Concept - Isolation of Elements Class 12 Notes | EduRev

Class 12 : Concept - Isolation of Elements Class 12 Notes | EduRev

 Page 1


 1
Class XII: Chemistry 
Chapter 6: General Principles & Processes Of Isolation of Elements 
Top concepts 
1. Minerals: The naturally occurring chemical substances in the earth’s 
crust which are obtained by mining are known as minerals. Metals may 
or may not be extracted profitably from them. 
2. Ores: The rocky materials which contain sufficient quantity of mineral 
so that the metal can be extracted profitably or economically are 
known as ores. 
3. Gangue: The earthy or undesirable materials present in ore are known 
as gangue. 
4. Metallurgy: The entire scientific and technological process used for 
isolation of the metal from its ores is known as metallurgy. 
5. Chief Ores and Methods of Extraction of Some Common Metals: 
Metals Occurrence Extraction Method Remark 
Sodium Rock salt: NaCl 
Feldspar:Na
3
AlSi
3
O
8
Electrolysis of fused 
NaCl or NaCl/ CaCl
2
Sodium is highly 
reactive, it reacts with 
water 
Copper Copper pyrites:CuFeS
2
 
Malachite:CuCO
3
.Cu(OH)
2 
Cuprite: Cu
2
O 
Copper glance: Cu
2
S 
Roasting of sulphide 
partially and reduction 
2Cu
2
O + Cu
2
S ? 6 Cu 
                          +SO
2
  
It is self reduction in a 
specially designed 
converter. Sulphuric 
acid leaching is also 
employed. 
Aluminium Bauxite: AlO
x
(OH)
3-2x 
where 0<x<1 
Cryolite: Na
3
AlF
6
Kaolinite: [Al
2
(OH)
4
Si
2
O
5
] 
Electrolysis of Al
2
O
3
 
dissolved in molten 
cryolite or in Na
3
AlCl
6
A good source of 
electricity is needed in 
the extraction of Al 
Zinc Zinc blende or Sphalerite: 
ZnS 
Zincite: ZnO 
Calamine: ZnCO
3
  
Roasting and then 
reduction with C 
The metal may be 
purified by fractional 
distillation. 
Lead Galena: PbS Roasting of the sulphide 
ore and then reduction 
of the oxide 
Sulphide ore is 
concentrated by froth 
floatation process 
Silver Argentite: Ag
2
S  
 
Sodium cyanide leaching 
of the sulphide ore and 
finally replacement of Ag 
by Zn 
It involves complex 
formation and 
displacement  
 
 
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 1
Class XII: Chemistry 
Chapter 6: General Principles & Processes Of Isolation of Elements 
Top concepts 
1. Minerals: The naturally occurring chemical substances in the earth’s 
crust which are obtained by mining are known as minerals. Metals may 
or may not be extracted profitably from them. 
2. Ores: The rocky materials which contain sufficient quantity of mineral 
so that the metal can be extracted profitably or economically are 
known as ores. 
3. Gangue: The earthy or undesirable materials present in ore are known 
as gangue. 
4. Metallurgy: The entire scientific and technological process used for 
isolation of the metal from its ores is known as metallurgy. 
5. Chief Ores and Methods of Extraction of Some Common Metals: 
Metals Occurrence Extraction Method Remark 
Sodium Rock salt: NaCl 
Feldspar:Na
3
AlSi
3
O
8
Electrolysis of fused 
NaCl or NaCl/ CaCl
2
Sodium is highly 
reactive, it reacts with 
water 
Copper Copper pyrites:CuFeS
2
 
Malachite:CuCO
3
.Cu(OH)
2 
Cuprite: Cu
2
O 
Copper glance: Cu
2
S 
Roasting of sulphide 
partially and reduction 
2Cu
2
O + Cu
2
S ? 6 Cu 
                          +SO
2
  
It is self reduction in a 
specially designed 
converter. Sulphuric 
acid leaching is also 
employed. 
Aluminium Bauxite: AlO
x
(OH)
3-2x 
where 0<x<1 
Cryolite: Na
3
AlF
6
Kaolinite: [Al
2
(OH)
4
Si
2
O
5
] 
Electrolysis of Al
2
O
3
 
dissolved in molten 
cryolite or in Na
3
AlCl
6
A good source of 
electricity is needed in 
the extraction of Al 
Zinc Zinc blende or Sphalerite: 
ZnS 
Zincite: ZnO 
Calamine: ZnCO
3
  
