General Principles and Processes of Isolation of Elements

Multiple Choice Questions (MCQs)

1. In the extraction of chlorine by electrolysis of brine…… .

(a) oxidation of Clion to chlorine gas occurs

(b) reduction of Clion to chlorine gas occurs

(c) for overall reaction ΔGs has negative value

(d) a displacement reaction takes place

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Answer

(a) Following reaction takes place in the extraction of chlorine by electrolysis

2H2O(l)+2Cl(aq)H2(g)+Cl2(g)+2OH(aq)

From the above reaction it is very clear that the oxidation of Clion to chlorine gas occurs. Thus, option (a) is the correct answer.

ΔG for this reaction is +422kJ. Therefore, thermodynamically reaction is not feasible. We know that

ΔG=nFE

By using this equation value of E can be calculated. Thus,

E=ΔGnF=2.2V

Therefore, for the occurrence of this reaction, external potential (emf) greater than 2.2V is required. Due to this fact (c) is not the correct option.

  • (b) Reduction of Cl ion to chlorine gas does not occur. Instead, oxidation of Cl ion to chlorine gas occurs, as shown in the reaction: 2H2O(l)+2Cl(aq)H2(g)+Cl2(g)+2OH(aq)

  • (c) The overall reaction ΔG has a positive value (+422kJ), indicating that the reaction is not thermodynamically feasible without external potential. Therefore, ΔG does not have a negative value.

  • (d) A displacement reaction does not take place in the electrolysis of brine. The process involves the oxidation of Cl ions to chlorine gas and the reduction of water to hydrogen gas, not a displacement reaction.

2. When copper ore is mixed with silica, in a reverberatory furnace copper matte is produced. The copper matte contains

(a) sulphides of copper (II) and iron (II)

(b) sulphides of copper (II) and iron (III)

(c) sulphides of copper (I) and iron (II)

(d) sulphides of copper (I) and iron (III)

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Answer

(c) When copper ore is mixed with sillica in a reverberatory furnace copper matte is produced. The copper matte contains sulphide of copper (I) and iron (II).

Copper matte Cu2S and FeS

  • (a) sulphides of copper (II) and iron (II): This option is incorrect because in the copper matte, copper is present as copper (I) sulfide (Cu2S) and not as copper (II) sulfide (CuS). The iron is correctly identified as iron (II) sulfide (FeS).

  • (b) sulphides of copper (II) and iron (III): This option is incorrect because in the copper matte, copper is present as copper (I) sulfide (Cu2S) and not as copper (II) sulfide (CuS). Additionally, iron is present as iron (II) sulfide (FeS) and not as iron (III) sulfide (Fe2S3).

  • (d) sulphides of copper (I) and iron (III): This option is incorrect because while copper is correctly identified as copper (I) sulfide (Cu2S), iron is present as iron (II) sulfide (FeS) in the copper matte, not as iron (III) sulfide (Fe2S3).

3. Which of the following reactions is an example of autoreduction?

(a) Fe3O4+4CO3Fe+4CO2

(b) Cu2O+C2Cu+CO

(c) Cu2+(aq)+Fe(s)Cu(s)+Fe2+(aq)

(d) Cu2O+12Cu2S3Cu+12SO2

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Answer

(d) Cu2O+12Cu2S3Cu+12SO2

This reaction includes reduction of copper (I) oxide by copper (I) sulphide. In this process, copper is reduced by itself hence this process is known as autoreduction and the solidified copper. So, obtained is known as blister copper.

  • (a) Fe3O4+4CO3Fe+4CO2: This reaction involves the reduction of iron oxide by carbon monoxide, not by itself. Therefore, it is not an example of autoreduction.

  • (b) Cu2O+C2Cu+CO: This reaction involves the reduction of copper(I) oxide by carbon, not by itself. Hence, it is not an example of autoreduction.

  • (c) Cu2+(aq)+Fe(s)Cu(s)+Fe2+(aq): This reaction involves the reduction of copper ions by iron, not by itself. Therefore, it is not an example of autoreduction.

4. A number of elements are available in earth’s crust but most abundant elements are…… .

(a) Al and Fe

(b) Al and Cu

(c) Fe and Cu

(d) Cu and Ag

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Answer

(a) Among a number of elements which are available in earth crust, the most abundant elements are aluminium and iron. Aluminium is third most abundant element in earth crust. i.e., 8.3% by weight while iron present in earth crust with 4.2% by weight. Copper and silver are also found in earth crust but their abundance percentage is low.

  • Option (b) is incorrect because copper (Cu) is not among the most abundant elements in the earth’s crust. While aluminum (Al) is indeed abundant, copper’s abundance percentage is much lower compared to iron (Fe).

  • Option (c) is incorrect because copper (Cu) is not among the most abundant elements in the earth’s crust. Iron (Fe) is abundant, but copper’s abundance percentage is significantly lower compared to aluminum (Al).

  • Option (d) is incorrect because neither copper (Cu) nor silver (Ag) are among the most abundant elements in the earth’s crust. Both elements have much lower abundance percentages compared to aluminum (Al) and iron (Fe).

5. Zone refining is based on the principle that…… .

(a) impurities of low boiling metals can be separated by distillation.

(b) impurities are more soluble in molten metal than in solid metal.

(c) different components of a mixture are differently adsorbed on an adsorbent.

(d) vapours of volatile compound can be decomposed in pure metal.

