Principles of Metallurgical Operations

CHAPTER - 1

Principles of Metallurgical Operations(Sodium, Aluminium, Iron, Copper, Silver,

Zinc and Lead)

1. Occurrence of Metals.

A few metals particularly noble metals (e.g.

Ag, Au, Pt, etc.) having least electropositive

character occur in nature in free (native)

state. Sometimes lumps of almost pure

metals (nuggets) are also found. However,

most of the metals occur in nature as their

compounds. These metallic compounds

occur in the earth’s crust along with a

number of rocky and other impurities and are

known as minerals. The impurities present

are known as gangue or matrix.

Thus the compound of a metal found in

nature is called a mineral. A mineral may be

a single compound or a complex mixture.

Those minerals from which metal can be

economically extracted are called ores.

Thus all ores are minerals but all minerals

are not ores. For example, copper occurs in

nature in the form of several minerals like

cuprite (Cu2O), copper glance (Cu2S),

copper pyrites (CuFeS2) and malachite

[CuCO3. Cu (OH)2], copper pyrites is

considered as the most economical mineral

for the extraction of the metal. Hence copper

pyrites is the chief ore of copper.

1.1 Ores may be divided into

four groups.

(i) Native ores. These ores contain the

metal in free or metallic state, e.g.,

silver, gold and platinum. These are

usually found in the company of rock or

alluvial impurities like clay, sand, etc.

Sometimes lumps of almost pure

metals (nuggets) are also found.

(ii) Oxidised ores. These ores consist of

oxides or oxysalts (e.g., carbonates,

phosphates and silicates) of the metals.

Important oxide ores are haematite (Fe2O3),

bauxite (Al2O3.2H2O), tinstone or cassiterite

(SnO2), zincite (ZnO), pyrolusite (Mn2O3),

etc.

Important carbonate ores are limestone

(CaCO3), dolomite (CaCO3. MgCO3),

magnesite (MgCO3) , calamine (ZnCO3)malachite [CuCO3. Cu(OH)2], etc.

Important sulphate ores are gypsum

(CaSO4.2H2O), barytes (BaSO4) , and

anglesite (PbSO4).

(iii) Sulphurised ores. These ores consist

of sulphides of the metals like iron, lead,

mercury, copper, zinc, etc. Important

sulphide ores are iron pyrites (FeS2),

ga lena (PbS) , copper pyr i t ies

(CuFeS2), zinc blende (ZnS) and

cinnabar (HgS).

(iv) Halide ores. Metallic halides are very

few in nature. However, among the

halide ores, chlorides are the most

common. Important halide ores are

sodium chloride. (NaCl), horn silver

(AgCl), carnallite

AISECT TUTORIALS : CHEMISTRY : SET-10

(1)

(KCl.MgCl2.6H2O), fluorspar (CaF2)

and cryolite (AlF3.3NaF).

2.1 Ores of Few Important Metals.

Commercially important ores of few of the

metals are summarised below.

1. Magnesium

(i) Magnesite, MgCO3

(ii) Dolomite, MgCO3. CaCO3

(iii) Epsomite MgSO4. 7H2O

(Epsom salt),

(iv) Carnallite, MgCl2.KCl. 6H2O

(v) Asbestose, CaMg3 (SiO3)4

(vi) Talc Mg2 (Si2O5)2Mg(OH)2

2. Copper

(i) Copper pyrites CuFeS2 or Cu2S.

Fe2S3

(ii) Cuprite Cu2O

(Ruby copper)

(iii) Copper glance, Cu2S

(iv) Malachite, Cu(OH)2. CuCO3

(v) Azurite, Cu(OH)2 . 2CuCO3

3. Silver

(i) Argentite Ag2S

(Silver glance),

(ii) Horn silver, AgCl

(iii) Ruby silver 3 Ag2S Sb2S3

(Pyrargyrite),

4. Zinc

(i) Zinc blende, ZnS

(ii) Calamine, ZnCO3

(iii) Zincite ZnO

(Red zinc oxide),

(iv) Willemite Zn2SiO4

5. Aluminium

(i) Bauxite, Al2O3

(ii) Cryolite, Na3AIF3

(iii) Felspar, KAI Si3O8

(iv) Kaolinite, Al2O3.2 SiO2. 2H2O

(v) Mica, K2O.3Al2O3.6SiO2.

2H2O

(vi) Corundum, Al2O3

(vii) Diaspore, Al2O3.H2O

6. Tin

(i) Cassiterite SnO2

(Tin stone)

7. Lead

(i) Galena, PbS

(ii) Anglesite, PbSO4

(iii) Cerussite, PbCO3

(iv) Lanarkite, PbO. PbSO4

8. Iron

(i) Haematite Fe2O3

(Red haematite)

(ii) Limonite 2Fe2O3. 3H2O

(Brown haematite)

(iii) Magnetite, Fe3O4

(iv) Siderite FeCO3

(Spathic iron ore),

(v) Iron pyrites FeS2

(vi) Copper pyrites, CuFeS2

3. Metallurgy

Metallurgy is the branch of chemistry

which deals with the method of extraction

of metals from their ores and preparation

of alloys. The extraction of metals cannot be

carried out by any universal. method

because extraction of each metal requires

different procedure of extraction which

depends upon the nature and properties of

the metal. In general, noble metals such as

Au, Ag etc. are usually extracted by

amalgamation or cyanide process. Active

metals, such as Na, K, Ca, Mg, Al etc. are

usually obtained by electrolysis of their

chlorides, oxides or hydroxides. Heavy


(2)

metals, e.g., Cu, Zn. Fe, Pb, Sn etc. are

extracted by making use of roasting and

smelting methods.

4. REFRACTORY MATERIALS.

The substances which are capable of

withstanding very high temperatures without

melting or becoming soft are called

refractory materials. They are thus used in

the form of bricks for the internal lining of

furnaces, fluxes and hotter parts of

chimney and also for the lining of laddles

and converters.

The refractory materials are generally

metals, metal oxides or mixture of metal

oxides and sometimes carbides also. A

suitable refractory material : (a) Does not

melt or soften to an appreciable extent on

exposure to intense heat. (b) Resists sudden

variations of temperature. (c) Does not

crumble at high temperature and pressure.

(d) Can withstand the corrosive action of

slags which are rich in iron and other metallic

oxides.

Refractory materials are generally of

three types- Acidic, basic and neutral

refractories.

Acidic refractories are those which react with

bases. Examples are silica in the form of

ganister (a silicious rock containing 92%

SiO2) and 2.7% Al2O3, silicious sandstones

etc. Basic refractories are those which

react with acids. Examples are magnesite

(MgCO3) , do lomite (MgCO3.CaCO3),

l imestone (CaCO3) etc. Neutral

refractories are those which neither react

with acids nor with bases. Examples are

graphite, chromite etc. Some semi neutral

refractories are also known. For example,

fire clay consisting of 50-60% SiO2 and

20-35% Al2O3 (alumina) is an example of

semi neutral refractory material.

Graphite is one of the best material for the

manufacture of electrodes and crucibles

because it neither melts nor softens even at

the highest temperature of the furnace.

Metals such as platinum, thorium, tungsten

and their oxides are suitable for refractory

material. Silicon carbide or carborundum

(SiC) is used as refractory for special

purposes. Silica resists temperatures upto

1750oC, bauxite bricks upto 1800

oC,

alumina (Al2O3) upto 2000oC and magnesia

and chromite bricks upto 2200oC.

5. Various Type of Furnaces.

(i) Reverberatory furnace. In this type of

furnace, the charge is placed on the

hearth and heated by the flames

deflected from its concave roof. Air

supply can be controlled by vents and

direct blast.

In reverberatory furnace since the fuel

does not come in direct contact with the

charge, it can be used for reduction

as well as oxidation process. For

reduction the material is mixed with a

reducing agent like coke and heated

while for oxidation it is heated in a

current of air. The calcination and

roast ing are usual ly done in a

reverberatory furnace. It has been used

in case of copper, tin, lead and wrought

iron.

(ii) Blast furnace. It has double cup and

cone arrangement at the top to prevent

the exit of hot gases during the addition

of charge. The maximum temprature

attained is 1500oC near the tuyers. It

has three zones : zone of combustion

(bottom), zone of fusion (middle) and

zone of reduction (upper).

The temperature range decreases from

the bottom i.e. at the tuyers to the top.

In other words the zone of combustion


(3)

present at the bottom has the maximum

temperature of about 1500oC, while the

zone of reduction present at the top has

the minimum temperature of about

200-300oC.

The charge is introduced through a

hopper and a cup-and-cone

arrangement provided at the top. Air,

heated by combustion of waste gases,

is blown into the furnace under pressure

through 8-20 nozzles called tuyers.

Thus the downcoming charge meets

the upward moving hot air blast. Blast

furnaces are used for the extraction of

iron and copper.

(iii) Electric furnaces. In such furnaces

electrical energy is converted into heat

energy. These furnaces are largely

used where a cheap power is available

and very high temperatures are

required, and also for electrolytic

reduction.

(iv) Regenerative furnaces. In these

furnaces, the heat carried away by fuel

gases is not allowed to be wasted.

Refractory materials. Substances which

resist high temperatures and do not become

soft are called refractory materials. Acidic

refractories are SiO2 and gannister (SiO2 +

Al2O3); basic refractories are CaO and MgO;

neutral refractories are graphite, chromite

and carborundum (SiC).

Refractory material should not combine with

the ore or metal and must be able to protect

the furnace from high temperatures.

Fig. 1

6. ORE DRESSING

The process of removing gangue or matrix

(non-metallic and rocky materials, such as

quartz mica, felspars and other silicates)

from the meatel is called ore dressing, which

may be accomplished by the following

meathods.

(i) Hand Picking - The gross lumps of the

rocks may be removed from the ore by

simple hand picking and these are

then broken away with the hammer.

The stony impurties from the iron ore

haematite are removed by this

method.

(ii) Hydraulic Washing or Levigation -

This method is based on the difference

in the densities of the gangue and the

mineral particles. The ore after grinding,

is washed with a running stream of

water as a result of which the lighter

gangue particles are washed away and

the heavier ore particle settle down

rapidly. Gravity separation is usually

carried out by using. Wilfley table or

hydraulic clasifier.

(iii) Froath Floatation- This process is

especially suitable for the concentration

of low grade ores and sulphide ores.

The process is based on the different

wetting characteristics of the ore and

gangue particles with water and oil. The

ore is preferentially wetted by oil and the

gangue particles by water. The crushed

sulphide ore is treated with water to

form a pulp or paste or slurry. This is

introduced in a tank and water is added.

Now a frother or foaming agent such as

pine, oil, together with a little lime or

Na2CO3 is added to the floatation tank.

Now another substance, (called

col lec tor) such as potassium

ethylxanthate or amyl xanthate is

added. The contents of the tank are


(4)

agitated with a mechanical stirrer and

air, under pressure, is blown in. The ore

particles selectively become attached

to air bubbles produced in the aqueous

pulp of the ground ore and float on the

surface, from where they can be

skimmed off. The gangue particles,

which are strongly attracted to water, do

not attach themselves to foam bubbles

(not affected by the floatation reagent)

and hence sink to the bottom of the tank

and are separately withdrawn. The

froath is removed and suitably treated

to get concentrated ore. The ores like

copper pyrites (CuFeS2) galena

(PbS) and zinc blende (ZnS) are

purified by this method.

Fig. 2

(iv) Magnetic Concentration. This

process is used in case of

ferromagnetic ores such as iron,

tinstone, associated with wolfram and in

the processing of monazite sand etc.

Hence the process is used when the

mineral is attracted by a magnet, but not

the gangue.

(v) Electromagnetic Separation - This

method is used for separating ore from

magnetic impurities. The crushed or

powdered ore is dropped over a belt

moving over two rollers, one of which is

magnetic. As the mass passes over the

elect romagnet ic ro l ler , the

non-magnetic ore falls off and the

magnetic impurities are held and travel

round the magnetic roller so long as

they are attracted by it. When the

magnetic force of attraction disappears,

the impurities fall down into a separate

heap (collector). The tinstone ore is

separated from magnetic impurity,

wolframite (FeWO4) by this method.

(B) Extraction of Crude Metal - The

following chemical reactions are

commonly used.

