Chapter:-6
General
Principles & Process of Isolation of Elements
Important
Points :
1.
The
chemical substances present in
the earth’s crust are known as
minerals
2.
Minerals, which act as source for
metal, are called Ore.
3.
The unwanted impurities present in
ore are called Gangue.
4.
The entire process of extraction of
metal from its ore is called Metallurgy.
5.
Removal of gangue from ore is called
Concentration, Dressing or Benefaction of ore.
6.
Concentration by Hydraulic washing is
based on the difference in gravities of ore and gangue particles.
7.
Concentration by Magnetic separation
is based on differences in magnetic properties of ore components. If either of
ore or gangue is capable of attracted by a magnet field, then such separation
is carried out.
8.
Concentration by Froth Flotation
Process is based on the facts that sulphide ore is wetted by oil & gangue
particles are wetted by water.
9.
Concentration by Leaching is based on
the facts that ore is soluble in some suitable
reagent & gangue is insoluble in same reagent.
e.g. Bauxite ore contains impurities of silica, iron oxide & TiO2
.The powdered ore is treated with NaOH which dissolves Alumina & impurities
remains insoluble in it.
Al2O3
+2NaOH + 3 H2O
2 Na[Al(OH)4].
10. Calcination involves
heating of ore in absence of air below melting point of metal. In this process
volatile impurities escapes leaving behind metal oxide.
Fe2O3.xH2O
Fe2O3 +xH2O
|
ZnCO3
|
ZnO
+CO2
|
|
CaCO3.MgCO3
|
CaO
+ MgO + 2CO2
|
|
2 ZnS + 3 O2
|
2ZnO+2SO2
|
|
2PbS
+ 3 O2
|
2
PbO +2 SO2
|
|
2 Cu2S
+ 3 O2
|
2Cu2O
+ 2 SO2
|
Coke or CO.
13. Reactions
taking place at different zones of blast furnace in extraction of iron:-
|
(i) Zone of
reduction:-
|
Temperature range 250oC-700oC
|
|
3Fe2O3+CO
|
2Fe3O4+CO2
|
|
Fe3O4+CO
|
3FeO+
CO2
|
|
FeO
+CO
|
Fe
+ CO2
|
CaCO3
CaO+CO2
CaO+SiO2
CaSiO3,
P4O10+10C
4P+10CO,
SiO2+2C
Si+2CO,
MnO2+2C
Mn+2CO
CO2
+ C
2CO
(IV) Zone of
fusion: - Temperature range 1450oC-1950oC
C +O2
CO2
14. FLOW SHEET
FOR EXTRACTION OF IRON:-
Iron
ore (Magnetite Fe3O4)
Concentration is
done by Gravity separation followed by magnetic separation
↓
Calcination &Roasting i.e.2,SO2 Ore,As23
removed And FeO oxidized to Fe2O3
Smelting of charge i.e. mixture of ore, coke &
CaCO3 takes place in long BLAST FURNACE. Following reaction
take place at different zones:-
(refer
to point 13)
↓
Pig iron is
obtained, which is remelted and cooled then cast iron is obtained
15.
Pig Iron: - It contains Fe 93-95%, Carbon
2.5-5%, and Impurities 3%.
16.
Cast Iron: - It contains Fe 99.5-99.8%,
Carbon 0.1-0.2% Impurities 0.3%.
17. Spongy
iron: - Iron formed in the zone of reduction of blast furnace is called spongy
iron. It contains impurities of C, Mn , Si, etc.
18. 18.
FLOW SHEET FOR EXTRACTION OF COPPER:-
Copper
Pyrites CuFeS2
Powdered ore +
water +pine
↓
Roasting
is presence of air following reactions take place:-
↓
A mixture of Cu2S,
FeS & silica is obtained from blast furnace known as Copper matte
Bessemerisation of copper matte is done in Bessemer
converter in presence of air. Following reactions take place:-
2FeS + 3O2→2FeO
+2FeO +SOSiO2 →FeSiO3(slag), 2Cu2S + 3O2
→2CuO+2SO2, 2Cu 2O+2Cu2S→ Cu6+ SO2
Melted copper is cooled, and then SO2 is
evolved such copper is known as BLISTER COPPER(98%Cu+2% impurities)
Bauxite
Al2O3.2H2O
Concentration
of ore is done by leaching .Bauxite is treated with NaOH
.Following
reaction takes place:-
Al2O3 +2NaOH + 3 H2O
2 Na [Al(OH) 4]
and impurities of Fe2O3, TiO2 & SiO2 are
removed.
