CBSE Class 12 Chemistry General principles and processes of isolation of elements Questions Answers

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Chapter 6 General principles and processes of isolation of elements

One mark Questions

1.Differentiate between a mineral and an ore.

Ans: The naturally occurring chemical substances present in the earth’s crust which can be obtained by mining are called minerals while minerals from which metals can be extracted economically are called ores.

2. Why is it that only sulphide ores are concentrated by froth floatation process.

Ans: This is because sulphide ores particles are preferentially wetted by oil and gangue particles are wetted by water.

3. Name one acidic flux and one basic flux.

Ans: silica and lime

4. Name the chief ore of silver.

Ans: argentite or silver glance

5. Name a reagent used during leaching of bauxite ore.

Ans : NaOH (sodium hydroxide)

6. Why is silica added to sulphide ore of copper in the reverberatory furnace?

Ans : In order to remove the iron impurity as slag.

7. What is the role of flux in metallurgical processes?

Ans : Flux is used for making the molten mass more conducting.

8. What is the thermodynamic relation between Gibbs free energy and emf of the cell?

Ans: ΔG= —nFE

9. What is the relation between Gibbs free energy and equilibrium constant?

Ans: ΔG= —RTlnK

10. Give the expression for Gibbs Helmholtz equation.

Ans : ΔG= ΔH—TΔS

11. Name one chemical which can be used to concentrate galena selectively by froth floatation process.

Ans: sodium cyanide (NaCN)

12. What type of ores is roasted?

Ans : Sulphide ores .

13. Out of C and CO which is a better reducing agent for ZnO?

Ans: The free energy of formation of CO from C becomes lower at temp. above 1120K whereas that of CO2 from C becomes lower above 1323K than free energy of formation of ZnO. The free energy of formation of CO2 from CO is always higher than that of ZnO. Therefore, C can reduce ZnO to Zn better than CO.

14. What is the chemical principle on which chromatography separation based on?

Ans : Adsorption.

15. What are the products obtained during the electrolysis of brine solution? Also write the name of this process.

Ans : chlorine, hydrogen and sodium hydroxide. The process is popularly known as chlor-alkali process. 

16. What is roasting ?

Ans : The preliminary treatment of the concentrated ore in which the ore is heated in excess of air below its melting point.

17. What is calcination ?

Ans: The process of heating the concentrated ore in absence/ limited supply of air below its melting point.

18. What is smelting?

Ans: Reduction of metal oxide into metal in the presence of carbon or carbon monoxide.

19. What is blister copper/ copper matte?

Ans: The copper obtained after extraction has blistered appearance due to the evolution of SO2. It is called blistered copper/ copper matte.

20.What is meant by beneficiation process?

Ans: The process of removal of unwanted earthy and silicious impurities form the ore is called beneficiation process. 

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