Notes (Chapter # 16) Metals and their extraction

 

UNIT# 16

METALS AND THEIR EXTRACTION

 

Q#	Question	Year
Q# 01	What is alloy? Write names of two alloys of copper with their composition.	[2016]
Q# 02	Describe the extraction of iron from its Hematite ore in the blast furnace. Also write equation.	[2017] [2016] [2010]
Q# 03	How is Aluminum extracted from bauxite ore? Describe the process of giving balanced chemical equation. Also draw a labeled diagram of the electrolytic cell used in the manufacture of aluminum.	[2005]
Q# 04	Describe the Refining of Blister copper.	[2015] [2013]
Q# 05	Give chemical formulae of  Copper pyrite.	[2012]
Q# 06	Give chemical formulae of   Hematite.	[2013] [2012] [2010]
Q# 07	Give chemical formulae of   Iron pyrite.	[2012] [2010]
Q# 08	Give chemical formulae of   Bauxite.	[2013]
Q# 09	Give chemical formulae of   Copper pyrite.	[2013]
Q# 10	Define steel and name three methods of conversion of pig iron.	[2014]
Q# 11	Write the name and chemical formulae of two ores of copper and describe the process of Electrolytic refining of Blister copper. Also draw a labeled diagram	[2005]
Q# 12	Write the composition and one use of each of the following alloys ·        Brass ·        Bronze ·         Nichrome	2010

 

 

 

 

 

Q. Describe the chemical differentiations between metals and non-metals.

CHEMICAL DIFFERENTIATIONS BETWEEN METALS AND NON METALS

METALS	NON METALS
Metals have few electrons in its valence shell that is why they form ionic bond.	Non-metals have more electrons in valence shell so they have ability to form either ionic bond or covalent bond
Metals react with dilute acids to liberate Hydrogen gas	Non-metals do not react with dilute acids.
Metals are generally reducing agents as they are able to lose their valence electrons easily	Non-metals are generally oxidizing agent as they are able to gain valence electrons easily.
Metallic chlorides are usually non-volatile.	Non-metallic chlorides are usually volatile
They are electrolytes as they can be used in electrolysis.	They are non-electrolytes

 

Q. Define the following terms.

·        Minerals

·        Ores

·        Gangue particles

·        Metallurgy

·        Alloy

 

MINERALS

The combine forms of metals with less definite chemical impurities are known as Minerals.

 

ORES

Minerals which are found in contact with other materials are called ores.

 

GANGUE PARTICLES

The rocky materials present in ores are called gangue particles. 

 

METALLURGY

Metallurgy is the science of extraction of metals from their natural resources like ores.

 

 

ALLOY

A metal made by combining two or more metallic elements, especially to give greater strength or resistance to corrosion.

Q. Name the ores of:

·        Iron

·        Copper

·        Silicates

·        Fluorides

·        Sulphate

·        Oxides

 

ORES OF IRON
Hematite	Fe2O3
Magnetite	Fe3O4
Iron pyrite	FeS2
Siderite or Spathic	FeCO3
Limonite	Fe2O3. 3H2O

 

ORES OF COPPER
Coppery pyrite	CeFeS2
Cuprite	Cu­2O
Chalcocite	Cu2S
Malachite	CuCO3. Cu(OH)2
Azurite	2CuCO3.Cu(OH)2
Bornite	Cu2S.CuS.FeS

 

ORES OF SILICATES
Kaolin	Al2O3.2SiO2.2H2O
Potash Felspar	K2O.Al2O3.6 SiO2
Potash mica	K2O.3Al2O3.6SiO2.2H2O

 

FLOURIDE ORE
Cryolite	Na3AlF6

 

SULPHATE ORE
Alunite	K2SO4.Al2(SO4)3.4Al(OH)3

 

ORES OF OXIDES
Bauxite	Al2O3.nH2O
Gibbsite	Al(OH)3
Diaspore	Al2O3.H2O
Corundum	Al2O3

 

Q. Describe various techniques of Metallurgy.

TECHNIQUES OF METALLURGY

The important steps which are involved in this technique consists of the following steps.

