d and f Block Elements — Page 25 | JEE Chemistry

Q241

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Aluminium is extracted from bauxite by the electrolysis of molten mixture of Al2O3 with cryolite. Reason (R) : The oxidation state of Al in cryolite is +3. In the light of the above statements, choose the most appropriate answer from the options given below :

A (A) is true but (R) is false.

B (A) is false but (R) is true.

C Both (A) and (R) are correct and (R) is the correct explanation of (A)

D Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Correct Answer

Option D

Solution

(A) Aluminium is reactive metal so Aluminium is extracted by electrolysis of Alumina with molten mixture of Cryolite (B) Cryolite, Na3AlF6 Here, Al is in +3 O.S.

So, answer is (d).

Q242

In isolation of which one of the following metals from their ores, the use of cyanide salt is not commonly involved?

A Zinc

B Gold

C Silver

D Copper

Correct Answer

Option D

Solution

In the extraction of Silver and Gold, NaCN is used to leach the metal.

4\text{Au(s)} +8C\overline{N} (aq)+2H_{2}O+O_{2}(g)

\to 4\left[ Au(CN)_{2}\right]^{-} (aq)+4OH^{-}(aq)

2\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-}(\mathrm{aq})+\mathrm{Zn} \rightarrow 2 \mathrm{Au}(\mathrm{s})+\left[\left(\mathrm{Zn}(\mathrm{CN})_{4}\right)\right]^{2-}(\mathrm{aq})

In case of ore containing ZnS and PbS, the depressant used is NaCN.

Q243

In the metallurgical extraction of copper, following reaction is used : FeO + SiO2

\to

FeSiO3 FeO and FeSiO3 respectively are.

A gangue and flux.

B flux and slag.

C slag and flux.

D gangue and slag.

Correct Answer

Option D

Solution

FeO + SiO2 → FeSiO3 FeO = Gangue and FeSiO3 = Slag

Q244

Given are two statements one is labelled as Assertion A and other is labelled as Reason R. Assertion A : Magnesium can reduce Al2O3 at a temperature below 1350

^\circ

C, while above 1350

^\circ

C, while above 1350

^\circ

C aluminium can reduce MgO. Reason R : The melting and boiling points of magnesium are lower than those of aluminium. n light of the above statements, choose most appropriate answer from the options given below :

A Both A and R are correct, and R is correct explanation of A.

B Both A and R are correct, but R is NOT the correct explanation of A.

C A is correct R is not correct.

D A is not correct, R is correct.

Correct Answer

Option B

Solution

Magnesium can reduce Al2O3 at a temperature below 1350°C while above 1350°C aluminium can reduce MgO because below 1350°C

\Delta

G of MgO (formation) is more negative and above 1350°C

\Delta

G of Al2O3 (formation) is more negative.

The melting and boiling point of magnesium are lower than those of aluminium but it is not the correct reason.

Q245

Given below are two statements. Statement I : During electrolytic refining, blister copper deposits precious metals. Statement II : In the process of obtaining pure copper by electrolysis method, copper blister is used to make the anode. In the light of the above statements, choose the correct from the options given below.

A Both Statement I and Statement II are true.

B Both Statement I and Statement II are false.

C Statement I is true but Statement II is false.

D Statement I is false but Statement II is true.

Correct Answer

Option A

Solution

Copper is refined using an electrolytic method.

Anodes are of impure copper and pure copper strips are taken as cathode.

Impurities from the blister copper deposit as anode mud which contains antimony, selenium, tellurium, silver, gold and platinum.

Hence both statements are true

Q246

Leaching of gold with dilute aqueous solution of NaCN in presence of oxygen gives complex [A], which on reaction with zinc forms the elemental gold and another complex [B]. [A] and [B], respectively are :

A

{[Au{(CN)_4}]^ - }

and

{[Zn{(CN)_2}{(OH)_2}]^{2 - }}

B

{[Au{(CN)_2}]^ - }

and

{[Zn{(OH)_4}]^{2 - }}

C

{[Au{(CN)_2}]^{ - }}

and

{[Zn{(CN)_4}]^{2 - }}

D

{[Au{(CN)_4}]^{2 - }}

and

{[Zn{(CN)_6}]^{4 - }}

Correct Answer

Option C

Solution

In the metallurgy of gold

4 \mathrm{Au}+8 \mathrm{CN}^{-}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2} \rightarrow 4\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-}+4 \mathrm{OH}^{-}

2\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-}+\mathrm{Zn} \rightarrow\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]^{2-}+2 \mathrm{Au}

Q247

Which of the following chemical reactions represents Hall-Heroult Process?

A Cr2O3 + 2Al

\to

Al2O3 + 2Cr

B 2Al2O3 + 3C

\to

4Al + 3CO2

C FeO + CO

\to

Fe + CO2

D 2[Au(CN)2]

_{(aq)}^ -

+ Zn(s)

\to

2Au(s) + [Zn(CN4)]2

-

Correct Answer

Option B

Solution

Hall-Herault process is used for the extraction of aluminium by electrolysis molten

\mathrm{Al}_{2} \mathrm{O}_{3}

2 \mathrm{Al}_{2} \mathrm{O}_{3}+3 \mathrm{C} \rightarrow 4 \mathrm{Al}+3 \mathrm{CO}_{2}

Q248

The compound(s) that is (are) removed as slag during the extraction of copper is : (A) CaO (B) FeO (C) Al2O3 (D) ZnO (E) NiO Choose the correct answer from the options given below:

A (C), (D) only

B (A), (B), (E) only

C (A), (B) only

D (B) only

Correct Answer

Option D

Solution

The compound(s) that are removed as a slag during the extraction of copper is :

\mathrm{FeS} \stackrel{\mathrm{O}_2 / \mathrm{SiO}_2}{\longrightarrow} \underset{\text{ slag }}{\mathrm{FeSiO}_3}+\mathrm{SO}_2

$\therefore$ Only iron oxide (FeO) formed slag during extraction of copper.

Q249

Given below are two statements. Statement I : Pig iron is obtained by heating cast iron with scrap iron. Statement II : Pig iron has a relatively lower carbon content than that of cast iron. In the light of the above statements, choose the correct answer from the options given below.

A Both Statement I and Statement II are correct.

B Both Statement I and Statement II are not correct.

C Statement I is correct but Statement II is not correct.

D Statement I is not correct but Statement II is correct.

Correct Answer

Option B

Solution

Cast iron is made by melting pig iron with scrap iron and coke using hot air blast.

Hence Statement-I is incorrect But Pig iron has relatively more carbon content Hence statement-II is incorrect

Q250

Match with : .tg .tg

List - I		List - II
(A)	Sphalerite	(I)	FeCO $_3$
(B)	Calamine	(II)	PbS
(C)	Galena	(III)	ZnCO $_3$
(D)	Siderite	(IV)	ZnS Choose the most appropriate answer from the options given below :

A (A)-(IV), (B)-(III), (C)-(II), (D)-(I)

B (A)-(IV), (B)-(I), (C)-(II), (D)-(III)

C (A)-(II), (B)-(III), (C)-(I), (D)-(IV)

D (A)-(III), (B)-(IV), (C)-(II), (D)-(I)

Correct Answer

Option A

Solution

.tg .tg List - I List -II (A) Sphalerite (IV) ZnS (B) Calamine (III) ZnCO

_3

(C) Galena (II) PbS (D) Siderite (I) FeCO

_3

Hence, the most appropriate option is (A).