MCQ Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 13

Froth floatation process is used for the concentration of

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oxide ores
0%
sulphide ores
0%
chloride ores
0%
amalgams

Froth - floatation method is successful in separating impurities from ores because

0%
the pure ore is lighter than water containing additives like pine oil , cresylic acid etc.
0%
the pure ore is soluble in water containing additives like pine oil , cresylic acid etc.
0%
the impurities are soluble in water containing additives like pine oil , cresylic acid etc.
0%
the pure ore is not as easily wetted by water as by pine oil , cresylic acid etc.

Aluminium is used:

0%
in thermite welding
0%
as an oxidiser in metallurgy
0%
for making untensils
0%
in silvery paints

The white precipitate (P) is of :

0%
$Cu_{2}I_{2}$
0%
$CuI_{2}$
0%
$K_{2}\left [ CuI_{4} \right ]$
0%
None

A layer of coke is spread over bauxite during electrolytic reduction of alumina by Hall Heroult process. This layer acts as a/an

0%
flux
0%
slag to remove impurities
0%
reducing agent
0%
insulation and does not allow heat to escape

The reactions which does/do not occur in the reduction zone in the extraction of iron from haematite ore is

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$Fe_{2}O_{3}+CO\rightarrow 2FeO + CO_{2}$
0%
$FeO+CO\rightarrow FeO + CO_{2}$
0%
$Fe_{2}O_{3}+3C\rightarrow 2Fe+3CO$
0%
$CaO+SiO_{2}\rightarrow CaSiO_{3}$

Explanation

Solution:

Extraction of iron is based on the reduction of Haematite $Fe_2O_3$ with carbon.

In reduction zone following reactions took place:

$Fe_2O_3+CO\rightarrow 2Feo+CO_2$

$FeO+CO\rightarrow Fe+CO_2$

In fusion Zone at higher temperature following reaction took place:

$Fe_2O_3+3C\rightarrow 2Fe+3CO$

Reaction in slag formation:

$CaO+SiO_2\rightarrow CaSiO_3$
Hence option C and D are correct as this reaction doesn't took place in reduction zone.

Which one of the following statements is incorrect?

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In Hall-Heroult process, the electrolyte used is molten mixture of alumina, sodium hydroxide and cryolite.
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Lead is extracted from is chief ore by both carbon reduction and self reduction
0%
Zinc is extracted from its chief ore by carbon reduction
0%
Extraction of gold involves the leaching of ore with cyanide solution followed by reduction with zinc.

Explanation

The Hall–Héroult process is the major industrial process for smelting aluminum. It involves dissolving aluminum oxide (alumina) (obtained most often from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite, and electrolyzing the molten salt bath, typically in a purpose-built cell It is molten mixture of alumina and cryolite not sodium hydroxide.

(B) Lead is extracted from its chief ore by both self reduction and carbon reduction, reaction are as follows:

Self-reduction of Lead

$PbS+2PbO\rightarrow 3Pb+SO_2$

Carbon reduction of Sn

$2SnO+C\rightarrow 2Sn+CO_2$

(C) The ore is concentrated by froth floatation process using pine oil. The concentrated ore is then roasted in presence of excess of air at 1200 K. If roasting is carried out below this temperature, ZnS is converted into $ZnSO_4$ , which convert back to ZnS during carbon reduction of roasted ore.

(D) Extraction of gold involves the leaching of ore with cyanide solution followed by reduction with zinc.

So option A is incorrect, Rest all are correct

In the metallurgical extraction of zinc from

$ZnO$ , the reducing agent used is

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Carbon monoxide
0%
Sulphur dioxide
0%
Carbon dioxide
0%
Nitric oxide

Explanation

$ZnO + CO \rightarrow CO_2 + Zn$

Carbon monoxide is used as a reducing agent in the extraction of carbon monoxide.

Option A.

The impurities associated with minerals used in metallurgy are collectively called

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Slag
0%
Flux
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Gangue
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Ore

The substance used in the thermite process of reducing metal ores is

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Aluminium
0%
Thorium
0%
Heated platinum gauze
0%
Carbon

Explanation

In thermite process a mixture of aluminium powder and ferric oxide in the rate of

$1 : 3$ is used.

