NCERT Exemplar Class 12 Chemistry Solutions Chapter 6 Principles and Processes of isolation of elements

NCERT Exemplar Class 12 Chemistry Solutions Chapter 6: MCQ (Type 1)

Question:1

In the extraction of chlorine by electrolysis of brine ____________.
(i) oxidation of ion to chlorine gas occurs.
(ii) reduction of ion to chlorine gas occurs.
(iii) For the overall reaction, has a negative value.
(iv) a displacement reaction takes place.
Answer:

The answer is the option (i). The oxidation reaction of ion is responsible for the extraction of chlorine from brine

The for this reaction is

Question:2

When copper ore is mixed with silica, in a reverberatory furnace copper matte is produced. The copper matte contains ____________.
(i) sulphides of copper (II) and iron (II)
(ii) sulphides of copper (II) and iron (III)
(iii) sulphides of copper (I) and iron (II)
(iv) sulphides of copper (I) and iron (III)
Answer:

The answer is the option (iii). Inside a reverberatory furnace iron silicate on mixing copper ore with silica in a reverberatory furnace, iron silicate comes off as slag producing copper in the form of copper matte containing copper sulphide and some iron sulphide

Question:3

Which of the following reactions is an example of autoreduction ?
(i)
(ii)
(iii)
(iv)
Answer:

In this reaction reduction of copper (I) oxide by copper (I) sulphide takes place. Since, copper is reduced by itself, this process is known as auto-reduction and the solidified copper so, obtained is known as blister copper. We get the copper metal on reaction of sulphide ore of copper with its oxide.

Question:4

A number of elements are available in earth’s crust but most abundant elements are ____________.
(i)
(ii)
(iii)
(iv)
Answer:

The answer is the option (i). A number of elements are available in the earth’s crust but the most abundant elements in the earth’s crust include .

Question:5

Zone refining is based on the principle that ___________.
(i) impurities of low boiling metals can be separated by distillation.
(ii) impurities are more soluble in molten metal than in solid metal.
(iii) different components of a mixture are differently adsorbed on an absorbent.
(iv) vapours of the volatile compound can be decomposed in pure metal.
Answer:

The answer is the option (ii). The basic principle of zone refining method is that impurities are more soluble in molten metal compared to the solid state of the metal.

Question:6

In the extraction of copper from its sulphide ore, the metal is formed by the reduction of with




Answer:

The answer is the option (iii). In the process of extraction of copper from its sulphide ore, the metal is formed by the reduction of with
Since, copper is reduced by itself the process is known as autoreduction.
Chemical reaction occuring in this reaction is
In this process, copper appears as blister copper.

Question:7

Brine is electrolysed by using inert electrodes. The reaction at anode is ________.
(i)
(ii)
(iii)
(iv)

Answer:

The answer is the option (i). Electrolysis of brine solution is a process of decomposition of solution using the electric current. Anode is positive; therefore it attracts negative hydroxide and chlorine ions. Chloride ions get oxidized by electron loss to chlorine molecules.

Question:8

In the metallurgy of aluminium ________________.
(i) is oxidised to .
(ii) graphite anode is oxidised to carbon monoxide and carbon dioxide.
(iii) the oxidation state of oxygen changes in the reaction at the anode.
(iv) the oxidation state of oxygen changes in the overall reaction involved in the process
Answer:

The answer is the option (ii). The graphite anode is oxidized to carbon monoxide and carbon dioxide in the process of metallurgy of aluminium .

Question:9

Electrolytic refining is used to purify which of the following metals?




Answer:

The answer is the option (i). Copper and zinc can be purified by using electrolyte refining method. In this process, impure metal acts as anode and a strip of pure metal is used as a cathode. Impurities from the blister copper or impure zinc deposit are used as anode mud. The electrolytic refining of copper and zinc is done to get high grade metals.

Question:10

Extraction of gold and silver involves leaching the metal with ion. The metal is recovered by ________________.
(i) displacement of metal by some other metal from the complex ion.
(ii) roasting of the metal complex.
(iii) calcination followed by roasting.
(iv) thermal decomposition of the metal complex.
Answer:

The answer is the option (i). Extraction of gold and silver involves leaching with ion. The metal in cyanide process is recovered by displacement of metal by some other metal from the complex ion. The reaction taking place is as:

Question:11

Answer the questions 11-13 on the basis of Fig. 6.1.

