$$NaCN$$ is sometimes added in the froth floatation process as a depressant when $$ZnS$$ and $$PbS$$ minerals are expected because:

$$ZnS$$ forms soluble complex $${ Na }_{ 2 }\left[ Zn{ \left( CN \right) }_{ 4 } \right] $$ while $$PbS$$ form froth

$$Pb{ \left( CN \right) }_{ 2 }$$ is precipitated while no effect on $$ZnS$$ form froth

$$PbS$$ forms soluble complex $${ Na }_{ 2 }\left[ Zn{ \left( Pb \right) }_{ 4 } \right] $$ while $$ZnS$$ form froth

$$NaCN$$ is never added in froth floatation process

MCQ Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 7

A process employed for the concentration of sulphide ore is:

0%
froth floatation
0%
gravity separation
0%
froth separation
0%
gravity floatation

Gold does not occur in the combined form. It does not react with air or water. It is in the_______state.

0%
native
0%
combined
0%
original
0%
liquid

The process of leaching, alumina using sodium carbonate is called _________.

0%
bayer's process
0%
decomposition
0%
cyanide process
0%
hall's process

Which of the following is an oxide ore?

0%
Malachite
0%
Haematite
0%
Chalcopyrite
0%
Zinc blende

Explanation

Hint: The ore in which the desired element is present in the form of its oxide is termed oxide ore.

Explanation:

Malachite is widespread copper ore. Its chemical formula is $Cu_2CO_3\left ( OH \right )_2$ . It is also known as Copper carbonate hydroxide mineral.
Haematite is an important ferric oxide of the chemical formula $Fe_2O_3$ . It is an oxide ore.
Chalcopyrite is an important copper mineral having the chemical formula $CuFeS_2$ . It is a sulphide type of copper and iron ore.
Zinc blende is important iron ore. It is otherwise known as zinc sulfide with the chemical formula $ZnS$ .

Final Answer:

Therefore, haematite is an oxide ore.

Thus, the final answer is option $B$ .

In chromite ore, the oxidation number of iron, and chromium are respectively.

0%
+3, +2
0%
+3, +6
0%
+2, +6
0%
+2, +3

Explanation

Chromite or chrome iron ore is

F e C r_{2} O_{4}

$FeCr_2O_4$ . Its actual composition is

F e O . C r_{2} O_{3}

$FeO.Cr_2O_3$ .

F e O

$FeO$ , oxidation state of

F e

$Fe$ is calculated as:

x + (- 2) = 0

$x+(-2)=0$

x = + 2

$x=+2$

Similarly, in

C r_{2} O_{3}

$Cr_2O_3$ , the oxidation state of

C r

$Cr$ is calculated as

2 \times x + (- 2) \times 3 = 0

$2\times x+(-2)\times 3=0$

2 x = + 6

$2x=+6$

x = + 3

$x=+3$

Hence, the correct option is

D

$D$

N a C N

$NaCN$ is sometimes added in the froth floatation process as a depressant when

Z n S

$ZnS$ and

P b S

$PbS$ minerals are expected because:

0%
$ZnS$ forms soluble complex ${ Na }_{ 2 }\left[ Zn{ \left( CN \right) }_{ 4 } \right]$ while $PbS$ form froth
0%
$Pb{ \left( CN \right) }_{ 2 }$ is precipitated while no effect on $ZnS$ form froth
0%
$PbS$ forms soluble complex ${ Na }_{ 2 }\left[ Zn{ \left( Pb \right) }_{ 4 } \right]$ while $ZnS$ form froth
0%
$NaCN$ is never added in froth floatation process

Explanation

N a C N

$NaCN$ is used as a depressant in the separation and concentration of

Z n S

$ZnS$ and

P b S

$PbS$ ore. Here,

N a C N

$NaCN$ acts as a depressant for

Z n S

$ZnS$ but does not prevent

P b S

$PbS$ from forming the froth.

Which of the following is the most common use of copper:

0%
roofing
0%
plumbing
0%
electrical equipment
0%
construction

Explanation

Cupper is a d-block element, its symbol is

C u

$Cu$ a soft malleable and ductile metal and very high thermal and electrical conductivity. A freshly cut surface of pure copper has a reddish bright color. Due to its good conductivity of electricity, it is used in electrical equipment.

