is a method in which impurities sink to the bottom

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

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 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

MCQ Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 4

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?

0%
$Al_2O_3$
0%
$Cu_2O$
0%
$MgO$
0%
$ZnO$

Explanation

C u_{2} O

$Cu_2O$ is least stable among all so the oxidation reaction of carbon to carbon monoxide may be used to reduce this at the lowest temperature.

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

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

Explanation

As both oxides met at

1000^{o} C

$1000^oC$ in graph so at this temperature both C and Zn have equal affinity for oxygen.

Froth flotation process used for the concentration of sulfide ore _______________.

0%
is based on the difference in wettability of different minerals
0%
uses sodium ethly xanthate, $C_{2}H_{5}OCS_{2}Na$ as collector
0%
uses $NaCN$ as depressant in the mixture of ZnS and PbS when ZnS forms soluble complex and Pbs forms froth
0%
all of the above statements are correct

Explanation

(A) Froth floatation process used for the concentration of sulphide ore is based on the difference in wettability of different minerals. The metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water.
(B) Froth floatation process used for the concentration of sulphide ore uses sodium ethyl xanthate,

C_{2} H_{5} O C S_{2} N a

$C_{2}H_{5}OCS_{2}Na$ as collector. Other examples of collector include ethyl xanthate and potassium ethyl xanthate. They attach themselves to the grains of mineral by polar groups so that minerals become water repellent and pass on into the froth.
(C) Froth floatation process used for the concentration of sulphide ore uses NaCN as depressant in the mixture of ZnS and PbS when ZnS forms soluble complex and Pbs forms froth. Other depressant used is KCN.
Depressants depress the floating property of one of the components of the ore and help in the separation of different minerals present in the same ore.
Thus, all of the above statements are correct.

Select the correct statement.

0%
During the decomposition of an oxide into oxygen and metal vapour, entropy increases.
0%
Decomposition of an oxide is an endothermic change.
0%
To make $\triangle G^{0}$ negative, temperature should be high enough so that $T$ $\triangle$ $S^{0}$ > $\triangle$ $H^{0}$ .
0%
All are correct answers.

Explanation

During the decomposition of an oxide into oxygen and metal vapour entropy increases as gas is produced in the reaction.

Decomposition of an oxide is an endothermic change. This is because it is reverse of combustion reaction and all combustion reactions are exothermic in nature.

Since both

Δ H

$\Delta H$ and

Δ S

$\Delta S$ are positive, the temperature should be high enough so that

T Δ S > Δ H

$T\Delta S >\Delta H$ ,

Thus, all are correct answers.

Aluminothermy used for the spot welding of large iron structures is based upon the fact that :

0%
As compared to iron, aluminium has greater affinity for oxygen.
0%
As compared to aluminium, iron has greater affinity for oxygen.
0%
Reaction between aluminium and oxygen is endothermic..
0%
Reaction between iron oxide and aluminium is exothermic.

Explanation

Aluminothermy used for the spot welding of large iron structures is based upon two facts
(i) As compared to iron, aluminum has greater affinity for oxygen. hence, aluminum acts are reducing agent.
(ii) Reaction between iron oxide and aluminum is exothermic. High temperature is involved in the reaction.
Aluminum reduces iron oxide to iron.

F e_{2} O_{3} + 2 A l \to 2 F e + A l_{2} O_{3}

$Fe_2O_3 + 2 Al \rightarrow 2 Fe + Al_2O_3$

The function of adding cryolite in the electrolyte reduction of alumina by Hall-Heroult process is to :

0%
dissolve alumina
0%
lower melting point of alumina
0%
lower the fuel bill
0%
increase the electrical conductivity of alumina

The advantage(s) of using carbon to reduced a number of oxides and other compounds are :

0%
easy availability of coke.
0%
low cost of carbon.
0%
tendency of carbon to show catenation..
0%
presence of carbon lowers the melting point of the oxide.