Option A.

When a metal is to be extracted from its ore if the gangue associated with the ore is silica , then

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An acidic flux is needed
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A basic flux is needed
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Both acidic and basic flux are needed
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Neither of them is needed

Explanation

$\underset {Acidic\ impurity} {SiO_2} + \underset {Basic\ Flux} {CaO} \rightarrow \underset {Slag}{CaSiO_3}$

Option B is correct.

Thermite process is used to extract metals

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when their oxides can't be reduced by carbon
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when their carbonates do not yield oxides by thermal decomposition
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when their sulphides can't be converted into oxides by roasting
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when their melting points are very high

Which one of the following metals is extracted by thermal reduction process ?

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Copper
0%
Iron
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Aluminium
0%
Magnesium

Carbon reduction process is used for the extraction of

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$Hg$
0%
$Zn$
0%
$Cr$
0%
$Fe$

Explanation

The oxides of less electropositive metals are reduced by strongly heating them with coal or coke. Carbon combines with the oxygen of the metal oxide to form carbon monoxide which can also act as a reducing agent.

$Fe_2O_3 + 3C \rightarrow 3CO + 2Fe$

Option D.

In Hall's process the main reagent is mixed with

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$NaF$
0%
$Na_{3}AlF_{6}$
0%
$AlF_{3}$
0%
None of these

Explanation

Pure alumina is a bad conductor of electricity and the fusion temperature of pure alumina is about

$2000^{o}C$ and at this temperature when the electrolysis is carried of fused mass the metal formed vapourises as the boiling point of

$Al$ is

$1800^{o}C$

To overcome this difficulty.

$Na_{3}AlF_{6}$ and

$CaF_{2}$ are mixed with alumina.

Heating with carbon in absence of air is known as

0%
Reduction
0%
Carbon - reduction
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Smelting
0%
Roasting

Explanation

Heating with carbon in absence of air is known as carbon reduction.

This is used in Iron metallurgy.

$Fe_2O_3 + C \xrightarrow {in\, blast \,furnace}Fe$

Zone refining is a technique used primarily for which one of the following process

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Alloying
0%
Tempering
0%
Sintering
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Purification

Explanation

Zone refining is a method of purification used for semiconductors like

$Si , Ge$ and

$Ga.$

The chemical processes in the production of steel from haematite ore involve

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reduction
0%
oxidation
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reduction followed by oxidation
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oxidation followed by reduction

Explanation

The chemical processes in the production of steel from haematite ore involve oxidation followed by reduction. Firstly, carbon which is added along which crushed haematite ore is oxidised to

$CO$ and

$CO_2$ and second, the produced

$CO$ acts as the chief reducing agent for the reduction of haematite to steel.

The extraction of nickel involves

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the formation of $Ni(CO)_4$
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the decomposition of $Ni(CO)_4$
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the formation and thermal decomposition of $Ni(CO)_4$
0%
the formation and catalytic decomposition of $Ni(CO)_4$

Explanation

The extraction of nickel involves the formation and thermal decomposition of

$Ni(CO)_4$ .

$Ni+4CO\to Ni(CO)_4 (vap)\xrightarrow {\Delta} Ni(s)+4CO(g)$

While extracting an element from its ore, the ore is ground and leached with dilute KCN solution to form the soluble product potassium argentocyanide. The element is

0%
Lead
0%
Chromium
0%
Manganese
0%
Silver

Explanation

Silver metal is extracted from the argenite ore

$Ag_2S$ . By cyanide process, in this method the concentrated ore is treated with dilute solution of potassium cyanide, then a soluble complex potassium dicyanoargenate(I) is formed which when reacted with zinc, silver is extracted as a ppt.