·        Mining

·        Concentration of the ore

·        Reduction of the ore

·        Refining  of the metals

·        Mixing

·        Production of alloy

 

Q. Write down the preliminary operations involved in the metallurgy of metals from their ores?

MINING

Mining is usually carried out by the application of some heavy machineries which are used to drill out the ores.

 

CONCENTRATION [FROTH FLOATATION PROCESS]

The froth floatation process is involved in the mixing of finely divided ore with water and oil, to form froth which floats on the surface. The froth is washed and dried and is called concentrated Ore.

 

ROASTING

To remove the impurity [sulphur, carbon and other]; concentrated ore is roasted.

Sulphide and carbonated are eliminated as SO₂ and CO₂.

4CuFeS₂ + 5O₂       ⟶       2Cu₂S + 2FeO + 2FeS + 4SO₂

 

SMELTING

In this stage, the roasted ore is mixed with silica (SiO₂) and coke (C) by heating strongly until it melts. The remaining impurities from this process react with silica to form Slag of molten silicates. The slag is removed from the top of the molten mass and is discarded. The remaining molten mass left is called matte.

 

REDUCTION

Reduction process is applied to get the impurity free metal. The reduction can be brought by following three methods:

·        Chemical reduction

·        Thermal reduction

·        Electrolytic reduction

 

CHEMICAL REDUCTION

The less electro positive metals are obtained by reducing their oxides with coke or carbon mono oxide.

2ZnS + 3SO₂           ⟶       2ZnO + 2SO₂

ZnO + C                    ⟶       Zn + CO

 

THERMAL REDUCTION

Metals can be reduced by direct heating.

HgS + O₂                   ⟶       Hg + SO₂

 

ELECTROLYTIC REDUCTION

Electropositive metals are very stable and difficult to reduce chemically. Although, electrolytic reduction is expensive and is applied when chemical method is not acceptable.

2NaCl                        ⟶       2Na⁺ + 2Cl^-

 

Q. Describe the extraction of Iron.

EXTRACTON OF IRON

 

RAW MATERIALS

·        Haematite (Fe₂O₃)

·        Limonite (Fe₂O₃. 3H₂O)

 

REDUCTION OF OXIDES

Reduction of oxide is the first stage in the manufacture of iron. The process involves in the crushing of oxide ore to produce lumps. Such lumps are pre heated from hot gases from the blast furnace which removes water and other impurities.

 

 

OXIDATION OF COKE

In this stage, roasted iron ores are charged with coke and lime stone (CaCO₃), along with hot air is introduced into it from the small pipes.

C + O₂                                                                ⟶       CO₂                 ∆H = -394 KJ/ mol

CO₂ + C + ∆H                      ⟶       2CO                ∆H= +173 KJ/mol

The produced CO reduces the iron into free iron metal.

Fe₂O₃ + 3CO                        ⟶       2Fe + 3CO₂

The introduced lime stone decomposes at higher temperature and pressure to produce CaO and CO₂ which then treats with Silica (SiO₂) and aluminium oxide (Al₂O₃), present as impurities to form calcium silicates (CaSiO₃) and calcium alumniate (CaAl₂O₄)

CaCO₃                                               ⟶       CaO + CO₂

CaO + SiO₂                           ⟶       CaSiO₃

CaO + Al₂O₃                         ⟶       CaAl₂O₄

The mixture of CaSiO₃ and CaAl₂O₄ which remains molten at the furnace temperature is known as slag. Slag is a useful by product which is used in road and building making material, also for the production of cement.

 

Q. Describe the components and uses of the following types of iron.

 

1)   PIG IRON

The molten iron metal obtained from the blast furnace then it is cool down to solid blocks called Pig iron. It is quite impure.