The extraction of metals from oxide ores involve :

0%
reduction with carbon
0%
reduction with aluminium
0%
electrolyte reduction
0%
reduction with $CO$

Froth floatation:

0%
is a physical method of separating mineral from the gangue
0%
is a method to concentrate the ore depending on the difference in wetability of gangue and the ore
0%
is used for the sulphide ores
0%
is a method in which impurities sink to the bottom

The oxide of metal

R

${R}$ can be reduced by the metal

P

${P}$ and metal

R

${R}$ can reduce the oxide of metal

Q

${Q}$ . Then the decreasing order of the reactivity of metal

P

${P}$ ,

Q

${Q}$ and

R

${R}$ with oxygen is:

0%
$P>Q>R$
0%
$P>R>Q$
0%
$R>P>Q$
0%
$Q>P>R$

Explanation

Correct Answer: Option

B

$B$ .

Explanation:

A more reactive metal can reduce the oxide of a less reactive metal.

Since $P$ can reduce the oxide of $R$ , $P$ is more reactive than $R$ .
Since $R$ can reduce the oxide of $Q$ , $R$ is more reactive than $Q$ .

So, the order of reactivity will be

P > R > Q

$P>R>Q$

Ultra pure silicon is prepared by reduction of

S i O_{2}

$SiO_2$ with carbon.

0%
True
0%
False

Method used for obtained highly pure silicon, used as a semiconductor material, is

0%
oxidation
0%
electrochemical
0%
crystallization
0%
zone refining

NaCN is sometimes added in the froth flotation process as a depressant when ZnS and PbS minerals are expected because __________.

0%
$Pb(CN)_2$ is precipitated while no effect on ZnS.
0%
ZnS forms soluble complex $Na_2[Zn(CN)_4]$ while PbS forms froth
0%
PbS forms soluble complex $Na_2[Pb(CN)_4]$ while ZnS forms froth
0%
NaCN is never added in froth flotation process

Explanation

When the minerals are expected to contain

P b S

$PbS$ and

Z n S

$ZnS$ , suitable depressants such as

N a C N

$NaCN$ are added.
The added

N a C N

$NaCN$ , selectively prevents

Z n S

$ZnS$ from coming to the froth by forming soluble complex

N a_{2} [Z n (C N)_{4}]

$Na_2[Zn(CN)_4]$ and

P b S

$PbS$ is removed along with the froth.

Oxides of the various metals are converted into metal by heating but not in :

0%
$Ag_2O$
0%
CuO
0%
HgO
0%
all are correct

Explanation

Oxides of various metal oxides are converted into metals on heating but CuO (copper oxide) does not not converted into metal on heating but by reaction with Cu2S.

CuO + Heat

\to

$\rightarrow$ no reaction

So, answer is B.

Siderite is an ore of:

0%
$Cu$
0%
$Al$
0%
$Ag$
0%
$Fe$

Explanation

Siderite is a mineral composed of iron (II) carbonate (

F e C O_{3}

$FeCO_3$ ).

Option D is correct.

Which one of the following is the chief ore of copper?

0%
Galina
0%
Copper pyrite
0%
Sphalerite
0%
Siderite

Explanation

The principle ore of copper is copper pyrite (

C u F e S_{2}

$CuFeS_2$ ) and copper is extracted from this ore.

Option B is correct.

Identify the ore not containing iron.

0%
Limonite
0%
Siderite
0%
Carnelite
0%
Chalcopyrites

Explanation

Limonite,

F e_{2} O_{3} .3 H_{2} O

$Fe_2O_3.3H_2O$ and Silderite,

F e C O_{3}

$FeCO_3$ are iron ore.

Carnallite is an evaporite mineral, a hydrated potassium magnesium chloride with formula

K M g C l_{3} .6 H_{2} O

$KMgCl_3.6H_2O$ .

Chalcopyrite is the most important and major source of copper metal. It is widely spread copper–iron sulphide mineral with chemical formula,

C u F e S_{2}

$CuFeS_2$ .

Thus, Carnelite and chalcopyrite are not the ore of iron.

Hence, option C and D are correct.

Select correct statement(s) about differentiation floatation.