Choose the correct option of temperature at which carbon reduces to iron and produces .
(i) Below temperature at point A.
(ii) Approximately at the temperature corresponding to point A.
(iii) Above temperature at point A but below a temperature at point D.
(iv) Above temperature at point A.
Answer:

The answer is the option (iv)
It can be seen as a couple of two simpler reactions


Total Gibbs energy change becomes
In versus T plot, the plot to goes upward and the plot for to goes downwards.
At temperature above point A, the to lines comes below to and
So in this range, will reduce to and itself be oxidised to .

Question:12

Below point ‘A’ can ______________.
(i) be reduced by carbon monoxide only.
(ii) be reduced by both carbon monoxide and carbon.
(iii) be reduced by carbon only.
(iv) not be reduced by both carbon and carbon monoxide.
Answer:

The answer is the option (i). Below point A, can be reduced by carbon monoxide only.

Question:13

For the reduction of at the temperature corresponding to point D, which of the following statements is correct?
(i) value for the overall reduction reaction with carbon monoxide is zero.
(ii) value for the overall reduction reaction with a mixture of 1 mol carbon and 1 mol oxygen is positive.
(iii) value for the overall reduction reaction with a mixture of 2 mol carbon and 1 mol oxygen will be positive.
(iv) value for the overall reduction reaction with carbon monoxide is negative.
Answer:

The answer is the option (i). At point D, the curves of oxidation of iron and oxidation of intersect each other.
Thus, for the reaction is zero.


Resulting in

NCERT Exemplar Class 12 Chemistry Solutions Chapter 6: MCQ (Type 2)

Question:14

At the temperature corresponding to which of the points in Fig.6.1, will be reduced to by coupling the reaction with all of the following reactions?
(i)
(ii) and
(iii)
(i) Point A
(ii) Point B
(iii) Point D
(iv) Point E
Answer:

The answer is the option (ii, iv) The reduction reaction ranges can be determined from the intersection points on versus T plots.
The reduction of to takes place at point B and E because at these points value of all three oxidation reactions is lesser than that of reduction reaction.

Question:15

Which of the following option are correct?
(i) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.
(ii) In the extraction of silver, silver is extracted as cationic complex.
(iii) Nickel is purified by zone refining.
(iv) and are purified by van Arkel method
Answer:

The answer is the option (i, iv) Iron obtained from blast containing about 4% carbon and many impurities such as Mn, P, Si, etc is called pig iron. It is remelted with scrap iron to obtain cast iron which has slightly less carbon content (3%) compared to pig iron and is extremely hard and brittle.
For refining of Van Arkel method based on the thermal decomposition of metal components is used. In this method, the impurities i.e. oxygen and nitrogen are removed by heating metal in an evacuated vessel with iodine.


Zone refining is used for semiconductors like Ge, Si. For purification of Nickel, Mond’s process is used.

Question:16

In the extraction of aluminium by Hall-Heroult process, purified is mixed with to
(i) lower the melting point of
(ii) increase the conductivity of molten mixture.
(iii) reduce into Al(s).
(iv) acts as a catalyst
Answer:

The answer is the option (i, ii) Purified is mixed with in Hall-Heroult process to lower the melting point of and increase the conductivity of the molten mixture. Hence, option a and b are correct.

Question:17

Which of the following statements is correct about the role of substances added in the froth floatation process?
(i) Collectors enhance the non-wettability of the mineral particles.
(ii) Collectors enhance the wettability of gangue particles.
(iii) By using depressants in the process two sulphide ores can be separated.
(iv) Froth stabilisers decrease wettability of gangue.
Answer:

The answer is the option (i, iii) To enhance the non-wettability of mineral particles as well as froth stabilisers, collectors like sodium ethyl xanthate are used.
For example, sodium cyanide acts as a depressant for zinc sulphide in the process of concentration of galena ore. Depressants can be used for the separation of two sulphide ores.
Froth stabilizers are used to stabilize the froth in the process.