 

Composition of Pig Iron
Component	Percentage
Iron	94-96%
Carbon	3.5-4%
Silica	1.2%
Sulphur	0.05--.1%
Phosphorous	0.05-1.0%
Manganese	0.05-1.0%

 

PROPERTIES OF PIG IRON

1.     It is low grade iron.

2.     It contains graphite and iron carbide (Fe₃C)

3.     It is hard and brittle.

2)   CAST IRON

A type of iron which is obtained when pig iron us re-melted and mixed with scrap steel and cooled in mold is called Cast iron.

 

PROPERTIES OF CAST IRON

1.     It is low grade iron.

2.     It can be molded in regular shapes.

3.     It is brittle and cannot be welded.

4.     The tensile strength of cast iron is very low.

 

3)   WROUGHT IRON

The type of iron which is purest is called Wrought iron. It is obtained by heating cast iron in a furnace with haematite (Fe₂O₃). During this process, carbon and sulphur are oxidized and are removed as CO₂ and SO₂ respectively.

2Fe₂O₃ + 3C            ⟶                   4Fe + 3CO₂

2Fe₂O₃ + 3S            ⟶                   4Fe + 3SO₂

           

PROPERTIES OF WROUGHT IRON

1.     It contains only 0.1% carbon.

2.     It is soft but very tough and malleable.

3.     It can easily be welded.

 

USES OF WROUGHT IRON

Wrought iron is used for making nails, chains, iron rods, sheets and horse shoes.

 

STEEL

Most of the pig iron is used for the production of Steel. About 90% of the pig iron is converted into steel.

Steel is an alloy of iron with carbon and other elements such as Mn, Cr, W, V etc.

There are three methods for manufacturing of steel.

a.      The basic Oxygen process

b.     Open Hearth process

c.      The Electric Arc process

 

 

 

 

Q. Describe the extraction of iron by Blast furnace.

EXTRACTING IRON FROM IRON ORE USING A BLAST FURNACE

Copper metal is usually extracted from its sulphide ore.

1.     Copper metal is mainly extracted from Copper pyrite which contains only 6% carbon. In this process, the pyrite ore is first purified by concentration. Forth floatation process is used for concentrating the ore.

2.     The enriched concentrated ore is then roasted on an open hearth furnace in air. Part of sulphur and other impurities like arsenic and antimony are burnt off and are removed as their oxides.

4CuFeS₂ + O₂          ⟶       2Cu₂S + 2FeO + 2 FeS + 4SO₂

3.     The roasted ore is then charged into blast furnace together with a little coke and silica (SiO₂)

2 FeS + 3O₂             ⟶       2 FeO + 2SO₂

FeO + SiO₂               ⟶       FeSiO₃

4.     The molten copper matte is carried out to a converter called Bessemer converter where it is treated with some silica by blowing hot air.

2FeS + 3O₂              ⟶       2FeO + 2SO₂

FeO + SiO₂               ⟶       FeSiO₃

2Cu₂S + 3O₂            ⟶       2Cu₂O + 2SO₂

2CuO + 2Cu₂S        ⟶       6Cu + SO₂

 

The molten copper is poured into sand molds. On cooling, thus solidified in sand molds and is known as Blister copper.

The blisters are produced during solidification on cooling due to the escape of dissolved SO₂ gas.

 

Q. Give the process of refining of Blister copper.

REFINING OF BLISTER COPPER

Blister copper is refined by electrolysis in which the blocks of blister copper are used as anodes and thin sheets of pure copper are used as cathode. The cathode plates or sheets are coated with graphite in order to remove depositing copper easily. The electrolyte is CuSO₄ acidified with H₂SO₄. The current of 1.3 volts is used for electrolysis which helps to deposit copper only on the cathode having impurities which are soluble and fall to the bottom of the cell as sludge or anode mud.

AT ANODE

Cu                   ⟶       Cu⁺² + 2e^-

AT CATHODE

Cu⁺² + 2e^-    ⟶       Cu

 

Q. What is mean by Forth Floatation process?

FORTH FLOATATION PROCESS

Forth flotation process is used for concentrating the ore. In this process, the ore is crushed and is mixed with water and pine oil or creosote oil. Air is blown into the mixture, oil forms froth with sulphide ore, which floats to the surface.