$Ag_2S + 4KCN \rightarrow 2K[Ag(CN)_2] + NaS$

$2K[Ag(CN)_2] + Zn \rightarrow K_2[Zn(CN)_4] + 2Ag \downarrow$

In the electrolytic purification of copper some gold is found in the

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cathode
0%
cathode mud
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anode mud
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electrolyte

Select correct statement:

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The decomposition of an oxide into oxygen and metal vapour increases
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Decomposition of an oxide is an endothermic change
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To make $\Delta G^{o}$ negative, temperature should be high enough so that $T \Delta S^{o} > \Delta H^{o}$
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All are correct statements

Ellingham diagram represent :

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Change of $\Delta G$ with temperature
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$\Delta H$ with temperature
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$\Delta G$ with pressure
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change of ( $\Delta G - T \Delta S$ -)

Copper metal is used in :

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Making electric wires
0%
Filing tooth cavities
0%
Making fuse wires
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Preparation of hydrogen

In the alumino-thermite process, Al acts as:

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

Aluminium is not used to make

0%
Foils
0%
Wires
0%
Fireworks
0%
Utensils

Explanation

Aluminium is not used to make fireworks because aluminum is a metal that can melt but can not burn, during fire tests when the temperature exceeds the melting point in the range of $600^\circ C$ .
The thermal conductivity of aluminum is four times greater than steel and its specific heat is twice that of steel. So, it acts as effective protection against fire rather than being used in fireworks.
So, aluminum is not used to make fireworks but it is frequently used to make foils, wires, and utensils due to its ductile and strong metallic bond capacity.

Forth floatation process used for the concentration of sulphide ore:

0%
Is based on the difference in wettability of different minerals
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uses sodium ethyl xanthate $C_{2}H_{5}OCS_{2}Na$ as collector
0%
uses NaCN as depressant in the mixture of ZnS forms soluble complex and Pbs forms forth
0%
All are correct statements

Explanation

Forth floatation process used for the concentration of sulphide ore is based on the difference in wettability of different minerals, uses sodium ethyl xanthate

$C_{2}H_{5}OCS_{2}Na$ as collector & uses NaCN as depressant in the mixture of ZnS forms soluble complex and Pbs forms forth.

Hence, Option "D" is the correct answer.

Which of the following pair is incorrectly matched ?

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van Arkel method - Zirconium
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Kroll's process - Titanium
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Froth floatation - Cerussite
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Distillation - Zinc

NaCN is sometimes added in the forth flotation process as depressant when ZnS and PbS minerals are expected because:

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$Pb (CN)_{2}$ is precipitated while no effect on ZnS
0%
Zns forms soluble complex $Na_{2}[Zn(CN)_{4}]$ While PbS forms forth
0%
PbS forms soluble complex $Na_{2}[Zn(CN)_{4}]$ while ZnS forms forth
0%
NaCN is never added in forth floatation process

Explanation

Depressant is a substance that is added to suppress the floating characteristic of metal sulphide present as an impurity

$PbS+ ZnS\overset{4NaCN}{\rightarrow}Na_{2}[Zn(CN)_{4}]+PbS$
1767696_1819591_ans_b62544753fcd436397b4e6d21efe86a6.PNG

correct statement in the electrolysis of

$Al_{2}O_{3}$ by Hall-Heroult process is:

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Cryolite $Na_{3}[AlF_{5}]$ lowers the m.pt. of $Al_{2}O_{3}$ and increases its electrical conductivity
0%
Al is obtained at cathode and $CO_{2}$ at anode
0%
both (a) and (b) are correct
0%
none of the above

Explanation

The electrolysis of alumina by Hall and Heroult's process is carried by using a fused mixture of alumina and cryolite along with minor quantities of aluminum fluoride and fluorspar.
The addition of cryolite and fluorspar increases the electrical conductivity of alumina and lowers the fusion temperature.
At cathode $Al(III)$ is reduced to $Al$ metal.
At the anode, alumina reacts with fluorine to liberate oxygen. Oxygen reacts with carbon to form carbon dioxide.

