CLS Aipmt 18 19 XII Che Study Package 6 SET 2 Chapter 6

Chapter

6

General Principles and Processes of Isolation of Elements Solutions

SECTION - A

Objective Type Questions (Occurrence of metals and thermodynamical principles of metallurgy) 1.

Whic Wh ich h of of the the fo foll llow owin ing g is is not not correctly matched?

→ → → →

(1) Ch Chal alco copy pyrit rites es (2) Sm Smit iths hson onit ite e (3) Ma Magn gnet etit ite e (4) Ar Arge gent ntit ite e

CuFeS2 ZnCO3 Fe3O4 Na3AlF6

Sol. Answer (4) Argentite is Ag2S whereas Na3AlF6 is cryolite. Therefore option (4) is not correctly matched. 2.

Whic Wh ich h of the the foll follow owing ing is not not a mine minera rall of alum alumini inium um? ? (1) Bauxite

(2)

Cryolite

(3)

China clay

(4)

Malachite

Sol. Answer (4) Malachite is not a mineral of aluminium. Malachite is CuCO 3⋅Cu(OH)2, an are of copper. 3.

Whic Wh ich h of th the e foll follow owin ing g is ac acid idic ic flu flux? x? (1) CaO

(2)

MgO

(3)

SiO2 Si

(4)

All of these

Sol. Answer (3) SiO2 is an acidic oxide and used as an acidic flux to remove basic impurities in the form of slag. FeO FeO + SiO SiO 2

 →

FeSi FeSiO O2 slag

SiO2 is used in metallurgy of Cu to remove FeO. 4.

In th the e met metal allu lurg rgy y of of iro iron, n, th the e sla slag g is is (1) FeSiO3

(2)

CaCO3

(3)

CaSiO3

(4)

CaO

Sol. Answer (3) In the metallurgy of iron, the impurity is SiO 2 and it is removed as CaSiO 3 by using CaO. SiO SiO 2 + CaO CaO

 →

CaSi CaSiO O3

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5.

General Principles and Processes of Isolation of Elements

Solutions of Assignment (Set-2)

Which of the following is concentrated by magnetic separation method? (1) Pyrolusite MnO2

(2)

Chromite ore FeO⋅Cr 2O3

(3) Magnetite Fe3O4

(4)

All of these

Sol. Answer (4) Pyrolusite (MnO2), Chromite ore (FeO ⋅Cr 2O3) and Magnetite (Fe 3O4) are magnetic in nature and can be concentrated by magnetic separation method. 6.

Which of the following is commonly used to produce foam in froth floatation process? (1) Pine oil

(2)

Cresol

(3)

NaCN

(4)

Xanthate

Sol. Answer (1) In froth floatation process, pine oil is used to produce foam and work as collector/transforming agent. 7.

Serpeck’s method involves the heating of bauxite with (1) NaOH

(2)

Na2CO3

(3)

N2 + C

(4)

CaCO3

Sol. Answer (3) In Serpeck's method white bauxite is heated with coke in presence of N 2 gas. Al 2O 3 + N2 + 3C AlN + 3H2O

∆  →

 →

3CO + 2AlN

NH3 + 2Al ( OH) 3

Aluminium nitride formed in 1 st step is reacted with water to produce Al(OH) 3 which gives Al 2O3 on ignition. 8.

Sulphide ore is converted to oxide form by using the process (1) Calcination

(2)

Roasting

(3)

Smelting

(4)

Leaching

Sol. Answer (2) Sulphide ores are generally roasted in free supply of air below their melting point 2ZnS + 3O 2

9.

 →

2ZnO + 2SO 2

Which of the following has the lowest percentage of carbon in it? (1) Pig iron

(2)

Cast iron

(3)

Wrought iron

(4)

Haematite

Sol. Answer (3) Wrought iron is the purest form of iron and contains least amount of carbon (upto 0.5%). 10. Roasting of sulphide ore is generally performed in (1) Muffle furnace

(2)

Bessemer converter

(3)

Blast furnace

(4)

Reverberatory furnace

(4)

Ore of Zn

Sol. Answer (4) Roasting of sulphide ore is generally performed in reverberatory furnace. 11.