↓
Na[Al(OH)4]
,then reacts with CO2 then pure Alumina is obtained.
↓
|
Electrolytic
reduction of pure alumina takes place in iron box (cathode) with cryolite (Na3AlF6)
& fluorspar CaF2.Graphite rods act as anode. Following
reactions take place:-
|
At
cathode
Al3+
+ 3e Ã
Al
At
Anode
2
O Ã O2
By
this process 98.8% pure Aluminum is obtained.
20. Vapour
phase refining is used for extraction of Nickel (MOND PROCESS) and Zirconium
&Titanium (VAN ARKEL PROCESS).
21.
Zone refining is used for extraction of
Si, Ge, Ga, etc.
22. Chromatography
method is based on selective distribution of various constituents of a mixture
between two phases, a stationary phase and a moving phase. The stationary phase
can be either solid or liquid on solid support.
22. Column
chromatography is based on adsorption phenomenon. This method is useful for
those elements, which are available in small amounts and the impurities are not
much different in chemical properties from the element to be purified.
VERY SHORT ANSWER TYPE QUESTION
A.1-
It is easily fusible material, which is formed when gangue still present in
roasted ore combines with the flux.e.g. CaO (flux) + SiO2 (gangue)
→CaSiO3 (slag)
Q.2- Which is better reducing agent at 983K, carbon or
CO?
A.2- CO, (above 983K CO being more stable & does
not act as a good reducing agent but carbon does.) Q.3- At which temperature
carbon can be used as a reducing agent for FeO?
A.3- Above 1123K,
carbon can reduce FeO to Fe.
Q.4- What is the
role of graphite rods in electrometallurgy of aluminium?
A.4- Graphite rods act as anode, are attacked by
oxygen to form CO2 and so are to be replaced from time to time.
Q.5- What is
the role of cryolite in electrometallurgy of aluminium?
A.5- alumina cannot be fused easily because of high
melting point. Dissolving of alumina in cryolite furnishes Al3+
ions, which can be electrolyzed easily.
Q.6- What are
depressants?
A.6-
It is possible to separate two sulphide ore by adjusting proportion of oil to
water in froth flotation process by using a substance known as depressant.
e.g. NaCN is used to separate ZnS and PbS.
Q.7- Copper can be
extracted by hydrometallurgy but not Zn. Why?
A.7- The E0 of Zn is lower than that of Cu
thus Zn can displace Cu2+ ion from its solution. On other hand to displace Zn from Zn2+ ion, we
need a more reactive metal than it.
Q.8- Give name and
formula of important ore of iron .
A.8- Haematite –Fe2O3, Magnetite
–Fe3O4, Iron pyrites FeS2. Q.9- Give name and
formula of important ore of Copper .
A.9- Copper pyrites CuFeS2, Malachite CuCO3
. Cu(OH)2, Cuprite Cu2O.
Q.10- Give name
and formula of important ore of Zinc .
A.10- Zinc blende
- ZnS, Calamine- ZnCO3, Zincite –ZnO .
SHORT ANSWER TYPE QUESTION (2 marks)
Q.1 Describe the
method of refining of nickel.
A.1- In the Mond Process, Ni is heated in a stream of
CO forming a volatile complex, which then decomposes at higher temperature to
give Ni.
At 330-350K: -
Ni + 4CO →
Ni(CO) 4
At 450-470K
Ni (CO)4 → Ni
+ 4CO
Q.2- What is Zone
Refining? Explain with example.
A.2-
Zone refining is a method of obtaining a metal in very pure state. It is based
on the principal that impurities are more soluble in molten state of metal than
solidified state.
In
this method, a rod of impure metal is moved slowly over circular heater. The
portion of the metal being heated melts & forms the molten zone. As this
portion of the rod moves out of heater, it solidified while the impurities pass
into molten zone. The process is repeated to obtain ultrapure metal and end of
rod containing impure metal cutoff.
Q.3 Write the principal
of electro-refining.
A.3-
In this method of purification impure metal is made Anode and pure metal is
made the cathode. On passing electricity, pure metal is deposited at the
cathode while the impurities dissolve in solution as anode
mud. E.g. electro-
refining of copper:-
At Cathode: - Cu2+ + 2e- → Cu
Q.4- Write difference between calcinations and roasting.
Q.5- Describe the
method of refining of Zirconium and Titanium.
