Chemistry NCERT Exemplar Solutions Class 12th Chapter Six: Overview, Questions, Preparation

1. Explain the following :

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

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

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

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

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

4. 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 sulfur, silicon and phosphorus be removed from cast iron?

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

17. Write down the reactions taking place in Blast furnaces related to the metallurgy of iron in the temperature range 500-800 K. 

53. Assertion: Sulfide ores are concentrated by Froth Flotation method.

Reason: Cresols stabilize the froth in the Froth Flotation method.

54. Assertion: Zone refining method is very useful for producing semiconductors.

Reason: Semiconductors are of high purity.

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

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

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

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

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

10. The mixture of compounds A and B is passed through a column of Al₂O₃ 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?

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

20. In the extraction of chlorine by electrolysis of brine

(i) Oxidation of Cl⁻ion to chlorine gas occurs.

(ii) Reduction of Cl⁻ion to chlorine gas occurs.

(iii) For overall reaction ΔG^? has a negative value.

(iv) A displacement reaction takes place.

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

(i) sulfides of copper (II) and iron (II)

(ii) sulfides of copper (II) and iron (III)

(iii) sulfides of copper (I) and iron (II)

(iv) sulfides of copper (I) and iron (III)

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

(i) Fe₃O₄ + 4CO→3Fe + 4CO₂

(ii) Cu₂O + C→2Cu + CO 

(iii) Cu²⁺(aq) + Fe(s)→Cu(s) + Fe²⁺(aq)

(iv) Cu₂O + $\frac{1}{2}$ Cu₂S → 3Cu + 12SO₂

23. A number of elements are available in earth's crust but most abundant elements are

(i) Al and Fe

(ii) Al and Cu

(iii) Fe and Cu

(iv) Cu and Ag

24. 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 adsorbent.

(iv) Vapors of volatile compounds can be decomposed in pure metal.

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

(i) FeS

(ii) CO

(iii) Cu₂S

(iv) SO₂

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

(i) Cl⁻(aq)→ $\mathbf{}\frac{1}{2}$ Cl₂(g)+ e−;E $°$ _cell =1.36 V

(ii) 2H₂O(l)→O₂(g) + 4H⁺ + 4e⁻, E $°$ _cell  = 1.23 V

(iii) Na+(aq.)+ e→Na(s); E $°$ _cell = 2.71 V

(iv) H⁺(aq) + e⁻→12H₂(g); E $°$ _cell  = 0.00 V

27. In the metallurgy of aluminum

(i) Al³⁺ is oxidized to Al (s).

(ii) Graphite anode is oxidized to carbon monoxide and carbon dioxide.

(iii) Oxidation state of oxygen changes in the reaction at anode.

(iv) Oxidation state of oxygen changes in the overall reaction involved in the process.

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

(i) Cu and Zn

(ii) Ge and Si

(iii) Zr and Ti

(iv) Zn and Hg

29. Extraction of gold and silver involves leaching the metal with CN⁻ion. The metal is recovered by

(i) Displacement of metal by some other metal from the complex ion.

(ii) Roasting of metal complexes.

(iii) Calcination followed by roasting.

(iv) Thermal decomposition of metal complexes.

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

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

(i) Below temperature at point A.

(ii) Approximately at the temperature corresponding to point A.

(iii) Above temperature at point A but below the temperature at point D.

(iv) Above temperature at point A.

31. Below point ' A ' FeO 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.

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

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

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

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

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

Note: In the following questions two or more options may be correct.

33. At the temperature corresponding to which of the points in Fig.6.1, FeO will be reduced to Fe by coupling the reaction 2FeO→2Fe+O₂with all of the following reactions?

(a) C+O₂ → CO₂ 

(b) 2C+O₂ → 2CO and

(c) 2CO + O₂ → 2CO₂.

(i) Point A

(ii) Point B

(iii) Point D

(iv) Point E

34. Which of the following options are correct?

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

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

(iii) Nickel is purified by zone refining.

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

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

(i) Lower the melting point of Al₂O₃.

(ii) Increase the conductivity of molten mixture.

(iii) Reduce Al³⁺ into Al(s).

(iv) Acts as a catalyst.

36. 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 sulfide ores can be separated.

(iv) Froth stabilizers decrease wettability of the gangue.

37. In the Froth Floatation process, zinc sulfide and lead sulfide can be separated by

(i) Using collectors.

(ii) Adjusting the proportion of oil to water.

(iii) Using depression.

(iv) Using froth stabilizers.

