MCQ Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 5

The ore that is concentrated by froth floatation process is ___________.

0%
cinnabar
0%
bauxite
0%
malachite
0%
zineite

Explanation

Ores which are concentrated by froth floatation process include Galena (

$PbS$ ), zinc blende (

$ZnS$ ) and cinnabar (

$HgS$ ).

Zone-refining has been employed for preparing ultra-pure samples of:

0%
Cu
0%
Zn
0%
Ge
0%
Ag

Select the correct statement(s) :

0%
When temperature is reised, a point will be reached where the graph crosses the $\Delta$ G = 0 line. Below this temperature, the free energy of formatin of the oxide is negative, so the oxide is stable
0%
When temperature is raised, a point will be reached where the graph crosses the $\Delta$ G = 0 line. Above this temperature, the free energy of formation of the oxide is positive, and the oxide becomes unstable, and should decompose into the metal and dioxygen.
0%
Theoretically, all oxides can be decomposed to give the metal and dioxygen if.a sufficiently high temperature can be attained.
0%
Theoretically, all oxides cannot be decomposed to give the metal and dioxygen if a sufficiently high temperature can he attaincd

Explanation

Ellingham diagram us a plot between

${ \triangle }_{ f }G°$ and T

$\triangle G°=-RTlnK$
The metal oxide (MxO) is stable at a point in a curve below which

$\triangle G$ is negative. Above this point, the metal oxide is unstable.

In which of the following isolations is no reducing agent required?

0%
Iron from haematire
0%
Tin from tin oxide
0%
Mercury from cinnabar
0%
Zine from zinc blende

Which of the following metal is sometimes found native in nature?

0%
Aluminium
0%
Copper
0%
Sodium
0%
Magnesium

Lead obtained from galena ore (PbS) by air reduction or carbon reduction process contains base metal (Cu, Bi, As, Sn, Zn) as impurities. Gelatin acts as an addition agent in the electrolysis of Pb. In the presence of gelatin, Pb becomes :

0%
hard and brittle
0%
soft and rubbery
0%
smooth and uniform
0%
only brittle

Explanation

Lead obtained contains impurities like

$Cu, Sb, Sn, As, Ag, Au, etc.$ which make it hard. During electrolytic refining of lead, the electrolyte

$(PbSiF_6+H_2SiF_6)$ is mixed with a little gelatin. Gelatin is added for smooth and uniform deposition of lead in this process.

Hence, the correct option is (C).

When

$FeCr_2O_4$ (chromite) is reduced with

$Al$ :

0%
$Cr$ and $Fe_2O_3$ , are formed
0%
$Fe$ and $Cr_2O_3$ are formed
0%
$Fe$ and $Cr$ (ferrochrome) are formed
0%
$FeCrO_4$ . is formed

Explanation

For the production of ferrochrome (

$Fe$ and

$Cr$ ), the chromite ore (

$Fe{ Cr }_{ 2 }{ O }_{ 4 }$ ) is reduced with either aluminium or silicon in an aluminothermic reaction.

Select the correct statements for Ellingham diagram.

0%
Any metal will reduce the oxide of other metals which lie above it in the Ellingham diagram
0%
According to the Ellingham diagram, Al will not reduce MgO at temperature below 1350 $^{\circ}$ C
0%
According to the Ellingham diagram, Al will reduce MgO at temperature below 1350 $^{\circ}$ C
0%
Any metal will not reduce the oxide of other metals which lie above it in the Ellingham diagram

Explanation

Any metal will reduce the oxide of other metals which lie above it in the Ellingham diagram because the free energy will become more negative by an amount equal to the difference between the two graphs at that particular temperature.

Al metal can reduce the oxide of metal placed above it. Due to more negative free energy, Al can reduce Zn but not Mg below

$1350^oC$ . However, above

$1350^oC$ , Al can reduce Mg.

Hence, option A and B are correct.

$H_2$ is not widely used as the reducing agent in metallurgic process because :

0%
many metals react with $H_2$ at elevated temperature forming hydrides
0%
there is a risk of explosion from $H_2$ and $O_2$ present in the air
0%
reducing power of $H_2$ does not increase with temperature
0%
reducing power of $H_2$ , increases with temperature

Explanation

$H_2$ is not widely used as the reducing agent in metallurgic process because metals react with

$H_2$ at elevated temperature forming hydrides. When

$H_2$ and

$O_2$ present in the air are combined it will be explosive. Reducing power of

$H_2$ does not increase with temperature, which is essential in metallurgy.