A.5- Van Arkel process is used for obtaining ultrapure
metal. The impure metal is converted into volatile compound, which then
decomposes electrically to get pure metal.
|
At 850K: -
|
Zr
impure) + 2 I2 → ZrI4
|
|
At 2075K:-
|
ZrI4 →
Zr (pure) + 2 I2
|
Q.6- Out of C
& CO, which is better reducing agent for ZnO?
A.6- Since free energy of formation of CO from C is
lower at temperature above 1120K while that of CO2 from carbon is
lower above 1323K than free energy of formation 0f ZnO. However, the free
energy of
formation of CO2
from CO is always higher than that of ZnO. Hence, C is better reducing agent of
ZnO.
0
Q.7- The value of ∆fG for Cr2O3
is -540kJ/mole & that of Al2O3 is -827kJ/mole.
Is the reduction of Cr2O3
possible with
aluminium?
A.7- The desired
conversion is
4
Al + 2Cr2O3 → 2Al2O3 + 4Cr
It is obtained by
addition of following two reactions:-
4Al + 3O2 → 2
Al2O3 ∆f G0= -827kJ/mole
2Cr2O3 → 4Cr +3O2 ∆fG0== + 540kJ/mole
Therefore, ∆G desired reaction is -827+540= -287, as a
result reductionis possible.
Q.8:- Why copper matte is put in silica lined
converter?
A.8:- Copper matte consists of Cu2S and
FeS. When blast of air is passed through molten matte in silica-lined
converter, FeS present in matte is oxidized to FeO, which combines with silica
to form slag.
Q.9- What is meant
by term chromatography?
A.9-Chromato means Colour and graphy means writing
because the method was first used for separation of coloured substance. It is
based on selective distribution of various constituents of a mixture between
two phases, a stationary phase and a moving phase. The stationary phase can be
either solid or liquid on solid support.
Q.10-Why is reduction of metal oxide easier if metal
formed is in liquid state at temperature of reduction. A.10- The entropy of a
substance is higher in liquid state than solid state. In the reduction of metal
oxide,
0
the
entropy change will be positive and ∆G of metal is negative, reduction occurs easily.
SHORT ANSWER TYPE
Q.1- Explain the
following:-
(i)
Zinc but not copper is used for recovery
of Ag from the complex [Ag(CN)2]-.
(ii)
Partial roasting of sulphide ore is done
in the metallurgy of copper.
(iii)
Extraction of Cu from pyrites is difficult
than that from its oxide ore through reduction.
A.1- (i) Zn is
more powerful reducing agent in comparison to copper.Zn is also cheaper than
Cu.
(ii) Partial roasting of sulphide ore forms some
oxide. This oxide then reacts with remaining sulphide ore to give copper i.e.
self-reduction occurs.
2Cu2S + 3O2
→ 2CuO + SO2, 2CuO + Cu2S →
4Cu + SO2
(iii) Though carbon is good reducing agent for oxide
but it is poor reducing agent for sulphides. The reduction of metal sulphide
does not have large negative value.
Q.2- Explain the
method for obtaining pig iron from magnetite.
A.2- Extraction of
iron from Magnetite takes place in following steps:-
(i)
Concentration of ore: - It is done by
Gravity separation followed by magnetic separation process.
(ii)
Calcination: - It involves heating when
the volatile matter escapes leaving behind metal oxide.
Fe2O3.xH2O→ 2FeO3+ x H2O
.
(iii) Roasting:
- It involves heating of ore in presence of air, thus moisture, CO2,
SO2, As2O3 removed And FeO oxidized to Fe2O3.
(iv) Smelting
of roasted ore: - A mixture of ore, coke & CaCO3 is smelted in
long BLAST FURNACE. Following
reaction takes place at different temperature zones:-
(i)
Zone of reduction: - Temperature range 250oC-700oC
|
3Fe2O3+CO →
|
2Fe3O4+CO2
|
|
Fe3O4+CO →
|
3FeO+
CO2
|
|
FeO
+CO →
|
Fe+
CO2
|
|
(ii) Zone of
slag formation:- Temperature range 800oC-1000oC
|
|
|
CaCO3 Ã CaO+CO2
|
|
|
|
P4O10+10C Ã P4
+ 10 CO
|
|
|
MnO2 + 2C Ã
Mn + 2CO
|
|
|
|
CO2
+ C
2CO
(iv)
Zone of fusion:- Temperature range 1450oC-1950oC
C + O2
CO2
Thus, Pig iron is obtained from
Blast Furnace.