The gangue particles in ore, settle down. The sulphide are particles turn to go coated with oil and are carried to the surface along with froth. The froth along with the mineral particles is skimmed off and is dried to get concentrated ore.

Q. Describe the extraction of aluminium from Bauxite ore.

EXTRACTION OF ALUMINIUM FROM BAUXITE ORE

Aluminium is generally extracted from its bauxite ore (Al₂O₃.2H₂O). This extraction is commercially done by using process known as Hall-Herault process. The extraction of aluminium has following stages.

i.                    The bauxite ore contain major impurities of Fe₂O₃ and SiO₂.

In the first stage, bauxite ore is grinded and crushed to finely divided bauxite ore. It is then heated with concentrated solution of NaOH.

Al₂O₃.2H₂O + 2NaOH + 3H₂O         ⟶       2NaAl(OH)₄ + impurities

ii.                 The filtrate which is sodium aluminate is hydrolyzed with excess of water.

2NaAl₂O₂ + 4H₂O                    ⟶                   Al₂O₃.3H₂O + 2NaOH

OR

2NaAl(OH)₄                                                      2Al(OH)₃ + 2NaOH

iii.               Al₂O₃.3H₂O obtained is strongly heated up to 1500^oC to yield pure alumina (Al₂O₃) on dehydration.

Al₂O₃.3H₂O                                ⟶                   Al₂O₃ + 3H₂O

OR

2Al(OH)₃                                    ⟶                   Al₂O₃ + 3H₂O

iv.               The electrolysis of alumina is carried in a steel tank inside with graphite which act as cathode while anodes are the graphite rods dipped in the molten mixture of pure alumina dissolved CaF₂.

On passing electric current, the reaction that take place in the tank are as following.

AT CATHODE

4Al⁺³ + 12e^-                              ⟶                   4Al

AT ANODE

6O^-2                                              ⟶                   3O₂ + 12e^-

Q. Define Alloy. Describe the composition, properties and uses of following alloys.

·        Bronze

·        Brass

·        Nichrome

ALLOY

The mixture of two or more than two metals is called Alloy.

BRONZE

Bronze is common alloy of baser metal Copper (Cu).

It is composed of 90-95% Cu and 5-10% Tin.

	Bronze	Brass	Nichrome
Definition	It is the alloy of Copper.	It is the alloy of Copper.	It is an alloy of Iron.
Composition	90-95% Cu and 5-10% Tin	60-80% Cu and 20-40% Zn	60% Ni, 25% Fe, 15% Cr
Uses	Making coins, manufacture of metals and sulphates.	Making watches, nuts and bolts, rods, tubes, musical instruments, household utensils etc.	Resistant wire, heating elements like toasters, space heaters etc.
Properties	·        Shows great resistance to chemical attack. ·        It is strong alloy of copper. ·        It is quite attractive	·        It is stronger and more malleable than copper. ·        It is yellow in color ·        It has low melting point.	·        It is hard and elastic. ·        It is resistant to heat and corrosion. ·        It hasl also electrical resistance.

 

 

 

Choose the correct option for each of the following statement.

i.                   The formula of iron rust is:

a.      Fe₂O₃

b.     Fe₂O₃. H₂O

c.      Fe₂SO₄

d.     FeO

ii.                The most important ore of copper is:

a.      Cu₂O

b.     Cu₂S

c.      CeFeS₂

d.     CuCO₃.Cu(OH)₂

iii.             Chromite is found in pakitan at:

a.      Azad Kashmir

b.     Sindh

c.      Baluchistan

d.     Punjab

iv.              Iron metal obtained from blast furnace is impure and is called:

a.      Cast iron

b.     Pig iron

c.      Wrought iron

d.     Steel

v.                 Nichrome contains major percentage of:

a.      Cr

b.     Zn

c.      Ni

d.     Fe

vi.              The medal given to the third position holder is made up of:

a.      Bronze

b.     Brass

c.      Nichrome

            d.    Copper