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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
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(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
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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
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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
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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.
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(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
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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
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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.
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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
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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
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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
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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
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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
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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.
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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
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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
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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.
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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.
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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
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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.
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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
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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.
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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.
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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.
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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
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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
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(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
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(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
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(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.
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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
(d) None of the above
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
(d) None of the above
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
(d) None of the above
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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