Which of the following statement(s) is/are correct"?

0%
The chemical processes in the production of steel from haematite ore involve reduction followed by

oxidation.
0%
In Hall-Heroult process, the electrolyte used is a molten mixture of alumina and cryolite or fluorspar.
0%
Lead is extracted from its chief ore galena by both carbon reduction as well as self reduction,
0%
Haematitic, cassiterite, and argentite are oxide ores.

Explanation

A) In the furnace, first the coke reacts with oxygen in the air blast to produce carbon monoxide(oxidation):

$2C+O2\rightarrow 2CO$ The carbon monoxide reduces the iron ore (hematite) to molten iron, becoming carbon dioxide in the process:

$3CO + Fe_2O_3\rightarrow 2Fe + 3CO_2$
B) The HallHroult process is the major industrial process for smelting of alumina. It involves dissolving alluminium oxide(allumina) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell.
C) Lead is extracted from its chief ore galena by both carbon reduction as well as self reduction,
D) Haematitic(

$Fe_2O_3$ ),cassiterite (

$SnO_2$ ) and argentite(

$Ag_2S$ ).So Haematite and cassiterite are oxide ores but argentite is sulphide ore.Incorrect.
Hence options A,B & C are correct.

The metal oxide which cannot be reduced to metal by carbon is _________.

0%
$ZnO$
0%
$Fe_2O_3$
0%
$PbO$
0%
$Al_2O_3$

Explanation

Reduction of the oxide with carbon at high temperature is known as smelting. The oxides of less electropositive metals like Pb, Zn, Fe, Sn, Cu etc. are reduced by strongly heating them with coal or coke, in the blast furnace.

So among the given options only

$Al_2O_3$ cannot be reduced by carbon.

Hence, the correct option is

$C$

Which of the given metal oxides is having minimum thermal decomposition temperature?

0%
CaO
0%
FeO
0%
PbO
0%
MgO

Explanation

$PbO$ has the minimum thermal decomposition temperature, as it crosses zero

$\Delta G$ line at minimum temperature.

Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out _______________.

0%
in the presence of NaCl
0%
in the presence of fluorite
0%
in the presence of cryolite which forms a melt with lower melting temperature
0%
in the presence of cryolite which forms a melt with higher melting temperature

Explanation

Correct Answer: Option C

Explanation:

Metallurgy of aluminum is carried out by the Hall-Heroult process.

Cryolite $(Na_{3}AlF_{6})$ acts as a solvent for Aluminum oxide.

It lowers the melting point of the ore and also increases conductivity to ease the electrolysis.

Which of the following metal's oxide can be reduced by Fe as reducing agent at temperature

$T_1$ ?

0%
Pb
0%
Ca
0%
Mg
0%
None of these

Explanation

$T_1$ temperature,

$\Delta G_f$ of

$FeO$ is more negative than that of

$PbO$ . So,

$PbO$ can be reduced by

$Fe$ as reducing agent at temperature

$T_1.$

Which one of the above oxidation curve is wrongly presented in the given Gibbs free energy vs temperature graph ?

0%
$C \rightarrow CO_2$
0%
$Ti \rightarrow TiO_2$
0%
$Pb \rightarrow PbO$
0%
$Mg \rightarrow MgO$

Explanation

$Ti(s) + \cfrac{1}{2}O_{2(g)} \xrightarrow[]{\Delta} TiO_2(s)$

By increasing temperature,

According to

$\Delta G = \Delta H - T\Delta S, \ \Delta G$ for formation of

$TiO_2$ will move toward +ve value.

Aquaregia is ___ part conc. HCI and ___ part conc.

$HNO_3$ .

0%
one,three
0%
one,one
0%
three,three
0%
three,one

Explanation

Aqua regia is three parts conc.

$HCI$ and one part conc.

$HNO_3$ .