Auto-reduction is employed in the metallurgy of :

0%
$Hg$
0%
$Al$
0%
$Ti$
0%
$Zn$

Explanation

Autoreduction is employed in the metallurgy of less electropositive metals such as

H g, P b

$Hg, Pb$ and

C u

$Cu$ e.g.,

H g S + O_{2} ⟶ H g O

$Hg S + O_2 \longrightarrow HgO$

H g O △ - \to H g + O_{2}

$HgO \xrightarrow {\triangle} Hg + O_2$

Thermal decomposition of ammonium dichromate gives:

0%
${ N }_{ 2 },{ H }_{ 2 }O$ and ${ Cr }_{ 2 }{ O }_{ 3 }$
0%
${ N }_{ 2 },N{ H }_{ 3 }$ and $CrO$
0%
${ \left( N{ H }_{ 4 } \right) }_{ 2 }Cr{ O }_{ 4 }$ and ${ H }_{ 2 }O$
0%
${ N }_{ 2 },{ H }_{ 2 }O$ and $Cr{ O }_{ 3 }$
0%
${ N }_{ 2 },{ H }_{ 2 }O$ and $CrO$

Explanation

Thermal decomposition of ammonium dichromate

{(N H_{4})}_{2} {C r}_{2} O_{7}

${ \left( N{ H }_{ 4 } \right) }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 }$ on heating gives

N_{2}, {C r}_{2} O_{3}

${ N }_{ 2 },{ Cr }_{ 2 }{ O }_{ 3 }$ and

H_{2} O

${ H }_{ 2 }O$ as follows:

{(N H_{4})}_{2} {C r}_{2} O_{7} Δ - -------- \to N_{2} + {C r}_{2} O_{3} + 4 H_{2} O

${ \left( N{ H }_{ 4 } \right) }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 }\xrightarrow [ ]{ \quad \quad \Delta \quad \quad } { N }_{ 2 }+{ Cr }_{ 2 }{ O }_{ 3 }+4{ H }_{ 2 }O$

Bessemer converter is used for the preparation of:

0%
Steel
0%
Wrought iron
0%
Pig iron
0%
Cast iron

Explanation

Bessemer converter is used for the preparation of steel. This process is based on the fact that the impurities present in the pig iron are completely oxidised to form almost pure wrought iron. It is then mixed with known amount of spiegeleisen (an alloy of Fe, Mn and C) to obtain steel.

S i + O_{2} \to S i O_{2}

$Si+ O_2 \rightarrow SiO_2$

2 M n + O_{2} \to 2 M n O

$2Mn+O_2\rightarrow 2MnO$

4 P + 5 O_{2} \to 2 P_{2} O_{5}

$4P + 5O_2 \rightarrow 2P_2O_5$

M n O + S i O_{2} \to M n S i O_{3} s l a g

$MnO + SiO_2 \rightarrow \underset{slag}{MnSiO_3}$

P_{2} O_{5} + 3 C a O \to C a_{3} (P O_{4})_{2} s l a g

$P_2O_5+ 3CaO \rightarrow \underset{slag}{Ca_3(PO_4)_2}$

C a O + S i O_{2} \to C a S i O_{3}

$CaO + SiO_2 \rightarrow CaSiO_3$

C u_{2} O + F e S \to C u_{2} S + F e O

$Cu_2O + FeS \rightarrow Cu_2S + FeO$

F e O + S i O_{2} \to F e S i O_{3} s l a g

$FeO + SiO_2 \rightarrow \underset{slag}{FeSiO_3}$

Which of the following metal is used with copper in the formation of alloy brass?

0%
Zinc
0%
Iron
0%
carbon
0%
silver

The purest zinc is made by.

0%
Electrolytic refining
0%
Zone refining
0%
The van-Arkel method
0%
Mond process

Which metallurgy involves leaching?

