NCERT Solutions for Class 12 Chemistry Chemistry Part-1 Chapter 6

General Principles and Processes of Isolation of Elements Class 12

Chapter 6 General Principles and Processes of Isolation of Elements Exercise Solutions

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In text : Solutions of Questions on Page Number : 150

Q1 :  

Which of the ores mentioned in Table 6.1 can be concentrated by magnetic separation method?


Answer :

If the ore or the gangue can be attracted by the magnetic field, then the ore can be concentrated by the process of magnetic separation. Among the ores mentioned in table 6.1, the ores of iron such as haematite (Fe2O3), magnetite (Fe3O4), siderite (FeCO3), and iron pyrites (FeS2) can be separated by the process of magnetic separation.

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Q2 :  

What is the significance of leaching in the extraction of aluminium?


Answer :

In the extraction of aluminium, the significance of leaching is to concentrate pure alumina (Al2O3) from bauxite ore.

Bauxite usually contains silica, iron oxide, and titanium oxide as impurities. In the process of leaching, alumina is concentrated by digesting the powdered ore with a concentrated solution of NaOH at 473-523 K and 35-36 bar. Under these conditions, alumina (Al2O3) dissolves as sodium meta-aluminate and silica (SiO2) dissolves as sodium silicate leaving the impurities behind.

The impurities are then filtered and the solution is neutralized by passing CO2 gas. In this process, hydrated Al2O3 gets precipitated and sodium silicate remains in the solution. Precipitation is induced by seeding the solution with freshly prepared samples of hydrated Al2O3.

Hydrated alumina thus obtained is filtered, dried, and heated to give back pure alumina (Al2O3).

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Q3 :  

The reaction,

is thermodynamically feasible as is apparent from the Gibbs energy value.

Why does it not take place at room temperature?


Answer :

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Q4 :  

The reaction,

is thermodynamically feasible as is apparent from the Gibbs energy value.

Why does it not take place at room temperature?


Answer :

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<< Previous Chapter 5 : Surface Chemistry Next Chapter 7 : The p-Block Elements >>

Exercise : Solutions of Questions on Page Number : 163

Q1 :  

Copper can be extracted by hydrometallurgy but not zinc. Explain.


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Q2 :  

What is the role of depressant in froth floatation process?


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Q3 :  

Why is the extraction of copper from pyrites more difficult than that from its

oxide ore through reduction?


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Q4 :  

Explain: (i) Zone refining (ii) Column chromatography.


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Q5 :  

Out of C and CO, which is a better reducing agent at 673 K?


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Q6 :  

Name the common elements present in the anode mud in electrolytic refining

of copper. Why are they so present ?


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Q7 :  

Write down the reactions taking place in different zones in the blast furnace

during the extraction of iron.


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Q8 :  

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


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Q9 :  

State the role of silica in the metallurgy of copper.


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Q10 :  

What is meant by the term "chromatography"?


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Q11 :  

What criterion is followed for the selection of the stationary phase in

chromatography?


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Q12 :  

Describe a method for refining nickel.


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Q13 :  

How can you separate alumina from silica in bauxite ore associated with

silica? Give equations, if any.


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Q14 :  

Giving examples, differentiate between 'roasting' and 'calcination'.


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Q15 :  

How is 'cast iron' different from 'pig iron"?


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Q16 :  

Differentiate between "minerals" and "ores".


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Q17 :  

Why copper matte is put in silica lined converter?


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Q18 :  

What is the role of cryolite in the metallurgy of aluminium?


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Q19 :  

How is leaching carried out in case of low grade copper ores?


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Q20 :  

Why is zinc not extracted from zinc oxide through reduction using CO?


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Q21 :  

The value of for formation of Cr2O3 is - 540 kJmol-1 and that of Al2 O3 is - 827 kJmol-1. Is the reduction of Cr2O3 possible with Al?


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Q22 :  

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


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Q23 :  

The choice of a reducing agent in a particular case depends on

thermodynamic factor. How far do you agree with this statement? Support

your opinion with two examples.


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Q24 :  

Name the processes from which chlorine is obtained as a by-product. What

will happen if an aqueous solution of NaCl is subjected to electrolysis?


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Q25 :  

What is the role of graphite rod in the electrometallurgy of aluminium?


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Q26 :  

Outline the principles of refining of metals by the following methods:

(i) Zone refining

(ii) Electrolytic refining

(iii) Vapour phase refining


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Q27 :  

Predict conditions under which Al might be expected to reduce MgO.


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<< Previous Chapter 5 : Surface Chemistry Next Chapter 7 : The p-Block Elements >>

Chemistry Part-1 - Chemistry : CBSE NCERT Exercise Solutions for Class 12th for General Principles and Processes of Isolation of Elements will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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