$HNO_3 + 3HCl \rightarrow NOCl + 2H_2O + 2CI$

So, the correct option is

$D$

(i) Metals can be recovered from their ores by chemical methods.

(ii) High purity metals can be obtained by zone refining method.

Which one is true /false.

0%
(i) is true and (ii) is false
0%
(ii) is true and (i) is false
0%
(i) and (ii) are true
0%
(i) and (ii) are false

Pb is a very important element of carbon family. It forms a number of compounds which are very useful in industries. The process of removal of base metals (Cu, Sn, Bi, As) from lead is called:

0%
softening process
0%
liquation
0%
parke's process
0%
cupellalion

The better reducing agent at

$7100^oC$ is:

0%
$CO$ (Ellingham diagram)
0%
Coke
0%
Both are equal
0%
None of these

Explanation

Ellingham diagram is a graph between

$\Delta G^o$ and temperature values which determines the spontaneity of a reaction. At

$7100^oC,$

$CO$ acts as better reducing agent by seeing the diagram

NaCN used in the froth flotation method for the purification of ore is:-

0%
$ZnS$ which contain $PbS$
0%
${Cu_2 S}$ which contain ${Fe_2 S_3}$
0%
$PbS$ which contain $ZnS$
0%
$PbS$ which contain ${SiO_2}$

Explanation

FROTH FLOATATION PROCESS - This method is used when a higher ore contains impurities with higher density. This method is used for the concentration of Sulphide ores (e.g.: Copper pyrites, iron pyrites, Galena, Zinc blende etc.,)

In this process, collectors and froth stabilisers are added.

Collectors - (e.g., pine oils, fatty acids, xanthates, etc.); Froth Stabilisers - (e.g., cresols, aniline)

The mineral particles become wet by oils while the gangue particles by water. A rotating paddle agitates the mixture and draws air in it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for recovery of the ore particles.

Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using 'depressants'. Example: In case of an ore containing

$ZnS$ and

$PbS$ , the depressant used is

$NaCN$ . It selectively prevents

$ZnS$ from coming to the froth but allows

$PbS$ to come with the froth.

Which is wrongly mached:

0%
Gun metal- $\displaystyle Cu+Zn+Sn$
0%
Duralumin $\displaystyle Cu+Al+Mn$
0%
German silver $\displaystyle Cu+Zn+Ni$
0%
Electron $\displaystyle Pb+Sn$

Froth floatation process is used to concentrate magnetic ores.

0%
True
0%
False

Explanation

Froth floatation process is used to concentrate sulphide ores. In some cases, sulphide ores of copper, zinc and lead concentration are brought by this method. It is the referential wetting of the ore by an oil. A strong current of air is blown through the suspension producing a heavy froth e.g. Galena

$(PbS)$ is associated with Sphalerite

$(ZnS)$ and Pyrite

$(FeS)$ .

Composition of azurite mineral is:

0%
$CuCO_3.CuO$
0%
$Cu(HCO_3)_2.Cu(OH)_2$
0%
$2CuCO_3.Cu(OH)_2$
0%
None of these

Explanation

Azurite is one of the basic copper (II) carbonate minerals, the other being bright green malachite. Simple copper carbonate (CuCO3) is not known to exist in nature. Azurite has the formula $Cu(CO_3)_2(OH)_2$ with the copper (II) cations linked to two different anions, carbonate and hydroxide.

Hence the composition of azurite mineral is $2CuCO_3.Cu (OH)_2$

Predict the mode of occurrence of the following metals:

The correct answer is:

0%
$Na \rightarrow$ combined form
0%
$Fe \rightarrow$ combined form
0%
$Au \rightarrow$ combined form
0%
none of these

Volatile metals are purified by :

0%
oxidation
0%
distillation
0%
liquation
0%
electrolytic refining

Which one of the following metals can not be extracted by using Al as a reducing agent ________________.

0%
$\displaystyle Na$ from $\displaystyle { Na }_{ 2 }O$
0%
$\displaystyle Cr$ from $\displaystyle { Cr }_{ 2 }{ O }_{ 3 }$
0%
$\displaystyle Mn$ from $\displaystyle { MnO }_{ 2 }$
0%
$\displaystyle Fe$ from $\displaystyle { Fe }_{ 2 }{ O }_{ 3 }$

Explanation

As sodium (alkali metal) is more reactive than Al so it cannot be extracted from

$Na_2O$ by using Al as a reducing agent.