0%
$Au$
0%
$Ag$
0%
Both (a) and (b)
0%
None of these

Number of electrons involved in the electrodeposition of

63.5 g

$63.5\ g$ of

C u

$Cu$ from a solution of

C u S O_{4}

$CuSO_{4}$ is?

0%
$6.022\times 10^{23}$
0%
$3.011\times 10^{23}$
0%
$12.044\times 10^{23}$
0%
$6.022\times 10^{22}$

Explanation

$\begin{array}{l} 63.5gm\, of\, Cu=1mol\, of\, Cu. \\ No.\, of\, equivalent=No.\, of\, moles\times valency\, factor \\ =1\times 2=2 \\ 1\, mole\, of\, electron\, \, will\, deposite\, 1\, equivalent. \\ Number\, of\, electron=2\times 6.022\times { 10^{ 23 } } \\ =12.044\times { 10^{ 23 } }. \\ Hence,\, option\, C\, is\, the\, correct\, answer. \end{array}$

The ore that is concentrated by froth floatation process is:

0%
Cinnabar
0%
Dawdle
0%
Malachite
0%
Zincite

Explanation

Froth floatation process is used for the concentration of sulphide ores only.

Cinnabar,

$HgS$ is a sulphide ore. Hence, it is concentrated by froth floatation method.

Which method is used to get very pure germanium used in semiconductor ?

0%
Vapour-phase refining
0%
Electrolysis
0%
Liquation
0%
Zone-refining

Usually refractory metals are used in construction of furances because:

0%
they are chemically inert
0%
their melting point is high
0%
they can withstand high temperature
0%
none of the above

A solution is a homogeneous mixture of two or more substances. Which of the following is a solution?

0%
Milk
0%
Smoke
0%
Brass
0%
Face Cream

Explanation

Alloys are the homogeneous mixture of metals or metals and non metals. Brass is an alloy of copper and zinc
Brass

$Cu-70$ %

$Zn-30$ %
Alloys are solid-solid solution

Due to its high heat exchange rate, copper is used in:

0%
dispenser
0%
refrigerator
0%
AC
0%
all of them

Explanation

Copper is a very good conductor of heat and electricity. Due to high heat exchange capacity of copper

$Cu$ it has the wide range of uses in electrical types of equipment as a dispenser, refrigerator air conditioners, and electrical wires.

The transition element used for making calorimeters is:

0%
$Cr$
0%
$Ni$
0%
$Zn$
0%
$Cu$

Among

$K, Mg, Au$ and

$Cu$ , the one which is extracted by heating its ore in air is:

0%
$K$
0%
$Mg$
0%
$Au$
0%
$Cu$

Explanation

Among

$K, Mg, Au$ and

$Cu$ , the one which is extracted by heating its ore in air is

$Cu$ .
In a reverberatory furnance, the concentrated ore is roasted in presence of limited supply of air. A mixture of

$\displaystyle FeS$ and

$\displaystyle Cu_2S$ is formed.

$\displaystyle 2CuFeS_2+O_2 \rightarrow Cu_2S + 2FeS+SO_2$

$\displaystyle Cu_2S$ is then converted to

$\displaystyle Cu$ by auto reduction method.

$\displaystyle 2Cu_2S+3O_2 \rightarrow 2Cu_2O+2SO_2$

$\displaystyle Cu_2S+2Cu_2O \rightarrow 6Cu+SO_2$

Stainless steel contains:

0%
$Fe,Ni,Cr$
0%
$Fe,Ni,Sn$
0%
$Fe,C,S$
0%
$Fe,P,Cr$

Purification of aluminium by electrolytic refining is called:

0%
Serpeck's process
0%
Hoope's process
0%
Hall's process
0%
Baeyer's process

Considering Ellingham diagram, which of the following metals can be used to reduced alumina?

0%
$Mg$
0%
$Fe$
0%
$Cu$
0%
$Zn$

Explanation

Considering Ellingham diagram,

$Mg$ metal can be used to reduced alumina.
The negative free energy change for the formation of

$\displaystyle MgO$ from

$Mg$ is greater than that for the formation of

$\displaystyle Al_2O_3$ from

$Al$ .