0%
It is used to concentrate mixture of sulphides at different stages
0%
Zinc sulphate is used to depress zinc sulphide and PbS forms froth
0%
Copper sulphate is used to active depressed lead sulphide and $O_2$ is blown to make froth
0%
All of the above are correct statements

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

Hall and Heroult's process:

2 A l_{2} O_{3} + 3 C \to 4 A l + 3 O_{2}

$2Al_2O_3 + 3C \rightarrow 4Al + 3O_2$

Cathode :

A l^{3 +} (m e l t) + 3 e^{-} \to A l (l)

$Al^{3+} (melt) + 3e^- \rightarrow Al(l)$

Anode :

C (s) + O^{2 -} (g) (m e l t) \to C O (g) + 2 e^{-}

$C(s) + O^{2-}(g) (melt) \rightarrow CO(g) + 2e^-$

C (s) + 2 O^{2 -} (g) (m e l t) \to C O_{2} (g) + 4 e^{-}

$C(s) + 2O^{2-}(g) (melt) \rightarrow CO_2 (g) + 4e^-$

The electrolysis of alumina by Hall and Heroult's process is carried by using a fused mixture of alumina (

A l_{2} O_{3}

$Al_2O_3$ ) and cryolite (

N a_{3} A l F_{6}

$Na_3AlF_6$ , sodium hexafluoroaluminate) along with minor quantities of aluminum fluoride (

A l F_{3}

$AlF_3$ ) and fluorspar (

C a F_{2}

$CaF_2$ ). The addition of cryolite and fluorspar increases the electrical conductivity of alumina and lowers the fusion temperature.

In electrolysis of

A l_{2} O_{3}

$Al_2O_3$ by Hall-Heroult process, _____________.

0%
Cryolite $Na_3[AlF_6]$ lowers the m.p. of $Al_2O_3$ and increases its electrical conductivity
0%
Al is obtained at cathode and probably $CO_2$ at anode
0%
Both (a) and (b) are correct
0%
None of the above

Selection of temperature to carry out a reduction process depends so as to make :

0%
$\Delta G$ negative
0%
$\Delta G$ positive
0%
$\Delta H$ negative
0%
$\Delta H$ positive

Explanation

When the fre energy change

Δ G

$\Delta G$ has a negative value, the process becomes spontaneous. Hence, the selection of temperature to carry out a reduction process depends so as to make

Δ G

$\Delta G$ negative.

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?

0%
reaction proceeds in forward
0%
reaction proceeds in backward
0%
no effects
0%
none of these

Explanation

Forward reaction is endothermic so that formation of cementite (

$Fe_3C$ ) is favoured at high temperatures and as we increase temperature, reaction will go forward.

When steel containing

$Fe_3C$ is cooled slowly, equilibrium is displaced in left hand side and the carbon separates. If the steel is cooled rapidly, equilibrium is not attained and the carbon remains in the form of

$Fe_3C$ .

The reduction of an oxide by aluminium is called __________.

0%
Ellingham process
0%
Goldschmidts aluminothermite process
0%
Krolls process
0%
Van Arkel process

Explanation

The reduction of oxide by aluminum is called Goldschmidt's aluminothermite process.

Aluminium is a strong reducing agent. Due to its strong affinity for oxygen, it can reduce certain metal oxides such as

$Fe_2O_3$ and

$Cr_2O_3$ to corresponding metals.

Option B is correct.

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

0%
Iron from haematite
0%
Aluminium from bauxite
0%
Mercury from cinnabar
0%
Zinc from zinc blende

Explanation

In the isolation of Mercury from cinnabar, no reducing agent is required. Mercury is obtained by the self-reduction method.

$HgS +O_2 \xrightarrow {\Delta} HgO + SO_2$

$HgO + HgS \rightarrow Hg +SO_2$

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?

0%
$ZnS$
0%
$HgS$
0%
$CdS$
0%
None of these

Explanation

$\Delta G\ =\ -n{ E }^{ o }F\\$

$\text{For the reduction to be favourable, } \Delta G \text { must be -ve. So,} \ { E }^{ o } \text{ should be positive}$ .

The highest positive value will be the most favourable to reduce to metal from the sulphide.

Purification of alumina takes place by _________________.