Roasting and then 
reduction with C 
The metal may be 
purified by fractional 
distillation. 
Lead Galena: PbS Roasting of the sulphide 
ore and then reduction 
of the oxide 
Sulphide ore is 
concentrated by froth 
floatation process 
Silver Argentite: Ag
2
S  
 
Sodium cyanide leaching 
of the sulphide ore and 
finally replacement of Ag 
by Zn 
It involves complex 
formation and 
displacement  
 
 
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Gold Native, small amounts in 
many ores such as those of 
copper and silver  
Cyanide leaching, same 
as in case of silver  
Gold reacts with cyanide 
to form complex 
Iron Haematite: Fe
2
O
3
Magnetite: Fe
3
O
4
Siderite: FeCO
3
Iron pyrites: FeS
2
 
Reduction with the help 
of CO and coke in blast 
furnace. 
 
Limestone is added as 
flux which removes SiO
2
 
as calcium silicate (slag) 
floats over molten iron 
and prevents its 
oxidation. Temperatures 
approaching 2170 K is 
required. 
 
6. Steps of metallurgy: 
a. Concentration of ore 
b. Conversion of concentrated ore to oxide 
c. Reduction of oxide to metal 
d. Refining of metal 
7. Concentration of ore: The process of removal unwanted materials like 
sand, clay, rocks etc from the ore is known as concentration, ore – 
dressing or benefaction. It involves several steps which depend upon 
physical properties of metal compound and impurity (gangue). The 
type of metal, available facilities and environmental factors are also 
taken into consideration. 
8. Hydraulic washing (or gravity separation): It is based on difference in 
densities of ore and gangue particles. Ore is washed with a stream of 
water under pressure so that lighter impurities are washed away 
whereas heavy ores are left behind. 
9. Magnetic separation: This method is based on the difference in 
magnetic and non – magnetic properties of two components of ore 
(pure and impure). This method is used to remove tungsten ore 
particles from cassiterite (SnO
2
). It is also used to concentrate 
magnetite (Fe
3
O
4
), chromite (FeCr
2
O
4
) and pyrolusite (MnO
2
) from 
unwanted gangue. 
10. Froth Floatation Process: The principle of froth floatation process is 
that sulphide ores are preferentially wetted by the pine oil, whereas 
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 1
Class XII: Chemistry 
Chapter 6: General Principles & Processes Of Isolation of Elements 
Top concepts 
1. Minerals: The naturally occurring chemical substances in the earth’s 
crust which are obtained by mining are known as minerals. Metals may 
or may not be extracted profitably from them. 
2. Ores: The rocky materials which contain sufficient quantity of mineral 
so that the metal can be extracted profitably or economically are 
known as ores. 
3. Gangue: The earthy or undesirable materials present in ore are known 
as gangue. 
4. Metallurgy: The entire scientific and technological process used for 
isolation of the metal from its ores is known as metallurgy. 
5. Chief Ores and Methods of Extraction of Some Common Metals: 
Metals Occurrence Extraction Method Remark 
Sodium Rock salt: NaCl 
Feldspar:Na
3
AlSi
3
O
8
Electrolysis of fused 
NaCl or NaCl/ CaCl
2
Sodium is highly 
reactive, it reacts with 
water 
Copper Copper pyrites:CuFeS
2
 
Malachite:CuCO
3
.Cu(OH)
2 
Cuprite: Cu
2
O 
Copper glance: Cu
2
S 
Roasting of sulphide 
partially and reduction 
2Cu
2
O + Cu
2
S ? 6 Cu 
                          +SO
2
  
It is self reduction in a 
specially designed 
converter. Sulphuric 
acid leaching is also 
employed. 
Aluminium Bauxite: AlO
x
(OH)
3-2x 
where 0<x<1 
Cryolite: Na
3
AlF
6
Kaolinite: [Al
2
(OH)
4
Si
2
O
5
] 
Electrolysis of Al
2
O
3
 
dissolved in molten 
cryolite or in Na
3
AlCl
6
A good source of 
electricity is needed in 
the extraction of Al 
Zinc Zinc blende or Sphalerite: 
ZnS 
Zincite: ZnO 
Calamine: ZnCO
3
  