38. Common impurities present in bauxite are

(i) CuO

(ii) ZnO

(iii) Fe₂O₃

(iv) SiO₂

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

(i) Haematite

(ii) Galena

(iii) Copper pyrites

(iv) Magnetite

40. Which of the following reactions occur during calcination?

(i) CaCO₃→CaO+CO₂

(ii) 2FeS₂ + $\frac{11}{2}$ O₂→Fe₂O₃+4SO₂

(iii) Al₂O₃⋅?H₂O→Al₂O₃+ ? H₂O

(iv) ZnS + $\frac{3}{2}$ O₂→ZnO+SO₂

41. 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

42. The main reactions occurring in blast furnaces during extraction of iron from haematite are

(i) Fe2O₃+3CO→2Fe+3CO₂

(ii) FeO+SiO₂→FeSiO₃

(iii) Fe₂O₃+3C→2Fe+3CO

(iv) CaO+SiO₂→CaSiO₃

43. In which of the following methods 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.

44. Which of the following statements are correct?

(i) A depressant prevents a certain type of particle from coming to the froth.

(ii) Copper matte contains Cu₂S and ZnS.

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

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

45. In the extraction of chlorine from brine

(i) ΔG° for the overall reaction is negative.

(ii) ΔG° for the overall reaction is positive.

(iii) E° for overall reaction has negative value.

(iv) E° for overall reaction has positive value.

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

Code:

A (1) B (2) C (3) D (4)

A (2) B (4) C (5) D (3)

A (2) B (3) C (4) D (5)

A (4) B (5) C (3) D (2)

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

Code :

A (1) B (2) C (4) D (5)

A (4) B (3) C (1) D (2)

A (3) B (4) C (2) D (1)

A (5) B (4) C (3) D (2)

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

Code :

A (4) B (2) C (3) D (1)

A (2) B (3) C (1) D (5)

A (1) B (2) C (3) D (4)

A (3) B (4) C (5) D (1)

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

Code :

A (3) B (4) C (2) D (1)

A (5) B (4) C (3) D (2)

A (2) B (3) C (4) D (5)

A (1) B (2) C (3) D (4)

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

Code :

A (2) B (3) C (4) D (1)

A (1) B (2) C (3) D (5)

A (5) B (4) C (3) D (2)

A (4) B (5) C (3) D (2)

51. In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

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

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

(iii) Assertion is true but the reason is false.

(iv) Assertion is false but the reason is true.

(v) Assertion and reason both are wrong.

1. Assertion: Nickel can be purified by the Mond process.

Reason: Ni(CO)₄ is a volatile compound which decomposes at 460 K to give pure Ni.

52. Assertion: Zirconium can be purified by Van Arkel method.

Reason: ZrI₄ is volatile and decomposes at 1800 K.

55. Assertion: Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.

Reason: Copper is extracted by hydrometallurgy.

A commercially sold conc. HCl is 35% HCl by mass. If the density of this commercial acid is 1.46 g/mL, the molarity of this solution is

Given below are two statements:

Statement I: According to the Ellingham diagram, any metal oxide with higher  is more stable that the one with lower .

Statement II: The metal involved in the formation of oxide placed lower in the Ellingham diagram can reduce the oxide of a metal placed higher in the diagram.

In the light of the above statements, choose the most appropriate answer form the options given below

Which of the following sets are correct regarding polymer?

(A) Copolymer: Buna-S

(B) Condensation polymer: Nylon-6,6

(C) Fibres: Nylon-6,6

(D) Thermosetting polymer: Terylene

(E) Homopolymer: Buna-N

Choose the correct answer form given options below

An evacuated glass vessel weights 40.0g when empty, 135.0g when filled with a liquid of density 0.95 g mL^-1 and 40.5 g when filled with an ideal gas at 0.82 atm at 250 K. The molar mass of the gas in g mo^-1 is:

(Given: R = 0.082 L atm K^-1 mol^-1)

If the radius of the 3^rd Bohr’s orbit of hydrogen atom r₃ and the radius of 4^th Bohr’s orbit is r₄. Then

The ${\left(\frac{\partial E}{\partial T}\right)}_P$ of different types of half cells are as follows:

(Where E is the electromotive force )

Which of the above half cells would be preferred to be used as reference electrode

Consider the following reaction:

A + alkali  → B(Major Product)

If B is an oxoacid of phosphorous with no P-H bond, then A is

Given below are two statements:

Statement I: In ‘Lassaigne’s Test’, when both nitrogen and sulphur are present in an organic compound, sodium thiocyanate is formed.

Statement II: If both nitrogen and sulphur are present in an organic compound, then the excess of sodium used in sodium fusion will decompose the sodium thiocyanate formed to given NaCN and Na₂S.

In the light of the above statements, choose the most appropriate answer from the option given below

For complete combustion of methanol

$C{H}_{3}OH\left(1\right)+\frac{3}{2}{O}_2\left(g\right)\to C{O}_2\left(g\right)+2H_{2}O\left(I\right)$            

The amount of heat produced as measured by bomb calorimeter is 726 kJmol^-1 at 27°C. The enthalpy of combustion for the reaction is -x kJ mol^-1, where x is_________

(Nearest integer)

(Given : R = 8.3 J K^-1 mol^-1).