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Answer

(b) Zone refining is based on the principle that the impurities are more soluble in molten state than in solid state of the metal. A circular mobile heater fixed at one end of impure metal rod. The molten zone moves along with heater which is moved forward.

As the heater moves forward, the pure metal crystallises out of the melt and the impurities pass on into adjacent molten zone. The process is repeated several times and the heater is moved in the same direction.

At one end, impurities get concentrated. This end is cut off. e.g., germanium, silicon, gallium etc., are refined by this method.

  • (a) Impurities of low boiling metals can be separated by distillation: This option is incorrect because distillation is a process used to separate components based on differences in their boiling points, not on their solubility in molten versus solid states.

  • (c) Different components of a mixture are differently adsorbed on an adsorbent: This option is incorrect because adsorption is a surface phenomenon where different components adhere to the surface of an adsorbent material, which is not related to the solubility of impurities in molten and solid states.

  • (d) Vapours of volatile compound can be decomposed in pure metal: This option is incorrect because it describes a process involving the decomposition of volatile compounds, which is not related to the principle of solubility differences between molten and solid states in zone refining.

6. In the extraction of copper from its sulphide ore, the metal is formed by the reduction of Cu2O with

(a) FeS

(b) CO

(c) Cu2S

(d) SO2

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Answer

(c) In the extraction of copper from its sulphide ore, the metal is formed by the reduction of Cu2O with Cu2S. This reaction completes with the process of autoreduction.

Chemical reaction occurring in this reaction is as follows

Cu2O+12Cu2S3Cu+12SO2

In this process, copper appears as blister copper.

  • (a) FeS: Iron sulfide (FeS) is not used in the reduction of Cu2O to form copper. FeS does not participate in the autoreduction process that is specific to copper extraction.

  • (b) CO: Carbon monoxide (CO) is a reducing agent used in various metallurgical processes, but it is not used in the reduction of Cu2O in the extraction of copper from its sulphide ore. The specific autoreduction process involves Cu2S.

  • (d) SO2: Sulfur dioxide (SO_2) is a byproduct of the reduction reaction and not a reducing agent. It does not reduce Cu2O to copper.

7. Brine is electrolysed by using inert electrodes. The reaction at anode is…… .

(a) Cl(aq)12Cl2(g)+e; ECell s=1.36V

(b) 2H2O(l)O2(g)+4H++4e; ECell s=1.23V

(c) Na+(aq)+eNa(s); ECell s=2.71V

(d) H+(aq) +e12H2(g); ECell s=0.00V

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Answer

(a) Brine is electrolysed by using inert electrodes. The possible reactions occurring at anode are

Cl(aq)12Cl2(g)+e;ECells=1.36V2H2O(l)O2(g)+4H++4e;ECells=1.23V

The reaction at anode with lower value of E is preferred and therefore water should get oxidised in preference to Cl(aq). However, Cl2 is produced instead of O2. This unexpected result is explained on the basis of the fact that water needs greater voltage for oxidation to O2 (as it is kinetically slow process) than that needed for oxidation of Clions to Cl2.

  • Option (b): Although the standard electrode potential for the oxidation of water to oxygen is lower (ECells=1.23,V) compared to the oxidation of chloride ions to chlorine (ECells=1.36,V), the oxidation of water is kinetically slow and requires a higher overpotential. Therefore, in practice, chloride ions are oxidized preferentially.

  • Option (c): This option describes the reduction of sodium ions to sodium metal, which occurs at the cathode, not the anode. The question specifically asks for the reaction at the anode.

  • Option (d): This option describes the reduction of hydrogen ions to hydrogen gas, which also occurs at the cathode, not the anode. The question specifically asks for the reaction at the anode.

8. In the metallurgy of aluminium…… .

(a) Al3+ is oxidised to Al(s).

(b) graphide anode is oxidised to carbon monoxide and carbon dioxide.

(c) oxidation state of oxygen changes in the reaction at anode.

(d) oxidation state of oxygen changes in the overall reaction involved in the process.

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Answer

(b) In the metallurgy of aluminium, electrolysis is performed in a steel vessel with lining of carbon acts as cathode and graphite acts as anode. During this process graphite anode is oxidised to CO and CO2.

Chemical reaction occurring in this process is as follows

2Al2O3+3C4Al+3CO2

This process is known as Hall - Heroult process. The electrolytic reactions are

At cathode Al3+( melt )+3eAl(l)

At anode C(s)+O2( melt )CO(g)+2e

C(s)+2O2 (melt) CO2(g)+4e

  • (a) Al3+ is oxidised to Al(s): This statement is incorrect because in the electrolysis process, Al3+ ions are reduced, not oxidized. The reduction reaction at the cathode is Al3++3eAl(s).

  • (c) oxidation state of oxygen changes in the reaction at anode: This statement is incorrect because the oxidation state of oxygen does not change in the reaction at the anode. The anode reactions involve the oxidation of carbon to form carbon monoxide (CO) and carbon dioxide (CO2), but the oxidation state of oxygen remains -2 in both products.

  • (d) oxidation state of oxygen changes in the overall reaction involved in the process: This statement is incorrect because the oxidation state of oxygen remains -2 throughout the overall reaction. The overall reaction is 2Al2O3+3C4Al+3CO2, where oxygen is in the -2 oxidation state in both Al2O3 and CO2.

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

(a) Cu and Zn

(b) Ge and Si

(c) Zr and Ti

(d) Zn and Hg

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Answer

(a) Copper and zinc are two metals which are generally purified by using electrolyte refining. In this process, impure metal is used as anode and pure metal is used as a cathode. Impurities from the blister copper or impure zinc deposit as anode mud.