Q.3- Describe the
principles of extraction of copper from its ore.
Q.4- Name the
principal ore of aluminium and describe how Al is extracted from its ore.
A.4-
Important ores -(i) Bauxite Al2O3.xH20 (ii)
Corrundum Al2O3. Bauxite is commercially important ore of
Al.
Extraction from
Bauxite ore involves the following two stages:-
(i) Purification of bauxite
to get pure alumina (Al2O3) (ii)Electrolysis of
pure alumina in molten cryolite
Step:-1 Bauxite is
treated with NaOH .Following reaction takes place:-
Al2O3 +2NaOH + 3H2O
2 Na[Al(OH)4]
and
impurities of Fe2O3,TiO2&SiO2 are
removed . Na[Al(OH)4] ,then reacts with CO 2 then pure
Alumina is obtained.
Na[Al(OH)4]
+ 2CO2 → Al2O3.xH2O
+ 2NaHCO3
Step:-2
Electrolytic reduction of pure alumina takes place in iron box (cathode) with
cryolite (Na3AlF6) & fluorspar CaF2.Graphide
rods act as anode. Following reactions take place:-
|
At cathode:- Al3+
|
|
+ 3e
|
-
|
→
|
|
|
|
|
|
|
Al, At Anode: -2O2-
|
→O2+4e
|
|
By
this process 98.8% pure Aluminum is obtained.
Q.5- Describe the
principles of extraction of Zinc from zinc blende .
A.5-
Important ores of Zn:-Zinc blende - ZnS, Calamine- ZnCO3, and
Zincite –ZnO. ZnS is commercially important ore of Zn.Various stages involved
in the extraction of Zn from ZnS are as following:-
(i) Concentration of ore:-It is concentrated by Froth
flotation process followed by gravity separation process.
(ii)
Roasting: - The concentrated ore is roasted in presence of air. Following
reactions take place:-
2ZnS + 3O2 → 2ZnO +
2SO
The mass obtained
during roasting is porous and is called porous clinker.
(iii)
Reduction of ZnO to Zn: - ZnO is made into bricketts with coke and clay and
heated ai1163K.Zn formed distills off and is collected by rapid cooling of zinc
vapours.
ZnO
+ C → Zn+CO
VALUE
BASED QUESTIONS
Q1 . After entering a closed coal mine
area, Ravi found difficulty in breathing, also felt nausea.
a. What could be the reason for this? (1)
b. How could Ravi estimate the level of
the pollutant? (1)
c. As a citizen of the country what should
be his course of action further? (1)
Ans: a. In coal mines due to lack of
oxygen a small percentage of carbon monoxide is formed. This carbon monoxide
being poisonous gives the symptoms.
b. Ravi could estimate the level of CO
using I2O5.
c. Ravi should inform the concerned authorityabout the excess of CO in the coal
mine.
Q2. A stain of rust is there on your
clothe. You are worried how to remove this stain. Shyam tells you to remove
this stain using ripened guava.a. Why? (2)
b. What is the value you are having when
doing this? (1)
Ans:
a. The rust is iron oxide. The oxalic acid in guava fruit dissolves iron
oxide.
b. Help your friends and neighbours when
you know some simple home techniques instead of chemicals.
.
Q3. An innovative washer woman while
washing a copper miner’s clothes found that sand and similar dirt particle fell
to the bottom, while the ore particles stuck to the soapsuds and came to the
top. The washer woman discussed this matter with a client who was a chemist.
a. What is the reason for this
observation? (2)
b. What value do you get from this
episode? (1)
Ans: a. The miner’s clothes had particles
of CuS / Cu2S on it. This adhered to the froth and came up.
b. Keen observation can lead to
great discoveries.
Large amount of electricity is obtained in
our country from burning of coal. The carbon in coal is lost as carbon dioxide,
and water as water vapour. The substances left behind are minerals. These are
known as fly ash. Fly ash is a major environmental hazard. Faseeh did a project
on how to use this fly ash in building roads and in making roofing tiles. He
was appreciated by the judges. What was the value for which he was appreciated?
Ans: Recycling of industrial waste keeps
the environment clean. (3)
Q4.Asha gives an induction stove to her
friend Nish as a gift. Nisha immediately places
a curved base copper cooker to cook but it failed to work. Thinking that
the piece is defective she gets annoyed and wants to call up the service
center.nHer son beside her reads the catalogue and instructs her to use Al and
steam flat based cooker .
a. What is the chemistry behind it and
what are the values derived from this incident?