Hence,

$Mg$ has greater tendency to undergo oxidation than

$Al$ . Hence,

$Mg$ is oxidised and

$Al_2O_3$ is reduced to

$Al$ .

Note: More negative the value of

$\displaystyle \Delta G$ , the greater is the tendency, of the element to combine with oxygen.

Bauxite, the ore of aluminium, is purified by which process?

0%
Hoope's process
0%
Hall's process
0%
Mond's process
0%
Liquation process

Explanation

Bauxite, the ore of aluminium, is purified by either Hall's process or Baeyer's process or Serperck's process. Mond's process is used for refining nickel. Liquation process is used for refining

$Bi,\ Sn,\ Pb$ and

$Hg$ .

The ore that can be concentrated by magnetic separation method is:

0%
bauxite $(Al_{2}O_{3}.xH_{2}O)$
0%
pyrolusite $(MnO_{2})$
0%
cuprite $(Cu_{2}O)$
0%
zincite $(ZnO)$

Explanation

The ore that can be concentrated by magnetic separation method is pyrolusite

$(MnO_{2})$ .
In this method, the ferromagnetic and non-magnetic particles in the ore are separated by an electromagnetic separator.

The most common ore of iron is ___________.

0%
calamine
0%
hematite
0%
zinc blende
0%
copper pyrite

Explanation

Calamine is an ore of zinc and hematite is an ore of iron.

Option

$B$ is correct.

In the silver plating of copper, K[Ag

$(CN)_2$ ] is used instead of Ag

$NO_3$ . The reason is:

0%
a thin layer of Ag is formed om Cu
0%
more voltage is required
0%
$Ag^+$ ions are completely removed from solution
0%
less availability of $Ag^+$ ions, as Cu cannot displace Ag from $[Ag(CN)_2]^-$ ion

Which of the following is the ore of

$Cu$ ?

0%
Ciderite
0%
Magnetite
0%
Calamine
0%
Malachite

Explanation

Ore of copper is malachite

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

Which of the following factors is of no significance for roasting sulphide ores to the oxides and not subjecting the sulphide ores to carbon reduction directly?

0%
Metal sulphides are thermodynamically more stable than $CS_2$
0%
$CO_2$ is thermodynamically more stable than $CS_2$
0%
Metal sulphides are less stable than the corresponding oxides
0%
$CO_2$ is more volatile than $CS_2$

Explanation

The reduction of metal sulfides by the carbon reduction process is not spontaneous as the change in Gibb's free energy (

$\triangle G$ ) for such a process is positive.

The reduction of metal oxides by the carbon reduction process is spontaneous as

$\triangle G$ for such a process is negative.

Thus

$CO_2$ is more stable than

$CS_2$ and the metal sulfides are more stable than the corresponding oxides.

Hence, the factor listed in option

$C$ is of no significance.

Which of the following is a non-metallic mineral?

0%
Bauxite
0%
Magnesium
0%
Gypsum
0%
Manganese

Identify the metal

$M$ whose extraction is based on the following reactions:

$MS+2{ O }_{ 2 }\longrightarrow M{ SO }_{ 4 }$

$2MS+3{ O }_{ 2 }\longrightarrow 2MO+2S{ O }_{ 2 }$

$MS+2MO\longrightarrow 3M+S{ O }_{ 2 }$

$MS+M{ SO }_{ 4 }\longrightarrow 2M+2S{ O }_{ 2 }\quad$

0%
magnesium
0%
aluminium
0%
lead
0%
tin

Match the columns.

List I	List II
A. Bauxite	$1.$ Lead
B. Haematite	$2.$ Thorium
C. Galena	$3.$ Aluminium
D. Monazite	$4.$ Iron

0%
$A - 3, B - 1, C - 4, D - 2$
0%
$A - 4, B - 2, C - 1, D - 3$
0%
$A - 3, B - 4, C - 1, D - 2$
0%
$A - 2, B - 4, C - 3, D - 1$

Explanation

Solution:-

(A) Bauxite

$\rightarrow \left( {Al}_{2}{O}_{3}.2{H}_{2}O \right)$ It is an ore of Aluminium containing

$15-20 \%$ aluminium.

