CBSE Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 4 - MCQExams.com

According to Ellingham diagram, the oxidation reaction of carbon to carbon monoxide may be used to reduce which one of the following oxides at the lowest temperature?
  • $$Al_2O_3$$
  • $$Cu_2O$$
  • $$MgO$$
  • $$ZnO$$
At what temperature, zinc and carbon have equal affinity for oxygen?
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  • $$1000^{\small\circ}C$$
  • $$1500^{\small\circ}C$$
  • $$500^{\small\circ}C$$
  • $$1200^{\small\circ}C$$
Froth flotation process used for the concentration of sulfide ore _______________.
  • is based on the difference in wettability of different minerals
  • uses sodium ethly xanthate, $$C_{2}H_{5}OCS_{2}Na$$ as collector
  • uses $$NaCN$$ as depressant in the mixture of ZnS and PbS when ZnS forms soluble complex and Pbs forms froth
  • all of the above statements are correct
Select the correct statement.
  • During the decomposition of an oxide into oxygen and metal vapour, entropy increases.
  • Decomposition of an oxide is an endothermic change.
  • To make $$\triangle G^{0}$$ negative, temperature should be high enough so that $$T$$ $$\triangle$$ $$S^{0}$$> $$\triangle$$ $$H^{0}$$.
  • All are correct answers.
Aluminothermy used for the spot welding of large iron structures is based upon the fact that :
  • As compared to iron, aluminium has greater affinity for oxygen.
  • As compared to aluminium, iron has greater affinity for oxygen.
  • Reaction between aluminium and oxygen is endothermic..
  • Reaction between iron oxide and aluminium is exothermic.
The function of adding cryolite in the electrolyte reduction of alumina by Hall-Heroult process is to :
  • dissolve alumina
  • lower melting point of alumina
  • lower the fuel bill
  • increase the electrical conductivity of alumina
The advantage(s) of using carbon to reduced a number of oxides and other compounds are :
  • easy availability of coke.
  • low cost of carbon.
  • tendency of carbon to show catenation..
  • presence of carbon lowers the melting point of the oxide.
The extraction of metals from oxide ores involve :
  • reduction with carbon
  • reduction with aluminium
  • electrolyte reduction
  • reduction with $$CO$$
Froth floatation:
  • is a physical method of separating mineral from the gangue
  • is a method to concentrate the ore depending on the difference in wetability of gangue and the ore
  • is used for the sulphide ores
  • is a method in which impurities sink to the bottom
The oxide of metal $${R}$$ can be reduced by the metal $${P}$$ and metal $${R}$$ can reduce the oxide of metal $${Q}$$. Then the decreasing order of the reactivity of metal $${P}$$, $${Q}$$ and $${R}$$ with oxygen is:
  • $$P>Q>R$$
  • $$P>R>Q$$
  • $$R>P>Q$$
  • $$Q>P>R$$
Ultra pure silicon is prepared by reduction of $$SiO_2$$ with carbon.
  • True
  • False
Method used for obtained highly pure silicon, used as a semiconductor material, is
  • oxidation
  • electrochemical
  • crystallization
  • zone refining
NaCN is sometimes added in the froth flotation process as a depressant when ZnS and PbS minerals are expected because __________.
  • $$Pb(CN)_2$$ is precipitated while no effect on ZnS.
  • ZnS forms soluble complex $$Na_2[Zn(CN)_4]$$ while PbS forms froth
  • PbS forms soluble complex $$Na_2[Pb(CN)_4]$$ while ZnS forms froth
  • NaCN is never added in froth flotation process
Oxides of the various metals are converted into metal by heating but not in :
  • $$Ag_2O$$
  • CuO
  • HgO
  • all are correct
Siderite is an ore of:
  • $$Cu$$
  • $$Al$$
  • $$Ag$$
  • $$Fe$$
Which one of the following is the chief ore of copper?
  • Galina
  • Copper pyrite
  • Sphalerite
  • Siderite
Identify the ore not containing iron.
  • Limonite
  • Siderite
  • Carnelite
  • Chalcopyrites
Select correct statement(s) about differentiation floatation.
  • It is used to concentrate mixture of sulphides at different stages
  • Zinc sulphate is used to depress zinc sulphide and PbS forms froth
  • Copper sulphate is used to active depressed lead sulphide and $$O_2$$ is blown to make froth
  • All of the above are correct statements
Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out ______________.
  • in the presence of NaCl
  • in the presence of fluorite
  • in the presence of cryolite which forms a melt with lower melting temperature
  • in the presence of cryolite which forms a melt with higher melting temperature
In electrolysis of $$Al_2O_3$$ by Hall-Heroult process, _____________.
  • Cryolite $$Na_3[AlF_6]$$ lowers the m.p. 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 
Selection of temperature to carry out a reduction process depends so as to make :
  • $$\Delta G$$ negative
  • $$\Delta G$$ positive
  • $$\Delta H$$ negative
  • $$\Delta H$$ positive

Consider following equilibrium

$$3Fe(s)\, +\, C(s)\, \rightleftharpoons\, Fe_3C(s),\quad \Delta H^{\circ}\, >\, 0$$

What is the effect of increasing temperature on this equilibrium?
  • reaction proceeds in forward
  • reaction proceeds in backward
  • no effects
  • none of these
The reduction of an oxide by aluminium is called __________.
  • Ellingham process
  • Goldschmidts aluminothermite process
  • Krolls process
  • Van Arkel process
In which of the following isolations no reducing agent is required?
  • Iron from haematite
  • Aluminium from bauxite
  • Mercury from cinnabar
  • Zinc from zinc blende

Zinc, cadmium and mercury are found in nature as sulphides. Values of standard reduction potentials for the half-reactions are : 

$$M^{2+}(aq)\, +\, 2e^{-}\,
\rightarrow\, M(s)$$ 

$$\begin{matrix}M & E^{\circ}\\ Zn &-\,0.76\,V \\ Cd & -\,0.40\,V \\ Hg & +\,0.79\,V\end{matrix}$$ . 