Ans a) Al is
better conductor than Cu. Critical
Thinking, Correct applicationof knowledge
Q5. At a site, low grade copper ores are
available and zinc and iron scrapes are also available. As a student of chemistry
, which of the two scrapes will you suggest for reducing the leached copper and
why? What are the values associated with the above decision?
|
S.
No.
|
CBSE
QUESTION WITH ANSWER/ VALUE POINTS
|
|
1
|
Why is the froth floatation method
selected for the concentration of sulphide ores?
As only sulphide ore particles are
wetted by oil while gangue particles are wet by water.
|
|
2
|
Explain the role of (i)Cryolite in the
electrolytic reduction of alumina (ii) NaCN in the extraction of silver from
a silver ore. (iii) Graphite in the electrometallurgy of aluminium (iv) SiO2
in the extraction of copper.
(i)
Cryolite lowers the melting point
of alumina and increases the conductivity of the mixture.
(ii)
Dilute NaCN forms a soluble complex
with Ag or Ag2S while the impurities remain unaffected which are
filtered off.
(iii)
Graphite rods are used as
electrodes in the electrometallurgy of aluminium.
(iv)
SiO2 acts as a flux in
the extraction of copper. Sulphide ore of copper contains iron as impurity
which is removed as iron
silicate (slag).
FeO + SiO2
Ã
FeSiO3 (slag)
|
|
3
|
Explain Mond’s Process for refining of
Nickel
When nickel is heated with carbon
monoxide it forms a volatile complex nickel tetracarbonylwhich on further
heating at higher temperature decomposes to give pure nickel.
|
|
4
|
Explain Refining of zirconium by van Arkel
method.
van Arkel Method for
Refining Zirconium or Titanium: In this
method, The crude metal is
heated in an evacuated
vessel with iodine. The metal iodide being more covalent, volatilises:
Zr + 2I2 → ZrI4
The metal iodide is
decomposed on a tungsten filament, electrically heated to about 1800K. The
pure metal is thus deposited on the filament.
ZrI4 → Zr + 2I2
|
|
5
|
What is meant by the term
‘pyrometallurgy’?
It is a thermal process of extracting a
metal from its ore.
|
|
6
|
Differentiate between a mineral and an
ore.
The naturally occurring chemical
substances present in the earth’s crust which can be obtained by mining are
called minerals, while mineral from which metals can be extracted economically
are called ores.
|
|
7
|
Name one chief ore each of copper and
aluminium. Name the method used for concentration of these two ores.
|
|
8
|
How can you separate alumina (Al2O3)
from silica present in bauxite ore? Write the chemicalequations for the reactions
involved.
|
|
9
|
What is the role of (i) Collectors (ii)
Stabilizers (iii) depressant in Froth
Floatation process for the concentration of a sulphide ore? Give an example.
Collectors (e. g., pine
oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral
particles and froth stabilizers (e. g., cresols, aniline) stabilise the
froth.
Depressant is used to prevent the
formation of froth from one of the two sulphide ores. For example, in case of an ore containing ZnS and PbS, the depressant
used is NaCN. It selectively prevents ZnS from coming to the froth but allows PbS to come
with the froth.
|
|
10
|
How is copper extracted from a low grade
ore of it?
Copper is extracted by hydrometallurgy
from low grade copper ores. It is leached out using acid or
bacteria. The solution containing Cu2+
ion is treated with scrap iron or H2.
Cu2+ (aq) + Fe(s)
Fe2+(aq) + Cu(s)
OR
Cu2+ (aq) + H2(g)
Cu(s) + 2H+(aq)
|
|
11
|
What is the composition of ‘Copper
matte’?
Cu2S and FeS.
|
|
12
|
How is wrought iron different from
steel?
Wrought iron is the purest form of iron
whereas steel is an alloy of iron.
|
|
13
|
(a) Which solution is used for
the leaching of silver metal in the presence of air in the metallurgy of
silver?
(b) Out of C and CO, which is a
better reducing agent at the lower temperature range in the blast furnace to
extract iron from the oxide ore?
(a) Dilute solution of NaCN.
(b) CO.
|
|
14
|
State
briefly the principles which serve as basis for the following operations in
metallurgy:
(i)
Froth floatation process (ii)
Zone refining (iii) Refining by
liquation(iv) Vapour phase refining (v) Electrolytic refining (vi) Column chromatography for purification of
rare elements.