Roasting and then 
reduction with C 
The metal may be 
purified by fractional 
distillation. 
Lead Galena: PbS Roasting of the sulphide 
ore and then reduction 
of the oxide 
Sulphide ore is 
concentrated by froth 
floatation process 
Silver Argentite: Ag
2
S  
 
Sodium cyanide leaching 
of the sulphide ore and 
finally replacement of Ag 
by Zn 
It involves complex 
formation and 
displacement  
 
 
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Gold Native, small amounts in 
many ores such as those of 
copper and silver  
Cyanide leaching, same 
as in case of silver  
Gold reacts with cyanide 
to form complex 
Iron Haematite: Fe
2
O
3
Magnetite: Fe
3
O
4
Siderite: FeCO
3
Iron pyrites: FeS
2
 
Reduction with the help 
of CO and coke in blast 
furnace. 
 
Limestone is added as 
flux which removes SiO
2
 
as calcium silicate (slag) 
floats over molten iron 
and prevents its 
oxidation. Temperatures 
approaching 2170 K is 
required. 
 
6. Steps of metallurgy: 
a. Concentration of ore 
b. Conversion of concentrated ore to oxide 
c. Reduction of oxide to metal 
d. Refining of metal 
7. Concentration of ore: The process of removal unwanted materials like 
sand, clay, rocks etc from the ore is known as concentration, ore – 
dressing or benefaction. It involves several steps which depend upon 
physical properties of metal compound and impurity (gangue). The 
type of metal, available facilities and environmental factors are also 
taken into consideration. 
8. Hydraulic washing (or gravity separation): It is based on difference in 
densities of ore and gangue particles. Ore is washed with a stream of 
water under pressure so that lighter impurities are washed away 
whereas heavy ores are left behind. 
9. Magnetic separation: This method is based on the difference in 
magnetic and non – magnetic properties of two components of ore 
(pure and impure). This method is used to remove tungsten ore 
particles from cassiterite (SnO
2
). It is also used to concentrate 
magnetite (Fe
3
O
4
), chromite (FeCr
2
O
4
) and pyrolusite (MnO
2
) from 
unwanted gangue. 
10. Froth Floatation Process: The principle of froth floatation process is 
that sulphide ores are preferentially wetted by the pine oil, whereas 
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the gangue particles are wetted by the water. Collectors are added to 
enhance the non-wettability of the mineral particles. Examples are 
pine oil, fatty acids and xanthates are added to it. Froth stabilizers are 
added to stabilize the froth. Examples are cresols, aniline. If two 
sulphide ores are present, it is possible to separate the two sulphide 
ores by adjusting proportion of oil to water or by adding depressants. 
For example- In the case of an ore containing ZnS and PbS, the 
depressant used is NaCN. It selectively prevents ZnS from coming to 
froth but allows PbS to come with the froth. 
11. Leaching (Chemical separation): It is a process in which ore is treated 
with suitable solvent which dissolves the ore but not the impurities. 
12. Purification of Bauxite by Leaching: Baeyer’s process: 
Step 1: 
 Al
2
O
3 
(s) + 2NaOH (aq) + 3H
2
O (l) ? 2Na[Al(OH)
4
](aq) 
Step 2:  
() ( )
2232 3
4
2Na[Al OH ](aq) CO g Al O .xH O (s) 2NaHCO (aq) +? +
Step 3: 
( )
Heat at1470K
23 2 2 3 2
Al O .xH O(s) Al O s xH O(g) ? ?? ??? ??+ 
13.   Concentration of Gold and Silver Ores by Leaching: 
--
22 2
-2-
24
4M(s)8CN (aq) 2H O(aq)O (g) 4[M(CN) ] (aq) + 4OH (aq)
2[M(CN) ] (aq) Zn(s) [Zn(CN) ] (aq) 2M(s)
Where :
[M Ag or Au]
-
++ + ?
+? +
=
 