(i) Calcination - Calcination is the process

in which the ore is subjected to the

action of heat at high temperature in the

absence of air but below its melting

point. The process of calcination is

carried out in the case of carbonate and

hydrated ores. As a result of calcination

(a) The moisture is removed (b) Gases

may be expelled (c) Volati le

impurities are removed (d) The mass

becomes porous (e) Thermal

decomposition of the ore takes

place. For example.

CaCO3 (limestone) -

→ CaO + CO2 ↑ ; MgCO3 ; (Magnesite)

MgO + CO2 ↑

MgCO3 CaCO3 (Dolomite) →

MgO + CaO + 2CO2 ↑

CuCO3.Cu(OH) 2 (Malachite) →

2CuO + H2O + CO2 ↑

ZnCO3 (Calamine) → ZnO + CO2 ↑ ;

2Fe2O3.3H2O (Limonite)

→ 2Fe2O3 + 3H2O ↑

The name calcination originated from the

ore calci te, which on thermal

decomposit ion gives quick l ime.

Calcination is usually carried out in

reverberatory furnace.


(5)

(ii) Roasting - In the process of roasting,

the ore either alone or with the addition

of suitable material, is subjected to the

action of heat in excess of air at

temperatures below its melting point.

Roasting is usually carried out in a

reverberatory furnace or in a blast

furnace. During roasting (a) Volatile

impurities like S, As, Sb etc. get

oxidised and escape out as volatile

gases SO2, As2O3 and Sb2O3 (b) The

sulphide ores de-compose to their

oxides evolving SO2 (c) The

moisture is removed (d) Mass

becomes porous and thus it can

easily be reduced. Roasting may be

of many types.

(a) Oxidising Roasting - In this type of

roasting S, As and Sb impurities are

removed in the form of their volatile

oxides as SO2, As2O3 and Sb2O3 etc.

due to combined action of heat and air.

The ore is simultaneously converted

into its oxides. This type of roasting is

used for copper pyrites, zinc blende

and lead ores (PbS) etc.

2ZnS + 3O2 → 2ZnO + 2SO2

2PbS + 3O2 → 2PbS + 2SO2

(b) Blast Roasting - In this, the oxidation

is carried out by a blast of hot air. This

process is applied for galena and

copper pyrites.

(c) Reducing Roasting - In this process,

the oxidised metal l ic mineral is

subjected to the action of reducing

agents (e.g., active hydrogen, carbon or

meta l l ic su lphides etc. ) at a

temperature below the point of fusion.

For example, in the extraction of Cu or

Pb, iron sulphide acts are reducing

agent.

2CuFeS2 + O2 → Cu2S + 2FeS + SO2 ;

2Cu2S + 3O2 → 2Cu2S + 2SO2

2FeS + 3O2 → 2FeO + 2SO2

(d) Sulphating Roasting - In this type of

roasting, the sulphide is not converted

to an oxide, but to a soluble sulphate.

For example, CuS to CuSO4 or ZnS to

ZnSO4. The resulting soluble salt is

then leached with water.

PbS + 2O2 → PbSO4 ; CuS + 2O2 → CuSO4 ;

ZnS + 2O2 → znSO4

(e) Chlorodising Roasting - In th is

process, the metal or its ore is

converted into a chloride by heating the

ores with NaCl in presence of air. For

example,

Ag2S + 2NaCl → 2AgCl + Na2S

AgCl + 2Hg → AgHg + HgCl

(iii) Smelting - It is the process used for all

operat ions where the metal is

separated by fusion from the ore. The

process of smelting is that in which ore

is melted with a flux and often with a

reducing agent, and it involves,

calcination, roasting and reduction. In

general, the process of separation of a

metal or its sulphide mixture from its ore

is fused state is called smelting.

Smelting is generally carried out in a

blast furnace and high temperature is

produced by buring coal or by using

electric energy.

In smelting, the roasted or calcined ore

is mixed with coke and then heated in a

furnace. As a result, carbon and CO

produced by the incomplete

combustion of carbon reduce the oxide

to the metal. For example, in the

extraction of iron, haematite ore

(Fe2O3) is smelted with coke and


(6)

l imestone ( f lux) . As a result of

reduction, iron is obtained in fused or

molten state.

Fe2O3 + 3C → 2Fe + 3CO

Fe2O3 + 3CO → 2Fe + 3CO2

CaCO3 → CaO + CO2

CaO + SiO2 → CaSiO3

Flux Gangue Slag

Similarly, in the extraction of copper from

copper pyrites, the ore is mixed with coke

and heated in blast furnace (smelted).

Infusible impurity FeO is converted to

FeSiO3 (slag) and is removed. A mixture

containing sulphide of copper and iron,

called matte is formed in the molten state.

Other exmple -

FeO + SiO2 → FeSiO3

Gangue Flux Slag

ZnO + C → Zn + CO ; SnO2 + 2C → Sn + 2CO

MnO2 + 2C → Mn + 2CO

(iv) Reduction - Extraction of metals from

their ore generally means reduction. It

can be carried out in a number of ways.

(a) Reduction with Hydrogen - The

oxides of certain metals such as WO3,

NiO, Co2O3, In2O3 may be conveniently

reduced by means of hydrogen to the

corresponding metal.

In2O3 + 3H2 → 2In + 3H2O

Co2O3 + 6H → 3H2O

NiO + 2H → Ni + H2O

WO3 + 6H → 3H2O + W

This method is suitable for metals which are

heavier than manganese.

(b) Reduction with Magnesium -

Reduction of an oxide of a metal can

also be carried out by means of

magnesium.

Rb2O3 + 3Mg → 3MgO + 2Rb

(c) Reduction with Coke or Carbon

Monoxide - The reduction of an oxide

ore using carbon (coke) or CO is a clean

cut method. The calcined or roasted ore

is mixed with coke and heated in a

suitable furnace. Carbon and CO

(formed by incomplete combustion of

carbon) reduce the oxide to the metal.

For example,

(1) SnO2 + 2C → Sn + 2CO

(2) Fe2O3 + 3CO → 2Fe + 3CO2

(3) CaCO3 → CaO + CO2

Flux

(4) ZnO + C → Zn + CO

(5) FeO + CO → Fe + CO2

(6) CaO + SiO2 → CaSiO3

Flux Impurity Slag

(1) The concentrated cassiterite (SnO2) is

reduced to metallic tin by heating with coke

in a reverberatory or blast furnace. (2) The

oxide of zinc is reduced by carbon to metallic

zinc. (3) The oxides of iron are reduced to

spongy iron by CO. (4) Same as (3). (5) Flux

limestone is decomposed into CaO and CO2

and in the middle of the furnace at about

1275 K, slag is formed. (6) In the lower part

of the blast furnace at 1575 K, the spongy

iron undergoes melting and sinks at the

bottom and forms a layer below the slag. It

is removed periodically and called pig iron

or cast iron and contains about 5%

carbon.

(d) Reduction by Heating In Air - Metals

whose oxides are unstable towards

heat (e.g., less active metals such as

Hg, Pb, Cu Sb etc.) are extracted by air

reduction. For example, roasting of

sulphide or of mercury (cinnabar) yields

the metal and not the oxide. Mercury


(7)

vapours are allowed to condense the

condensing chamber.

2HgS + 3O2 → 2HgO + 2SO2 ; 2HgO → 2Hg + O2

2HgO + HgS → 3Hg + SO2

Similarly, self reduction takes place in

the extraction of copper from sulphide

ore.

Cu2S + 2Cu2O → 6Cu + SO2

(e) Reduction by Aluminium - Certain

metal oxides, such as Cr2O3, Mn3O4

etc. cannot be reduced effectively with

carbon or carbon monoxide. In such

cases aluminium is used as reducing

agent because Al is more

electropositive than Cr and Mn. The

oxides of all refractory metals are

commercially reduced by aluminium

and the process is known as

Goldschmidt alumino thermite

process. A mixture of iron oxide

(Fe2O3) and aluminium powder in the

ratio of 3 : 1 is called thermite. The

thermite is taken in a graphite crucible

and covered wi th a mixture of

a luminium powder and bar ium

peroxide. A piece of magnesium ribbon

is placed in the mixture. When the

ribbon is lighted, the ignition mixture

catches fire and burns. The reaction is

higly exothermic. The much heat is

produced, which is sufficient to melt the

metal. This process is called thermite

welding in which iron oxide is reduced

by aluminium.

Fe2O3 + 2Al → Al 2O3 + 2Fe + 185 k.cals (3000º C)

Fe is obtained in molten state, because

the reaction is exothermic, Similarly.

Cr2O3 + 2Al → Al2O3 + 2Cr + Heat ;

3Mn3O4 + 8Al → 4Al2O3 + 9Mn + Heat

Coke can not be used for extracting

the above metals because of the

possibility of formation of their

carbides. Aluminothermic process is

used for welding together the broken

pieces of rails, machinery, parts of ships

etc., without removing them from their

position.

(f) Auto Reduction Method - This method

does not involve any addit ional

reducing method and similar to

reduction by heating in air. In this

method, sulphide is heated in air until a

part is converted into oxide. On further

heating in the air, the unchanged

sulphide reduces the oxide to metal. For

example,

2PbS + 3O2 → 2PbO + 2SO2

2PbO + PbS → 3Pb + SO2

(g) Reduction with Na or Ca - Certain

metal halides are also reduced with

Na or Ca in a closed vessel by heating.

TiCl4 + 4Na → Ti + 4NaCl

(h) Reduction with Silicon, Calcium

carbide etc. - For example,

MnO. FeO + Si + FeO → MnSiO3 + 2Fe ;

MgCl2 + CaC2 → Mg + 2C + CaCl2

(i) Reduction with Water Gas

(CO + H2) − Both CO and H2 present in

water gas act as reducing agents. For

example,

NiO + CO → Ni + CO2 ;

NiO + H2 → Ni + H2O

(j) Reduction of Complex Salts - Metals,

like gold, silver etc. can be precipitated

from the complex salt solutions by more

electropositive zinc metal.

2NaAg(CN) 2 + Zn → Na2Zn(CN) 4 + 2Ag ;

2KAu(CN) 2 + Zn → K2Zn(CN) 4 + 2Au

Metals such as Ti, Zr, Ta etc. are

obtained by reducing their complex

salts with alkali metals or Al.


(8)

K2TiF6 + 4K → 6KF + Ti ;

K2ZrF6 + 2Al → 2AlF3 + 2K + Zr

(k) Amalgamation Process - This

process consists of formation of an

amalgam of the crushed ore with

mercury. The metal amalgam thus

formed is distilled to get the metal and

mercury vapours are condensed and

recovered. The process is usually

employed in the extraction of noble

metals, like gold, silver etc. Some

amalgams, such as sodium amalgam

and zinc amalgam have also been used

for the separation of metals from their

solutions. For example.

2Ti3+ + 3Zn ⁄ Hg → 3Zn2+ + 2Ti ⁄ Hg;

2In3+ + 3zn ⁄ Hg → 3zn2+ + 2In ⁄ Hg

In fact, above reactions are known as

displacement reactions, in which one

metal is displaced by the other in the

amalgam. A metal can be displaced

from its solution by another whose

posit ion is higher than it in the

electrochemical series. Usually a more

expensive metal is displaced from its

solution by a cheap metal.

For example, in the electro refining of

zinc, the liquid in the vats is rich in Cd.

This metal can be recovered by

precipitating it by adding zinc.

Cd2+ + Zn → Zn2+ + Cd

Similarly, the sulphide ore with low

copper content, when exposed to air,

copper sulphide is formed which is

leached with excess of water. The scrap

iron is then added to the leached

solution to precipitate Cu.

Cu2+ + Fe → Cu + Fe2+

(1) Electrolytic Reduction - Chemically

active and highly electropositive

elements such as alkali metals and

alkaline earth metals and metals with

high negative oxidation potentials can

not be obtained by above chemical

methods. These metals can also not be

obtained by reducing their oxides, with

carbon, because oxides of these metals

are very stable and have to the heated

very strongly with carbon to reduce

them to metals. Moreover, they are

expected to form metal carbides with

carbon at such a higher temperature.

These metals are, therefore, extracted

by electrolytic reduction.