0%
Bosch process
0%
Hall's process
0%
Hoope's process
0%
Quartation process

Thermite is a mixture of iron oxide and :

0%
Aluminium powder
0%
Zinc powder
0%
Potassium metal
0%
Sodium metal

Explanation

Thermite is a mixture of iron oxide and aluminium powder.
It is used in alumonithermy or thermite process,
Aluminium reduces certain

$Fe_2O_3$ Fe metal.

The method of zone refining of metals is based on the principle of:

0%
greater noble character of the solid metal than that of the impurity
0%
greater solubility of the impurity in the molten state than in the solid
0%
greater mobility of the pure metal than that of impurity
0%
higher melting point of the impurity than that of the pure metal

Most abundant metal in earth crust is___________.

0%
Al
0%
O
0%
Fe
0%
Si

Froth flotation is a process of _____________.

0%
oxidation
0%
reduction
0%
refining
0%
concentration

Explanation

Froth flotation is a process of concentration. Froth floatation process is suitable for sulphide ores It is based on the difference in wetting properties of the ore and gangue with water and oil. This method is used for the concentration of

$FeCr_2O_4$ .

The methods chiefly used for the extraction of lead and tin from their ores are respectively _________________.

0%
self reduction and carbon reduction
0%
self reduction and electrolytic reduction
0%
carbon reduction and self reduction
0%
cyanide process and carbon reduction

Explanation

The methods chiefly used for the extraction of lead and tin from their ores are respectively self reduction and carbon reduction. Self reduction for lead is as follows.

$2PbS+3O_2 \rightarrow 2PbO+2SO_2 \uparrow$

$PbS+2O_2 \rightarrow PbSO_4$

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

$PbSO_4+PbS \rightarrow 2Pb+2SO_2 \uparrow$
Carbon reduction for tin is as follows.

$SnO_2+2C \rightarrow Sn+2CO \uparrow$

Cryolite,

$Na_3AlF_6$ is added to

$Al_2O_3$ in Hall-Heroult process to ____ m.p. and to ___________ electrical conductivity.

0%
higher, increase
0%
higher, decrease
0%
lower, increase
0%
lower, decrease

Explanation

In the Hall–Héroult process alumina,

$Al_2O_3$ , is dissolved in molten cryolite,

$Na_3AlF_6$ to lower its melting point for easier electrolysis. It also increases the conductivity of the solution.

CO is toxic because it forms complex with _________ in the blood.

0%
carbohydrate
0%
protein
0%
haemoglobin
0%
none of these

Which of the following metals are found in native state?

Ag, Pt, C, Si, N, O, Mg, Na, Pb

0%
Ag, Pt, C, N, O
0%
Ag, Pt, Mg
0%
Ag, Pt, Pb, Mg
0%
Ag, Pt

Which will not give metal on heating ?

0%
$Ag_2CO_3$
0%
$ZnCO_3$
0%
$HgO$
0%
$CuO$

Explanation

$Ag_2CO_3(s)\rightarrow 2Ag(s) + CO_2(g) + O_2(g)$ on heating gives Ag(metal).

$ZnCO_3(s)\rightarrow ZnO(s) + CO_2(g)$ on heating do not give metal it gives ZnO(zinc oxide).

$2HgO(heat)\rightarrow 2 Hg + O_2$ on heating gives Hg(metal).

D) CuO when heated in presence of sulfuric acid it also gives CuO again, hence CuO on heating do not give metal.

Hence option B and D are correct.

0%
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
0%
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
0%
Assertion is correct but Reason is incorrect
0%
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?

0%
A
0%
B
0%
C
0%
D

The constituents of the electrolyte for the extraction of aluminium is ____________.

0%
40 parts cryolite + 40 parts fluorspar + 20 parts pure $Al_2O_3$
0%
60 parts cryolite + 30 parts fluorspar + 10 parts pure $Al_2O_3$
0%
30 parts cryolite + 30 parts fluorspar + 40 parts pure $Al_2O_3$
0%
60 parts cryolite + 20 parts fluorspar + 20 parts pure $Al_2O_3$

Explanation

Pure alumina melts at about

$2000^oC$ and is a bad conductor of electricity. If fused cryoliteand fluorspar is added, the mixture melts at

$900^oC$ and

$Al_2O_3$ becomes a good conductorof electricity.
Electrolyte: 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.

