Chemistry 12 Chapter 6 General Principles and Processes of Isolation of Elements Part 4

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III. Short Answer Type

Question 27:

Why is an external of more than required for the extraction of from brine?

Answer:

For the reaction

Value of . Using the equation the value of comes out to be . Therefore extraction of from brine will require an external emf of greater than

Question 28:

At temperatures above coke can be used to reduce to . How can you justify this reduction with Ellingham diagram?

Answer:

As per Ellingham diagram at temperatures greater than . Hence coke can reduce to .

Question 29:

Wrought iron is the purest form of iron. Write a reaction used for the preparation of wrought iron from cast iron. How can the impurities of sulphur, silicon and phosphorus be removed from cast iron?

Answer:

Limestone is added as flux and sulphur, silicon and phosphorus change to their oxides and pass into the slag.

Question 30:

How is copper extracted from low grade copper ores?

Answer:

Copper is extracted by hydrometallurgy from low grade copper ores. It is leached out using acid or bacteria. The solution containing is treated with scrap iron, or .

Question 31:

Write two basic requirements for refining of a metal by Mond process and by Van Arkel Method.

Answer:

Basic requirements for both processes are:

(i) The metal should form a volatile compound with an available reagent.

(ii) The volatile compound should be easily decomposable, so that recovery of metal is easy.

Question 32:

Although carbon and hydrogen are better reducing agents but they are not used to reduce metallic oxides at high temperatures. Why?

Answer:

It is because at high temperature carbon and hydrogen react with metals to form carbides and hydrides respectively.

Question 33:

How do we separate two sulphide ores by Froth Floatation Method? Explain with an example.

Answer:

Two sulphide ores can be separated by adjusting proportion of oil to water or by using depressants. For example, in the case of an ore containing and , the depressant is used. It forms complex with and prevents it from coming with froth but remains with froth.

Question 34:

The purest form of iron is prepared by oxidising impurities from cast iron in a reverberatory furnace. Which iron ore is used to line the furnace? Explain by giving reaction.

Answer:

Haematite

Question 35:

The mixture of compounds A and B is passed through a column of by using alcohol as eluent. Compound A is eluted in preference to compound B. Which of the compounds A or B, is more readily adsorbed on the column?

Answer:

Since compound ‘A’ comes out before compound ‘B’, the compound ‘B’ is more readily adsorbed on column.

Question 36:

Why is sulphide ore of copper heated in a furnace after mixing with silica?

Answer:

Iron oxide present as impurity in sulphide ore of copper forms slag which is iron silicate and copper is produced in the form of copper matte.

Question 37:

Why are sulphide ores converted to oxide before reduction?

Answer:

Sulphides are not reduced easily but oxides are easily reduced.

Question 38:

Which method is used for refining and ? Explain with equation.

Answer:

van Arkel method is used for refining Zr and Ti. In this method crude metal is heated with iodine.

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Question 39:

What should be the considerations during the extraction of metals by electrochemical method?

Answer:

Generally two things are considered so that proper precautions can be taken.

(i) Reactivity of metal produced.

(ii) Suitability of electrodes.

Question 40:

What is the role of flux in metallurgical processes?

Answer:

Flux is used for making the molten mass more conducting.

Question 41:

How are metals used as semiconductors refined? What is the principle of the method used?

Answer:

Semiconducting metal is produced by zone refining method which is based on the principle that the impurities are more soluble in melt than in the solid state of metals.

Question 42:

Write down the reactions taking place in Blast furnace related to the metallurgy of iron in the temperature range .

Answer:

Question 43:

Give two requirements for vapour phase refining.

Answer:

(i) The metal should form a volatile compound with available reagent.

(ii) The volatile compound should be easily decomposable so that the recovery is easy.

Question 44:

Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.

Answer:

In this reaction zinc acts as a reducing agent.