Alkali metals, usually occur in nature as

chlorides e.g. NaCl, MgCl2.KCl.6H2O

(carnallite). Calcium, strontium and

barium (alkaline earth metals) occur as

carbonates, which can readily be

converted into the halides. Metals such

as Li, Na, K, Rb, Cs, Ca, Sr, Ba etc. are

best obtained by electrolysis of their

fused salts (chlorides). In general,

electrolytic reduction is carried out by

the electrolysis of fused salts (such as

chlorides or hydroxides) under an inert

atmosphere using a cathode and anode

separated by a diaphragm in order to

avoid recombination of the products

formed at the anode and cathode.

For example, electrolysis of fused

sodium chloride using iron cathode and

graphite anode gives sodium metal.

NaCl ⇒ Na+ + Cl−

At cathode Na+ + e− → Na

At Anode 2Cl− − 2e− → Cl2

Similarly, magnesium is prepared by

the electrolysis of fused carnallite.

MgCl2 ⇒ . Mg2+ + 2Cl−

At cathode Mg2+ + 2e− → Mg


(9)

At Anode 2Cl− − 2e− → Cl2

Aluminium is obta ined by the

electrolysis of fused aluminium oxide.

Since fused aluminium oxide (alumina)

is not an electrolyte, it is made an

electrolyte by dissolving in fused

cryolite and then electrolysed using

carbon electrodes. Molten aluminium

collects at the cathode.

2Al2O3 → 4Al + 3O2

(C) Purification of Metals- A metal

obtained by the above methods is not

pure. Hence the metal obtained by

above methods require adequate

refining method, however, depends

upon the use to which a metal has to be

put.

(A) PHYSICAL METHODS

(i) Fusion Method - This method is

especially employed when the metal is

associated with adsorbed gases. For

example, fusion method is used to

remove dissolved oxygen from silver

and dissolved SO2 gas from copper

metal.

(ii) Liquation - This method is used when

the melting point of metal is less than

that of impurities. For example, zinc is

separated from lead by liquation. The

impure lead is heated on the sloping

hearth of a furnace, when lead melts at

a much lower temperature than many of

the impurities and flows down the slope.

The impurities remain sticking to the

hearth at the temperature which is

slightly greater than the m.p. of lead.

Hg, Sn, Bi etc. are also purified by

liquation.

(iii) Distillation - Low boiling point metals,

such as Hg, Cd and Zn (volatile metal)

etc. are refined by distillation method.

The process consists in heating the

impure metal in a retort as a result of

which pure metal distils over and

col lects in the receiver, whi le

non-volatile impurities are left behind.

The volatile compounds are further

separated by distillation to get the pure

metal.

(iv) Fractional Crystallisation - This is

another method of purification of

metals. For example, the method has

been used for the separation of

p lat inum and i r id ium through

ammonium hexachloroplatinate and

irridate.

(v) Cage-Zone Melting Technique- This

method is capable of reducing the

concentration of impurities to less than

one part per billion parts and is based

on the principle that an impure metal on

solidification will deposit crystals of the

pure metal and the impurities will be left

behind in the molten part of the metal.

Ge, Si, Ga etc. used as semi conductors

are refined by this method.

(vi) Vacuum Arc Sublimation Method -

This method consists in compressing

the impure metal to an electrode. The

electrode is then allowed to melt

progressively under vacuum in an

electric furnace. As a result, volatile

impurities are given off. The molten

metal is chilled in an externally cooled

copper crucible when an ingot of pure

metal is obtained. Refractory metals

such as Te, Zr, Mo etc. are refined by

this this method.

(B) CHEMICAL METHODS

(i) Pyrometallurgical Oxidation - In this

process impurities are oxidised in a

suitable manner. The oxidation may be


(10)

carried out by poling or farnace refining,

cupellation or electrolytic refining.

(a) Poling or Furnace Refining -

Impurities of reducible oxides from the

metals are removed by poling. For

example, blister copper containing

traces of cuprous oxide as impurity is

refined by melting the impure metal on

the hearth of a reverberatory furnace.

The melt is stirred with green logs of

wood. As a result, cuprous oxide is

reduced to copper metal by the

hydrocarbons produced from the green

wood and reducing gases, such as

SO2, As2O3 etc. are given off. The

reoxidation of copper metal by air is

prevented by covering the molten

copper surface with a layer of charcoal

powder. Tin is also refined by poling.

(b) Cupellation - This method is used to

purify silver containing lead as impurity

and depends upon the selective

oxidation of lead over silver. The impure

silver is smelted in a cupel made of

bone ash in a blast of air in a

reverberatory furnace. The lead is

oxidised to lead oxide. (PbO, litharge)

which is partly blown away from the

crucible by blast of air. The remaining

part melts and is absorbed by the bone

ash cupel. The completion of the

purification process is indicated by a

flash produced by the pure molten silver

in the cupel.

(c) Electrolytic Refining - This is one of

the most convenient and important

method of refining and gives a metal of

high purity. This method is applicable to

many metals such as Cu, Ag, Pb, Au,

Ni, Sn, Zn etc. The blocks of impure

metal form the anode and thin sheets of

metal form the cathode. A solution of a

salt of the metal is taken as an

electrolyte. On passing an electric

current through the solution pure metal

dissolves from the oxidation of anode.

The insoluble impurities either dissolve

in the electrolyte or fall at the bottom

and collect as anode mud.

For example, in the refining of copper,

impurities like Fe and Zn dissolve in the

electrolyte, while Au, Ag and Pt are left

behind as anode mud.

(d) Thermal Decomposition Methods -

Thermal methods include methods as

carbonyl method, decomposition of

hydrides etc. The carbonyl method is

used for the refining of metals like Ni

and Fe. For example, in case of nickel,

the impure metal is heated with CO. The

nickel carbonyl thus formed is then

decomposed (after distilling off the

impurities) to get pure nickel metal and

CO. The process is known as Mond’s

process.

Ni + 4CO → Ni(CO) 4 → Ni + 4CO

7. Extraction of Iron

Iron occurs in the free state as meteorites

which also contain 20 to 30% nickel. In the

combined state, iron occurs in the following

minerals-

Magnetite. Fe3O4

Haematite. Fe2O3

Limonite. 3Fe2O3 . 3H2O

Spathic iron ore. Fe Co3

Iron pyrites, FeS2

Copper pyrites, CuFeS2

Iron and tin may be extracted by the carbon

reduction method.

Extraction : Iron is extracted from its

pr inc ipal ore, haemati te , After the

preliminary washing, concentration and


(11)

roasting, the ore is smelted in the presence

of coke and limestone in a blast furnace.

Roasted ore (8 parts) with desulphurized

coke (4 parts) and limestone pieces (1 part)

is fed into the blast furnace from the top.

Preheated a ir is blown in through

water-jacketed pipes called tuyeres fixed in

the lower part of the furnace. There is a

temperature gradient as we move from the

bottom (temperature about 2000 K) of the

blast furnace. The blast furnace may be

broadly divided into three main parts as

described in the following-

(1) Zone of fusion - The lower portion where

coke burns and produce carbon dioxide and

a lot of heating is known as zone of fusion.

C + O2 → CO2; ∆H = − 406 kJ mol−1

Here the temperature is about 1775 K. A little

above this, where temperature is about 1475

K - 1575 K, iron coming from above melts.

(2) Zone of heat absorption - The middle

portion (temperature 1075 K-1275 K), CO2

rising up is reduced to CO w ith the

absorption of heat.

CO2 + C → 2CO; ∆H = 163 kJ mol−1

Fig.3

In this portion, limestone coming from above

is decomposed and the resultant lime (CaO)

which acts as flux, combines with silica

(present as impurity, gangue) to form

calcium silicate (fusible slag).

CaCO3 → CaO + CO2

CaO + SiO2 → CaSiO3

(3) Zone of reduction - The upper portion

(675 K-975 K) where iron oxide is

reduced to spongy iron by carbon

monoxide rising up the furnace.

Fe2O3 + 3CO → 2Fe + 3CO2

The reduction is believed to take place

in stage :

3Fe2O3 + CO → 2Fe3O4 + CO2

Fe3O4 + CO → 3FeO + CO2

FeO + CO → Fe + CO2

At the bottom of the furnace the molten iron

sinks down while above this floats the fusible

slag which protects the molten iron from

oxidation. These two can be removed from

different holes. Waste gases escaping at the

top consists of about 30% CO, 10% CO2 and

the rest nitrogen.

Iron obtained from the blast furnace is known

as pig iron.

Pig iron contains about 2 - 5% carbon as well

as other impurities (usually Si, Mn, S and P).

Pig iron is converted into cast iron by

remelting in a vertical furnace heated by

coke. Cast iron expands on solidification and

is used for casting various articles. Wrought

iron, which is the purest form of iron can be

obta ined by heat ing cast i ron in a

reverberatory furnace lined with iron oxide.

Wrought iron contains about 0.2% carbon.

8. Extraction of Copper.

Copper occurs in the native state as well as

in the compounds form. The natural ores of

copper are.

Copper pyrites, CuFeS2

Malachite, Cu (OH)2 .CuCO3


(12)

Cuprite or ruby copper, Cu2O

Azurite, Cu(OH)2 2CuCO3

Copper glance, Cu2S

Copper and lead may be extracted by

Self-reduction method.

Extraction : Copper is mainly extracted from

copper pyrites. After the concentration of its

ore froth flotation process, the ore is roasted

in a current of air to remove arsenic,

antimony and much of sulphur. The

reactions occurring are.

(i) 2CuFeS2 + O2 → Cu2S + 2FeS + SO2 ↑

(major reaction)

(ii) 2Cu2S + 3O2 → 2Cu2O + 2SO2

(iii) 2FeS + 3O2 → 2FeO + 2SO2

(minor reaction)

The ore is then mixed with a little coke and

sand and smelted in a water-jacketed blast

furnace. The minor reactions that occurred

during roasting continue here. Ferrous oxide

combines with sand to form a fusible slag.

Cuprous oxide formed combines with

ferrous sulphide to give ferrous oxide and

cuprous sulphide. This is because iron has

more affinity for oxygen than copper.

(iv) FeO + SiO2 → FeSiO3

(v) Cu2O + FeS → Cu2S + FeO

Molten mass collected from the bottom of

furnace contains largely cuprous sulphide

and a little ferrous sulphide. This molten

mass is known as matte.

Fig. 4

The molten matte is finally transferred to

bessemer converter. A blast of sand and air

is blown in the converter through tuyeres

which are situated a little above the bottom.

This causes removal of S and As as oxides

and ferrous oxide as slag [reaction (iv)]. At

the same time Cu2S is oxidized mostly into

Cu2O [reaction (ii)] and partly into CuO and

CuSO4. All these react with Cu2S giving

copper. The reactions are.

2Cu2S + 3O2 → 2Cu2O + 2SO2 ↑

2Cu2S + 5O2 → 2CuSO4 + 2CuO

2Cu2O + Cu2S → 6Cu + SO2 ↑

CuSO4 + Cu2S → 3Cu + 2SO2 ↑

Cu2S + 2CuO → 4Cu + SO2 ↑

Final ly , copper may be ref ined

electrolytically (electrolyte; copper sulphate;

anode; impure copper and cathode; pure

copper).

9. Extraction of Lead

Lead is widely distributed in nature. It is the

stable end product of all natural radioactive

elements. It occurs in traces in the native

form. In the combined form, it occurs as

Galena, PbS

Cerussite, PbCO3

Anglesite, PbSO4

Wulfenite, PbMnO4

Stolzite, PbWO4

Extraction : Lead is mainly extracted from

galena. After the concentration of the ore by

froth flotation process. the ore is roasted in

a reverberatory furnace for about six hours

at a moderate temperature in a current of air.

Part of galena is converted into lead oxide

and lead sulphate. After this, the supply of

air is stopped and small quantities of carbon,

quicklime and cheap iron ore are added

along with increase of temperature. At this


(13)

stage, unreacted sulphide reacts with the

lead oxide and sulphate giving metallic lead.

PbS + 2PbO → 3Pb + 2SO2

PbS + PbSO4 → 2Pb + 2SO2

The obtained lead contains impurities such

as Cu, Ag, Bi, Sb and Sn. Silver is removed

by Parke’s process where molten zinc is

added to molten impure lead. The former is

immiscible with the latter. Silver is more

soluble in molten zinc than in molten lead.