Which of the following is leached with NaCN? (1) Ore of Al

(2)

Ore of Cu

(3)

Ore of Ag

Sol. Answer (3) Ore of Ag is leached with NaCN during extraction of Ag –

→ 4 [ Au ( CN) 2 ]( aq) + 4OH (–aq) 4Au(s) + 8CN (–aq) + 2H 2O ( aq) + O 2 ( g)  Aakash Educational Services Pvt. Ltd. -

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(Ellingham diagrams) 12. Ellingham diagrams are plots of ∆G°f Vs T for the formation of (1) Oxides

(2)

Halides

(3)

Sulphides

(4)

All of these

Sol. Answer (4) Ellingham diagram is plotted graphs of formation of oxides, sulphides and halides versus temperature. 13. Which of the following statement is correct w.r.t. the following graph? 2Mg + O2 → 2MgO 0

4 Al + O → 2 Al O 2 3 2 3 3

–900

∆G° –1000 1 –

l o m J k

–1100

T

1623 K

(1) Below 1623 K, Mg reduces Al2O3

(2)

Above 1623 K, Al reduces MgO

(3) Both (1) & (2) are correct

(4)

Both (1) & (2) are wrong

Sol. Answer (3) The Ellingham diagram, the element which is present below can reduce the metal which is present above it. Below 1623 K, Mg can reduce Al 2O3 since curve of Mg lies below the curve of Al 2O3 below 1623 K but after 1623 K curve of Al 2O3 is present below the slope of Mg, so after 1623 K, Al can reduce MgO. 14. In Ellingham diagrams of ∆f G oxide formation Vs T, which of the following graphs has negative slope? (1) C → CO

(2)

Fe → Fe2O3

(3)

Mg → MgO

(4)

All of these

Sol. Answer (1) In Ellingham diagram the slope of C → CO is negative because entropy change is negative. Therefore, ∆G becomes more negative with increase in temperature. 15. Which of the following is incorrect w.r.t. metallurgy of iron in the blast furnace? (1) Zone of combustion : C + O2 → CO2

(2)

Zone of heat absorbtion : CO2 → C + O2

(3) Zone of slag formation : CaO + SiO2 → CaSiO3

(4)

Zone of reduction : Fe2O3 + 3C → 3CO + 2Fe

Sol. Answer (2) Zone of heat absorbtion : CO 2 → C + O2 In zone of heat absorption CO 2 reacts with coke to reduce the temperature C + CO2 → 2CO. (Electrochemical principles of metallurgy) 16. Which metal is used for extraction of Au and Ag and also for galvanisation of iron objects? (1) Mg

(2)

Zn

(3)

Cr

(4)

Co

Sol. Answer (2) Zinc is used as reducing agent for the extraction of Au and Ag. –

2–

Zn(s) + 2 [ Au ( CN) 2 ] aq  → 2Au(s) + [ Zn (CN) 4 ] aq

Zinc being a more electropositive metal used for the galvanization of iron to prevent it from rusting. Aakash Educational Services Pvt. Ltd. -

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17. Which of the following oxides cannot be reduced by auto or self reduction? (1) HgO

(2)

Cu2O

(3)

PbO

(4)

Al2O3

Sol. Answer (4) Less reactive metals like Cu, Hg and Pb form unstable sulphides which can undergo auto-oxidation. Al is reactive metal and does not undergo auto-oxidation. 18. Which of the following is used as reducing agent in Gold schmidt method? (1) Al

(2)

K

(3)

C

(4)

Mg

(4)

H2

Sol. Answer (1) In Gold Schmidt method, aluminium is used as reducing agent 3Mn 3O 4 + 8Al

 →

4Al 2 O 3 + 9Mn

19. Which of the following is used to reduce TiCl4 to Ti? (1) C

(2)

Al

(3)

Mg

Sol. Answer (3) In Kroll's process for titanium, Mg is used as reducing agent

TiCl 4 + 2Mg  → 2MgCl2 + Ti 20. Zinc is extracted from zinc blende by (1) Carbon reduction process

(2)

Nitrogen reduction process

(3) Oxygen reduction process

(4)

All of these

Sol. Answer (1) Zinc is extracted from zinc blende by carbon reduction process

 →

2ZnS + 3O 2 ZnO + C

 → 1673 K

2ZnO + 2SO 2 Zn + CO

21. Hall Heroult method is used for the extraction of (1) Ti

(2)

Al

(3)

Au

(4)