Question:18

In the Froth Floatation process, zinc sulphide and lead sulphide can be separated by ______________.
(i) using collectors.
(ii) adjusting the proportion of oil to water.
(iii) using depressant.
(iv) using froth stabilisers.
Answer:

The answer is the option (ii, iii) Froth floatation method is used in extraction of metal from sulphide ore. The two sulphide ores can be separated by using depressant and adjusting the proportion of oil to water in the froth floatation process. Depressant used in separation of zinc sulphide and lead sulphide is . It is utilized in selective prevention of from coming to the froth.

Question:19

Common impurities present in bauxite are ____________.
(i)
(ii)
(iii)
(iv)
Answer:

The answer is the option (iii, iv) some of the major impurities in bauxite are iron oxides (goethite and hematite), silicon dioxide, kaolinite and small amounts of anatase.

Question:20

Which of the following ores are concentrated by froth flotation?
(i) Haematite
(ii) Galena
(iii) Copper pyrites
(iv) Magnetite
Answer:

The answer is the option (ii, iii) Sulphide ores are concentrated by froth floatation process as pine oil selectively wets the sulphide ore. Galena and copper pyrite, being sulphide ores are concentrated by froth floatation process.

Question:21

Which of the following reactions occur during calcination?
(i)
(ii)
(iii)
(iv)
Answer:

The answer is the option (i, iii). In the process of calcination, heating of the ore below its melting in limited supply of air takes place. Ores that contain oxygen like oxide, hydroxides or carbonates are calcined. The reaction that takes place is:

Question:22

For the metallurgical process of which of the ores calcined ore can be reduced by carbon?
(i) haematite
(ii) calamine
(iii) iron pyrites
(iv) sphalerite
Answer:

The answer is the option (i, ii). Oxides reduction can be done by using carbon. Haematite (Iron ore - ) and calamine contain oxygen, so they can be reduced by carbon.
Sulphide ores cannot be reduced by carbon. Iron pyrite and sphalerite are sulphide ores of iron and zinc respectively.

Question:23

The main reactions occurring in the blast furnace during the extraction of iron from haematite are ________.
(i)
(ii)
(iii)
(iv)
Answer:

The answer is the option (i, iv). The 2 main reactions taking place in blast furnace during extraction of iron are:
(i) Reduction of


(ii) Slag formation

Question:24

In which of the following method of purification, metal is converted to its volatile compound which is decomposed to give pure metal?
(i) heating with a stream of carbon monoxide.
(ii) heating with iodine.
(iii) liquation.
(iv) distillation.
Answer:

The answer is the option (i,ii)
(i) Heating of metal with stream of

(ii) Heating with Iodine

Question:25

Which of the following statements are correct?
(i) A depressant prevents a certain type of particle to come to the froth.
(ii) Copper matte contains and
(iii) The solidified copper obtained from the reverberatory furnace has blistered appearance due to evolution of during the extraction.
(iv) Zinc can be extracted by self-reduction.
Answer:

The answer is the option (i, iii). Frothing of a particular sulphide can be prevented by depressants. The solidified copper that we get in reverberatory furnace has blistered appearance due to evolution of during extraction. Hence, it is called blister copper.

Question:26

In the extraction of chlorine from brine _____________.
(i) for the overall reaction is negative.
(ii) for the overall reaction is positive.
(iii) for the overall reaction has negative value.
(iv) for the overall reaction has positive value.
Answer:

The answeris the option (ii,iii).
for the reaction is
Using we get

NCERT Exemplar Class 12 Chemistry Solutions Chapter 6: Short Answer Type

Question:27

Why is an external emf of more than 2.2V required for the extraction of from brine?
Answer:

In the process of extraction of from brine solution :
the value of is
For this the value of is or
Hence, An external emf more than 2.20 V is required for extraction of from brine solution for electrolysis process.

Question:28

At temperatures above 1073K coke can be used to reduce . How can you justify this reduction with the Ellingham diagram?
Answer:

As per Ellingham diagram at temperature greater than 1073 K, for the formation is less negative than for the formation of carbon monoxide from carbon.
Thus, above 1073 K, carbon can reduce , i.e., for the reaction

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:

Wrought iron is an alloy with a very low carbon content (less than 0.08%).
The reaction is:


In extraction of cast iron from haematite ore, on addition of limestone as flux, the impurities of sulphur, silicon and phosphorus pass into slag on changing to their oxides.