A 0.5 percent solution of potassium choride was found to freeze at -0.24°C. The percentage dissociation of potassium chloride is__________. (Nearest integer)

(Molal depression constant for water is 1.80 K kg mol^-1 and molar mass of KCl is 74.6 g mol^-1)

50 mL of 0.1 M CH₃COOH is being titrated against 0.1 M NaOH. When 25 mL of NaOH has been added, the pH of the solution will be_________× 10^-2. (Nearest integer)

(Given : pKa (CH₃-COOH) = 4.76)

log 2 = 0.30

log 3 = 0.48

log 5 = 0.69

log 7 = 0.84

log 11 = 1.04

A flask is filled with equal moles of A and B. The half lives of A and B are 100s and 50s respectively and are independent of the initial concentration. The time required for the concentration of A to be four times that of B is ______________s.

(Given : In 2 = 0.693)

2.0g of H₂ gas is adsorbed on 2.5g platinum powder at 300K and 1 bar pressure. The volume of the gas adsorbed per gram of the adsorbent is ______________mL.

(Given : R = 0.083 L bar K^-1 mol^-1)

The spin- only magnetic moment value of the most basic oxide of vanadium among V₂O₃, V₂O₄ and V₂O₅ is _____________B. M (Nearest integer)

The spin only magnetic moment value of an octhahedral complex among CoCl₃.4NH₃, NiCl₂.6H₂O and PtCl₄.2HCl, which upon reaction with excess of AgNO₃ gives 2 moles of AgCl is____________B. M. (Nearest integer)

On complete combustion 0.30g of an organic compound gave 0.20g of carbon dioxide and 0.10 g of water. The percentage of carbon in the given organic compound is __________. (Nearest integer)

Compound ‘P’ on nitration with dil. HNO₃ yields two isomers (A) and (B). These isomers can be separated by steam distillation. Isomers (A) and (B) show the intramolecular and intermolecular hydrogen bonding respectively. Compound (P) on reaction with conc. HNO₃ yields a yellow compound ‘C’___________

The number of oxygen’s present in a nucleotide formed from a base, that is present only in RNA is_______________.

Copper reduces $N{O}_3^{-}$ into NO and NO₂ depending upon the concentration of HNO₃ in solution. (Assuming fixed $\left[C{u}^{2+}\right]and{P}_{NO}=P_{N{O}_2}$ ), the HNO₃ concentration at which the thermodynamic tendency for reduction of $N{O}_3^{-}into$ NO and NO₂by copper is same is 10^x M. The value of 2x is…….. (rounded-off to the nearest integer).

$[Given,E_{C{u}^{2+}/Cu}^0=0.34V,E_{N{O}_3^{-}/NO}^0=0.96V,E_{N{O}_3^{-}/N{O}_2}^0=0.79Vandat298K,\frac{RT}{F}\left(2.303\right)=0.059]$

The rate constant of a reaction increases by five times on increase in temperature from 27°C to 52°C. The value of activation energy in kJ mol^-1 is……….. (Rounded-off to the nearest integer).

[R = 8.314JK^-1mol^-1]

The unit cell of copper corresponds to a face centered cube of edge length 3.596 $\stackrel{o}{A}$  with one copper atom at each lattice point. The calculated density of copper in kg/m³ is……..

[Molar mass of Cu = 63.54g : Avogadro Number = 6.022 × 10²³]

Five moles of an ideal gas at 293K is expanded isothermally from an initial pressure of 2.1 MPa to 1.3 MPa against at constant external pressure 4.3 MPa. The heat transferred in this process is…….. kJ mol^-1. (Rounded-off to the nearest integer).

[Use R = 8.314 J mol^-1 K^-1]

If a compound AB dissociates to the extent of 75% in an aqueous solution, the molality of the solution which shows a 2.5K rise in the boiling point of the solution is…….. molal.

(Rounded-off to the nearest integer).

[K_b = 0.52 K kg mol^-1]

Consider titration of NoOH solution versus 1.25M oxalic acid solution. At the end point following burette readings were obtained.

(i) 4.5mL                                                                          (ii) 4.5mL

(iii) 4.44mL                                                                      (iv) 4.4mL

(v) 4.44mL

If the volume of oxalic acid taken was 10.0mL then the molarity of the NaOH solution is……….M.

(Rounded-off to the nearest integer).

The number of compound/s given below which contain/s – COOH group is………….

(Integer answer)

(a) Sulphanilic acid                                                        (b) Picric acid

(c) Aspirin                                                                       (d) Ascorbic acid

Electromagnetic radiation of wavelength 663nm is just sufficient to ionize the atom of metal A. The ionization energy of metal A in kJ mol^-1 is…………… (Rounded-off to the nearest integer)

[h = 6.63 × 10^-34Js,c = 3.00 × 10⁸ms^-1, N_A = 6.02 × 10²³ mol^-1]