CBSE Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 10 - MCQExams.com

Gravity separation method is used to concentrate which type of ores?
  • Sulphide ores
  • Phosphate ores
  • Silicate ores
  • Oxide ores
The impurities present with minerals are collectively known as
  • Slag
  • Flux
  • Matrix
  • Ores
Which of the following is used in froth floatation process for the benefication of ore?
  • Coconut oil
  • Olive oil
  • Pine oil
  • None of these
Which of the following statement is true?
  • All ore are minerals
  • All minerals are ore
  • A mineral cannot be an ore
  • An ore cannot be a mineral
Malachite and azurite are used respectively are : 
  • Blue and green pigment
  • Red and green pigment
  • Green and blue pigment
  • Green and red pigment
For which of the following ores froth floatation method is used for concentration ?
  • Haematite
  • Zinc blende
  • Magnetite
  • Carnallite
Metal used for making joints in jewellery is 
  • Zn
  • Cu
  • Ag
  • Cd
Which of the following metals is sometimes found native in nature ?
  • Aluminium
  • Copper
  • Iron
  • Magnesium
Froth flotation method cannot be employed for the concentration of:
  • Zinc blende
  • Pyrolusite
  • Copper pyrites
  • Cinnabar
Observe the following statements regarding purification of bauxite:
I. During Hall's process, silica is removed as Si (vapour).
II. Bauxite ore contaminated with  $$Fe_{2} O_{3}$$ is purified in Baeyer's process.
III. During Serpeck's process, $$AlN$$ is formed.
  • I , II and III are correct
  • Only I and II are correct
  • Only I and III are correct
  • Only II and III are correct
A solution of $$Na_{2}SO_{4}$$ in water is electrolysed using inert electrodes. The products at the cathode and anode respectively, are:
  • $$O_{2}, \ H_{2}$$
  • $$O_{2},\ Na$$
  • $$H_{2},\ O_{2}$$
  • $$O_{2},\ SO_{2}$$
Metals which can be obtained by carbon reduction of their oxides are _________.
  • Cu
  • Fe
  • Al
  • Pb
Metals that are refined by liquation are:
  • Si
  • Pb
  • Sn
  • Bi
The principle of fractional crystallisation is involved in which one of the following processes?
  • Van Arkel's method
  • Distillation
  • Cupellation
  • Zone refining
Which of the following statements is/are correct?
a) In the decomposition of an oxide into oxygen and metal vapour, entropy increases.
b) Decomposition of an oxide is an endothermic change.
c) To make $$\Delta G^{0}$$ negative, temperature should be high enough so that $$T\Delta S^{0}> \Delta H^{0}$$.
  • (a), (b) only are correct
  • (b), (c) only are correct
  • (a), (c) only are correct
  • (a), (b), (c) are correct
Choose the correct statement(s) for froth flotation process, which is used for the concentration of sulphide ore.
a) It is based on the difference in the ability of different minerals to become wet.
b) It uses sodium ethyl xanthate, $$C_{2}H_{5}OCS_{2}Na$$ as collector.
c) It uses $$NaCN$$ as a depressant in the mixture of $$ZnS$$ and $$PbS$$, where $$ZnS$$ forms soluble complex and $$PbS$$ forms froth.
  • Only (a) and (b) are correct
  • Only (b) and (c) are correct
  • Only (a) and (c) are correct
  • All statements are correct
The mass of carbon anode consumed (giving the only carbon dioxide) in the production of $$270\ kg$$ of aluminium metal from bauxite by the Hall process is:
[Atomic mass : $$Al = 27$$]
  • $$90\ kg$$
  • $$540\ kg$$
  • $$180\ kg$$
  • $$270\ kg$$
The method of zone refining of metals is based on the principle of:
  • greater mobility of the pure metal than that of the impurity
  • higher melting point of the impurity than that of the pure metal
  • greater noble character of the solid metal than that of the impurity
  • greater solubility of the impurity in the molten state than in the solid
The main function of frothers is to _________________.
  • stick to the ore and take it to the top
  • convert the insoluble ore into soluble part
  • make the ore hydrophobic
  • none of the above
Select the correct statement for electrolysis of $$Al_2O_3$$ by Hall-Heroult process.
  • Cryolite $$Na_3[AlF_6]$$ lowers the melting point of $$Al_2O_3$$ and increases its electrical conductivity.
  • Al is obtained at cathode and probably $$CO_2$$ at anode.
  • Both of the above statements are correct.
  • None of the above statements are correct.
Froth floatation process is used for the concentration of sulphide ores. This process is an illustration of the practical application of:
  • adsorption
  • absorption
  • sedimentation
  • coagulation
Which of the following is not correctly matched with respect to the processes involved in the extractive metallurgy of the respective metal?
  • $$Al_2O_3.2H_2O\rightarrow Al$$: Leaching, precipitation, calcination and electrolytic reduction (molten state)
  • $$Ag_2S\rightarrow Ag$$: Leaching and displacement method
  • $$PbS\rightarrow Pb$$: Froth flotation process, roasting and self reduction
  • $$KCl.MgCl_2.6H_2O\rightarrow Mg$$: Dehydration by simple heating and electrolytic reduction in aqueous phase
Which of the following reaction is a part of Hall's process?
  • $$Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O$$
  • $$Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3$$
  • $$AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3$$
  • $$Al_2O_3. 2H_2O + 2Na_2CO_3 \rightarrow 2NaAlO_2 + CO_2 + 2H_2O$$
At what temperature do zinc and carbon have equal affinity for oxygen?
119180.jpg
  • $$1000^oC$$
  • $$1500^oC$$
  • $$500^oC$$
  • $$1200^oC$$
Concentration of which of the following ore is carried out by froth floatation process?
  • Bauxite
  • Chalcocite
  • Haematite
  • Calamine
When copper rod is dipped in $$CuSO_4$$ solution, the potential developed at the interface is called as __________ .
  • electrode potential
  • standard potential
  • cell potential
  • none of the above
At temperature $$1000^oC$$, $$\Delta G$$ of the reaction $$ZnO+C\rightarrow Zn+CO$$ is _________.
119180.jpg
  • -ve
  • +ve
  • zero
  • nothing can be said
Which of the above given curves is wrongly presented?
122308.png
  • $$C\rightarrow CO_2$$
  • $$Pb\rightarrow PbO$$
  • $$Zr\rightarrow ZrO_2$$
  • $$Mg\rightarrow MgO$$
Which occurs to minimum extent in nature?
122557.png
  • $$HgS$$
  • $$H_2S$$
  • $$Bi_2S_3$$
  • $$CS_2$$
At what approximate temperature, zinc and carbon have equal affinity for oxygen?
122552.png
  • $$1000^{\small\circ}C$$
  • $$1500^{\small\circ}C$$
  • $$500^{\small\circ}C$$
  • $$1200^{\small\circ}C$$
Which of the above metal oxide has the minimum thermal decomposition temperature?
122308.png
  • $$CaO$$
  • $$FeO$$
  • $$ZrO_2$$
  • $$MgO$$
To make the following reduction process spontaneous, temperature should be:
    