Identify the process to which the following reaction belongs :

$\displaystyle { Al }_{ 2 }{ O }_{ 3 }.{ 2H }_{ 2 }O+{ Na }_{ 2 }{ CO }_{ 3 }\longrightarrow { 2NaAlO }_{ 2 }+{ 2H }_{ 2 }O+{ CO }_{ 2 }$

$\displaystyle { 2NaAlO }_{ 2 }+{ 2H }_{ 2 }O+{ CO }_{ 2 } \underrightarrow { 50-{ 60 }^{ o }C } { Al }_{ 2 }{ O }_{ 3 }.{ 2H }_{ 2 }O+{ Na }_{ 2 }{ CO }_{ 3 }$

0%
Hall's process
0%
Baeyer's process
0%
Serpeck's process
0%
None of these

Explanation

Hall's Process: (Red bauxite)

Bauxite one +

$Na_2CO_3 \xrightarrow{Fused} NaAlO_2$

$\downarrow$ extracted with water

Solution

$\downarrow$ warmed

$50^o - 60^oC$

$CO_2$ is circulated

$\downarrow$

$Al(OH)_3 + Na_2CO_3$

Silver is purified by the distillation process.

0%
True
0%
False

Explanation

Silver is not purified by a distillation process, but by cyanide process.

Cyanide Process: Silver and gold are extracted by cyanide process (Mac Arthur - Forrest process). After the preliminary crushing and concentration by froth floatation process, the ore (crushed auriferous rocks in the case of gold) is leached with dilute (0.4 - 7%) solution of sodium cyanide made alkaline by adding lime kept agitated by a current of air. Silver (or gold) pass into solution as argentocyanide (or aurocyanide):

$Ag_2S + 4NaCN \rightarrow 2Na[Ag(CN)_2 ] + Na_2S$

Silver is obtained by reaction with Zn:

$2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4 ] + 2Ag$

Metals can be recovered from their ores by chemical methods.

0%
True
0%
False

Silver is found in nature both in native and combined state.

0%
True
0%
False

Sulphide ore of copper can be concentrated by froth floatation process.

0%
True
0%
False

Which of the following metal is present in native state?

0%
platinum
0%
iron
0%
potassium
0%
copper

The most abundant metal in the earth crust is:

0%
Copper
0%
Silver
0%
Aluminium
0%
Silicon

Which of the following is not a property of aluminium?

0%
Good conductor of heat and electricity
0%
It is malleable
0%
It is heavy
0%
It is ductile

Silk moth feed on:

0%
eucalyptus leaf
0%
grapes Leaves
0%
mulberry Leaves
0%
neem leaves

Zone refining process is used for the:

0%
Concentration of an ore
0%
Reduction of a metal oxide
0%
Purification of metal
0%
Purification of an ore

Sulfide ores are usually dressed by the _____ process.

0%
sieve process
0%
froth floatation
0%
magnetic floatation
0%
none of these

Which of the following chemical reaction correctly shows Aqua-regia dissolving in gold?

0%
$Au+2[Cl]\longrightarrow AuCl_2\overset{HCl}{\longrightarrow} H_2[AuCl_4]$
0%
$Ag+3[Cl]\longrightarrow AgCl_3\overset{HCl}{\longrightarrow} H[AgCl_4]$
0%
$Au+3[Cl]\longrightarrow AuCl_3\overset{HCl}{\longrightarrow} H[AuCl_4]$
0%
$Ag+2[Cl]\longrightarrow AgCl_2\overset{HCl}{\longrightarrow} H_2[AgCl_4]$

Explanation

Aqua regia is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange fuming liquid. It can dissolve the noble metals gold and platinum.

$Au+3[Cl]\longrightarrow AuCl_3\overset{HCl}{\longrightarrow} H[AuCl_4]$

During concentration of _____ ores by froth floatation process potassium ethyl xanthate is added.

0%
sulphide
0%
carbonate
0%
halide
0%
amide

The oil used in the froth floatation method for the purification of ore is _________.