(i)
The principle of froth floatation process is that sulphide ore particle
are preferentially wetted by
pine oil, whereas the gangue particles
are wetted by water.
(ii) Zone refining is
based on the principle that the impurities are more soluble in (liquid state)
than
in the solid state of the metal.
(iii) The principle of refining
by liquation is that the impurities whose melting points are higher
than
the
metal are left behind on melting the impure metal. Hence pure metal separates
out.
(iv) Vapour phase refining. In
this, metal is converted into its volatile compound and collected elsewhere.
It is the decomposed to give pure metal. So, the two requirements are:
(a) the metal should form a
volatile compound with an available reagent.
(b) the volatile compound should
be easily decomposable, so that the recovery is easy.
(v) In electrolytic refining
impure metal is made to act as anode. A strip of the same metal in pure
form is used as cathode. They are put in
a suitable electrolytic bath containing soluble salt of the
same metal. When electric current is
passed, impure metal forms metal ions which are
discharged at cathode forming pure
metal.
Anode: M -Ã
Mn+ + ne-
Cathode: Mn+
+ ne- Ã
M
(vi) Column chromatography is
based on the principle that different components of a mixture are differently
adsorbed on an adsorbent. In purification of rare earth elements ion-exchange
is used as an adsorbent.
|
|
15
|
Describe how the following changes are
brought about:
(i) Pig iron into steel.
(ii) Zinc oxide into metallic
zinc.
(iii) Impure titanium into pure
titanium.
OR
Describe the role of
(i) NaCN in the extraction of
gold from gold ore.
(ii) SiO2 in the extraction of
copper from copper matte
(iii) Iodine in the refining of
Zirconium
Write chemical equations for the
involved reactions.
(i) Pig iron into steel: Pig
iron is converted into steel by heating in a converter. A blast of oxygen
diluted with carbon dioxide is blown through the converter. Oxygen reacts
with impurities and raised the temperature to 2173K. Carbon gets oxidised to
CO which burns off at the mouth of the converter. Oxides of silicon and Mg
form slag. When the flame is stopped, slag is tapped
off and other metals like Mn, Cr, Ni, W
may be added in the end.
(ii) Metallic zinc can be
obtained from zinc oxide. At first calcination of ZnO is done and converted
into sinters of oxide.
ZnO + C Zn + CO
The oxide is then made into brickettes
with coke and clay and heated by producer gas in vertical retorts at 1673 K, zinc,
boiling point is 1183 K, distills off and is collected by rapid chilling.
(iii) Impure Titanium into pure
Titanium: Impure Titanium is heated with I2 to form volatile complex
(TiI4), which on heating at higher temperature decomposes to give pure titanium.
Ti (impure) + 2 I2 TiI4
Ti (pure) + 2I2
OR
(i) Role of NaCN in the
extraction of gold is to do the leaching of gold ore in the presence of air
from which the gold is obtained later by replacement.
4Au(s) + 8NaCN(aq) + 2H2O + O2
4Na[Au(CN)2] + 4KOH
(ii) SiO2 is added to
copper matte to convert the leftout FeS, FeO into slag.
FeO + SiO2 Ã FeSiO3 (Slag)
(iii) Iodine is heated with
impure Zr to form volatile compound which on further heating
decomposes to give pure zirconium.
Zr (Impure) + I2 Ã ZrI4 Ã
Zr (pure) + 2I2
|
|
16
|
Describe how the following changes are
brought about:
(i)
Bauxite into pure alumina (ii)
Impure copper into pure copper.
(ii) Impure copper into pure
copper
Pure copper is obtained by
electro-refining process. In this method, the impure metal is made
to act as anode. A strip of the same
metal in pure form is used as cathode. They are put in a
suitable electrolyte bath containing
soluble salt of the same metal.
Anode: Cu
Ã
Cu 2+ + 2e
Cathode: Cu
2+ + 2e à Cu
(Pure copper)
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17
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Describe the principle controlling each
of the following processes:
(i) Vapour phase refining of
titanium metal.
(ii) Froth floatation method of
concentration of a sulphide ore.
(i) In this method, the metal is
converted into its volatile compound and collected elsewhere. It is then
decomposed to give pure metal.
(ii)
This method of concentration of ore is based upon the principle that the
surface of sulphide ores is preferentially wetted by oils while that a gangue
is preferentially wetted by water.
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