     $$ZnO + C \longrightarrow Zn + CO$$

122564.png
  • $$1000^{\small\circ}C$$
  • $$>1000^{\small\circ}C$$
  • $$<500^{\small\circ}C$$
  • $$<1000^{\small\circ}C$$
At $$1100^{\small\circ}C$$, which reaction is spontaneous to a maximum extent?
122564.png
  • $$MgO + C \rightarrow Mg + CO$$
  • $$ZnO + C \rightarrow Zn + CO$$
  • $$MgO + Zn \rightarrow Mg + ZnO$$
  • $$ZnO + Mg \rightarrow MgO + Zn$$
To make the following reduction process spontaneous, temperature should be 
$$ZnO+C\xrightarrow {\Delta} Zn+CO$$

119180.jpg
  • $$< 1000^oC$$
  • $$ > 1000^oC$$
  • $$< 500^oC$$
  • $$> 500^oC$$ but $$ < 1000^oC$$
Which of the above given metal oxides can be reduced by $$Fe$$ (reducing agent) to its respective metal  at temperature $$T_1$$?
122061_3fd66b9109d84e6b9edd52046a634886.png
  • $$ZrO_2$$
  • $$CaO$$
  • $$MgO$$
  • None of the above
At  $$1000^oC$$, $$\Delta G^{\small\circ}$$ of the reaction is:
$$ZnO + C \longrightarrow Zn + CO$$
122554_5f6e03105ff94e0b927707ebebadc361.png
  • $$-ve$$
  • $$+ve$$
  • zero
  • None of these
To make the following reduction process spontaneous, temperature should be
$$ZnO + C \longrightarrow ZN + CO$$
122552.png
  • $$<1000^{\small\circ}C$$
  • $$>1100^{\small\circ}C$$
  • $$<500^{\small\circ}C$$
  • $$>500^{\small\circ}C$$ but $$<1000^{\small\circ}C$$

Which sulphide occurs to minimum extent in nature?
122573_21f9a267dc9f466eb0e03dba4bdd7296.JPG
  • $$HgS$$
  • $$H_2S$$
  • $$Bi_2S_3$$
  • $$CS_2$$

Formation of which of the sulphides is most spontaneous?
122572_f0440b69458c461d96e3e875122eb027.JPG
  • $$HgS$$
  • $$Bi_2S_3$$
  • $$PbS$$
  • $$CS_2$$
As per the Ellingham diagram of oxides which of the following conclusion is true?
122808.png
  • Al reduces $$Fe_{2}O_{3}$$, whereas $$MgO$$ cannot be reduced by Al at $$1500^{o}C$$
  • Fe reduces $$Al_{2}O_{3}$$, whereas $$MgO$$ cannot be reduced by Al at $$1500^{o}C$$
  • Al reduces $$Fe_{2}O_{3}$$, whereas $$MgO$$ cannot be reduced by Ca at $$1500^{o}C$$
  • Al can reduce both $$Fe_{2}O_{3}$$ and $$MgO$$ to the corresponding metal at $$1500^{0}C$$
When $$FeCr_2O_4$$ (chromite) is reduced with Carbon in an electric-arc furnace:
  • Cr and $$Fe_2O_3$$ are formed
  • Fe and $$Cr_2O_3$$ are formed
  • Fe and Cr (ferrochrome) are formed
  • $$FeCrO_4$$ is formed