Zinc-silver alloy solidifies earlier than molten

lead and thus can be separated. After this,

crude lead is refined electrolytically

(electrolyte; lead silicofluoride PbSiF6 and

hydrofluosilicic acid H2SiF6 with a little

gelatine, anode; crude lead and cathode;

pure lead).

10. Extraction of Aluminium

Aluminium also does not occur free in

nature. In the combined state, it occurs in the

following forms-

Oxides :

Corundum, Al2O3

Diaspore. Al2O3 . H2O

Bauxite. Al2O3 . 2H2O

Fluorides :

Cryolite. Na3AlF6

Silicates :

Feldspar, KAlSi3O8,

Mica. (KAlSi3O10 (OH)2)

Kaolinite. (Al(OH)4, Si2O5)

Basic sulphates :

Alunite or Alumstone, K2SO4 . Al2 (SO4)3 .

4Al(OH)3

Basic Phosphates :

Turquoise. AlPO4 . Al(OH)3 . H2O

Aluminates : Aluminates of Mg, Fe and Mn.

Aluminium is the third most abundant

element of earth’s crust.

Extraction : Aluminium is isolated from the

electrolysis of bauxite Al2O3 . 2H2O. Since it

is difficult to purify aluminium, bauxite ore is

purified either by baeyer’s process (or hall’s

process) or serpek’s process depending

upon the impurity present in the ore.

If the bauxite contains iron oxide as the

impurity, one can use baeyer’s or hall’s

process as described below.

10.1 Baeyer’s process - Finally ground ore

is roasted to convert ferrous oxide to ferric

oxide and then digested with concentrated

caustic soda solution at 423 K. Al2O3

dissolves while Fe2O3 remains undisolved.

The latter is filtered off and from the solution

Al(OH)3 is precipitated by adding a weak

acid. The ignition of Al(OH)3 gives Al2O3.

Al2O3 + 2OH− + 3H2O → 2Al (OH) 4−

aluminate ion dissolves

Al(OH) 4− + H+ → Al(OH) 3 + H2O

precipitates

2Al(OH) 3 −−−>heat

Al2O3 + 3H2O

10.2 Hall’s process - In this process, the ore

is fused with sodium carbonate when soluble

meta-aluminate (NaAlO2) is produced. This

is extracted with water leaving behind iron

oxide. Carbon dioxide at 323-333 K is

passed through water extract to get Al(OH)3which on heating gives Al2O3.

fused

Al2O3 + Na2CO3 −−−−−> 2NaAlO2 + CO2

extracted with water

2NaAlO2 + 3H2O + CO2 → 2Al (OH) 3 + Na2CO3

heat

2Al(OH) 3 −−−−−> Al2O3 + 3H2O

If the impurity is silica, the serpek’s process

is used to purify bauxite.


(14)

Serpek’s process - The powdered ore is

mixed with coke and heated to 2075 K in a

current of nitrogen. Silica present is reduced

to silicon which volatilizes off and alumina

gives aluminium nitride. The hydrolysis of the

latter gives Al(OH)3. heating of which gives

Al2O3.

SiO2 + 2C → Si + 2CO2

Al2O3 + 3C + N2 → 2AlN + 3CO

AlN + 3H2O → Al(OH) 3 + NH3

2Al(OH) 3 −−−−> Al2O3 + 3H2O

heat

After obtaining pure Al2O3. it is dissolved in

fused cryolite Na3AlF6 with a little fluorspar

CaF2, and is electrolysed in an iron tank lined

with blocks of carbon which serve as the

cathode. The anode consists of a number of

graphite rods suspended verticaly inside the

tank.

Fig. 5

Aluminium gets settled at the bottom of the

tank and can be removed. The reactions

occurring at the electrodes are

Cathode : Al3+ + 3e− → Al

Anode : 2 O2−2 → O2 + 4e−

C + O2 → CO2

Anode is replaced periodically because of its

consumption.

11. Extraction of Silver

Silver in the native form is associated with

copper and gold. The main ores of silver are

Argentite or silver glance, Ag2 S

Pyrargyrite, 3A2 S . Sb2 S3

Proustite, 3Ag2 S . As2 S3

Horn silver, AgCl

Extraction : Silver is extracted from its ore

by the cyanide process (MacArthur-Forrest

process). After the preliminary crushing and

concentration by froth floatation process, the

ore is leached with 0.4 -7% solution of

sodium cyanide kept agitated by a current of

a i r . S i lver passes into solut ion as

argentocyanide :

Ag2 S + 4NaCN → 2Na[Ag(CN) 2] + Na2S

The air blown in remove Na2 S as

Na2S2 O3 and Na2SO4 causing the above

reaction to proceed to completion.

2Na2S + 2O2 + H2 O → Na2S2O3 + 2NaOH

Na2S2O3 + 2 NaOH + 2O2 → 2Na2SO4 + H2O

The solution obtained above is filtered and

treated with scrap iron or zinc when silver

gets precipitated.

2Ag(CN) 2− + Zn → Zn (CN) 4

−2 + 2Ag

The obtained silver is purified electrolytically

(electrolyte : silver nitrate solution containing

1% nitric acid, anode : impure silver and

cathode : pure silver). The impurities like zinc

and copper pass into the solution while gold

falls down as anode mud.

12. PROPERTIES OF METALS

12.1 Sodium and Potassium

Sodium and potassium are the members of

group 1.

Their electronic configurations are

11 Na : 1s2 , 2s22p6 , 3s1


(15)

19K : 1s2 , 2s2 2p6 , 3s23p6 , 4s1

Only one electron per atom is available for

the metallic bonding, therefore, these metals

are soft and low melting. These have low

ionization energy and thus are good

reducing agents. These metals can be

detected by flame photometry as the

electronic excitation requires radiation in the

vis ible region (sodium : yellow and

potassium : lilac). Potassium (also caesium)

is used in photoelectric cells as this element

emits electrons when irradiated with light.

Both sodium and potassium (and also other

a lka l i meta ls except l i th ium at low

temperature) crystallize in the body-centred

cubic lattice. Sodium and potassium are the

sixth and seventh most abundant elements

in the earth’s crust. Being the strongest

reducing agents, these metals are not

prepared by reducing oxides. These are

usually obtained by the electrolysis of fused

halides with impurity added to lower the

melting point.

Chemically, these elements are very

reactive and tarnish rapidly in air to form the

oxide. With oxygen, sodium forms peroxide

(Na2O2) whereas potassium

forms superoxide (KO2) . Both react with

hydrogen, nitrogen, halogens, sulphur and

phosphorus to form corresponding hydride,

nitride, halides, suplhide and phosphide,

respectively.

Both react with water to form hydroxide and

hydrogen; potassium catches fire when it

reacts with water and the reaction of sodium

with water is less violent.

Both sodium and potassium dissolve in very

high concentration in liquid ammonia. These

solutions conduct electricity very similar to

the pure metals. This is due to presence of

solvated electrons along with solvated metal

ions. The colour of the solution is dark blue.

12.2 Aluminium

Aluminium belongs to group 3. Its electronic

configuration is

13Al : 1S2 , 2s22p6 , 3s23p1

It is a silvery white metal, nontoxic and

capable of taking high polish. It has a high

thermal and electrical conductivity, excellent

corrosion resistance and good malleability

and ductility.

Aluminium is a self - protective metal. This is

due to the formation of protective layer of

aluminium oxide.

At high temperature, aluminium reacts with

nitrogen and chlorine giving nitride and

chloride. Pure water has almost no action on

aluminium when cold. Salt water corrodes it

rapidly especially when it is hot.

Aluminium dissolves rapidly in hydrochloric

acid liberating hydrogen. The reaction is

vigorous if the acid is hot and concentrated.

Dilute sulphuric acid does not attack

aluminium. Hot concentrated sulphuric acid

reacts with aluminium liberating SO2.

SO42− + 4H+ + 2e− → SO2 + 2H2O] × 3

Al → Al3+ + 3e−] × 2

2Al + 3SO42− + 12H+ → 2Al3+ + 3SO2 + 6H2O

Nitric acid both dilute and concentrated does

not attack aluminium because the latter

becomes passive due the formation of oxide

layer.

Strong alkalis react with metal producing

meta aluminates.

2Al + 6OH+− 6H2O → 2[Al (OH) 6]3− + 3H2

Aluminium has great affinity for oxygen and

is, therefore, good reducing agent. It reduces

many other metallic oxides.

Fe2O3 + 2Al → 2Fe + Al2 O3


(16)

In the above reaction, a lot of heat is

generated and forms the basis of

aluminothermit process.

12.3 Lead

Lead is member of group 14. Its electronic

conf igurat ion is

82Pb : [Xe] 4f14, 5d10, 6s2 6p2

Lead is a soft, bluish grey metal. It is highly

malleable.

Dry air has no action on lead but in moist air

a protective coating of basic carbonate is

formed and protects it from further oxidation.

When heated in air, it forms litharge which at

very high temperature is converted to red

lead.

6pb + 3O2 → 6PbOlitharge

O2T > 725 K

2Pb3 O4red lead

Lead is rapidly corroded by water containing

dissolved oxygen to form loose deposit of

lead hydroxide which is soluble in water

rendering it poisonous. This solvent action of

water is known as plumbo solvency. The

presence of nitrates, ammonium salts and

organic matter in water accelerates this

dissolution whereas bicarbonates. sulphates

and phosphate retard the dissolution due to

the formation of protective layer.

Hydrochloric acid and sulphuric acid have

little effect on lead but nitric acid reacts

vigorously. With dilute nitric acid. NO is

evolved while with concentrated nitric acid,

NO2 is evolved.

(i) NO3− + 4H+ + 3e− → NO + 2H2 O] × 2

Pb → Pb2+ + 2e− ] × 3

3Pb + 2NO3− + 8H+ → 2NO + 4H2O

(dilute)

(ii) NO3− + 2H+ + e− → NO2 + H2 O] × 2

Pb → Pb2+ + 2e−

Pb + 2NO3− + 4H+

(concentrated )

→ Pb2+ + 2NO2 + 2H2 O

With concentrated HCl, Pb forms H2PbCl4.

Pb + 2HCl → PbCl2 + H2

PbCl2 + 2HCl → H2 PbCl4chlorplumbic acid

With concentrated sulphuric acid, Pb forms

PbSO4 liberating SO2.

Pb + 2H2 SO4 → PbSO4 + 2H2 O + SO2

In caustic alkali, lead dissolves slowly

forming plumbite and hydrogen

Pb + 2NaOH → Na2bo2 + H2

On heating, lead also combines with Cl2 and

S forming PbCl4 and PbS, respectively.

12.4 Iron

Iron belongs to group 8 of the periodic table.

I ts e lec t ronic conf igurat ion is

1s2 , 2s22p6 , 3s23p63d6, 4s2.

Pure iron is a silvery white metal. It combines

with a number of nonmetals (e.g. oxygen,

halogens, sulphur, nitrogen and carbon) on

heating. Dry air has no affect on iron.

However moist air results in the rusting of

iron - and electrochemical process in which

iron is converted in to

Fe(OH) 3 or FeO(OH) .

Red hot iron combines with steam resulting

in the formation of magnetic oxide of iron

(Fe3O4) and releasing

hydrogen.

3Fe + 4H2O → Fe3O4 + 4H2

Dilute HCl and H2SO4 displaces H2 when

reacted with iron.


(17)

Fe + 2H+ → Fe2+ + H2

Dilute HNO3 forms ferrous nitrate and

ammonium nitrate.

Fe + 2H+ → Fe2+ + H2

Dilute HNO3 forms ferrous nitrate and

ammonium nitrate.

Fe → Fe2+ + 2e−] × 4

NO3− + 10H+ + 8e− → NH4

+ + 3H2O

4Fe + NO3− + 10H+ → 4Fe2+ + NH4

+ + 3H2O

Hot concentrated H2SO4 acid liberates

SO2 and a mixture of ferrous and ferric

sulphates.

Fe + 2H2SO4 → FeSO4 + SO2 + 2H2 O

2FeSO4 + 2H2SO4 → Fe2(SO4) 3 + SO2 + 2H2 O

Moderately concentrated nitr ic acid

dissolves iron giving ferric nitrate and librates

oxides of nitrogen. With fuming nitric acid,

the reaction does not occur as the metal

becomes passive.