$\rightarrow$ (3) Aluminium

(B) Haematite

$\rightarrow \left({Fe}_{2}{O}_{3} \right)$ A reddish-black mineral consisting of ferric oxide. It is an important ore of iron.

$\rightarrow$ (4) Iron

$\rightarrow \left( PbS \right)$ Galena, also called lead glance, is the natural mineral form of lead(II) sulfide.

$\rightarrow$ (1) Lead

(D) Monazite

$\rightarrow$ Monazite is an important ore for thorium, lanthanum, and cerium. It is radioactive due to the presence of thorium.

$\rightarrow$ (2) Thorium

Which of the following statements is correct about the role of collectors added during forth floatation process?

0%
Collectors enhance the non-wettability of ore particles
0%
Collectors enhance the wettability of gangue particles
0%
Collectors help in separating two sulphide ores present in the mixture
0%
Collectors help ore particles to settle down below the froth

An excess of molybdenum in grassy areas results in poor growth of animals because it blocks the utilization of:

0%
oxygen
0%
iron
0%
copper
0%
selenium

Which of the following is a halide ore?

0%
Cassiterite
0%
Anglesite
0%
Siderite
0%
Carnallite

Explanation

Carnallite is

$KCl.MgCl_2.6H_2O$

Sulphide ore of zinc/copper is concentrated by:

0%
forth floatation
0%
electromagnetic process
0%
gravity process
0%
distillation

An ore of tin containing,

$FeCrO_4$ is concentrated by:

0%
gravity separation
0%
magnetic separation
0%
forth floatation
0%
leaching

Explanation

Magnetic separation based on differences in magnetic properties of the ore components.
If either the ore or the gangue is attracted towards the magnetic field, then the separation is carried out by this method.
For example, iron ores are attracted towards the magnet, hence, non–magnetic impurities can be separated from them using magnetic separation.
Here, $FeCrO_4$ being an iron ore can be separated by magnetic separation.

Forth 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 ganaue and ore particles in frothing agent and water
0%
difference in reactivity of gangue and ore particles with water and frothing agent.

Gold paint is made from:

0%
copper
0%
platinum
0%
gold
0%
antimony

Lithopone is a mixture of zinc sulphide and barium sulphate. It is used as a paint instead of white lead, because it:

0%
does not become black in air
0%
is more white
0%
is more bright
0%
does not become yellow in air

Explanation

Lithopone is a mixture of zinc sulphide and

${ BaSO }_{ 4 }$ . It is used as paint instead of white lead, because of doesn't become black in air.

For which of the following ores forth floatation method is used for concentration?

0%
Haematite
0%
Zinc blende
0%
Magnetite
0%
Carnallite

Explanation

Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water
Among the given options Zinc blend ( $ZnS$ ) is the only sulphide ore and hence Froth floatation process is used for its concentration.
Hence, option B is the right answer.

Study the Ellingham diagram for the formation of some oxides and answer the following question.
At the point of intersection of

$Al_2O_3$ and

$MgO$ curves (A),

$\triangle G^0$ becomes zero for the reaction,

$\frac{2}{3}Al_2O_3+2Mg \rightarrow + \frac{4}{3} Al$

Below this point, magnesium can reduce alumina. Although thermodynamically feasible, Al is not used for reduction of

$MgO$ because:

0%
temperature required is very high
0%
the yields of metal is very low
0%
the value of $\triangle G^0$ becomes positive
0%
magnesium is not used as reducing agent for any reaction

Explanation

Temperatures above the point of intersection of

$Al_2O_3$ and

$MgO$ curves, Al can reduce MgO. But the temperature required would be so high that the process will be uneconomic and technology is difficult.

Which of the following is not a method of refining of metals?

0%
Electrolysis
0%
Smelting
0%
Poling
0%
Liquation

From the Ellingham graph between Gibb's energy and temperature, out of

$C$ and

$CO$ which is a better reducing agent for

$ZnO$ ?

