking an ore between two copper electrodes immersed in water, a dark red colloidal solution of copper is obtained.

Uses of copper :

• Due to its very high electrical conductivity it is largely used for telegraph and telephone, and also for electrical machinary.
• Copper is not attacked by air or water. So, it can be used for making household utensils, and water pipes.
• It is used in electroplating and electrotyping and in coinage.
• It is used in making a number of useful alloys.
  e.g. Brass: Cu (60-80)%, Zn (40-20%); Bronze: Cu (75-90)%, Sn (25-10)%

Alloy : It is homogeneous mixture (or, sometimes, a heterogeneous combination) of two or more metals, behaving as single metal in most of its physical properties.

Alloy is formed not only combination metals alone but also many non-metals viz. C, Si, S, P are added to prepare alloys.

Amalgam : If one of the component metals of an alloy be mercury, it is termed as amalgam, e.g. sodium amalgam (Na/Hg), aluminium amalgam (Al/Hg) etc.

Advantages of using alloys over pure metals :

• Increase of hardness: as in gold for ornaments, high speed steel etc. N.B. Pure gold is somewhat soft. It is made harder by alloying with a little amount of Cu or Ag.
• Increase in resistance to corrosion: as in stainless steel.
• Increase in strength: as in steel, duralumin etc.
• Increase of resistance to electricity: as in nichrome.
• Increase in fusibility or decrease in melting point : as in solders, fuse wires etc.
• Betterment of appearance . as in aluminium bronze, stainless steel etc.
• Improvement of casting property : as in type metal.
• Change in chemical activity : as in sodium amalgam, zinc amalgam etc.

Some important alloys :