0%
Carbon
0%
Graphite rods
0%
Iron
0%
Aluminium

Explanation

$Al_2O_3 \rightleftharpoons 2Al^{3+} \ +\ 3O^{2-}$

At cathode :

$2Al^{3+} + 6e^- \longrightarrow 2Al$

At anode :

$3O^{2-} \longrightarrow 3O_2 +\ 6e^-$
Electrolysis of Molten mixture

Cathode : Carbon
Anode : Graphite rods
Electrolyte : 60 parts cryolite + 20 parts fluorspar + 20 parts pure

$Al_2O_3$
Temperature : 900

$^o$ C.

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.

0%
Both Assertion and Reason are true and Reason is the correct explanation of Assertion
0%
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
0%
Assertion is true but Reason is false
0%
Assertion is false but Reason is true
0%
Both Assertion and Reason are false

Followed by oxygen which element is the most abundant in human body?

0%
C
0%
H
0%
Ca
0%
P

$NaCN$ is sometimes added in the forth flotation process as a depressant when

$ZnS$ and

$PbS$ minerals are expected because :

0%
$Pb(CN)_2$ is precipitated while no effect as $ZnS$
0%
$ZnS$ forms soluble complex $Na_2[Zn(CN)_4]$ while $PbS$ forms froth
0%
$PbS$ forms soluble complex $Na_2[Pb(CN)_4]$ while $ZnS$ forms froth
0%
$NaCN$ is never added in froth flotation process

Explanation

When the minerals are expected to contain

$PbS$ and

$ZnS$ , suitable depressants such as

$NaCN$ are added.
The added

$NaCN$ , selectively prevents

$ZnS$ from coming to the froth by forming soluble complex

$Na_2[Zn(CN)_4]$ and

$PbS$ is removed along with the froth.

A thermite mixture contains iron

$[III]$ oxide and aluminium, in which ______ is in a higher ratio in the mixture.

0%
aluminium
0%
iron $[III]$ oxide
0%
both are equal
0%
none of these

Explanation

A termite mixture contain aluminium and iron oxide powder together in the ratio

$27:80$ . So, the iron oxide is higher in the ratio.

Copper is an __________ resource.

0%
Exhaustible
0%
Non-exhaustible
0%
Potential
0%
National

The conversion of aluminium hydroxide to pure alumina is carried out by:

0%
addition of $Al(OH)_3$ crystals
0%
thermal decomposition
0%
precipitation
0%
none of these

Explanation

By thermal decomposition as:

$2NaAlO_2 + CO_2 + 3H_2O \rightarrow 2Al(OH)_3 \downarrow + Na_2CO_3$

$2Al(OH)_3 \xrightarrow{1000^o C} Al_2O_3 + 3H_2O$

In zone-refining method, the molten zone:

0%
consists of impurities only
0%
contains more impurity than the original metal
0%
contains the purified metal only
0%
moves to either side

Aluminium is utilized in cooking utensils since it is :

0%
Good conductor of electricity
0%
Bright in appearance
0%
Good conductor of heat
0%
Tensile

In the froth floatation process, for the beneficiation of ores, the ore particles float because ______________.

0%
they are light
0%
their surface is not easily wetted by water
0%
they bear electrostatic charge
0%
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 __________ .

0%
good conductor of heat
0%
unaffected by food acids
0%
light
0%
bright

Aluminium powder a constituent of paints, prevents:

0%
conduction of electric current
0%
formation of rust
0%
heat radiation
0%
heat generation

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

duralumin is an alloy made up of aluminium, magnesium, manganese and copper. It is used in making light tools and aircraft. Aluminium is an important constituent metal in duralumin since it is unaffected by food acids.

0:0:2

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 4 - MCQExams.com

duralumin is an alloy made up of aluminium, magnesium, manganese and copper. It is used in making light tools and aircraft. Aluminium is an important constituent metal in duralumin since it is unaffected by food acids.

0:0:2

Practice Class 12 Engineering Chemistry Quiz Questions and Answers

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