  • (b) Ge and Si: Germanium (Ge) and Silicon (Si) are typically purified using methods such as zone refining or chemical vapor deposition, not electrolytic refining.

  • (c) Zr and Ti: Zirconium (Zr) and Titanium (Ti) are usually purified through processes like the Kroll process or the Van Arkel process, rather than electrolytic refining.

  • (d) Zn and Hg: While zinc (Zn) can be purified by electrolytic refining, mercury (Hg) is not typically purified using this method. Mercury is usually purified through distillation.

10. Extraction of gold and silver involves leaching the metal with CNion. The metal is recovered by…… .

(a) displacement of metal by some other metal from the complex ion.

(b) roasting of metal complex.

(c) calcination followed by roasting.

(d) thermal decomposition of metal complex.

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Answer

(a) Extraction of gold and silver involves leaching the metal with CNion. The metal is recovered by displacement of metal by some other metal from the complex ion.

This is an oxidation reaction.

4Au(s)+8CN(aq)+2H2O(aq)+O2(g)4[Au(CN)2](aq)+4OH(aq)

4[Au(CN2)](aq)+Zn(s)2Au(s)+[Zn(CN)4]2(aq)

Here, Zn acts as a reducing agent.

Direction (Q. Nos. 11-13) Answer the questions on the basis of figure

  • (b) Roasting of metal complex: Roasting is a process that involves heating the ore in the presence of oxygen. This method is typically used to convert sulfide ores into oxides, which can then be reduced to extract the metal. However, in the case of gold and silver extraction, the metal is already in a complex ion form with cyanide, and roasting is not applicable for recovering the metal from this complex.

  • (c) Calcination followed by roasting: Calcination is the process of heating the ore in the absence of air to remove volatile impurities, and roasting follows to convert the ore into an oxide. This method is generally used for carbonate and sulfide ores. Since gold and silver are leached with cyanide to form a complex ion, calcination and roasting are not relevant steps for recovering the metal from the cyanide complex.

  • (d) Thermal decomposition of metal complex: Thermal decomposition involves breaking down a compound by heating it. This method is not suitable for recovering gold and silver from their cyanide complexes because the complex ions are stable and do not decompose easily with heat. Instead, a displacement reaction with another metal, such as zinc, is used to recover the gold and silver.

11. Choose the correct option of temperature at which carbon reduces Fe0 to iron and produces CO.

(a) Below temperature at point A

(b) Approximately at the temperature corresponding to point A

(c) Above temperature at point A but below temperature at point D

(d) Above temperature at point A

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Thinking Process

This problem is based on concept of Ellingham diagram which relates Gibbs free energy of reaction and temperature. The point above which greater the negative value of formation of compound is observed, compound will form at that temperature. At a particular temperature compound having higher negative value of Gibbs free energy will be formed first.

Answer

(d) In the figure shown above point A

ΔfG(C,CO)<ΔfG(Fe,FeO)

Therefore, above point A,C reduces FeO to Fe forming carbon monoxide. Hence, reduction of FeO by carbon occurs above point A only.

  • Option (a) Below temperature at point A: Below point A, the Gibbs free energy change for the formation of CO from C is not sufficiently negative compared to the Gibbs free energy change for the formation of FeO from Fe. Therefore, carbon cannot effectively reduce FeO to Fe below this temperature.

  • Option (b) Approximately at the temperature corresponding to point A: At the temperature corresponding to point A, the Gibbs free energy changes for the formation of CO from C and FeO from Fe are approximately equal. This means that the reduction reaction is not favored or is at equilibrium, so carbon cannot effectively reduce FeO to Fe at this temperature.

  • Option (c) Above temperature at point A but below temperature at point D: This option is partially correct but not specific enough. While it is true that carbon can reduce FeO to Fe above point A, the critical information is that the reduction starts just above point A. The range between point A and point D is too broad and does not precisely indicate the onset of the reduction reaction.

12. Below point ‘A’ Fe0 can…… .

(a) be reduced by carbon monoxide only.

(b) be reduced by both carbon monoxide and carbon.

(c) be reduced by carbon only.

(d) not be reduced by both carbon and carbon monoxide.

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Answer

(a) Below point A Gibbs free energy change for the formation of CO2 from CO(ΔGCO2,CO2) has lower value (more negative value) than Gibbs free energy change for the formation of FeO(ΔGFe,FeO). Hence, FeO will be reduced by CO only below point A.

  • (b) FeO cannot be reduced by both carbon monoxide and carbon below point A because the Gibbs free energy change for the formation of CO₂ from CO is more negative than that for the formation of FeO, indicating that CO is a more effective reducing agent than carbon in this context.

  • (c) FeO cannot be reduced by carbon only below point A because the Gibbs free energy change for the formation of CO₂ from CO is more negative than that for the formation of FeO, making CO the preferred reducing agent over carbon.

  • (d) FeO can be reduced by carbon monoxide below point A, as indicated by the more negative Gibbs free energy change for the formation of CO₂ from CO compared to the formation of FeO. Therefore, it is incorrect to say that FeO cannot be reduced by both carbon and carbon monoxide.

13. For the reduction of Fe0 at the temperature corresponding to point D, which of the following statements is correct?

(a) ΔG value for the overall reduction reaction with carbon monoxide is zero.

(b) ΔG value for the overall reduction reaction with a mixture of 1mol carbon and 1 mol oxygen is positive.

