CBSE Class 12 Chemistry Processes Of Isolation Of Elements Notes Set 02

Revision Notes for Class 12 Chemistry: Unit 06 General Principles and Processes of Isolation of Elements

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Chapter:6

 

General Principles & Process of Isolation of Elements

 

Important Points :

 

1. The chemical substances in the earth’s crust obtained by mining are called Minerals.

 

2. Minerals, which act as source for metal, are called Ore. From ore metal can be obtained economically .

 

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 dissolve Al & 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

 

11. Roasting involves heating of ore in presence of air below melting point of metal in reverberatory furnace. In this process volatile impurities escapes leaving behind metal oxide and metal sulphide converts to metal oxide.

2 ZnS + 3 O2  —→2ZnO+2SO2

2PbS + 3 O2 2  —→ PbO +2 SO2

2 Cu2S + 3 O2  —→2Cu2O + 2 SO2

 

12. Reduction of metal oxide involves heating of metal in presence of suitable reagent Coke or CO2.

 

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

 

(ii) Zone of slag formation:- Temperature range 800oC-1000oC

CaCO3  —→CaO+CO2

CaO+SiO2 —→ CaSiO3,           P4O10+10C —→ 4P+10CO,

SiO2+2C  —→ Si+2CO,            MnO2+2C —→ Mn+2CO

 

(iii) Zone of fusion: - Temperature range 1150oC-1350oC

CO2 + C —→2CO

 

(iv) Zone of fusion: - Temperature range 1450oC-1950oC

class_12_chemistry_concept_53

CBSE Class 12 Chemistry notes and questions for Processes of Isolation of Elements Part B 1

 

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

 

Q.1- What is slag?
A.1- It is easily fusible material 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 Foe ?
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 to be replace 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 side 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
 
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 + 4 CO
 
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.

 

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