Rusting of iron - It is due to the formation of

local electrochemical cells on the surface of

metal. In case of iron, Fe is oxidized to Fe2+

at one spot which acts as an anode.

Electrons released from this spot move to

another spot where oxygen in the presence

of H+ (which is believed to be available by the

absorption of Co2 into moisture) is

reduced to oxide in the form of water. The

two reactions are as follows -

Anode (oxidation) :

Fe(s) → Fe2+ (aq) + 2e−

Cathode (reduction) :

O2(g) + 4H+ (aq) + 4e− → 2H2O(l)

The electrolytic solution is moisture on the

surface of iron. If the water present is saline,

it will help in increasing the speed of

corrosion.

Iron is available in different forms e.g. pig iron

cast iron, wrought iron and steel. Of these,

wrought iron is the purest form of iron

containing 0.1 to 0.25% of carbon and less

than 0.25% of other impurities like S, Si, P

and Mn.

The most important form of commercial iron

is steel which contains 0.15 - 2.0% of carbon

and traces of S and P. Increasing the carbon

content results into harder steel.

Steel alloy contains special constituents

such as tungsten, chromium, nickel, cobalt,

vanadium, molybdenum and manganese

which impart desired properties to steel.

Some of them are as follows -

Stainless steel : Fe (73), Cr(18), Ni(8) and

C(1)

Nickel steel : Fe(96 - 98), Ni(2 - 4)

Tungsten steel : Fe (94), W(5), C(1)

Invar : Fe(64), Ni(34)

Alnico : Fe(63), Al(12), Ni(20), Co(5)

Permalloy : Fe(21), Ni(78), C(1)

Manganese steel : Fe(86), Mn(13), C(1)

12.5 Copper and Silver

Copper and silver belong to group 11. Their

electronic configurations are

Cu : [Ar] 3d10 , 4s1

Ag : [Kr] 4d10 , 5s1

Both Cu and Ag are malleable and ductile,

Next to silver, copper is the best conductor

of heat and electricity.

Dry air and pure water have no affect on

Cu and Ag. In moist air, Cu slowly reacts

forming a coating of green basic carbonate,

CuCO3 Cu(OH) 2. In thermosphere of SO2.

a similar coating of basic sulphate,

CuSO4 3Cu(OH) 2 is formed. At high

temperature, Cu reacts with oxygen (or air)

forming cupric and cuprous oxides.


(18)

2Cu + O2 −−−−−−→Below1370 K

2CuO

4Cu + O2 −−−−−−→Above 1370 K

2Cu2O

Dilute HCl and H2SO4 have no action on

Cu and Ag. In the presence of air, however,

Cu reacts as follows.

2Cu + 2H2SO4 + O2 → 2CuSO4 + 2H2O

2Cu + 4HCl + O2 → 2CuCl2 + 2H2O

Hot concentrated H2SO4 liberates SO2 with

both Cu and Ag.

Cu + SO42− + 4H+ → Cu2+ + SO2 + 2H2O

2Ag + SO42− + 4H+ → 2Ag+ + SO2 + 2H2O

Dilute nitric acid produces NO whereas

concentrated nitric acid produces NO2 both

with Cu and Al

3Cu + 2NO3− + 8H+ → 3Cu2+ + 2NO + 4H2O

(dilute)

3Ag + NO3− + 4H+ → 3Ag+ + NO + 2H2O

(dilute)

Cu + 2NO3− + 4H+ → Cu2+ + 2NO2 + 2H2O

(concentrated)

Ag + NO3− + 2H+ → Ag+ + NO2 + H2O

(concentrated)

Heating with Cl2 and S both Cu and Ag react

forming halides and sulphides.

Copper dissolves in concentrated HBr and

HI forming

H2[Cu2Br4] and H2[Cu2I4].

In presence of air, copper dissolves in an

aqueous ammonium hydroxide solution.

Cu + H2O + 1

2 O2 → Cu2+ + 2OH−

Cu2+ + 4NH3 → Cu(NH3) 42+

Silver dissolves in the solution of an alkali

cyanide in the presence of oxygen forming

the complex argentocyanide ion.

2Ag + H2O + 1

2 O2 → 2Ag+ + 2OH−

Ag+ + 2CN

− → [Ag(CN) 2]

− × 2

2Ag + H2O + 1

2 O2 + 2CN

− → 2[Ag(CN) 2]

− 2OH

−

Copper forms a number of alloys. A few

important alloys of copper are as follows-

Brass : Cu(60.8) , Zn(20.4)

Bronze : Cu(75.9), Sn(10.25)

Aluminium bronze : Cu(90) , Al(10)

Monel metal :

Cu(30) , Ni(67) , Fe + Mn(3%)

Bell metal : Cu(80) , Sn(20)

Gun Metal : Cu(87) , Sn(10) , Zn(3)

German silver : Cu(50) , Zn(25) , Ni(25)

Nickel coin : Cu(75) , Ni(25)

14 Carat gold :

Au (58) , Ag (14.3) , Cu(12.28)

Zinc

Zinc belongs to group 12. Its electronic

configuration is [Ar] 3d10, 4s2.

Metallic zinc is bluish-white in colour, It is

brittle at room temperature but becomes

malleable and ductile between 370 K and

420 K.

Dry air has no action on zinc, However, in

moist air, a protective layer of basic zinc

carbonate is formed. In the atmosphere of

O2, zinc reacts at higher temperature

forming zinc oxide.

Pure water has no act ion on z inc.

Zinc-copper couple decomposes water

l iberat ing hydrogen. Impure z inc

decomposes boiling water slowly.

Dilute HCl and H2SO4 liberates H2 and

SO2, respectively with impure zinc.

Zn + 2Hcl → ZnCl2 + H2


(19)

Zn + 2H2SO4 → ZnSO4 + SO2 + 2H2O

With nitric acid, the following reactions

occur-

4Zn + 2NO3− + 10H+ → 4Zn2+ + N2O + 5H2O

(dilute)

4Zn + NO3− + 10H+ → 4Zn2+ + NH4

+ + 3H2O

(very dilute)

Zn + 2NO3− + 4H+ → Zn2+ + 2NO2 + 2H2O

(concentrated)

Caustic alkalies react with zinc forming

soluble zincate and liberate hydrogen.

Zn + 2OH− → ZnO22− + H2

Zinc combines with halogens and sulphur

forming halides and sulphides. Zn is fairly

electropositive element. It replaces Cu, Ag,

Au and Pb form their salt solutions.


(20)

13. SYNOPSIS & EXPLANATORY NOTES

General Properties of Metals

A metal may be defined as a substance

which is a good conductor of heat and

electricity and which possesses a bright

appearance called metallic clustre.

Certain mechanical properties such as

high tensile strength, malleability and

ductility are usually associated with

metallic state,

Pure metals in solid state are crystals in

which the particles are arranged in

definite geometrical order to form crystal

lattices, also called space lattices.

The lattice points are occupied by

positively charged ions and neutral

atoms, and in the space between them

free electrons move. Atoms in the crystal

lattices of metals are arranged very close

to one another and their valence

electrons may move not only ground their

own atoms, but also around neighbouring

atoms. Thus the valence electrons move

freely within the whole metal forming the

so called electron gas or electron sea.

The presence of free electrons in metals

is confirmed by the fact that metals

possess high electrical conductivity and

emit free electrons on heating.

All metals, except mercury are solid

under ordinary conditions.

In the compact form, that is, in the form

of plates and slabs metals possess

shining, lustrous appearance. This is due

to the reflection of light from their

surfaces.

In finely powdered form only magnesium

and aluminium do retain their metallic

lustre, while the powders of the other

metals are either black or dark grey in

colour.

Most of the metals have white silvery

colour and are non-transparent, since

nearly all of them absorb long range and

short wavelength of light spectrum to the

same extent.

Caesium and gold are yellow, while

copper is yellow-red.

Metals are classified as light metals and

dense metals in terms of their density.

Light metals have a density of less than

5g/cm3 (Li, K, Ca, Al etc). Heavy metals

are those which have a density of more

than 5g/cm3. Examples of heavy metals

are Sn, Pb, Hg, Fe etc.

Lithium (density 0.53g/cm3) is the

lightest and osmium (density 22.5 g/cm3)

is the heaviest metal.

Metals are classified as low melting and

high melting in terms of melting point.

Metals having m.p. 350ºC or below are

called low melting. Examples are : Pb

(327ºC), Sn (232ºC), Na(98ºC), K(63ºC),

calcium (28ºC) etc. Metals having m.p.

above 350ºC are classified as high

melting. Examples are : Fe(1539ºC), Cr

(1875ºC). Metal with the highest melting

point is tungsten (3380ºC).

Two important physical properties of

metals are electrical and thermal

conductivity which are due to the

presence of free electrons in all metals.

The best conductor of electricity is silver

followed by copper, gold, chromium,

aluminium and magnesium.

Among the mechanical properties,

mal leabi l i ty and duct i l i ty are

characteristic of metals. Malleability is a


(21)

property of metals by virtue of which they

can be hammered or pressed into new

shapes (beaten into sheets) at a

temperature below the m.p. of the metal.

Ductility is the capacity of metals to be

drawn into wires. Metals with low ductility

are fragile and those having high ductility

are strong enough to be ruptured. Gold

has the highest malleability and ductility.

The common chemical property of metals

is their ability to donate electrons and to

be transformed into positively charged

ions. The ability to give up electrons

varies from metals to metal.

Whether electrons in atoms are strongly

or loosely held is measured by the

ionisation energy.

Alkali metals have the lowest ionisation

energies and therefore they are strong

reducing agents.

The reducing properties of metals

account for their ability to enter into

reaction with various oxidising agents

such as non-metals, acids and salts of

less active metals. The names of all

compounds of metals with non-metals

end in-ide. For example, oxide, chloride,

nitride, sulphide, etc. Metals react with

non-metals. (a) Most metals easily react

with oxygen to form oxides.

2Mg + O2 → 2MgO

(b) They readily add halogens to form

halides. 2Fe + 3Cl2 → 2Fed3

(c) Metals react with nitrogen to yield

nitrides. 3Ba + N2 → Ba3N2

(d) Meta ls react under certain

condi t ions with sulphur to form

sulphides. 2AI + 3S → Al2S3

The more electronegative the element,

the stronger it oxidises a metal. For

example, in compounds formed by iron

and chlorine, the oxidation number of Fe

is +3, while in those with sulphur, it is +2.

Compounds of metals with carbon are

called carbides.

Ca + 2C → CaC2

Metals react wi th phosphorus at

600-1200ºC and form compounds known

as phosphides.

3Li + P → Li3P ; 3Zn + 2P → Zn3P2

Alkali and alkaline earth metals can react

directly with hydrogen to give hydrides.

2Li + H2 → 2Li+H− ; Ca + H2 → Ca2+H2−

Metals react with silicon to form silicates.

2Mg + Si → Mg2Si

Metals have been arranged in a series

called series of standard reduction

electrode potentials or electrochemical

series or activity series, according to the

ability to donate electrons in solutions.

Hydrogen has also been placed in this

series, because it is the only non-metal

which can, like metals, exist in aqueous

solution as positive ions (H3O+) . Metals

have been arranged in the series of

standard reduction electrode potentials in

order of their decreasing reducing

properties in solution or in order of the

increasing oxidising properties of their

ions in solution. Any metal in the series

can displace the metals placed below it

from their salt solutions. Metals arranged

above hydrogen replace the latter from

dilute acids, except HNO3. Alkali and

alkaline

earth metals replace hydrogen. even

from water. The series of standard

reduction electrode potentials is valid for

redox processes which take place only in

aqueous media. Important chemical

properties of metals are reflected in their

relation to water, acid solutions, alkalies

and slats.


(22)

Increase in oxidising properties follows

the order : Li+, K

+, Ca

2+, Na

+ , Mg

2+, Al

3+,

Mn2+

, Zn2+

, Cr3+

, Fe2+

, Ni2+

, Sn2+

, Pb2+

,

2H+, Cu

2+, Hg2

2+,

Ag+, P

t2+, Au

3+. Decrease in reducing

properties follows the order Li, K, Ca, Na,

Mg, Al, Mn, Zn, Cr, Fe, Ni, Sn, Pb, H2, Cu,

Ag, Pt, Au. Thus lithium is most powerful

reducing agent and Au is least powerful

reducing agent.