Which of the following sulphides can not be reduced to metal by $$H_2$$ at about $$1000^{\small\circ}C$$?
122574_85e950de4d5f41f683a43981c2ab7384.JPG
  • $$HgS$$
  • $$PbS$$
  • $$Bi_2S_3$$
  • All of these

Si of  high purity to be used in semiconductor can be prepared  by following methods :

I. $$SiO_2\, +\, 2C\, \rightarrow\, Si\, +\, 2CO$$

II. $$Si\, +\, 2Cl_2\, \rightarrow\, SiCl_4$$

$$SiCl_4\, +\, 2Mg\, \rightarrow\, Si\, +\, 2MgCl_2$$

Better method is :
  • I
  • II
  • both (A) and (B)
  • None of these
In electrtolysis of $$Al_2O_3$$ by Hall-Heroult process:
  • Cryolite $$Na_3[AIF_6]$$ lowers the melting point of $$Al_2O_3$$ and increases its electrical conductivity.
  • $$Al$$ is obtained at cathode and probably $$CO_2$$ at anode
  • both (a) and (b) are correct
  • none of the above is correct
Which of the following elements can be prepared by heating the oxide above $$400^{o}C $$?
122808.png
  • Hg
  • Mg
  • Fe
  • Al
$$FeCr_2O_4$$ (Chromite) is a good source of chromium and its compound like $$Na_2CrO_4$$ and $$Na_2Cr_2O_7$$

I.  $$FeCr_2O_4 + NaOH + air \longrightarrow (A) + Fe_2O_3$$

II.  $$(A) + (B) \longrightarrow Na_2Cr_2O_7$$

III.  $$Na_2Cr_2O_7 +  X \overset{\triangle}{\longrightarrow} Cr_2O_3$$

IV.  $$Cr_2O_3 + Y \overset{\triangle}{\longrightarrow} Cr$$

Compounds (A) and (B) are:
  • $$Na_2CrO_4, H_2SO_4$$
  • $$Na_2Cr_2O_7, HCl$$
  • $$Na_2CrO_6, H_2SO_4$$
  • $$Na_4[Fe(OH)_6], H_2SO_4$$

From the Ellingham diagram, identify the oxide which is reduced by the carbon at highest temperature among the following oxides.

$$MgO,$$ $$CaO,$$ $$TiO_2$$ and $$Al_2O_3$$ 

168341_01156180fd5f4a158f8bbfc13ab6250f.png
  • $$MgO$$
  • $$CaO$$
  • $$TiO_2$$
  • $$Al_2O_3$$

Use the relationship $$\Delta \,G^{\circ}\,=\,- nFE^{\circ}_{cell}$$ to estimate the minimum voltage required to electrolyse $$Al_2O_3$$ in the Hall-Heroult process.

$$\Delta G^{\circ}_{f}(Al_2O_3)\,=\,-1520\,kJ\,mol^{-1}$$

$$\Delta G^{\circ}_{f}(CO_2)\,=\,-394\,kJ\,mol^{-1}$$

The oxidation of the graphite anode to $$CO_2$$ permits the electrolysis to occur at a lower voltage than if the electrolysis reactions were :

$$Al_2O_3\,\rightarrow\,2Al\,+\,3O_2$$.

What is the approximate value of low voltage?
  • 2 V
  • 3 V
  • 4V
  • 5V
Match column A (process) with column B (electrolyte).

  A (process)  B (electrolyte)
 (I) Downs Cell (W) Fused $$MgCl_2$$
 (II) Dow sea water  (X) Fused $$Al_2O_3 + Na_3AlF_6$$
 (III) Hall-Heroult (Y) Fused $$KHF_2$$
 (IV) Moissan (Z) Fused 40% NaCl + 60% CaCl$$_2$$
Choose the correct alternative:
  • I-Z, II-W, III-X, IV-Y
  • I-X, II-Y, III-Z, IV-W
  • I-W, II-Z, III-X, IV-Y
  • I-X, II-Z, III-W, IV-Y
$$\Delta G$$ vs $$T$$ plot in the Ellingham diagram slopes downward for the reaction.
  • $$Mg + \dfrac {1}{2} O_{2} \longrightarrow MgO$$
  • $$2Ag + \dfrac {1}{2} O_{2} \longrightarrow Ag_2O$$
  • $$C + \dfrac {1}{2} O_{2} \longrightarrow CO$$
  • $$CO + \dfrac {1}{2} O_{2} \longrightarrow CO_{2}$$
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