Question:30

How is copper extracted from low-grade copper ores?
Answer:

Copper is extracted from low grade ores by the process of hydrometallurgy. Acid or bacteria is used in its leaching process. In the process, ore is treated with a suitable regent that dissolves ore but not the impurities. Scrap iron, zinc or is used to treat the solution containing copper ions and the reactions are as:


In this way, copper, is obtained.

Question:31

Write two basic requirements for refining of metal by Mond process and by Van Arkel Method
Answer:

Mond’s process and van arkel method are used for refining of nickel and zinc, respectively. The basic requirements for both the processes are:
(i) A volatile compound should be formed by the metal on reaction with an available reagent.
(ii) The volatile compound formed should be easily decomposable, enabling the metal to be easily recovered.

Question:32

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

Despite being better reducing agents, carbon and hydrogen are not used as carbon and hydrogen form carbides and hydrides respectively on reaction with metals at high temperature.

Question:33

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

The separation of two sulphide ores is done by adjusting proportion of oil to water or by using depressants. is used for an ore containing and . Sodium cyanide forms complex with and prevents it from coming with froth but lead sulphide 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 a reaction.
Answer:

Haematite is used to line the furnace. It supplies the oxygen and oxidises impurities present in the cast iron like carbon, silicon, manganese and phosphorus to and .



and escape and combine to form to form manganous silicate as slag (Manganous silicate-slag)

Question:35

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

Compound B is more readily adsorbed on the column as compound A is eluted in preference to compound B

Question:36

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

Iron oxide that is present as impurity in sulphide ore of copper forms an iron silicate slag and copper is produced in the form of copper matte. This is why, sulphide ore of copper is heated in a furnace after mixing with silica.

Question:37

Why are sulphide ores converted to oxide before reduction?
Answer:

Sulphides are not reduced easily unlike the oxides. This is why, sulphides are first oxidised and then subjected to reduction.

Question:38

Which method is used for refining ? Explain with equation.
Answer:

Van Arkel method is used in refining of . The crude metal, on heating with iodine forms volatile unstable compound. Pure metal is then obtained by decomposing the compound.
The equations are :

Question:39

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

During the extraction of metals by electrochemical method we should keep in mind the following factors
(i) Reactivity of the metal.
(ii) Suitability of the electrode.

Question:40

What is the role of flux in metallurgical processes?
Answer:

Flux is a chemical cleaning agent.
The ores contain some gangue even after concentration. Certain substances are mixed with concentrated ore for the purpose of removing the gangue. They combine with the gangue to form a fusible material that is insoluble in molten metal. These substances are called fluxes. Some examples of materials used as flux: Limestone, silica, dolomite, lime, borax etc.
Fluxes are classified as acidic or basic based on the type of impurities they remove.

Question:41

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

Semiconductor like silicon and germanium is produced by zone refining method and the principle used is that the impurities are more soluble in melt than the corresponding 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 500-800K.

Answer:

The reactions that take place in blast furnace during the metallurgy of iron at the temperature range 500-800 K are:

Question:43

Give two requirements for vapour phase refining.
Answer:

The two requirements for vapour phase refining are:
(i) A volatile compound should be formed by the metal on reaction with an available reagent.
(ii) The volatile compound formed should be easily decomposable, enabling the metal to be easily recovered.

Question:44

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

In extraction of gold by cyanide process, gold particles present in the ore are treated with a dilute solution of in the presence of atmospheric oxygen. Gold particles dissolve by forming complex cyanide that is soluble in nature.

On adding electropositive metal like zinc Au is recovered from solution.

The process of extraction of gold by cyanide oxidation as well as reduction. oxidation of gold takes place during the formation of cyanide complex whereas reduction takes place during its recovery. acts as a reducing agent.

NCERT Exemplar Class 12 Chemistry Solutions Chapter 6: Matching Type

Question:45

Match the items of Column I with items of Column II and assign the correct code:

(i) A (1) B (2) C (3) D (4)
(ii) A (2) B (4) C (5) D (3)
(iii) A (2) B (3) C (4) D (5)
(iv) A (4) B (5) C (3) D (2)

Answer:

Option (ii) is the answer.