(c) ΔG value for the overall reduction reaction with a mixture of 2mol carbon and 1 mol oxygen will be positive.

(d) ΔG value for the overall reduction reaction with carbon monoxide is negative.

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Answer

(a) At point D,ΔG curve for formation of CO2 from CO and FeO from Fe intersect each other therefore, overall reduction of FeO with CO is zero.

Hence, (a) is the correct choice.

  • (b) ΔG value for the overall reduction reaction with a mixture of 1mol carbon and 1 mol oxygen is positive.

    The statement is incorrect because the mixture of 1 mol carbon and 1 mol oxygen would form carbon dioxide (CO2), which is a highly exothermic reaction. This would result in a negative ΔG value, not a positive one.

  • (c) ΔG value for the overall reduction reaction with a mixture of 2mol carbon and 1 mol oxygen will be positive.

    The statement is incorrect because the mixture of 2 mol carbon and 1 mol oxygen would form carbon monoxide (CO), which is also an exothermic reaction. This would result in a negative ΔG value, not a positive one.

  • (d) ΔG value for the overall reduction reaction with carbon monoxide is negative.

    The statement is incorrect because at point D, the ΔG value for the overall reduction reaction with carbon monoxide is zero, not negative. This is due to the intersection of the ΔG curves for the formation of CO2 from CO and FeO from Fe.

Multiple Choice Questions (More Than One Options)

14. At the temperature corresponding to which of the points in Fig. Fe0 will be reduced to Fe by coupling the reaction 2Fe02Fe+O2 with all of the following reactions?

  1. C+OCO2
  2. 2C+O22CO
  3. 2CO+O22CO2

(a) Point A

(b) Point B

(c) Point D

(d) Point E

Show Answer

Answer

(b,d)

Below point B and E,FeO will be reduced to Fe by all the three reactions shown above in the question. ΔG(C,CO2),ΔG(C,CO),ΔG(CO2,CO2) lie below ΔfG(Fe,FeO) curve at point B and E. Therefore, FeO will be reduced by all three reactions.

Hence, options (b) and (d) are correct choice.

  • Option (a) Point A: At point A, the Gibbs free energy changes for the reactions involving carbon and carbon monoxide do not lie below the Gibbs free energy change for the reduction of FeO to Fe. Therefore, FeO will not be reduced by all three reactions at this point.

  • Option (c) Point D: At point D, the Gibbs free energy changes for the reactions involving carbon and carbon monoxide do not lie below the Gibbs free energy change for the reduction of FeO to Fe. Therefore, FeO will not be reduced by all three reactions at this point.

15. Which of the following options are correct?

(a) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.

(b) In extraction of silver, silver is extracted as cationic complex.

(c) Nickel is purified by zone refining.

(d) Zr and Ti are purified by van Arkel method.

Show Answer

Thinking Process

This process is based on concept of purification techniques and formation of cast iron.

Answer

(a,d)

Correct statements are

(a) Cast iron is obtained by remelting pig iron with scarp iron and coke using hot air blast.

(d) Zr and Ti are purified by van Arkel method as

Zr Impure +2I2ZrI4 Volatile ΔZr+2I2 Pure 

(b) and (c) can be correctly stated as

(b)In extraction of silver, silver is extracted as anionic complex [Ag(CN)2]

(c)Nickel is purified by vapour phase refining method.

Ni+4CONi(CO)4450470KNi+4CO

  • (b) In extraction of silver, silver is extracted as anionic complex [Ag(CN)2]: The statement is incorrect because silver is not extracted as a cationic complex but as an anionic complex, specifically [Ag(CN)2].

  • (c) Nickel is purified by zone refining: The statement is incorrect because nickel is not purified by zone refining. Instead, it is purified by the vapour phase refining method, where nickel reacts with carbon monoxide to form a volatile complex, nickel tetracarbonyl, which decomposes upon heating to yield pure nickel.

16. In the extraction of aluminium by Hall-Heroult process, purified Al2O3 is mixed with CaF2 to

(a) lower the melting point of Al2O3

(b) increase the conductivity of molten mixture.

(c) reduce Al3+ into Al(s)

(d) acts as catalyst

Show Answer

Thinking Process

This problem is based on extraction of aluminium using Hall-Heroult process.

Answer

(a,b)

In the metallurgy of aluminium Al2O3 is mixed with Na3AlF6 and CaF2 which causes following affects.

(i) Lower the melting point of Al2O3 (ii) Increase the conductivity of molten mixture

  • (c) CaF2 does not reduce Al3+ into Al(s). The reduction of Al3+ to Al(s) is achieved through electrolysis, where an electric current is passed through the molten mixture to facilitate the reduction process.
  • (d) CaF2 does not act as a catalyst in the Hall-Heroult process. Its primary roles are to lower the melting point of Al2O3 and increase the conductivity of the molten mixture.

17. Which of the following statements is correct about the role of substances added in the froth floatation process?

(a) Collectors enhance the non-wettability of the mineral particles.

(b) Collectors enhance the wettability of gangue particles.

(c) By using depressants in the process two sulphide ores can be separated.

(d) Froth stabilisers decrease wettability of gangue.

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Thinking Process

This problem is based on the method involved in froth floatation method and function of collector and depressants.

Answer

(a,c)

Froth floatation process is used to extract metal from sulphide ore. This method utilises collectors and depressants whose functions are as follows

(i) Collectors enhance the non-wettability of the mineral particles.

