VBQs General Principles and Processes of Isolation of Elements Class 12 Chemistry with General Principles and Processes of Isolation of Elements has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Chemistry with General Principles and Processes of Isolation of Elements. The following General Principles and Processes of Isolation of Elements Class 12 Chemistry value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.
General Principles and Processes of Isolation of Elements VBQs Class 12 Chemistry
VERY SHORT ANSWER TYPE QUESTION
Question. Name a method used for refining Indium.
Answer. Zone refining
Question. Name the method of extraction of low – grade copper .
Question. Copper can be extracted by hydrometallurgy but not Zn. Why?
Answer. The E0 of Zn is lower than that of Cu thus Zn can displace Cu2+ ion from its solution. On the other hand, to displace Zn from Zn2+ion, we need a more reactive metal than it.
Question. What is the role of graphite rods in electrometallurgy of aluminium?
Answer. Graphite rods act as anode, are attacked by oxygen to form CO2 and sois replaced from time to time.
Question. Give name and formula of important ore of Zinc .
Answer. Zinc blende ‐ ZnS, Calamine‐ ZnCO3, Zincite – ZnO
Question. What is the principle of chromatography?
Answer. It is based on adsorption
Question. Give name and formula of important ore of copper .
Answer. Copper pyrites CuFeS2, Malachite CuCO3 . Cu (OH)2, Cuprite Cu2O.
Question. Name the metals which can be refined by zone refining.
Answer. Silicon, Germanium, Gallium.
Question. What are depressants?
Answer. 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.
Question. What is slag?
Answer. 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)
Question. Give name and formula of important ore of iron .
Answer. Haematite – Fe2O3, Magnetite –Fe3O4, Iron pyrites FeS2.
Question. What is the role of cryolite in electrometallurgy of aluminium?
Answer. Alumina cannot be fused easily because of high melting point. Dissolving of alumina in cryolite furnishes Al3+ ions, which can be electrolyzed easily.
SHORT ANSWER TYPE QUESTION
Question. What is Zone Refining? Explain with example.
Answer. Zone refining is a method of obtaining a metal in very pure state. It is based on the principle 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 solidifies while the impurities pass into molten zone. The process is repeated to obtain ultrapure metal and end of rod containing impure metal is cut off.
Question. Explain the role of –(i) CO in the purification of Nickel (ii)SiO2 in the extraction of copper from copper matte.
Answer.(i) It forms a volatile complex with Ni while impurities do not.
( ii)It remove the impurities FeO to form FeSiO3 which is removed as slag .
Question. Write the principle of electro‐refining.
Answer. 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
At Anode :‐ Cu → Cu+2 + 2e–
Question. Describe the method of refining of nickel.
Answer. In the Mond Process, Ni is heated in a stream of CO forming a volatile complex, which then decompose at higher temperature to give Ni.
At 330 – 35OK : Ni + 4CO → Ni(CO)4
At 450 – 4 70K : Ni (CO)4 → Ni + 4CO
Question. Describe the method of refining of Zirconium and Titanium.
Answer. 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) + 2I2 →Zr I 4
At 2075K :‐ ZrI4 →Zr ( pure) +2 I2
SHORT ANSWER TYPE QUESTION
Question. Explain the method for obtaining pig iron from magnetite.
Answer. 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 involve heating when the volatile matter escapes leaving behind metal oxide.
Fe2O3 x H2O → Fe2O3 + xH2O.
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 250°C – 700°C 3Fe2O3+CO → 2Fe3O4+CO2
Fe3O4+CO → 3FeO+CO2
FeO+CO → Fe+CO2
ii) Zone of slag formation:‐ Temperature range 800°C – 1000°C CaCO3 → CaO+CO2
CaO+SiO2 → CaSiO3. P4O10+10C → 4P+10CO.
SiO2+2C →Si+2CO. MnO2+2C →Mn+2CO.
iii) Zone of fusion:‐ Temperature range 1150°C – 1350°C
CO2+C → 2CO
iv) Zone of fusion:‐ Temperature range 1450°C – 1950°C
C+O2 → CO2
Thus, Pig iron is obtained from blast furnace.
Question. Described the principles of extraction of Zinc from zinc blende.
Answer. 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) Concentraction of ore:‐ It is concentracted by Froth flotation process followed by gravity separation process.
Question. 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.
Answer. 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 → 2Cu2O+2SO2.
2Cu2O+2Cu2S →6Cu + 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.
Question. Name the principal ore of aluminium and describe how Al is extracted from its ore.
Answer. Important ores (i) Bauxite Al2O3 x H2O (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 → 2Na [Al(OH)4] and impurities of Fe2O3. TiO2 & SiO2 are re moved Na
[Al(OH)4], then reacts with CO2 then pure Alumina is obtained.
Na [Al(OH)4] + 2CO2 → Al2O3 x H2O + 2NaHCO3
Step:2 ‐ 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– → Al,
At a node : 2O2– → O2 + 2e_
By this process 98.8% pure Aluminum is obtained.