Alkali and alkaline earth metals dissolve

in water to form hydroxides known as

alkalies.

A number of heavy metals react with

water on heating to yield oxides.

3Fe + 4H2O →(Steam )

Fe3O4 + 4H2

Alkalies react only with those metals

which exhibit amphoteric properties.

2A1 + 2NaOH + 2H2O → 2NaA1O2 + 3H2

More active metals replace the less

active metals from their salt solutions.

Fe + CuSO4 → FeSO4 + Cu

The process of extraction of metals from

their ores is known as metallurgy.

The metal compound occurring in earth

crust is called mineral.

Amineral from which a metal can be

profitably extracted is called an ore.

The process of removing gangue from

the ore is called concentration.

The earthy impurities like sand, rock and

clay associated with the ore are called

gangue or matrix.

A substance added to convert the

gangue into fusible mass is called flux.

Gangue + Flux → Slag (Fusible mass).

Ox ide and carbonate ores are

concentrated by gravitational method.

Sulphide ores are concentrated by froath

floatation method.

Liquation process is used for the

concentration of oresQ‘ which are having

lesser melting point than impurities.

Tinstone (SnO2) containing

Wolframite (FeWO4) can be

concentrated by e lectromagnetic

separation. The process of heating the

ore to a high temperature below its

melting point in called calcination. The

process of strong heating of the ore below

its melting point in the presence of air is

called roasting. Sulphide ore is generally

roasted in air. Carbonate ores are

generally calcined. The high temperature

reduction process in which the metal is

obtained in molten state is called

smelting.

The important furnaces used in

metallurgy are blast furnace, open hearth

furnace, Bessemer converter and

reverberatory furnace. Open hearth

furnace is called heat regenerative

furnace and it is an special type of

reverberatory furnace. Calcination and

roasting are carried out in reverberatory

furnace. The metals are generally refined

by l iquat ion, d ist i l la t ion, pol ing,

cupellation and electrolysis. Smelting is

carried out in blast furnace.

An alloy is a solid solution of two or more

elements with metallic property.

The substances which can withstand

very high temperature with out melting or

becoming soft are called refractory

materials. Alloys of mercury are called

amalgams. Coating or alloying of metals

like Fe with zinc is called galvanising.

Coatings or alloying of metal with tin is

called tinning. Alloying of a metal with Hg

is known as amalgamation. Thomas slag

is Ca3(PO4) 2. It is used as fertilizer.


(23)

In alumino thermite process, Al is used as

reducing agent.

Some metals like Al, Mg, Na are prepared

by electrolysis of their fused halides or

oxides.

Copper is obtained by auto reduction.

Metals like Ag and Au are prepared by

hydrometallurgy.

The principal ores of copper are

malachite [Cu(OH) 2. CuCO3] and

copper pyrites (CuFeS2) .

Matte is a mixture of Cu2S containing little

FeS. 98% pure copper formed at the end

of Bessemerisation process of copper

pyrites is called blister copper. Spelter is

97-98% pure zinc.

Formation of alloy (a) Increases the

intensity of colour (b) Increases the

hardness (c) Decreases the conductivity

(d) Decreases the corrosion (e)

Decreases the melting point (f) Increases

the good casting.

The slow cooling of red hot steel is called

annealing.

In quenching or hardening, the steel

article is heated to a temperature which

is above 920ºC and then suddenly cooled

to normal temperature by dipping in a

bath of oil or water.

Heating of steel in contact with charcoal

is called cast hardening.

Heat ing steel in presence of an

atmosphere of NH3 is called nitriding.

Iron rusts in presence of oxygen and

moisture. The rusting metal always acts

as anode. Rusting in moist air involves

loss of electrons by Fe. Rusting is

oxidation. Rust is brown layer of hydrated

ferric oxide. Composition of rust is

Fe2 O3 + Fe (OH) 2 or Fe2O3. xH2O.

Rusting is prevented by applying grease.

painting, tinning and galvanising etc,

Rusting of iron is chemical combination

reaction.


(24)

Objective Questions

Principle of Metallurgical Operations

(Na, Al, Fe, Cu, Ag, Zn & Pb)

1. The most abundant element on earth

crust is

[MP PMT; Delhi PMT]

(a) Hydrogen (b) Oxygen

(c) Silicon (d) Carbon

2. Naturally occuring substances from

which a metal can be profitably (or

economically) extracted are called.

[CPMT; MP PET]

(a) Minerals (b) Ores

(c) Gangue (d) Salts

3. Sulphide ores are genera l ly

concentrated by

[CPMT; EAMCET; MNR;

Delhi PMT; KCET]

(a) Froth floatation process

(b) Magnetic separation

(c) Gravity separation

(d) By hand picking

4. Froth floatation process is used for the

concentration of

[NCERT; CPMT; MP PMT;

EAMCET; AMU; Delhi PMT; BHU]

(a) Oxide ores (b) Sulphide ores

(c) Chloride ores (d) Amalgams

5. Refractory materials are generally used

in furnaces because

[MNR; MP PMT]

(a) They possess great structural strength

(b) They can withstand high temperature

(c) They are chemically inert

(d) They do not require replacement

6. In the froth floatation process for the

purification of ores, the ore particles

float because

[MP PMT; NCERT; CPMT; MLNR]

(a) They are light

(b) Their surface is not easily wetted by

water

(c) They bear electrostatic charge

(d) They are insoluble

7. Which of the following metal is

sometimes found native in nature.

[CPMT; MP PET]

(a) Oxide ores (b) Silicate

(c) Sulphide ores (d) Carbonate ores

8. Heating of pyrites in air for oxidation of

sulphur is called

[CPMT; Delhi PMT]

(a) Roasting (b) Calcination

(c) Smelting (d) Slagging

9. A substance which reacts with gangue

to form fusible material is called

[MP PMT; Kurukshetra CEE]

(a) Flux (b) Catalyst

(c) Ore (d) Slag

10. Magnetic separation is used for

increasing concentrat ion of the

following

[MP PET]

(a) Horn silver (b) Calcite

(c) Haematite (d) Magnesite


(25)

11. Purpose of smelting of an ore is

[MP PMT; Kurukshetra CEE]

(a) To oxidise it

(b) To reduce it

(c) To remove vaporisable impurities

(d) To obtain an alloy

12. Titanium containing mineral found in

our country is

[NCERT]

(a) Bauxite (b) Bolomite

(c) Chalcopyrites (d) Elmanite

13. General method for the extraction of

metal from oxide ore is

[CPMT]

(a) Carbon reduction

(b) Reduction by hydrogen

(c) Reduction by aluminium

(d) Electrolytic reduction

14. Froth floatation process is used for

concentration of

[MLNR; IIT]

(a) Chalcopyrite (b) Bauxite

(c) Haematite (d) Calamine

15. Which ore is metalloid

[MP PMT]

(a) As (b) Na

(c) Au (d) Fe

16. When lime stone is heated strongly, it

gives off CO2. In metallurgy this

process is known as

[MP PET/PMT]

(a) Calcination (b) Roasting

(c) Smelting(d) Ore dressing

17. A mineral is called an ore if

[MP PMT]

(a) Metal present in mineral is precious

(b) Metal can be extracted from it

(c) Metal can be extracted profitably

from it

(d) Metal cannot be extracted from it.

18. In blast furnace iron oxide is reduced by

[MP PMT]

(a) Silica (b) CO

(c) Carbon (d) Lime stone

19. Inner layer of blast furnace is made of

[MP PMT]

(a) Graphite bricks (b) Silica bricks

(c) Fire - clay bricks (d) Basic bricks

20. Carnellite is a mineral of

[CBSE; Delhi PMT]

(a) Ca (b) Na

(c) Mg (d) Zn

21. The most abundant metal in the earth

crust is

[BHU, CPMT; MP PMT]

(a) Na (b) Mg

(c) Al (d) Fe

22. Formula of carnellite is

[MP PET; EAMCET]

(a) KCl. MgCl2. 6H2O

(b) K2SO4. MgCl2. 6H2O

(c) K2SO4. MgSO4. 6H2O

(d) K2SO4. MgSO4. CaSO4. 6H2O

23. Metal which can be extracted from all

the three dolomite, magnesite and

carnellite.

[MP PET]

(a) Na (b) K

(c) Mg (d) Ca

24. ‘Lapis-Lazuli ’ is a blue coloured

precious stone. It is mineral of the class

[NCERT; AIIMS; BHU]

(a) Sodium - alumino silicate

(b) Zinc cobaltate


(26)

(c) Basic copper carbonate

(d) Prussian blue

25. Which of the following metal is obtained

by leaching out process using a solution

of NaCN and then precipitating the

metal by addition of zinc dust.

[NCERT; AIIMS; CBSE]

(a) Copper (b) Silver

(c) Nickel (d) Iron

26. Cinnabar is an ore of

[NCERT]

(a) Hg (b) Cu

(c) Pb (d) Zn

27. Smelting is termed to the process in

which

[MP PMT]

(a) The ore is heated in the absence of air

(b) Ore is cold

(c) The ore is heated in the presence of air

(d) Ore is melted

28. The substance added in water in the

froth floatation process is

[EAMCET]

(a) Soap powder (b) Pine oil

(c) Coconut oil (d) None of the above

29. The substance used in the thermite

process of reducing metal ores is

[MP PET]

(a) Aluminium (b) Thorium

(c) Heated Pt gauge(d) Carbon

30. Cassiterite is concentrated by

[EAMCET]

(a) Levigation

(b) Electromagnetic separation

(c) Floatation

(d) Liquifaction

31. Which of the following substances

consists of only one element

[MP PET]

(a) Marble (b) Sand

(c) Diamond (d) Glass

32. A and B are two allotropes of an

element. One gram of A will differ from

one gram of B in

[NCERT]

(a) Oxidation number

(b) Chemical composition

(c) Total number of atoms

(d) Atomic arrangement

33. The phenomenon in which white

transparent crystals change into white

powder is known as

[EAMCET]

(a) Sublimation (b) Allotropy

(c) Efflorescence (d) Deliquescence

34. Which of the following substance can

be used for drying gases

[EAMCET; MP PET]

(a) CaCO3 (b) Na2 CO3

(c) NaHCO3 (d) CaO

35. The electrolytic method of reduction is

employed for the preparation of metals

that

[MP PMT; NCERT; CPMT]

(a) Are weakly electropositive

(b) Are moderately electropositive

(c) Are strongly electropositive

(d) Form oxides

36. Froth f loatat ion process for the

concentration of ores is an illustration of

the practical application of

[NCERT]

(a) Adsorption (b) Absorption


(27)

(c) Coagulation (d) Sedimentation

37. Cupellation process is used in the

metallugry of

[CPMT; MP PET]

(a) Copper (b) Silver

(c) Aluminium (d) Iron

38. An alloy is

[MP PMT]

(a) Intermetallic compound

(b) A solid substance containing two or

more metallic elements

(c) A solid which contains one non-metal

(d) A solid which contains more than one

nonmetal

39. Metals are

[MADT Bihar]

(a) Electropositive

(b) Electronegative

(c) Acceptor of electrons

(d) None of these

40. The cyanide process is used for

obtaining

[Delhi PMT; CPMT; MNR; MP PET/PMT]

(a) Na (b) Ag

(c) Cu (d) Zn

41. Alloy is an example of

[Delhi PMT; CPMT]

(a) Gel (b) Aerosol

(c) Solid sol (d) Emulsion

42. An example of halide ore is

[MP PMT]

(a) Galena (b) Bauxite

(c) Cinnabar (d) Cryolite

43. Which of the following is not an ore

[IIT]

(a) Bauxite (b) Malachite

(c) Zinc blende (d) Pig iron

44. The metallurgical process in which a

metal is obtained in a fused state is

called

[IIT; MP PET]

(a) Smelting(b) Roasting

(c) Calcination (d) Froth floatation

45. Of the following, which cannot be

obtained by electrolysis of the aqueous

solution of their salts

[IIT]

(a) Ag (b) Mg and Al

(c) Cu (d) Cr

46. One of the following metals forms a

volatile compound and this property is

taken advantage for its extraction. This

metal is

[NCERT]

(a) Iron (b) Nickel

(c) Cobalt (d) Tungsten

47. Van Arkel method of purification of

metals involves converting the metal to

a

[BHU]

(a) Volatile stable compound

(b) Volatile unstable compound

(c) Non volatile stable compound

(d) None of the above

48. Which one of the following metals is

ext racted by thermal reduct ion

process?