(ii) By using depressants in the process two sulphide ores can be separated. e.g., sodium cyanide is used as a depressant to separate lead sulphide ore from zinc sulphide ore.

  • Collectors do not enhance the wettability of gangue particles; they enhance the non-wettability of mineral particles, making option (b) incorrect.
  • Froth stabilisers do not decrease the wettability of gangue; they help in stabilizing the froth formed during the process, making option (d) incorrect.

18. In the froth floatation process, zinc sulphide and lead sulphide can be separated by…… .

(a) using collectors

(b) adjusting the proportion of oil to water

(c) using depressant

(d) using froth stabilisers

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Answer

(b,c)

Froth floatation method is used to extract metal from sulphide ore. ZnS and PbS can be separated by using depressant and adjusting the proportion of oil to water. Depressant used for this purpose is NaCN. It selectively prevents ZnS from coming to the froth.

Hence, (b) and (c) are correct choices.

  • (a) using collectors: Collectors are reagents that increase the non-wettability of the mineral particles, making them attach to air bubbles and rise to the froth. However, collectors do not specifically help in separating zinc sulphide (ZnS) from lead sulphide (PbS) as they generally enhance the floatability of both types of sulphide minerals.

  • (d) using froth stabilisers: Froth stabilisers are used to maintain the froth formed during the floatation process, ensuring that it is stable enough to carry the mineral particles to the surface. They do not play a role in selectively separating ZnS from PbS.

19. Common impurities present in bauxite are…… .

(a) CuO

(b) ZnO

(c) Fe2O3

(d) SiO2

Show Answer

Answer

(c,d)

Bauxite is an ore of aluminium which contain Fe2O3 and SiO2 as common impurities.

  • (a) CuO: Copper oxide (CuO) is not a common impurity in bauxite. Bauxite primarily contains impurities such as iron oxides and silica, not copper compounds.

  • (b) ZnO: Zinc oxide (ZnO) is not typically found in bauxite. The common impurities in bauxite are iron oxides and silica, rather than zinc compounds.

20. Which of the following ores are concentrated by froth floatation?

(a) Haematite

(b) Galena

(c) Copper pyrites

(d) Magnetite

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Answer

(b,c)

Haematite (Fe2O3) and magnetite (Fe3O4) are oxide ores while galena ( .PbS) and copper pyrites (CuFeS2) are sulphide ores. As we know sulphide ores are extracted by using froth floatation method. Hence, (b) and (c) are the correct choices.

  • Haematite (Fe2O3) and magnetite (Fe3O4) are oxide ores, and froth flotation is not typically used for concentrating oxide ores.

21. Which of the following reactions occur during calcination?

(a) CaCO3CaO+CO2

(b) 2FeS2+112O2Fe2O3+4SO2

(c) Al2O3xH2OAl2O3+xH2O

(d) ZnS+32O2ZnO+SO2

Show Answer

Thinking Process

This process is based on concept of calcination.

Answer

(a,c)

Calcination involves heating of the ore below its melting point in the absence of air or in limited supply of air. Oxygen containing ores like oxide, hydroxides and carbonates are calcined. Thus, the following reactions occur during calcination.

CaCO3ΔCaO+CO2Al2O3xH2OΔAl2O3+xH2O

  • Option (b): The reaction 2FeS2+112O2Fe2O3+4SO2 involves the oxidation of iron sulfide (FeS₂) in the presence of oxygen, which is a roasting process, not calcination. Calcination occurs in the absence or limited supply of air, whereas roasting requires a significant amount of air or oxygen.

  • Option (d): The reaction ZnS+32O2ZnO+SO2 also involves the oxidation of zinc sulfide (ZnS) in the presence of oxygen, which is another example of roasting. As with option (b), this process requires a significant amount of air or oxygen, which is not characteristic of calcination.

22. For the metallurgical process of which of the ores calcined ore can be reduced by carbon?

(a) Haematite

(b) Calamine

(c) Iron pyrites

(d) Sphalerite

Show Answer

Answer

(a,b)

In the metallurgical process, the oxide ores are reduced by carbon. Sulphide ore cannot be reduced by carbon. Here, haematite (Fe2O3) and calamine (ZnO) are oxide ores of iron and zinc respectively while iron pyrites (FeS2) and sphalerite (ZnS) are sulphide ores of iron and zinc respectively.

Therefore, haematite and calamine can be reduced by carbon.

  • Iron pyrites (FeS₂) is a sulphide ore and cannot be reduced by carbon.
  • Sphalerite (ZnS) is a sulphide ore and cannot be reduced by carbon.

23. The main reactions occurring in blast furnace during extraction of iron from haematite ore…… .

(a) Fe2O3+3CO2Fe+3CO2

(b) FeO+SiO2FeSiO3

(c) Fe2O3+3C2Fe+3CO

(d) CaO+SiO2CaSiO3

Show Answer

Answer

(a,d)

In extraction of iron from haematite ore following reactions take place.

(i) Fe2O3+3CO2Fe+3CO2

This reaction represents reduction of Fe2O3 to Fe.

(ii) CaO Formation of slag +SiO2CaSiO3Slag

  • Option (b) FeO+SiO2FeSiO3 is incorrect because this reaction does not occur in the blast furnace. Instead, FeO is reduced to Fe by carbon monoxide (CO) or carbon (C), and SiO2 reacts with CaO to form slag (CaSiO3).