1767551_1819773_ans_042ffb090c854de88ec3dad938ac718b.PNG

When ZnS and PbS minerals are present together, then NaCN is added to separaye them in the forth floaatation process as a depressant, because:

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$Pb (CN)_{2}$ is precipitated while no effect on ZnS
0%
ZnS forms soluble complex $Na_{2}[Zn(CN)_{4}]$
0%
PbS forms soluble complex $Na_{2}[Zn(CN)_{4}]$
0%
The cannot be separated by adding NaCN

Explanation

$ZnS+4NaCN\rightleftharpoons 4Na^{+}+[Zn(CN)_{4}]^{-2}+S^{2-}$
1767673_1819581_ans_5c96f52be23c49f7b6e340f69fbd3399.PNG

Which of the following substance acts as collector in froth floatation method?

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Sodium xenate
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Sodium pyrophosphate
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Sodium nitroprusside
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Sodium ethyl xanthate

High purity copper metal is obtained by :

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carbon reduction
0%
hydrogen reduction
0%
electrolytic reduction
0%
thermite reduction

Which sulphide occurs to minimum extent in nature

0%
$HgS$
0%
$H_{2}S$
0%
$Bi_{2}S_{3}$
0%
$CS_{2}$

Explanation

As the curve of

$CS_2$ has a consistent negative slope, it occurs in a minimum extent.

Hence, Option "D" is the correct answer.

Which of the following elements can be prepared by heating the oxide above

$400^{\circ}C$ ?

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Hg
0%
Mg
0%
Fe
0%
Al

Formation of which of the sulphides is most spontaneous?

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HgS
0%
Bi $_{2}$ S $_{3}$
0%
PbS
0%
CS $_{2}$

Explanation

As at all temperatures

$\Delta G^{0}$ of PbS is highest negative so it is the most spontaneous.

Hence, correct answer is option C.

Free energy change of Hg and Mg for the conversion of oxides the slope of

$\Delta G$ vs. T has been changed above the boiling point of the given metal because :

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above the boiling point of the given metal the entropy is increased
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above the boiling point of the metal the entropy is decreased
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above the boiling point of the metal the entropy change is equal to zero
0%
All of these

Explanation

Free energy change of Hg and Mg for the conversion of oxides the slope of

$\Delta G$ vs. T has been changed above the boiling point of the given metal because above the boiling point of the given metal the entropy is increased.

Hence, Option "A" is the correct answer.

At what temperature, zinc and carbon have equal affinity for oxygen?

0%
$1000^{\circ}C$
0%
$1500^{\circ}C$
0%
$500^{\circ}C$
0%
$1200^{\circ}C$

$1100^{\circ}C$ , which reaction is spontaneous to a maximum extent?

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$MgO+C\rightarrow Mg+CO$
0%
$ZnO + C \rightarrow Zn +CO$
0%
$MgO+Zn\rightarrow Mg + ZnO$
0%
$ZnO + Mg \rightarrow MgO + Zn$

In the electrolytic refining of copper, Ag and Au are found :

0%
on anode
0%
in electrolyte solution
0%
in anode mud
0%
in cathode mud

To make the following reduction process spontaneous, temperature should be :

$ZnO+C\rightarrow Zn+CO$

0%
$1000^{\circ}C$
0%
$>1100^{\circ}C$
0%
$<500^{\circ}C$
0%
$<1000^{\circ}C$

Which of the following sulphides can not be reduced to metal by

$H_{2}$ at about

$1000^{\circ}C$ ?

0%
$HgS$
0%
$PbS$
0%
$Bi_{2}S_{3}$
0%
All of these

Explanation

The curve which has value of

$\Delta$ G less than that of

$\mathrm{H_2S}$ can not be reduced by

$\mathrm{H_2}$ at

$\mathrm{1000^{\circ}C}$ .

So, the metal sulphide which can not be reduced by Hydrogen is PbS.

Hence, Option "B" is the correct answer.

Of the following reduction process, correct process are:

0%
$Fe_{2}O_{3}+C\rightarrow Fe$
0%
$ZnO + C \rightarrow Zn$
0%
$Ca_{3}(PO_{4})_{2}+C\rightarrow P$
0%
$PbO + C \rightarrow Pb$

Elements found in the combined state are often present as oxides, carbonates, sulphides and silicates.