[EAMCET]

(a) Copper (b) Iron

(c) Aluminium (d) Magnesium

49. Bauxite ore is concentrated by

[MP PET]

(a) Froth flotation

(b) Electromagnetic separation

(c) Chemical separation


(28)

(d) Hydraulic separation

50. Chemical reduction is not suitable for

converting

[MP PET]

(a) Bauxite into aluminium

(b) Cuprite into copper

(c) Haematite into iron

(d) Zinc oxide into zinc

51. Reverberatory furnace is employed in

the metallurgical process mainly for

[MP PMT]

(a) Reduction of oxide ores

(b) Smelting of sulphide ores

(c) Conversion of chloride to sulphate

(d) Getting magnetic materials

52. Globar salt is

[BHU; CPMT; IIT]

(a) MgSO4. 7H2O (b) CuSO4. 5H2O

(c) FeSO4. 7H2O (d) Na2SO4. 10H2O

53. The colour given to the flame by sodium

salts is

[CPMT; MP PET]

(a) Light red(b) Golden yellow

(c) Green (d) Pink

54. Sodium when heated in a current of dry

ammonia gives

[NCERT]

(a) Sodium nitrite (b) Sodium hydride

(c) Sodium amide (d) Sodium azide

55. Chile saltpetre is an ore of

[CPMT]

(a) Iodine (b) Sodium

(c) Bromine (d) Magnesium

56. Solvay’s process is used for the

preparation of

[CPMT; AIIMS]

(a) Ammonia

(b) Sodium bicarbonate

(c) Sodium carbonate

(d) Calcium carbonate

57. Washing soda is

[CPMT; Delhi PMT; CBSE; MP PMT]

(a) Na2CO3. 10H2O

(b) Na2CO3. H2O

(c) Na2CO3. 5H2O

(d) Na2CO3

58. The main salt soluble in sea water is

[MP PMT]

(a) MgCl2 (b) NaCl

(c) MgSO4 (d) CaSO4

59. The metallic lustre exhibited by sodium

is explained by

[IIT]

(a) Diffusion of sodium ions

(b) Oscillation of loose electrons

(c) Excitation of free protons

(d) Existence of body centred cubic lattice

60. Electrolysis of molten sodium chloride

leads to the formation of

[KCET]

(a) Na and H2 (b) Na and O2

(c) H2 and O2 (d) Na and Cl2

61. A solution of sodium metal in liquid

ammonia is strongly reducing due to the

presence of

[IIT]

(a) Sodium atoms (b) Sodium hydride

(c) Sodium amide (d) Solvated electron

62. Causticization process is used for the

preparation of

[CPMT; BHU]

(a) Caustic soda (b) Caustic potash

(c) Baryta (d) Slaked lime

63.


(29)

NaOH is manufactured by electrolysis

of brine solution. The products of the

reaction are

[Karnataka CET 1990]

(a) Cl2 and H2 (b) Cl2 and Na−Hg

(c) Cl2 and Na (d) Cl2 and O2

64. Sodium carbonate is manufactured by

Solvay process, the products that are

recycled are

[Karnataka CET 1993]

(a) CO2 and NH3 (b) CO2 and NH4Cl

(c) NaCl. CaO (d) CaCl2, CaO

65. In the preparation of sodium carbonate,

which of the following is used

[AFMC 1992]

(a) Slaked lime (b) Quick lime

(c) Lime stone (d) NaOH

66. Sodium carbonate reacts with SO2 in

aqueous medium to give

[MP PMT]

(a) NaHSO3 (b) Na2SO3

(c) NaHSO4 (d) Na2SO4

67. Soda lime is

[Karnataka CET]

(a) NaOH (b) CaO

(c) NaOH and CaO (d) Na2CO3

68. Molten sodium is used in nuclear

reactors to

[Karnataka CET]

(a) Absorb neutrons in order to control

the chain reaction

(b) Slow down the fast neutrons

(c) Absorb the heat generated by nuclear

fission

(d) Extract radio-isotopes produced in the

reactor

69. Sodium thiosulphate (Na2S2O35H2O)is used in photography to

[CPMT; Delhi PMT; Bihar CEE; MNR]

(a) Reduce silver bromide to metallic silver

(b) Convert metallic silver to silver salt

(c) Remove undecomposed AgBr as a

soluble silver thiosulphate complex

(d) Remove unreduced silver

70. Microcosmic salt is

[CPMT; BHU]

(a) Na2HPO42H2O

(b) Na(NH4) HPO44H2O

(c) (NH4) 2HPO42H2O


71. In the manufacture of metallic sodium

by the fused salt electrolysis (Down’s

process) a small amount of calcium

chloride is added to

[MP PET; MP PMT]

(a) Improve the electrical conduction

(b) Increase the temperature of electrolysis

(c) Bring down the melt temperature

(d) Stabilize the metallic sodium

72. In alumino-thermite process, aluminium

is used as

[IIT; DPMT; MP PMT;

MP PET/PMT; NCERT]

(a) Oxidising agent (b) Flux

(c) Reducing agent (d) Solder

73. Which of the following ore is used for

industrial extraction of aluminium in

India

[MP PET]

(a) Corundum (b) Keolin

(c) Cryolite (d) Bauxite

74. Which metal is extracted by electrolytic

reduction method

[CPMT; MP PET]

(a) Cu (b) Al


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(c) Fe (d) Ag

75. Bauxite is an oxide ore of

[CPMT; BHU; AFMC; Kurukshetra CEE]

(a) Barium (b) Boron

(c) Bismuth (d) Aluminium

76. Which metal is protected by a layer of

its own oxide

[NCERT; Delhi PMT; BHU]

(a) Al (b) Ag

(c) Au (d) Fe

77. Hoop’s process is used for the

purification of the metal

[MP PET]

(a) Al (b) Zn

(c) Ag (d) Cu

78. Cryolite is

[AMU]

(a) Magnesium silicate

(b) Sodium borofluoride

(c) Sodium aluminium fluoride

(d) Magnesium silicate

79. Purification of aluminium done by

electrolytic refining is known as

[CPMT; CBSE]

(a) Serpeck’s process

(b) Hall’s process

(c) Baeyer’s process

(d) Hoop’s process

80. Main ore of aluminium is

[CPMT; Raj. PMT]

(a) Bauxite (b) Corundum

(c) Cryolite (d) Magnetite

81. In duralumin, which metals are alloyed

with aluminium

[CPMT; Delhi PMT]

(a) Nickel

(b) Magnesium and Nickel

(c) Magnesium, Manganese and Copper

(d) Magnesium, Nickel and Manganese

82. Bauxite containing impurities of iron

oxide is purified by

[CPMT; AIIMS]

(a) Hoop’s process

(b) Serpeck’s process

(c) Baeyer’s process

(d) Electrolytic process

83. Thermite is the mixture of

[BHU]

(a) Fe2O3 + Al (b) Cu + Mg

(c) Zn + Mg (d) Fe + Al

84. Corundum is

[CPMT; DPMT; MP PAT]

(a) SrO2 (b) Al2O3

(c) CaCl2 (d) Cu2Cl2

85. Hydrogen gas will not reduce

[IIT]

(a) Heated cupric oxide

(b) Heated ferric oxide

(c) Heated stannic oxide

(d) Heated aluminium oxide

86. Anhydrous AlCl3 is obtained from

[BHU; CPMT]

(a) HCl and aluminium metal

(b) Aluminium and chlorine gas

(c) Hydrogen chloride gas and aluminium

metal


87. Aluminium is prepared in large

quantities by

[KCET]

(a) Heating cryolite in a limited quantity

of air

(b) Reducing aluminium oxide with coke


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(c) Reducing aluminium oxide with

sodium

(d) Electrolysing aluminium oxide

dissolved in fused electrolyte

88. Sapphire is mineral of

[BHU]

(a) Cu (b) Zn

(c) Al (d) Mg

89. Alum is used by dyers

[CPMT; MP PMT]

(a) For fire-proofing fabrics

(b) As first-aid for cuts

(c) For softening hard water

(d) As mordant

[MP PAT]

90. Which is not a mineral of aluminium

[BHU; MLNR]

(a) Anhydrite (b) Bauxite

(c) Corundum (d) Diaspore

91. Which of the following mineral does not

contain Al

[IIT Screening]

(a) Cryolite (b) Mica

(c) Feldspar (d) Fluorspar

92. In the extraction of aluminium the

electrolyte is

[CBSE]

(a) Fused cryolite with felspar

(b) Fused cryolite with fluorspar

(c) Pure alumina in molten cryolite

(d) Pure alumina with bauxite and molten

cryolite

93. The funct ion of f luorspar in the

electrolytic reduction of alumina

dissolved in fused cryolite (Na3AlF6) is

[Karnataka CET; IIT]

(a) As a catalyst

(b) To lower the temperature of the melt

and to make the fused mixture very

conducting

(c) To decrease the rate of oxidation of

carbon at the anode

(d) None of the above.

94. Which technique is used in the

manufacture of aluminium from bauxite

[NCERT]

(a) Reduction with magnesium

(b) Reduction with coke

(c) Electrolytic reduction

(d) Reduction with iron

95. When Al is added to KOH solution

[NCERT; CPMT]

(a) No action takes place

(b Oxygen is evolved

(c) Water is produced

(d) Hydrogen is evolved

96. Aluminium is more reactive than iron.

But aluminium is less easily corroded

than iron because

[Karnataka CET]

(a) Aluminium is a noble metal

(b) Oxygen forms a protective oxide layer

(c) Iron undergoes reaction easily with

water

(d) Iron forms mono and divalent ions

97. Aluminium vessels should not be

washed with materials containing

washing soda since.

[Karnataka CET]

(a) Washing soda is expensive

(b) Washing soda is easily decomposed

(c) Washing soda reacts with aluminium

to form soluble aluminate


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(d) Washing soda reacts with aluminium

to form insoluble aluminium oxide

98. Which of the following processes does

not involve a catalyst

[Karnataka CET]

(a) Haber’s process

(b) Thermite process

(c) Ostwald process

(d) Contact process

99. Which of the statements about

anhydrous aluminium chloride is

correct

[IIT]

(a) It exists as AlCl3 molecule

(b) It is not easily hydrolysed

(c) It sublimes at 100ºc under vacuum

(d) It is a strong Lewis base

100. Common alum is

[DPMT; CPMT; AMU]

(a) K2SO4Al2(SO4) 3 . 24H2O

(b) K2SO4.Cr2(SO4) 3 . 24H2O

(c) K2SO4.Fe2(SO4) 3.24H2O

(d) (NH4) 2SO4.FeSO4.6H2O

101. Which of the following is called alum

[CPMT; Delhi PMT; AIIMS]

(a) Aluminium NaAlO2

(b) Na2SO4.Al2(SO4) 3.24H2O

(c) KCl.MgCl2.6H2O

(d) FeSO4.(NH4) 2SO4.6H2O

102. Which of the following is not true about

potash alum

[MLNR]

(a) Its empirical formula is

KAl(SO4) 2.12H2O

(b) Its aqueous solution is basic

(c) It is used in dyeing industries

(d) On heating it melts in its water of

crystallization

103. An important oxide ore of iron is

[MP PAT; MP PET/PMT;

MP PET; MP PMT]

(a) Haematite (b) Siderite

(c) Pyrites (d) Malachite

104. In the manufacture of iron lime stone

added to the blast furnace, the calcium

ion ends in the form

[MP PMT; CPMT; KCET;

IIT; MADT Bihar]

(a) Slag (b) Gangue

(c) Calcium metal (d) CaCO3

105. Stainless steel is an alloy steel of the

following metals

[MP PET]

(a) Fe only (b) Cr and Ni

(c) W and Cr (d) Ni and Fe

106. Steel becomes soft and pliable by

[MP PET]

(a) Annealing (b) Nitriding

(c) Tempering (d) Case hardening

107. Most stable oxidation state of iron is

[AFMC; CPMT]

(a) + 2 (b) + 3

(c) - 2 (d) - 3

108. Nickel steel contain % of Ni

[MP PMT/PET]

(a) 1 - 5% (b) 3 - 5%

(c) 6 - 5% (d) 8 - 5%

109. Permanent magnet is made from

[MP PMT / PET; MP PMT]

(a) Cast iron (b) Steel

(c) Wrought Iron (d) All the above.