14. Conversion of ore into oxide: It is easier to reduce oxide than sulphide 
or carbonate ore. Therefore, the given ore should be converted into 
oxide by suitable method: 
Roasting Calcination 
It is a process in which ore is 
heated in a regular supply of air 
at a temperature below melting 
point of the metal so as to 
It is a process of heating ore in 
limited supply of air so as to 
convert carbonate ores into 
oxides. 
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Class XII: Chemistry 
Chapter 6: General Principles & Processes Of Isolation of Elements 
Top concepts 
1. Minerals: The naturally occurring chemical substances in the earth’s 
crust which are obtained by mining are known as minerals. Metals may 
or may not be extracted profitably from them. 
2. Ores: The rocky materials which contain sufficient quantity of mineral 
so that the metal can be extracted profitably or economically are 
known as ores. 
3. Gangue: The earthy or undesirable materials present in ore are known 
as gangue. 
4. Metallurgy: The entire scientific and technological process used for 
isolation of the metal from its ores is known as metallurgy. 
5. Chief Ores and Methods of Extraction of Some Common Metals: 
Metals Occurrence Extraction Method Remark 
Sodium Rock salt: NaCl 
Feldspar:Na
3
AlSi
3
O
8
Electrolysis of fused 
NaCl or NaCl/ CaCl
2
Sodium is highly 
reactive, it reacts with 
water 
Copper Copper pyrites:CuFeS
2
 
Malachite:CuCO
3
.Cu(OH)
2 
Cuprite: Cu
2
O 
Copper glance: Cu
2
S 
Roasting of sulphide 
partially and reduction 
2Cu
2
O + Cu
2
S ? 6 Cu 
                          +SO
2
  
It is self reduction in a 
specially designed 
converter. Sulphuric 
acid leaching is also 
employed. 
Aluminium Bauxite: AlO
x
(OH)
3-2x 
where 0<x<1 
Cryolite: Na
3
AlF
6
Kaolinite: [Al
2
(OH)
4
Si
2
O
5
] 
Electrolysis of Al
2
O
3
 
dissolved in molten 
cryolite or in Na
3
AlCl
6
A good source of 
electricity is needed in 
the extraction of Al 
Zinc Zinc blende or Sphalerite: 
ZnS 
Zincite: ZnO 
Calamine: ZnCO
3
  
Roasting and then 
reduction with C 
The metal may be 
purified by fractional 
distillation. 
Lead Galena: PbS Roasting of the sulphide 
ore and then reduction 
of the oxide 
Sulphide ore is 
concentrated by froth 
floatation process 
Silver Argentite: Ag
2
S  
 
Sodium cyanide leaching 
of the sulphide ore and 
finally replacement of Ag 
by Zn 
It involves complex 
formation and 
displacement  
 
 
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Gold Native, small amounts in 
many ores such as those of 
copper and silver  
Cyanide leaching, same 
as in case of silver  
Gold reacts with cyanide 
to form complex 
Iron Haematite: Fe
2
O
3
Magnetite: Fe
3
O
4
Siderite: FeCO
3
Iron pyrites: FeS
2
 
Reduction with the help 
of CO and coke in blast 
furnace. 
 
Limestone is added as 
flux which removes SiO
2
 
as calcium silicate (slag) 
floats over molten iron 
and prevents its 
oxidation. Temperatures 
approaching 2170 K is 
required. 
 
6. Steps of metallurgy: 
a. Concentration of ore 
b. Conversion of concentrated ore to oxide 
c. Reduction of oxide to metal 
d. Refining of metal 
7. Concentration of ore: The process of removal unwanted materials like 
sand, clay, rocks etc from the ore is known as concentration, ore – 
dressing or benefaction. It involves several steps which depend upon 
physical properties of metal compound and impurity (gangue). The 
type of metal, available facilities and environmental factors are also 
taken into consideration. 
8. Hydraulic washing (or gravity separation): It is based on difference in 
densities of ore and gangue particles. Ore is washed with a stream of 
water under pressure so that lighter impurities are washed away 
whereas heavy ores are left behind. 
9. Magnetic separation: This method is based on the difference in 
magnetic and non – magnetic properties of two components of ore 
(pure and impure). This method is used to remove tungsten ore 
particles from cassiterite (SnO
2
). It is also used to concentrate 
magnetite (Fe
3
O
4
), chromite (FeCr
2
O
4
) and pyrolusite (MnO
2
) from 
unwanted gangue. 
10. Froth Floatation Process: The principle of froth floatation process is 
that sulphide ores are preferentially wetted by the pine oil, whereas 
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 3
the gangue particles are wetted by the water. Collectors are added to 
enhance the non-wettability of the mineral particles. Examples are 
pine oil, fatty acids and xanthates are added to it. Froth stabilizers are 
added to stabilize the froth. Examples are cresols, aniline. If two 
sulphide ores are present, it is possible to separate the two sulphide 
ores by adjusting proportion of oil to water or by adding depressants. 
For example- In the case of an ore containing ZnS and PbS, the 
depressant used is NaCN. It selectively prevents ZnS from coming to 
froth but allows PbS to come with the froth. 
11. Leaching (Chemical separation): It is a process in which ore is treated 
with suitable solvent which dissolves the ore but not the impurities. 
12. Purification of Bauxite by Leaching: Baeyer’s process: 
Step 1: 
 Al
2
O
3 
(s) + 2NaOH (aq) + 3H
2
O (l) ? 2Na[Al(OH)
4
](aq) 
Step 2:  
() ( )
2232 3
4
2Na[Al OH ](aq) CO g Al O .xH O (s) 2NaHCO (aq) +? +
Step 3: 
( )
Heat at1470K
23 2 2 3 2
Al O .xH O(s) Al O s xH O(g) ? ?? ??? ??+ 
13.   Concentration of Gold and Silver Ores by Leaching: 
--
22 2
-2-
24
4M(s)8CN (aq) 2H O(aq)O (g) 4[M(CN) ] (aq) + 4OH (aq)
2[M(CN) ] (aq) Zn(s) [Zn(CN) ] (aq) 2M(s)
Where :
[M Ag or Au]
-
++ + ?
+? +
=
 