0%
Coconut oil
0%
Olive oil
0%
Pine oil
0%
Castor oil

Explanation

Froth Floatation process is suitable for sulphide ores. The process is based on different wetting characteristics of the ore and gangue particles with water and pine oil.

The ore is wetted by oil and impurities are wetted by water. Ore particles are adsorbed on potassium or sodium ethyl xanthate (as a collector) and come at the surface along with the froth. Froth stabiliser (cresols, aniline) stabilise the froth.

So, the correct option is

$C$

Which oil is used as frother in froth floatation process?

0%
Mustard oil
0%
Coconut oil
0%
Olive oil
0%
Pine oil

The diagram shows the sketch of an electrolytic cell used in the extraction of aluminium. At which electrode (A or B) is the aluminium formed?

0%
A (Cathode)
0%
B (Anode)
0%
At both A and B
0%
Cannot be determined

Explanation

Aluminium ions receive electrons at the negative electrode(Cathode) and are reduced to aluminium atoms:

$Al^{3+} + 3e^– \rightarrow Al$ (reduction – gain electrons)

The molten aluminium sinks to the bottom of the cell, where it is tapped off.

The diagram shows the sketch of an electrolytic cell used in the extraction of aluminium. What are the two aluminium compounds present in the electrolyte C?

0%
Pure alumina (Al $_2$ O $_3$ ) and cryolite (Na $_3$ AlF $_6$ )
0%
Duralumin, magnalium
0%
Cryolite, duralumin
0%
none of the above

The substance added in water in the froth floatation process is

0%
Olive oil
0%
Pine oil
0%
Coconut oil
0%
None of the above

Silicon is the main constituent of _______.

0%
alloys
0%
rocks
0%
animals
0%
vegetables

Explanation

Silicon is the most abundant element in the earth crust. It is found in rocks .

Therefore, the correct answer is

$B$

$\displaystyle Fe_{2}O_{3\left ( s \right )}+2Al_{\left ( s \right )}\rightarrow 2Fe_{\left ( l \right )}+Al_{2}O_{3\left ( s \right )}$
The above reaction is known as _________ and it is highly ________ .

0%
electrolysis, endothermic
0%
refining, endothermic
0%
calcination, exothermic
0%
thermite reaction, exothermic

Explanation

Thermite is a pyrotechnic composition of metal powder, fuel and metal oxide. When ignited by heat, thermite undergoes an exothermic reduction-oxidation reaction. Fuels include

$Al,\ Mg, \ Ti, \ Zn, \ Si,\ B$ and

$Al$ is common because of its high boiling point and low cost. Oxidizers include boron (III) oxide, iron (III) oxide, copper (II) oxide.

The diagram shows the sketch of an electrolytic cell used in the extraction of aluminium. What is the substance of which the electrodes A and B are made?

0%
Carbon and graphite
0%
Zinc and copper
0%
Copper and iron
0%
None of the above

In the alumino thermic process, aluminium acts as:

0%
an oxidizing agent
0%
a flux
0%
a reducing agent
0%
a solder

Which of the following methods is used in purification of mercury?

0%
Liquation
0%
Distillation
0%
Electrolytic refining
0%
Chemical reduction

Explanation

Liquation:
This method is used for the refining of metals having low melting point and are associated with high melting impurities, e.g.,

$Pb, Sn, Sb, Bi$ .
Distillation:
Metals having low boiling point are refined by this method. For example, zinc, cadmium and mercury.
Electrorefining of Metals:
Metals such as

$Cu, Ag, Zn, Sn, Pb, Al, Ni, Cr$ are refined by this method.

Liquation method is used for the purification of which of the following metals?

0%
Tin
0%
Lead
0%
Bismuth
0%
All of these

Explanation

Liquation is used for the refining of metals having low melting point and are associated with high melting impurities. For example,

$Pb,\ Sn,\ Sb,\ Bi$ and

$Hg$ . The impure metal is heated on the sloping hearth of a furnace. The pure metal flows down leaving behind the non-fusible material on the hearth.

CBSE Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 5 - MCQExams.com

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Practice Class 12 Engineering Chemistry Quiz Questions and Answers

CBSE Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 5 - MCQExams.com

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Practice Class 12 Engineering Chemistry Quiz Questions and Answers

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