  • Option (c) Fe2O3+3C2Fe+3CO is incorrect because, in the blast furnace, carbon monoxide (CO) is the primary reducing agent for Fe2O3, not carbon (C). The reaction involving carbon would require much higher temperatures and is not the main pathway in the blast furnace process.

24. In which of the following method of purification, metal is converted to its volatile compound which is decomposed to give pure metal?

(a) Heating with stream of carbon monoxide

(b) Heating with iodine

(c) Liquation

(d) Distillation

Show Answer

Thinking Process

This problem is based on purification of metal using vapour phase refining method.

Answer

( a,b )

Vapour phase refining method includes

(i) Heating of metal with stream of CO

Ni+4CONi(CO)4450470KNi+4CO (Mond’s process)

(ii) Heating with iodine

Zr+2I2870KZrI4 Tungsten  filament 2075KZr+2I2 (van Arkel method) 

  • Liquation: This method involves melting the metal and allowing it to flow away from impurities which have higher melting points. It does not involve the conversion of the metal to a volatile compound.

  • Distillation: This method involves heating the metal to its boiling point and then condensing the vapor to obtain the pure metal. It does not involve the formation of a volatile compound that decomposes to give the pure metal.

25. Which of the following statements are correct?

(a) A depressant prevents certain type of particle to come to the froth.

(b) Copper matte contains Cu2S and ZnS.

(c) The solidified copper obtained from reverberatory furnace has blistered appearance due to evolution of SO2 during the extraction.

(d) Zinc can be extracted by self-reduction.

Show Answer

Answer

(a,c)

Correct statements are

(i) A depressant prevents certain type of particle to come to the froth. e.g., NaCN is added as a depressant during separation of PbS and ZnS.

(ii) The solidified copper obtained from reverberatory furnace has blistered appearance due to evolution of SO2 during the extraction.

(b) and (d) are incorrect statements, and can be correctly stated as

(iii) Copper matte contains Cu2S and FeS.

(iv) Zinc can be extracted by reduction of ZnO with carbon.

  • (b) Copper matte contains (Cu_2S) and (FeS), not (ZnS).
  • (d) Zinc is extracted by reduction of (ZnO) with carbon, not by self-reduction.

26. In the extraction of chlorine from brine…… .

(a) ΔGs for the overall reaction is negative.

(b) ΔGs for the overall reaction is positive.

(c) Es for the overall reaction has negative value.

(d) Es for the overall reaction has positive value.

Show Answer

Answer

(b,c)

Electrolysis of brine solution is used to extract chlorine. Overall chemical reaction occurring in this process and value of ΔG can be shown as

2H2O(l)+2Cl(aq)H2(g)+Cl2(g)+2OH(aq)

For the given reaction, value of ΔG is 422kJ

Using ΔG=nFE, the value of E=E2.2V.

Therefore, ΔG for the overall reaction is positive and E has negative value.

  • Option (a) is incorrect because the value of ΔG for the overall reaction is positive, not negative. A positive ΔG indicates that the reaction is non-spontaneous under standard conditions.

  • Option (d) is incorrect because the value of E for the overall reaction is negative, not positive. A negative E indicates that the reaction is non-spontaneous under standard conditions.

Short Answer Type Questions

27. Why is an external emf of more than 2.2V required for the extraction of Cl2 from brine?

Show Answer

Answer

2Cl(aq)+2H2O(l)2OH(aq)+H2(g)+Cl2(g)

For the given reaction, value of ΔG is +422kJ.

Using ΔG=nFE, the value of E=2.2V.

Therefore, an external emf greater than 2.2V is required for the extraction of Cl2 from brine.

28. At temperature above 1073 K, coke can be used to reduce Fe0 to Fe. How can you justify this reduction with Ellingham diagram?

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Answer

Using Ellingham diagram, we observe that at temperature greater than 1073K; ΔG(C,CO)<ΔG(Fe,FeO). We know that according to Ellingham diagram, compound having lower ΔtGs undergo its formation.

Hence, coke can reduce FeO to Fe.

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?

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Answer

(a)

Fe2O3 Haematite  lining +3C Impurities  (present in cast iron) 2Fe Wrought  iron +3CO

This reaction takes place in reverberatory furnace lined with haematite.

(b) The haematite oxidises S to SO2, Si to SiO2 and P to P4O10. Sometimes limestone is added as flux. Impurities of S,Si and P oxidise and pass into slag. The metal is removed and freed from slag by passing through rollers.

30. How is copper extracted from low grade copper ores?

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Answer

Copper is extracted from low grade copper ore using hydrometallurgy method. For this purpose, ore is leached out using bacteria. The solution containing Cu2+ is treated with scrap iron and H2.

Cu2+(aq)+H2(g)Cu(s)+2H+(aq)

31. Write two basic requirements for refining of a metal by Mond’s process and by van Arkel Method.

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Answer

Two basic requirements are

(i) Metal should form volatile compound with available reagent.

(ii) The volatile compound should be easily decomposable so that it can be recovered easily.

(a) Mond’s process includes conversion of Ni to Ni(CO)4 and then decomposition of Ni(CO)4 to Ni.

Ni+4CONi(CO)4Ni(CO)4450470KNi+4CO

(b) van Arkel method includes conversion of Zr to volatile ZrI4 and then decomposition of ZrI4 to Zr and I2.

Zr+2I2870KZrI42075KZr+2I2

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

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Answer

Because at high temperatures, carbon and hydrogen react with metals to form carbides and hydrides respectively. So, carbon and hydrogen are not better reducing agents to reduce metallic oxide.