14. Conversion of ore into oxide: It is easier to reduce oxide than sulphide 
or carbonate ore. Therefore, the given ore should be converted into 
oxide by suitable method: 
Roasting Calcination 
It is a process in which ore is 
heated in a regular supply of air 
at a temperature below melting 
point of the metal so as to 
It is a process of heating ore in 
limited supply of air so as to 
convert carbonate ores into 
oxides. 
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convert the given ore into oxide 
ore. 
Sulphide ores are converted into 
oxide by roasting 
Carbonate ores are converted into 
oxide by roasting 
It is also used to remove 
impurities as volatile oxides 
It is also used to remove moisture 
and volatile impurities 
E.g.: 2ZnS+ 3O
2
 ? 2ZnO + 2SO
2 
E.g.: CaCO
3
  
heat
2
CaO CO ?? ? ??+
 
15. Reduction of oxide to metal: The process of converting metal oxide 
into metal is called reduction. It needs a suitable reducing agent 
depending upon the reactivity or reducing power of metal. The 
common reducing agents used are carbon or carbon monoxide or any 
other metals like Al, Mg etc. 
16. Thermodynamic principles of metallurgy: Some basic concepts of 
thermodynamics help in understanding the conditions of temperature 
and selecting suitable reducing agent in metallurgical processes: 
a.  Gibbs free energy change at any temperature is given by ?G = 
?H – T ?S where ?G is free energy change, ?H is enthalpy 
change and ?S is entropy change.  
b. The relationship between ?G
?
 and K is ?G
?
 = –2.303 RT log K 
where K is equilibrium constant. R = 8.314 JK
-
¹ mol
-1
, T is 
temperature in Kelvin. 
c. A negative ?G means +ve value of K i.e., products are formed 
more than the reactants. The reaction will proceed in forward 
direction.  
d. If ?S is +ve, on increasing temperature the value of T ?S 
increases so that T?S > ?H and ?G will become negative. 
 
17. Coupled reactions: If reactants and products of two reactions are put 
together in a system and the net ?G of two possible reactions is –ve 
the overall reaction will take place. These reactions are called coupled 
reactions. 
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Class XII: Chemistry 
Chapter 6: General Principles & Processes Of Isolation of Elements 
Top concepts 
1. Minerals: The naturally occurring chemical substances in the earth’s 
crust which are obtained by mining are known as minerals. Metals may 
or may not be extracted profitably from them. 
2. Ores: The rocky materials which contain sufficient quantity of mineral 
so that the metal can be extracted profitably or economically are 
known as ores. 
3. Gangue: The earthy or undesirable materials present in ore are known 
as gangue. 
4. Metallurgy: The entire scientific and technological process used for 
isolation of the metal from its ores is known as metallurgy. 
5. Chief Ores and Methods of Extraction of Some Common Metals: 
Metals Occurrence Extraction Method Remark 
Sodium Rock salt: NaCl 
Feldspar:Na
3
AlSi
3
O
8
Electrolysis of fused 
NaCl or NaCl/ CaCl
2
Sodium is highly 
reactive, it reacts with 
water 
Copper Copper pyrites:CuFeS
2
 