110. In nitriding process of steel

[MP PET/PMT; CBSE]


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(a) Steel is heated in an atmosphere of

ammonia

(b) Steel is made red hot and then cooled

(c) Steel is made red hot and then pluged

into oil for cooling


111. Iron is rendered passive by the action

of

[IIT; MP PET; MP PMT;

Delhi PMT; KCET]

(a) Conc. H2SO4 (b) Conc. H3PO4

(c) Conc. HCl (d) Cone. HNO3

112. I ron sheets are galvanized by

deposi t ing a coat ing of or in

galvanisation, iron surface is coated

with

[MP PET; NCERT; Bihar CEE]

(a) Zinc (b) Tin

(c) Chromium (d) Nickel

113. Chemical formula of rust is

[BHU; MP PET]

(a) FeO (b) Fe3O4

(c) Fe2O3 . xH2O (d) FeO. xH2O

114. Heating steel to bright redness and then

cooling suddenly by plunging it into oil

or water, makes it

(a) Hard and pliable

(b) Soft and pliable

(c) Soft and brittle

(d) Hard and brittle

115. Which of the following pairs of elements

might form an alloy

[NCERT]

(a) Zinc and lead

(b) Iron and mercury

(c) Iron and carbon

(d) Mercury and platinum

116. Green vitriol is

[Delhi PMT; BHU]

(a) CuSO4.5H2O (b) FeSO4.7H2O

(c) CaSO4.2H2O (d) ZnSO4.7H2O

117. Formula of magnetite is

[CPMT]

(a) Fe2O3 (b) FeS2

(c) FeCO3 (d) Fe3O4

118. The alloy of steel that is used in making

automobile parts and utensils

[EAMCET; MP PMT]

(a) Stainless steel (b) Nickel steel

(c) Tungstun steel (d) Chromium steel

119. Which of the following has lowest

percentage of carbon

[Delhi PMT; CPMT]

(a) Cast iron

(b) Wrought iron

(c) Steel

(d) All have same percentage

120. Which of the following is ferrous alloy

[Delhi PMT; CPMT]

(a) Invar (b) Solder

(c) Magnalium (d) Type metal

121. Galvanisation is the

[CPMT; MP PET/PMT]

(a) Deposition of Zn on Fe

(b) Deposition of Al on Fe

(c) Deposition of Sn on Fe

(d) Deposition of Cu on Fe

122. Best quality of steel is manufactured by

[BHU]

(a) Siemen-Martin’s open hearth process

(b) Electrical process

(c) Bessemer process

(d) Blast furnace

123.


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The chief constituents of stainless steel

made in India are

[MP PMT/PET]

(a) Mn and Cr (b) Al and Zn

(c) V and Co (d) Ni and Mg

124. In the manufacture of iron from

haematite, the function of lime stone is

as

[CPMT; MP PET]

(a) A reducing agent (b) Flux

(c) Slag (d) Gangue

125. Magnetic separation is used for

increasing concentrat ion of the

following

(a) horn silver (b) calcite

(c) haematite (d) magnesite

[M.P. PET]

126.The main function of roasting is

(a) To remove the volatile matter

(b) Oxidation

(c) Reduction

(d) To make slag

(M.P.)

127. Heating of pyrites in air for oxidation of

sulphur is called

(a) roasting (b) smelting

(c) calcination (d) slagging

(C.P.M.T.; D.P.M.T.)

128. In blast furnace iron oxide is reduced by

(a) silica (b) CO

(c) C (d) lime stone

(M.P.P.M.T.)

129. Blast furnace is employed in the

smelting of oxide ore with coke and flux

in the metallurgy of

(a) iron (b) copper

(c) lead (d) all the above

130. Cyanide process is used for obtaining

(a) Cr (b) Ag

(c) Cu (d) Zn

131. In the extraction of lead by air reduction

process, the reducing agent is

(a) PbS (b) O2

(c) C (d) A1

132. A common metal that is used for the

extraction of some metals from their

oxides is

(a) Cr (b) Fe

(c) Mn (d) Al

133. Which method of purif ication is

represented by the fo l lowing

equations?

T : + 2I2 −−−−> T : I4 −−−−−>1675k

T : + 2I2

(a) Cupellation (b) Poling

(c) Van Arkel (d) Zone refining

134. Zone refining is a method to obtain

(a) Very high temperature

(b) Ultra pure Al

(c) Ultra pure metals

(d) Ultra pure oxide

135. In metallurgy, flux is a subtance used to

convert

(E.A.M.C.E.T.)

(a) Infusible impurities to fusible material

(b) Soluble impurities to insoluble

impurities

(c) Fusible impurities to infusible

impurities

(d) Mineral into silicate

136. The lustre of a metal is due to

(a) its high density

(b) its high polishing

(c) its chemical inertness

(d) presence of free electrons


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137. Which one of the following reactions is

a example for calcination process?

(a) 2Ag + 2HCl + (O) → 2 AgCl + H2O

(b) 2Zn + O2 → 2

(c) 2ZnS + 3O2 → 2ZnO + 2SO2

(d) MgCO3 → MgO + CO2

(E.A.M.C.E.T.)

138. Malachite is an ore of

(a) iron (b) copper

(c) mercury (d) zinc

139. The extraction of which of the following

metals involves bessemerisation?

(a) Fe (b) Ag

(c) Al (d) Cu

(B.H.U.)

140. In Goldschmidt a luminothermic

process, reducing agent used is

(C.E.E. Bihar 1995)

(a) Coke (b) Al power

(c) Na (d) Ca

(B.H.U.)

141. Purification of silicon element used in

semiconductors is done by

(C.B.S.E.)

(a) zone refining

(b) heating

(c) froth floatation

(d) heating in vacuum

142. Purest form of iron is

[CPMT, DPMT; MP PMT; MP PET)

(a) Cast iron (b) Wrought iron

(c) Hot steel(d) Stainless steel

143. The formula of haematite is

[MLNR]

(a) Fe3O4 (b) Fe2O3

(c) FeCO3 (d) FeS2

144. Bessemer converter is used in the

manufacture of

[CPMT]

(a) Pig iron (b) Steel

(c) Wrought iron (d) Cast iron

145. Steel contains

(a) Fe + C + Mn (b) Fe + C + Al

(c) Fe + Mn (d) Fe + Mn + Cr

146. Mohr’s salt is

(a) FeSO4 7H2O

(b) Fe(NH4) SO4 6H2O

(c) (NH4) 2SO4 FeSO4 6H2O

(d) [Fe(NH4) 2](SO4) 2 6H2O

147. An example of double salt is

[CPMT; CBSE; Roorkee]

(a) Bleaching powder (b) K4[Fe(CN) 6]

(c) Hypo (d) Potash alum

148.Malachite is a mineral of

[MP PMT; MP PET; MP PET/PMT]

(a) Zn (b) Fe

(c) Hg (d) Cu

149. After partial roasting, the sulphide of

copper is reduced by

[MP PMT]

(a) Reduction by carbon

(b) Electrolysis

(c) Self-reduction

(d) Cyanide process

150. In extraction of copper, we use

[CPMT; MP PMT]

(a) Cu2S

(b) Pyrites

(c) Silver argentocyanide

(d) CuFeS2

151. Blister copper is

[CPMT; DPMT; MP PET; Bihar CEE]


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(a) Pure copper

(b) Ore of copper

(c) Alloy of copper

(d) 1% impure copper

152. The most important oxidation state of

copper is

[MP PMT]

(a) + 1 (b) + 2

(c) + 3 (d) + 4

153. Which of the following property is not

expected to be shown by copper

[MP PET/PMT; NCERT; MP PET]

(a) High thermal conductivity

(b) Low electrical conductivity

(c) Ductility

(d) Malleability

154. One of the constituent of german silver

is

[IIT; Kurukshetra CEE]

(a) Ag (b) Cu

(c) Mg (d) Al

155. Gun metal is an alloy of

[MP PMT; CPMT]

(a) Cu and Al (b) Cu, Sn and Zn

(c) Cu, Zn and Ni (d) Cu and Sn

156. Copper can be extracted from

[NCERT; CPMT]

(a) Kupfernickel (b) Dolomite

(c) Galena (d) Malachite

157. Which element is alloyed with copper to

from bronze

[CPMT; DPMT]

(a) Fe (b) Mn (c) Sn (d) Zn

158. German silver is an alloy of

[EAMCET; CPMT; MP PET/PMT]

(a) Copper, zinc and nickel

(b) Copper and silver

(c) Copper, zinc and tin

(d) Copper, zinc and silver

159. Brass contains

[Delhi PMT; CPMT; MLNR; AFMC;

EAMCET; MP PMT]

(a) (Cu + Sn) (b) (Cu + Ni)

(c) (Cu + Zn) (d) (Mg + Al)

160. An alloy which does not contain copper

is

[Delhi PMT]

(a) Solder (b) Bronze

(c) Brass (d) Bell metal

161. Percentage of silver in the alloy german

silver is

[CPMT]

(a) 1.5% (b) 2.5% (c) 10% (d) 0%

162. Reaction between the following pairs

will produce H2 except

[CPMT; CBSE]

(a) Na + ethyl alcohol

(b) Fe + steam

(c) Fe + H2SO4 (aq) .

(d) Cu + HCl (aq.)

163. An extremely hot copper wire reacts

with steam to give

(a) CuO (b) Cu2O

(c) Cu2O2 (d) CuO2

164. From a solution of CuSO4 the metal

used to recover copper is

[MP PET; CPMT]

(a) Sodium (b) Iron

(c) Silver (d) Hg

165. Indicate the mineral from which copper

is manufactured

[NCERT]

(a) Galena (b) Cuprite

(c) Sphalerite


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(d) Chalcopyrite

166. The slag obtained during the extraction

of copper from copper pyrites is

composed mainly of

[MNR; MP PMT]

(a) CaSiO3

(b) FeSiO3

(c) CuSiO3

(d) SiO2

167. Copper displaces which of the metal

from their salt solutions

[CPMT]

(a) AgNO3

(b) ZnSO4

(c) FeSO4

(d) All of the above

168. High purity copper metal is obtained by

[MP PMT]

(a) Carbon reduction

(b) Hydrogen reduction

(c) Electrolytic reduction

(d) Thermite reduction

169. Cuprous ion is colourless, while cupric

ion is coloured because

[EAMCET]

(a) Both have unpaired electrons in

d-orbital

(b) Cuprous ion has a completed d-orbital

and cupric ion has an incomplete

d-orbital

(c) Both have half-filled p and d-orbintals

(d) Cuprous ion has incomplete d-orbital

and cupric ion has a completed

d-orbital

170. Identify the statement which is not

correct regarding CuSO4

[MNR; Punjab PMT]

(a) It reacts with KI to give iodine

(b) It reacts with KCl to give Cu2Cl2

(c) It reacts with NaOH and glucose to

give Cu2O

(d) It gives CuO on strong heating in air

171. If excess of NH4OH is added to

CuSO4 solution, it forms blue coloured

complex which is

[MP PMT; Bihar CEE]

(a) Cu(NH3) 4SO4

(b) Cu(NH3) 2SO4

(c) Cu(NH4) 4SO4

(d) Cu(NH4) 2SO4

172. Bell metal is an alloy of

[Delhi PMT; CBSE]

(a) Cu, Zn and Sn

(b) Cu, Zn and Ni

(c) Cu and Zn

(d) Cu and Sn

173. Which composit ion amongst the

following represents the alloy ‘‘german

silver’’

[EAMCET; CPMT; BIT; MNR]

(a) Cu(52) , Ni(25) , Zn(18) , Fe(5)

(b) Cu(60) , Ni(40)

(c) Ni(60) , Fe(25) , Cr(15)

(d) Cu(55) , Ni(20) , Zn(25)

174. The metal commonly present in brass

and german silver is

[EAMCET]

(a) Mg (b) Zn

(c) C (d) Al

175. Complex is formed in the extraction of

[MP PET]

(a) Na (b) Cu

(c) Ag (d) Fe


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Documents

Principles of Metallurgical Operations