33. How do we separate two sulphide ores by froth floatation method? Explain with an example.

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Answer

Two sulphide ores can be separated by adjusting the proportion of oil and water or by using depressants, e.g., if an ore contains ZnS and PbS both, a depressant NaCN is added during froth floatation. It forms a complex with ZnS and prevents it from coming into froth. PbS comes into the froth and thus separated.

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.

Show Answer

Answer

(a) Haematite (Fe2O3) ore is used to line the furnace.

 (b) Fe2O3 Haematite  lining +3Cimpurites (present in cast iron) 2Fe Wrought  iron +3CO

35. The mixture of compounds A and B is passed through a column of AlO3 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?

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Answer

Compounds which are adsorbed to the more extent comes out later while the another one which absorbed to the less extent comes out readily. Since, compound ’ A ’ comes out before compound ’ B ‘, the compound ’ B ’ is more readily adsorbed on the column.

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

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Answer

Silica (flux) being an acidic flux removes the impurities of iron oxide the basic impurity, by reacting with it. Thus, iron silicate (slag) is formed.

FeO Gangue +SiO2 Flux FeSiO3 Slag 

37. Why are sulphide ores converted to oxide before reduction?

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Answer

This is because oxides are reduced to metals easily while sulphides are not. So, sulphide ores are converted to oxide before reduction.

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

Show Answer

Answer

Zr and Ti are refined by van Arkel method. It involves 2 steps

(a) Formation of iodide e.g., zirconium

Zr+2I2ZrI4

(b) Decomposition of iodide

ZrI41800KZr Pure +2I2

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

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Answer

During extraction of metals by electrochemical method the following two points must be considered

(i) Reactivity of metals If the metals are quite reactive and are expected to react with water then the metals should be extracted by the electrolysis of their purified molten ore rather than their aqueous solution.

(ii) Suitability of electrodes The electrods selected should not react with the product of electrolysis. If at all they react, then the electrodes must be made up of a material which is quite cheap since their periodic replacement should not increase the cost of the process.

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

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Answer

Role of flux in metallurgical process

(i) Flux is used to remove the gangue by combining with it. Thus, slag formation takes place.

(ii) It makes the molten mass more conducting.

41. How are metals used as semiconductors refined? What is the principle of the method used like germanium, silicon etc?

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Answer

Metals of high grade like germanium, silicon etc., used as semiconductors are refined by zone refining method.

Principle This method is based upon the principle that impurities are more soluble in molten state of metal than in solid state.

42. Write down the reactions taking place in blast furnace related to the metallurgy of iron in the temperature range 500-800 K.

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Answer

Chemical reactions occurring in blast furnace related to the metallurgy of iron in the temperature range 500800K are

(i) 3Fe2O3+CO2Fe3O4+CO2

(ii) Fe3O4+4CO3Fe+4CO2

(iii) Fe2O3+CO2FeO+CO2

43. Give two requirements for vapour phase refining.

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Answer

Two requirements for vapour phase refining are

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

(ii) The volatile compound should be easily recovered by decomposition.

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

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Answer

(i) 4Au(s)+8CN(aq)+2H2O(aq)+O2(g)4[Au(CN)2](aq)+4OH(aq)

(ii) 2[Au(CN)2](aq)+Zn(s)2Au(s)+[Zn(CN)4]2(aq)

Zinc acts as a reducing agent in this reaction.

Matching The Columns

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

Column I Column II
A. Pendulum 1. Chrome steel
B. Malachite 2. Nickel steel
C. Calamine 3. Na3AlF6
D. Cryolite 4. CuCO3Cu(OH)2
5. ZnCO3

Codes

A B C D
(a) 1 2 3 4
(b) 2 4 5 3
(c) 2 3 4 5
(d) 4 5 3 2
Show Answer

Answer

(b) A. (2)

B. (4)

C. (5)

D. (3)

A. Pendulum is made up of nickel steel.

B. Molecular formula of malachite is CuCO3Cu(OH)2.

C. Molecular formula of calamine is ZnCO3.

D. Molecular formula of cryolite is Na3AlF6.

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

Column I Column II
A. Coloured bands 1. Zone refining
B. Impure metal to volatile complex 2. Fractional distillation
C. Purification of Ge and Si 3. Mond’s process
D. Purification of mercury 4. Chromatography
5. Liquation

Codes

A B C D
(a) 1 2 4 5
(b) 4 3 1 2
(c) 3 4 2 1
(d) 5 4 3 2
Show Answer

Answer

(b) A. (4)

B. (3)

C. (1)

D. (2)

A. Coloured bands are observed in chromatography.

B. Impure metal is converted to volatile complex by using Mond’s process.

C. Purification of Ge ans Si are purified by zone refining method.

D. Purification of mercury is done by fractional distillation.

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

Column I Column II
A. Cyanide process 1. Ultrapure Ge
B. Froth floatation process 2. Dressing of ZnS
C. Electrolytic reduction 3. Extraction of Al
D. Zone refining 4. Extraction of Au
5. Purification of Ni

Codes

A B C D
(a) 4 2 3 1
(b) 2 3 1 5
(c) 1 2 3 4
(d) 3 4 5 1
Show Answer

Answer

(a) A. (4)