Malachite:CuCO
3
.Cu(OH)
2 
Cuprite: Cu
2
O 
Copper glance: Cu
2
S 
Roasting of sulphide 
partially and reduction 
2Cu
2
O + Cu
2
S ? 6 Cu 
                          +SO
2
  
It is self reduction in a 
specially designed 
converter. Sulphuric 
acid leaching is also 
employed. 
Aluminium Bauxite: AlO
x
(OH)
3-2x 
where 0<x<1 
Cryolite: Na
3
AlF
6
Kaolinite: [Al
2
(OH)
4
Si
2
O
5
] 
Electrolysis of Al
2
O
3
 
dissolved in molten 
cryolite or in Na
3
AlCl
6
A good source of 
electricity is needed in 
the extraction of Al 
Zinc Zinc blende or Sphalerite: 
ZnS 
Zincite: ZnO 
Calamine: ZnCO
3
  
Roasting and then 
reduction with C 
The metal may be 
purified by fractional 
distillation. 
Lead Galena: PbS Roasting of the sulphide 
ore and then reduction 
of the oxide 
Sulphide ore is 
concentrated by froth 
floatation process 
Silver Argentite: Ag
2
S  
 
Sodium cyanide leaching 
of the sulphide ore and 
finally replacement of Ag 
by Zn 
It involves complex 
formation and 
displacement  
 
 
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Gold Native, small amounts in 
many ores such as those of 
copper and silver  
Cyanide leaching, same 
as in case of silver  
Gold reacts with cyanide 
to form complex 
Iron Haematite: Fe
2
O
3
Magnetite: Fe
3
O
4
Siderite: FeCO
3
Iron pyrites: FeS
2
 
Reduction with the help 
of CO and coke in blast 
furnace. 
 
Limestone is added as 
flux which removes SiO
2
 
as calcium silicate (slag) 
floats over molten iron 
and prevents its 
oxidation. Temperatures 
approaching 2170 K is 
required. 
 
6. Steps of metallurgy: 
a. Concentration of ore 
b. Conversion of concentrated ore to oxide 
c. Reduction of oxide to metal 
d. Refining of metal 
7. Concentration of ore: The process of removal unwanted materials like 
sand, clay, rocks etc from the ore is known as concentration, ore – 
dressing or benefaction. It involves several steps which depend upon 
physical properties of metal compound and impurity (gangue). The 
type of metal, available facilities and environmental factors are also 
taken into consideration. 
8. Hydraulic washing (or gravity separation): It is based on difference in 
densities of ore and gangue particles. Ore is washed with a stream of 
water under pressure so that lighter impurities are washed away 
whereas heavy ores are left behind. 
9. Magnetic separation: This method is based on the difference in 
magnetic and non – magnetic properties of two components of ore 
(pure and impure). This method is used to remove tungsten ore 
particles from cassiterite (SnO
2
). It is also used to concentrate 
magnetite (Fe
3
O
4
), chromite (FeCr
2
O
4
) and pyrolusite (MnO
2
) from 
unwanted gangue. 
10. Froth Floatation Process: The principle of froth floatation process is 
that sulphide ores are preferentially wetted by the pine oil, whereas 
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the gangue particles are wetted by the water. Collectors are added to 
enhance the non-wettability of the mineral particles. Examples are 
pine oil, fatty acids and xanthates are added to it. Froth stabilizers are 
added to stabilize the froth. Examples are cresols, aniline. If two 
sulphide ores are present, it is possible to separate the two sulphide 
ores by adjusting proportion of oil to water or by adding depressants. 
For example- In the case of an ore containing ZnS and PbS, the 
depressant used is NaCN. It selectively prevents ZnS from coming to 
froth but allows PbS to come with the froth. 
11. Leaching (Chemical separation): It is a process in which ore is treated 
with suitable solvent which dissolves the ore but not the impurities. 
12. Purification of Bauxite by Leaching: Baeyer’s process: 
Step 1: 
 Al
2
O
3 
(s) + 2NaOH (aq) + 3H
2
O (l) ? 2Na[Al(OH)
4
](aq) 
Step 2:  
() ( )
2232 3
4
2Na[Al OH ](aq) CO g Al O .xH O (s) 2NaHCO (aq) +? +
Step 3: 
( )
Heat at1470K
23 2 2 3 2
Al O .xH O(s) Al O s xH O(g) ? ?? ??? ??+ 
13.   Concentration of Gold and Silver Ores by Leaching: 
--
22 2
-2-
24
4M(s)8CN (aq) 2H O(aq)O (g) 4[M(CN) ] (aq) + 4OH (aq)
2[M(CN) ] (aq) Zn(s) [Zn(CN) ] (aq) 2M(s)
Where :
[M Ag or Au]
-
++ + ?
+? +
=
 
