CBSE Class 12 Chemistry Processes Of Isolation Of Elements Notes Set 03

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GENERAL PRINCIPLES AND PROCESSES OF

ISOLATION OF ELEMENTS

VSA QUESTIONS (1 - MARK QUESTIONS)

1. Name three metals which occur in native state in nature.

[Ans. : Au, Ag and Pt]

2. What are collectors in froth flotation process? Give one example.

[Ex. : Pine oil]

3. Give the names and formulae of three ores which are concentrated by froth floatation process.

[Ans. : Galena (PbS), zinc blend (zns) cinnabar (HgS)]

4. Among Fe, Cu, Al and Pb, which metal (s) can not be obtained by smelting.

[Ans. : Al]

5. What is the thermodynamic criteria for the feasibility of a reaction?

[Ans. : ΔG should be –ve or log K = + ve]

8. Why can’t aluminium be reduced by carbon?

[Hint : Al is stronger reducing agent than carbon]

9. Name the most important form of iron. Mention its one use.

[Ans. : Cast iron is used for making gutter pipes, castings, railway sleepers,toys etc.]

10. Name the impurities present in bauxite ore.

[Ans. : SiO2, Fe2O3 and TiO2]

11. What is the composition of copper matte?

[Hint : Cu2S and FeS]

12. Which from of copper is called blister copper?

13. What are froth stabilizers? Give two examples.

[Ex. : Cresol and aniline].

14. A sample of galena is contaminated with zinc blend. Name one chemical which can be used to concentrate galena selectively by froth floatation method. [Ans. : NaCN]

15. What are the constituents of German silver?

[Ans. : Cu = 25-30%, Zn = 25-30%, Ni = 40-50%]

16. Why is froth floatation process selected for concentration of the sulphide ore?

[Ans. : Sulphide ore particles are wetted by oil (Pine oil) and gangue particles by water]

17. Write the reaction involved in the extraction of copper from low grade ores.

[Ans. : First step is leaching of ore with acid or bacteria then

Cu2+ (aq) + H2 (g) → Cu(s) + 2H+ (g)]

18. Although aluminium is above hydrogen in the electrochemical series, it is stable in air and water. Why?

19. Which method of purification is represented by the following reaction

class_12_chemistry_concept_54

20. Zinc is used but not copper for the recovery of metallic silver from the complex [Ag(CN)2]–, although electrode potentials of both zinc and copper are less than that of Ag. Explain why?

[Hint : Zinc reacts at faster rate as compared with copper, further zinc is cheaper than copper].

21. Write the composition of motlen mixture which is electrolysed to extract aluminium.

 

SA (I) QUESTIONS (2 - MARK QUESTIONS)

 

22. What is hydrometallurgy? Give one example where it is used for metal extraction.

 

[Ans. : Leaching followed by reduction is called hydrometallurgy. It is used in extraction and copper

 

23. Name the process for the benefaction/concentration of (i) an ore having lighter impurities (ii) sulphide ore.

 

24. Mention the role of cryolite in the extraction of aluminium.

 

25. Mention the role of following :

 

(a) SiO2 in the metallurgy of Cu.

 

(b) CaCO3 in the metallurgy of Fe.

 

(c) CO in the metallergy of iron

 

(d) I2 in the purification of zirconium.

 

26. Extraction of copper directly from sulphide ore is less favourable than from its oxide through reduction. Explain.

 

[Ans. : 2Cu S(s) + C(s) → CS2 (l) + 2Cu(s)

 

CuO(s) + C(s) → CO (g) + Cu(s)

 

ΔG value is more –ve in second case as compared with first case]

 

27. The graphite electrodes in the extraction of ‘alluminium’ by Hall-Heroult process need to be changed frequently. Why?

 

28. Write the chemical formulae of the following ores (a) Haematite (b) Magnetite

 

(c) Limonite (d) Siderite.

 

[Ans. : (a) Fe2O3 (b) Fe3O4 (c) Fe2O3.2H2O (d) FeCO3]

 

29. Give equations for the industrial extraction of zinc from calamine.

 

[Ans. : ZnCO3 →  ZnO + CO2 (Calcination) ZnO + C → Zn + CO (Reduction)]

 

30. Name the elements present in anode mud during refining of copper. Why does it contain such elements?

 

[Ans. : Au and Ag. They are not oxidised at anode. They are less electropositive than copper.]

 

31. Write the Chemical reactions taking place in different zones in the blast furnace for the extraction of iron from its ore.

 

32. How are impurities separated from bauxite ore to get pure alumina?

 

33. Why is the reduction of a metal oxide easier if metal formed is in liquid state at the temperature of reduction?

 

[Hint : Entropy is more positive when the metal is in liquid state as compared with solid state, so ΔG becomes more –ve]

 

34. What is pyrometallurgy? Explain with one example.

 

[Ans. : A process of reducing a metal oxide by heating with either coke or some other reducing agent e.g., Al, Mg etc.

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

 

35. Write the method to produce Copper matte from copper pyrites.

 

36. Copper can be extracted by hydrometallurgy but not zinc. Explain why?

CBSE Class 12 Chemistry notes and questions for Processes of Isolation of Elements Part C 2

 

*39. Gibbs energies of formation fG of MgO(s) and CO(g) at 1273K and 2273

 

K are given below:

 

ΔfG [MgO(s)] = –941 kJ mol–1 at 1273 K.

 

ΔfG [CO(g)] = –439 kJ mol–1 at 1273 K.

 

ΔfG [MgO(s)] = –314 kJ mol–1 at 2273 K.

 

ΔfG [CO(g)] = –628 kJ mol–1 at 2273 K.

 

On the basis of above data, predict the temperature at which carbon can be used as a reducing agent for MgO(s).

 

[Ans. : For the reaction, MgO(s) + C(s) → Mg(s) + CO(g)

 

At 1273K, ΔrG = ΔfG[CO(g)] – ΔfG[MgO(s)] = –439 – (–941) KJ mol–1 = 502 kJ mol–1

 

At 2273 K, ΔrG = –628 – (–314) kJ mol–1 = –314 kJ mol–1

 

The temperature is 2273 K]

 

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Unit 06 General Principles and Processes of Isolation of Elements Concepts and Summary for Class 12 Chemistry

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