NIOS Class 12 Chemistry Chapter 16 Occurrence and Extraction of Metals

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NIOS Class 12 Chemistry Chapter 16 Occurrence and Extraction of Metals

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Occurrence and Extraction of Metals

Chapter: 16

Module – VI: Chemistry of Elements

INTEXT QUESTIONS 16.1

1. Write the names of eight important metals. Give an example of one important ore of each metal.

Ans: Sodium (Na), Aluminium (Al), Silver (Ag), Iron (Fe), Zinc (Zn), Lead (Pb),Gold (Au), Mercury (Hg).

Ores: rock salt, bauxite, argentite, haematite, zincite, galena, native gold,cinnabar, respectively.

2. What is the difference between an ore and a mineral?

Ans: Mineral is a naturally occurring material in which a metal or its compound occurs.

An ore is that mineral in which metal is present in large quantity and from which the metal can be extracted in pure and high quality, economically.

3. Name some important methods of concentrating the ores.

Ans: Gravity separation, magnetic separation, froth floatation and chemical method.

4. Which method of concentration is applied in the following cases?

(i) Magnetic ores (ii) Sulphide ores (iii) Bauxite ore.

Ans: (i) Magnetic separation method.

(ii) Froth floatation method.

(iii) Chemical method.

5. Which metal is extracted from the mineral zinc blede?

Ans: zinc.

INTEXT QUESTIONS 16.2

1. Explain the following terms:

Calcination, Roasting, Smelting, Flux and Slag.

Ans: Calcination: it involves heating of the ore in a limited supply of air to a temperature that the ore does not melt.

Roasting: It involves heating of the ore in a free supply of air to a temperature that the ore does not melt.

Smelting: The extraction of metal in the fused state is termed smelting. The ore is reduced by carbon to the free metal.

Flux: it is a chemical substance which combines with gangue at higher temperatures to form easily fusible material called slag.

Slag is a fusible chemical compound formed by the reaction of flux with gangue. Slag is not soluble in the molten metal and is thus separated.

2. Which is the cheapest and most abundant reducing agent employed in the extraction of metals?

Ans: Carbon in the form of coke.

3. Name the process which is used for converting sulphide ores into oxides.

Ans: Roasting:

2ZnS + 3O₂ → 2ZnO 2SO₂ (g)

4. How are oxide ores reduced?

Ans: Oxide ores are reduced to metal by heating them with coke.

5. Name few materials which are used as flux in metallurgical processes.

Ans: Silica, borax and other non-metallic oxides are acidic fluxes. Lime stone

(CaCO₃) is a basic flux.

6. What happens to (i) Bauxite and (ii) Calamine ores during calcination?

Ans: (i) 2Al₂O₃ + 2H₂O → Al₂O₃ + 2H₂O

(ii) ZnCO₃ → ZnO + CO₂

INTEXT QUESTIONS 16.3

1. State the nature of materials used for constructing cathodes and anodes in the electrolytic cell for refining of copper. Write chemical equations for the reactions which take place.

Ans: Cathode: Pure metal At Cathode : Cu₂+ + 2e → Cu

Anode: Impure metal At Anode : Cu → Cu₂+ + 2e

2. Which method is used for the refining of metals that are easily fused?

Ans: Liquation.

3. Which metals are refined by poling ?

Ans: Copper and tin.

4. Name a metal which is purified by distillation.

Ans: Zinc.

5. Name any three elements which are refined by electrolytic refining.

Ans: Copper, Silver and Tin.

6. What is role of cryolyte in the extraction of Al.

Ans: (i) Decrease the melting point of alumino.

(ii) To increase the conductance.

7. Which one is responsible to reduce Fe₂O₃ to Fe C or CO.

Ans: CO.