14. Conversion of ore into oxide: It is easier to reduce oxide than sulphide 
or carbonate ore. Therefore, the given ore should be converted into 
oxide by suitable method: 
Roasting Calcination 
It is a process in which ore is 
heated in a regular supply of air 
at a temperature below melting 
point of the metal so as to 
It is a process of heating ore in 
limited supply of air so as to 
convert carbonate ores into 
oxides. 
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convert the given ore into oxide 
ore. 
Sulphide ores are converted into 
oxide by roasting 
Carbonate ores are converted into 
oxide by roasting 
It is also used to remove 
impurities as volatile oxides 
It is also used to remove moisture 
and volatile impurities 
E.g.: 2ZnS+ 3O
2
 ? 2ZnO + 2SO
2 
E.g.: CaCO
3
  
heat
2
CaO CO ?? ? ??+
 
15. Reduction of oxide to metal: The process of converting metal oxide 
into metal is called reduction. It needs a suitable reducing agent 
depending upon the reactivity or reducing power of metal. The 
common reducing agents used are carbon or carbon monoxide or any 
other metals like Al, Mg etc. 
16. Thermodynamic principles of metallurgy: Some basic concepts of 
thermodynamics help in understanding the conditions of temperature 
and selecting suitable reducing agent in metallurgical processes: 
a.  Gibbs free energy change at any temperature is given by ?G = 
?H – T ?S where ?G is free energy change, ?H is enthalpy 
change and ?S is entropy change.  
b. The relationship between ?G
?
 and K is ?G
?
 = –2.303 RT log K 
where K is equilibrium constant. R = 8.314 JK
-
¹ mol
-1
, T is 
temperature in Kelvin. 
c. A negative ?G means +ve value of K i.e., products are formed 
more than the reactants. The reaction will proceed in forward 
direction.  
d. If ?S is +ve, on increasing temperature the value of T ?S 
increases so that T?S > ?H and ?G will become negative. 
 
17. Coupled reactions: If reactants and products of two reactions are put 
together in a system and the net ?G of two possible reactions is –ve 
the overall reaction will take place. These reactions are called coupled 
reactions. 
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18.  Ellingham diagrams: The plots between ?
f
G
?
 of formation of oxides of 
elements vs. temperature are called Ellingham diagrams. It provides a 
sound idea about selecting a reducing agent in reduction of oxides. 
Such diagrams help in predicting the feasibility of a thermal reduction 
of an ore. ?G must be negative at a given temperature for a reaction 
to be feasible. 
19.  Limitations of Ellingham Diagrams: It does not take kinetics of 
reduction into consideration, i.e., how fast reduction will take place 
cannot be determined. 
20.  Reduction of iron oxide in blast furnace: Reduction of oxides takes 
place in different zones. 
 At 500 – 800 K (lower temperature range in blast furnace) 
 3Fe
2
O
3
 + CO ? 2Fe
3
O
4
 + CO
2
 Fe
3
O
4
 + 4CO ? 3Fe + 4CO
2
 Fe
2
O
3
 + CO ? 2FeO + CO
2
 At 900 – 1500 K (higher temperature range in blast furnace) 
 C + CO
2
 ? 2CO 
 FeO + CO ? Fe + CO
2
 Limestone decomposes to CaO and CO
2
 CaCO
3
  
heat
2
CaO CO ?? ? ??+
         Silica (impurity) reacts with CaO to form calcium silicate which forms 
slag. It floats over molten iron and prevents oxidation of iron. 
 CaO + SiO
2
 ? CaSiO
3 
            Calcium silicate 
                            (Slag) 
21. Types of iron: 
a. Pig iron: The iron obtained from blast furnace is called pig iron. It is 
impure from of iron contains 4% carbon and small amount of S,.P, 
Si and Mn. It can be casted into variety of shapes. 
b. Cast iron: It is made by melting pig iron with scrap iron and coke 
using hot air blast. It contains about 3% of carbon content. It is 
extremely hard and brittle. 
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