0%
True
0%
False

Explanation

Ans :- True

Elements found in combined state are of often present on oxides, carbonates, sulphides and silicates. Minerals can be classified on the basis of their Predominant anion groups. Silicates, according to their high abundance,

occupy the first position among the rest.

Examples:

Oxides

$\rightarrow$ Haematite, corundum

Sulphides

$\rightarrow$ Galena, pyrites

silicates

$\rightarrow$ feldspar, quartz

Corbonate

$\rightarrow$ Delomite, calite.

Froth floatation process of concentration is based on the

0%
preferential wetting properties with the frothing agent and water
0%
difference in the specific gravities of gangue and ore particles
0%
difference in solubility of gangue and ore particles in frothing agent and water
0%
difference in reactivity of gangue and ore particles with water and frothing agent.

Which one of the following ores is best concentration by forth-flotation method?

0%
Malachite
0%
Cassiterite
0%
Galena
0%
Magnetite

Explanation

Galena

$(Zn S)$ is a sulphide ore. Galena is best concentrated by forth floatation method. Froth floatation method is used to concentrate sulphide ores. Magnetite

$\left(\mathrm{Fe}_{3} \mathrm{O}_{4}\right)$ is an ore of iron . Malachite

$\left[\mathrm{Cu}_{2} \mathrm{CO}_{3}(\mathrm{OH})_{2}\right]$ is an ore of copper and cassiterite

$\left(Sn O_{2}\right)$ is an ore of tin.

Hence, only galena contains sulphide ion, thus it is best concentrated by forth floatation method.

Which of the following is most economically refined by fractional distillation?

0%
$Zn$
0%
$Ni$
0%
$Cu$
0%
$Fe$

Explanation

Main impurities in

$Zn$ are generally cadmium, lead and iron. There is very less difference in the boiling point of zinc and these impurities so zinc can be refined using fractional distillation.

For refining copper, we generally use electrorefining, cupellation or poling as the refining techniques.

For

$Ni$ , vapour phase refining i.e. Mond process is used.

For

$Fe$ , we use oxidative refining technique.

Hence, option (A) is the correct answer.

Match the following
Column I

$\quad$ Column II
(a) Sphalerite- (i)

$\mathrm{FeCO}_{3}$
(b) Malachite- (ii)

$\mathrm{ZnCO}_{3}$
(c) Calamine- (iii)

$\mathrm{Na}_{3} \mathrm{AlF}_{6}$
(d) Cryolite- (iv)

$CuCO_{3}.Cu(OH)_{2}$
(e) Siderite (v)

$\mathrm{ZnS}$

0%
$\begin{array}{lllll}\text { (a) }-(\mathrm{iii}), & \text { (b) }-(\mathrm{i}), & \text { (c) }-(\mathrm{v}), & \text { (d) }-(\mathrm{ii}), & \text { (e) }-(\mathrm{iv})\end{array}$
0%
$\begin{array}{lllll}\text { (a) }-(\mathrm{v}), & \text { (b) }-(\mathrm{iv}), & \text { (c) }-(\mathrm{ii}), & \text { (d) }-(\mathrm{i}), & \text { (e) }-(\mathrm{iii})\end{array}$
0%
$\begin{array}{lllll}\text { (a) }-(\mathrm{v}), & \text { (b) }-(\mathrm{iii}), & \text { (c) }-(\mathrm{ii}), & \text { (d) }-(\mathrm{i}), & \text { (e) }-(\mathrm{iv})\end{array}$
0%
$\begin{array}{lllll}\text { (a) }-(\mathrm{v}), & \text { (b) }-(\mathrm{iv}), & \text { (c) }-(\mathrm{ii}), & \text { (d) }-(\mathrm{iii}), & \text { (e) }-(\mathrm{i})\end{array}$
0%
$\begin{array}{lllll}\text { (a) }-(\mathrm{ii}), & \text { (b) }-(\mathrm{iii}), & \text { (c) }-(\mathrm{i}), & \text { (d) }-(\mathrm{v}), & \text { (e) }-(\mathrm{iv})\end{array}$

CBSE Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 13 - 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 13 - MCQExams.com

0:0:2

Practice Class 12 Engineering Chemistry Quiz Questions and Answers

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