Chemistry Class 12 NCERT Solutions: Chapter 6 General Principles and Processes of Isolation of Elements Part 2

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Q: 7. Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.

Answer:

During the extraction of iron, the reduction of iron oxides takes place in the blast furnace. In this process, hot air is blown from the bottom of the furnace and coke is burnt to raise the temperature up to in the lower portion itself. The temperature is lower in the upper part. Thus, it is the lower part where the reduction of iron oxides takes place.

The reactions taking place in the lower temperature range (500 − 800 K) in the blast furnace are:

The reactions taking place in the higher temperature range in the blast furnace are:

The silicate impurity of the ore is removed as slag by calcium oxide , which is formed by the decomposition of limestone .

Q 7 Ore Limestone, and Coke

Q 7 Ore Limestone, and Coke

Q 7 Ore Limestone, and Coke

Q: 8. Write chemical reactions taking place in the extraction of zinc from zinc blende.

Answer:

The different steps involved in the extraction of zinc from zinc blende are given below:

(i) Concentration of ore

First, the gangue from zinc blende is removed by the froth floatation method.

(ii) Conversion to oxide (Roasting)

Sulphide ore is converted into oxide by the process of roasting. In this process, is heated in a regular supply of air in a furnace at a temperature, which is below the melting point of .

(iii) Extraction of zinc from zinc oxide (Reduction)

Zinc is extracted from zinc oxide by the process of reduction. The reduction of zinc oxide is carried out by mixing it with powdered coke and then, heating it at .

(iv) Electrolytic Refining

Zinc can be refined by the process of electrolytic refining. In this process, impure zinc is made the anode while a pure copper strip is made the cathode. The electrolyte used is an acidified solution of zinc sulphate ( Electrolysis results in the transfer of zinc in pure from the anode to the cathode.

Anode:

Cathode:

Q: 9. State the role of silica in the metallurgy of copper.

Answer

During the roasting of pyrite ore, a mixture of, and is obtained.

The role of silica in the metallurgy of copper is to remove the iron oxide obtained during the process of roasting as ‘slag’. If the sulphide ore of copper contains iron, then silica is added as flux before roasting. Then, combines with silica to form iron silicate, (slag).

Q: 10. What is meant by the term “chromatography”?

Answer:

Chromatography is a collective term used for a family of laboratory techniques for the separation of mixtures. The term is derived from Greek words ‘Chroma’ meaning ‘colour’ and ‘graphein’ meaning ‘to write’. Chromatographic techniques are based on the principle that different components are absorbed differently on an absorbent. There are several chromatographic techniques such as paper chromatography, column chromatography, gas chromatography, etc.