0%
Carbon
0%
$CO$
0%
Both of these
0%
None of these

Explanation

$C$ is a better reducing agent. It reduces at 1180K but when comes to

$CO$ , it reduces at 1270 K.

During the formation of the slag by the reaction of flux and impurities which of the following is an example of acidic and basic flux?
(i)

$FeO + SiO_2\rightarrow FeSiO_3$
(ii)

$SiO_2+MgO\rightarrow MgO\rightarrow MgSiO_3$

0%
(i) $SiO_2$ - Acidic flux (ii) $MgO$ - Basic flux
0%
(i) $SiO_2$ - Basic flux (ii) $MgO$ - Acidic flux
0%
(i) $SiO_2$ - Basic flux (ii) $MgO$ - Basic flux
0%
(i) $SiO_2$ - Acidic flux (ii) $MgO$ - Acidic flux

Explanation

$FeO+Si{ O }_{ 2 }\longrightarrow FeSi{ O }_{ 3 }$

In it

$Si{ O }_{ 2 }$ is acidic flux and used to remove basic impurities.

ii)

$Si{ O }_{ 2 }+MgO\longrightarrow MgSi{ O }_{ 3 }$

$Si{ O }_{ 2 }$ is acidic impurity.

$MgO$ is basic flux used to remove

$MgSi{ O }_{ 3 }$ as slag.

The reaction

$Cr_2O_3+2Al\rightarrow Al_2O_3+2Cr(\triangle G^0 = -421 kJ)$ is thermodynamically feasible due to -ve value of

$\triangle G.$ Why does this reaction not take place at room temperature?

0%
Certain amount of activation energy is essential for thermodynamically feasible reactions also.
0%
Due to high melting point of chromium oxide the reaction does not take place.
0%
Overall value of $\triangle G$ for the net reaction becomes positive.
0%
Molecules of $Cr_2O_3$ and Al are not oriented properly.

Explanation

In thermite process,

${ Cr }_{ 2 }{ O }_{ 3 }+2Al\longrightarrow { Al }_{ 2 }{ O }_{ 3 }+2Cr+Q$

It is an exothermic and spontaneous process. It requires more activation energy. At room temperature it does not takes place as activation energy is less.

Sulphides ores are converted to oxides before reduction. This is explained on the basis of which of the following?

0%
Sulphides cannot be reduced easily while oxides can be reduced easily.
0%
Sulphides decompose on reduction hence they are fixed converted to oxides.
0%
Sulphide ores have higher melting points than oxides.
0%
Oxides are more stable than sulphides hence easy to reduce.

Fill in the blanks with the correct choice.
The undesired impurities present in the ores are called ___(i)___. To remove the volatile impurities from the ore, the ___(ii)___ process is carried out. Flux combines with non-fusible impurities to form ___(iii)___.

$CaO$ acts as a ___(iv)___ flux.

0%
(i) - gangue, (ii) -roasting, (iii) - slag, (iv) -acidic
0%
(i) - gangue, (ii) - calcination, (iii) - slag, (iv) - basic
0%
(i) - anode mud, (ii) - leaching, (iii) - matrix, (iv) -acidic
0%
(i) - gangue, (ii) -roasting, (iii) - solution, (iv) -acidic

Explanation

$(i)$ The undesired impurities present in the ores are called gangue.

$(ii)$ To remove the volatile impurities from the ore calcination is carried out.

$(iii)$ Flux combines with non-fusible impurities to form slag.

$(iv)$

$CaO$ acts as basic flux.

Extraction of chlorine from brine is based on:

0%
reduction
0%
displacement
0%
oxidation
0%
evaporation

Explanation

In the extraction of chlorine by electrolysis of brine, oxidation of

${ Cl }^{ - }$ ion to chlorine gas occurs.

$2{ Cl }^{ - }+2{ H }_{ 2 }O\rightarrow 2{ OH }^{ - }+{ H }_{ 2 }+{ Cl }_{ 2 }$

CBSE Questions for Class 12 Engineering Chemistry General Principles And Processes Of Isolation Of Elements Quiz 7 - 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 7 - MCQExams.com

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Practice Class 12 Engineering Chemistry Quiz Questions and Answers

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