Question:46

Match the items of Column I with the items of Column II and assign the correct code :

(i) A (1) B (2) C (4) D (5)
(ii) A (4) B (3) C (1) D (2)
(iii) A (3) B (4) C (2) D (1)
(iv) A (5) B (4) C (3) D (2)

Answer:

Option (ii) is the answer.

Question:47

Match items of Column I with the items of Column II and assign the correct code :

(i) A (4) B (2) C (3) D (1)
(ii) A (2) B (3) C (1) D (5)
(iii) A (1) B (2) C (3) D (4)
(iv) A (3) B (4) C (5) D (1)

Answer:

Option (i) is the answer.

Question:48

Match the items of Column I with the items of Column II and assign the correct code:

(i) A (3) B (4) C (2) D (1)
(ii) A (5) B (4) C (3) D (2)
(iii) A (2) B (3) C (4) D (5)
(iv) A (1) B (2) C (3) D (4)

Answer:

Option (i) is the answer.

Question:49

Match the items of Column I with items of Column II and assign the correct code :

(i) A (2) B (3) C (4) D (1)
(ii) A (1) B (2) C (3) D (5)
(iii) A (5) B (4) C (3) D (2)
(iv) A (4) B (5) C (3) D (2)
Answer:

Option (i) is the answer.

NCERT Exemplar Class 12 Chemistry Solutions Chapter 6: Assertion and Reason Type

Question:50

In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Nickel can be purified by Mond process.
Reason: is a volatile compound which decomposes at 460K to give pure .
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.
Answer:

The answer is the option (i). For Mond’s process, the pre-requisites include:
(i) A volatile compound should be formed by the metal on reaction with an available reagent.
(ii) The volatile compound formed should be easily decomposable, enabling the metal to be easily recovered.
is a volatile compound which decomposes to give pure nickel on heating at 460 K while (Carbon monoxide) is removed as gas.

Question:51

In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Zirconium can be purified by Van Arkel method.
Reason: is volatile and decomposes at 1800K.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.
Answer:

The answer is the option (i). Zirconium is also purified by Van Arkel method as it forms on treating with iodine and is easily decomposable to get pure zirconium.

Question:52

In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Sulphide ores are concentrated by Froth Flotation method.
Reason: Cresols stabilise the froth in the Froth Flotation Method.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.
Answer:

The answer is the option (ii). Sulphide ores on being wetted by oil, becomes lighter and rises to the surface along with froths. On the other hand, impurities wetted by water settle down as they get heavier.

Question:53

In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Zone refining method is very useful for producing semiconductors.
Reason: Semiconductors are of high purity.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.
Answer:

The answer is the option (ii).The principle of the zone refining method is that the the impurities of semiconductors are more soluble in the molten zone compared to the solid state and the ultrapure semiconductor crystallizes.

Question:54

In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.
Reason: Copper is extracted by hydrometallurgy.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.
Answer:

The answer is the option (ii). Copper is extracted by hydrometallurgical process. Suitable solvent like water is used for dissolving salts of metal. They are then reduced by more electropositive element in this process.

NCERT Exemplar Class 12 Chemistry Solutions Chapter 6: Long Answer Type

Question:55

Explain the following:

(i) is a better reducing agent below 710K whereas is a better reducing agent above 710K.
(ii) Generally sulphide ores are converted into oxides before reduction.
(iii) Silica is added to the sulphide ore of copper in the reverberatory furnace.
(iv) Carbon and hydrogen are not used as reducing agents at high temperatures.
(v) Vapour phase refining method is used for the purification of .
Answer:

(i) As per the Ellingham diagram, below 710 K

Hence, is better reducing agent compared to .
At temperature above 710 K,
Hence is better reducing agent.
(ii) Sulphide ores cannot be reduced easily but oxide ores can be esily reduced compared to them, hence sulphide ores are generally converted into oxides before reduction
(iii) In addition to copper sulphide, copper pyrites contain iron sulphide. In reverberatory furnace copper ore is roasted to give oxides.
is removed by adding silica from the matte containing copper sulphide and some iron sulphide.


(iv) Carbon and hydrogen react with metals at high temperature to form carbides and hydrides respectively hence they are not used as reducing agents.
(v) reacts with iodine to form which is volatile and decomposes to give at high temperature to give extra pure titanium. That is why vapour phase refining method is used for purification of