B. (2)

C. (3)

D. (1)

A. Cyanide process is used for extraction of Au through formation of anionic complex .[AuCN)2].

B. Froth floatation process is used for dressing of ZnS.

C. Electrolytic reduction method is used for extraction of aluminium. Graphite electrode is used for this purpose.

D. Zone-refining is used for purification of Ge.

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

Column I Column II
A. Sapphire 1. Al2O3
B. Sphalerite 2. NaCN
C. Depressant 3. Co
D. Corundum 4. ZnS
5. Fe2O3

Codes

A B C D
(a) 3 4 2 1
(b) 5 4 3 2
(c) 2 3 4 5
(d) 1 2 3 4
Show Answer

Answer

(a) A. (3)

B. (4)

C. (2)

D. (1)

A. Sapphire is a gemstone which contain Co.

B. Molecular formula of sphalerite is ZnS. C. NaCN is used as a depressant in froth floatation method.

D. Molecular formula of corundum is Al2O3.

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

Column I Column II
A. Blisterred Cu 1. Aluminium
B. Blast furnace 2. 2Cu2O+Cu2S6Cu+SO2
C. Reverberatory furnace 3. Iron
D. Hall-Heroult process 4. FeO+SiO2FeSiO3
5. 2Cu2S+3O22Cu2O+2SO2

Codes

A B C D
(a) 2 3 4 1
(b) 1 2 3 5
(c) 5 4 3 2
(d) 4 5 3 2
Show Answer

Answer

(a) A. (2)

B. (3)

C. (4)

D. (1)

A. Blisterred Cu can be prepared by means of following chemical reaction

2Cu2O+Cu2S6Cu+SO2

B. Iron is extracted by using blast furnace.

C. In reverberatory furnace formation of slag occurs as

FeO+SiO2FeSiO3Slag

D. Hall-Heroult process is used for extraction of aluminium.

Assertion and Reason

In the following questions a statement of Assertion (A) followed by a statement of Reason ( R ) is given. Choose the correct answer out of the following choices.

(a) Both assertion and reason are true and reason is the correct explanation of assertion.

(b) Both assertion and reason are true but reason is not the correct explanation of assertion.

(c) Assertion is true but reason is false.

(d) Assertion is false but reason is true.

(e) Assertion and reason both are wrong.

50. Assertion (A) Nickel can be purified by Mond’s process. Reason (R) Ni(CO)4 is a volatile compound which decomposes at 460K to give pure Ni.

Show Answer

Answer

(a) Both assertion and reason are true and reason is the correct explanation of assertion. Nickel can be purified by Mond’s process in which formation of a volatile compound Ni(CO)4 takes place which further decomposes to Ni at 460K.

51. Assertion (A) Zirconium can be purified by van Arkel method.

Reason (R) ZrI4 is volatile and decomposes at 1800K.

Show Answer

Answer

(a) Both assertion and reason are true and reason is the correct explanation of assertion. Zirconium can be purified by van Arkel method which include formation of volatile ZrI4 which decomposes at 1800K to Zr.

52. Assertion (A) Sulphide ores are concentrated by froth flotation method. Reason (R) Cresols stabilise the froth in froth floatation method.

Show Answer

Answer

(b) Both assertion and reason are true but reason is not the correct explanation of assertion.

Sulphide ores are concentrated by froth floatation method. Sulphide ore particles are preferentially wetted by oil, become lighter and rise to the surface along with the froth while gangue particles are preferentially wetted by water, become heavier and thus settle down at the bottom of the tank and cresols stabilise the froth in froth floatation method.

Formation of froth is main reason for extraction of metal. Metal ore comes out along with froth.

53. Assertion (A) Zone refining method is very useful for producing semiconductors.

Reason (R) Semiconductors are of high purity.

Show Answer

Answer

(b) Both assertion and reason are true but reason is not the correct explanation of assertion.

Zone refining method is very useful for producing semiconductors of high purity as in this process pure metal crystallises while impurities pass on into adjacent molten zone when impure metal rod is heated.

54. Assertion (A) Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.

Reason (R) Copper is extracted by hydrometallurgy.

Show Answer

Answer

(b) Assertion and reason both are correct but reason is not the correct explanation of assertion.

Hydrometallurgy involves dissolving the ore in suitable reagent followed by precipitation with the help of more electropositive metal in which pure metal is get replaced by more electropositive metal.

Long Answer Type Questions

55. Explain the following

(a) CO2 is a better reducing agent below 710K whereas CO is a better reducing agent above 710K.

(b) Generally sulphide ores are converted into oxides before reduction.

(c) Silica is added to the sulphide ore of copper in the reverberatory furnace.

(d) Carbon and hydrogen are not used as reducing agents at high temperatures.

(e) Vapour phase refining method is used for the purification of Ti.

Show Answer

Thinking Process

This problem is based on concept of Ellingham diagrams and purification of metal.

Answer

(a) As shown in Ellingham diagram which relates Gibbs free energy and temperature at below 710K.

ΔG(C,CO2)<ΔG(C,CO) So, CO2 is a better reducing agent than CO while above 710K it becomes a very good reducing agent.

(b) Generally, sulphide ores are converted to oxides before reduction as reduction of oxides can easily be done using C or CO depending upon metal ore and temperature.

(c) Silica is a flux added to the sulphide ore of copper in the reverberatory furnace leading to the formation of slag

FeO+SiO2FeSiO3Slag

(d) Carbon and hydrogen are not used as reducing agents at high temperature. At high temperature carbon and hydrogen readily form their carbides and hydrides respectively.

(e) Vapour phase refining method is used for the purification of Ti as

Ti+2I2523KTiI41700KTi+2I2