Which sulphides give element not oxide on roasting?
  • $$ZnS$$
  • $$HgS$$
  • $$CdS$$
  • None of these
Purification of alumina takes place by _________________.
  • Bosch process
  • Hall's process
  • Hoope's process
  • Quartation process
Thermite is a mixture of iron oxide and :
  • Aluminium powder
  • Zinc powder
  • Potassium metal
  • Sodium metal
The method of zone refining of metals is based on the principle of:
  • 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
  • greater mobility of the pure metal than that of impurity
  • higher melting point of the impurity than that of the pure metal
Most abundant metal in earth crust is___________.
  • Al
  • O
  • Fe
  • Si
Froth flotation is a process of _____________.
  • oxidation
  • reduction
  • refining
  • concentration

The methods chiefly used for the extraction of lead and tin from their ores are respectively _________________.
  • self reduction and carbon reduction
  • self reduction and electrolytic reduction
  • carbon reduction and self reduction
  • cyanide process and carbon reduction
Cryolite, $$Na_3AlF_6$$ is added to $$Al_2O_3$$ in Hall-Heroult process to ____ m.p. and to ___________ electrical conductivity.
  • higher, increase
  • higher, decrease
  • lower, increase
  • lower, decrease
CO is toxic because it forms complex with _________ in the blood.
  • carbohydrate
  • protein
  • haemoglobin
  • none of these
Which of the following metals are found in native state?

Ag, Pt, C, Si, N, O, Mg, Na, Pb
  • Ag, Pt, C, N, O
  • Ag, Pt, Mg
  • Ag, Pt, Pb, Mg
  • Ag, Pt
Which will not give metal on heating ?
  • $$Ag_2CO_3$$
  • $$ZnCO_3$$
  • $$HgO$$
  • $$CuO$$

192100_5b6054a10fbf436da4c9c7257d5f49fa.PNG
  • Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
  • Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
  • Assertion is correct but Reason is incorrect
  • Both Assertion and Reason are incorrect
Which of the elements indicated by A, B, C and D is expected to be found in native state?
170501_d655b400aae24a678bef4cdd122959a4.png
  • A
  • B
  • C
  • D
The constituents of the electrolyte for the extraction of aluminium is ____________.
  • 40 parts cryolite + 40 parts fluorspar + 20 parts pure $$Al_2O_3$$
  • 60 parts cryolite + 30 parts fluorspar + 10 parts pure $$Al_2O_3$$
  • 30 parts cryolite + 30 parts fluorspar + 40 parts pure $$Al_2O_3$$
  • 60 parts cryolite + 20 parts fluorspar + 20 parts pure $$Al_2O_3$$
Name the element which serves as the cathode in the extraction of aluminium.
  • Carbon
  • Graphite rods
  • Iron
  • Aluminium
Assertion: When an electric current is passed through the copper sulphate electrolyte, the impure copper anode gradually dissolve and pure copper is deposited on the cathode.
Reason: Pure metals are deposited in electroplating techniques.
  • Both Assertion and Reason are true and Reason is the correct explanation of Assertion
  • Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
  • Assertion is true but Reason is false
  • Assertion is false but Reason is true
  • Both Assertion and Reason are false
Followed by oxygen which element is the most abundant in human body?
  • C
  • H
  • Ca
  • P
$$NaCN$$ is sometimes added in the forth flotation process as a depressant when $$ZnS$$ and $$PbS$$ minerals are expected because :
  • $$Pb(CN)_2$$ is precipitated while no effect as $$ZnS$$
  • $$ZnS$$ forms soluble complex $$Na_2[Zn(CN)_4]$$ while $$PbS$$ forms froth
  • $$PbS$$ forms soluble complex $$Na_2[Pb(CN)_4]$$ while $$ZnS$$ forms froth
  • $$NaCN$$ is never added in froth flotation process
A thermite mixture contains iron $$[III]$$ oxide and aluminium, in which ______ is in a higher ratio in the mixture.
  • aluminium
  • iron $$[III]$$ oxide
  • both are equal
  • none of these
Copper is an __________ resource.
  • Exhaustible
  • Non-exhaustible
  • Potential
  • National
The conversion of aluminium hydroxide to pure alumina is carried out by:
  • addition of $$Al(OH)_3$$ crystals
  • thermal decomposition
  • precipitation
  • none of these
In zone-refining method, the molten zone:
  • consists of impurities only
  • contains more impurity than the original metal
  • contains the purified metal only
  • moves to either side
Aluminium is utilized in cooking utensils since it is :
  • Good conductor of electricity
  • Bright in appearance
  • Good conductor of heat
  • Tensile
In the froth floatation process, for the beneficiation of ores, the ore particles float because ______________.
  • they are light
  • their surface is not easily wetted by water
  • they bear electrostatic charge
  • they are insoluble
Complete the statement given below pertaining to metallurgy by filling the blank with the correct word.

Aluminium is an important constituent metal in duralumin since it is __________ .
  • good conductor of heat
  • unaffected by food acids
  • light
  • bright
Aluminium powder a constituent of paints, prevents:
  • conduction of electric current
  • formation of rust
  • heat radiation
  • heat generation
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