Zn

Sol. Answer (2) Hall Heroult method is used for the extraction of aluminium. The overall reaction is 2Al 2O 3 + 3C  → 4Al + 3CO 2

22. The process of converting hydrated alumina into anhydrous alumina is called (1) Roasting

(2)

Calcination

(3)

Dressing

(4)

Smelting

Sol. Answer (2) The conservation of hydrated oxides ores to their oxides by heating in the absence of O 2 below their melting point is called calcination. For example, Al 2O 3

⋅

xH 2O

∆  →

Al 2O 3 +xH 2O

23. Extraction of zinc from zinc blende is achieved by (1) Electrolytic reduction

(2)

(3) Roasting followed by reduction with another metal (4) Aakash Educational Services Pvt. Ltd. -

Roasting followed by reduction with carbon Roasting followed by self reduction




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Sol. Answer (2) Zinc is first roasted to form ZnO ZnS + 2O 2

∆  →

ZnO + S O 2 +

1 2

O2

The zinc oxide formed is reduced by using carbon ZnO + C

 → 1673 K

Zn + CO

24. Which of the following gives metal by electrolytic reduction conveniently and profitably? (1) PbO

(2)

Fe2O3

(3)

Cr2 O3

(4)

Al2O3

Sol. Answer (4) Aluminium can be profitabily and conveniently obtained by electrolytic reduction process. 25. Which of the following metal can be extracted by self reduction process? (1) Pb

(2)

Hg

(3)

Cu

(4)

All of these

Sol. Answer (4) Oxides of less reactive metal can undergo self reduction to produce metal. Oxides of Cu, Pb and Hg can undergo self reduction or auto reduction. (Refining) 26. Poling is used for purification of metals having impurities of (1) Metal sulphides

(2)

Metal carbonates

(3) Metal bicarbonates

(4)

Metal oxides

Sol. Answer (4) Poling method is used to purify a metal that has its oxide as impurity used for refining of Cu and Sn. 27. Impure zinc, as collected from earthen clay retort, is called (1) Blister zinc

(2)

Pig zinc

(3)

Zinc spelter

(4)

Cast zinc

Sol. Answer (3) During extraction of zinc when Zn metal is distilled off and collected by rapid chilling, the impure zinc is called spelter and contains Cd, Pb and Fe as major impurities. 28. Which of the following metal is purified by distillation process? (1) Zn

(2)

Fe

(3)

Al

(4)

Cu

(4)

All of these

Sol. Answer (1) Zn is distilled in horizontal earthen clay retort or vertical retort. 29. Vapour phase refining can be carried out in case of (1) Ni

(2)

Zr

(3)

Ti

Sol. Answer (4) Vapour phase refining is used for the purification of Ti, Zr and Ni. These metals form stable volatile compounds which on strong heating produces pure metal. 1700 K Til 4 (g)  → Ti + 2I2

2070 K → Zr(s) + 2I2(g) ZrI 4 (g) 

450 – 470 K Ni ( CO) 4 (g)  → Ni + 4CO



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30. Which of the following is not a method of purification of metals? (1) Liquation

(2)

Distillation

(3)

Zone refining

(4)

Galvanisation

Sol. Answer (4) In galvanisation process, Zn is used to protect iron from rusting. It is not a method of purification of metal. SECTION - B

Objective Type Questions (Occurrence of metals and thermodynamical principles of metallurgy) 1.

A substance which reacts with gangue to form fusible material is called (1) Flux

(2)

Catalyst

(3)

Ore

(4)

Slag

Sol. Answer (1) Flux is a substance used to react with impurities to form fusible substance. For example, SiO 2, CaO etc. 2.

Cyanide process is used for the extraction of (1) Au

(2)

Cu

(3)

Zn

(4)

Fe

Sol. Answer (1) Cyanide process is used for the extraction of Au and Ag –

→ 4 [ Au ( CN) 2 ]( aq) + 4OH – 4Au(s) + 8CN (–aq) + 2H 2O(aq) + O 2 (g)  –

2–

→ 2Au(s) + [ Zn ( CN) 4 ] ( aq) Zn(s) + 2 [ Au(CN) 2 ] ( aq)  3.

Calcination is the process in which (1) Heating the ore in presence of air

(2)

Heating the ore in absence of air

(3) Heating in vacuum

(4)

Heating of ore in presence of N 2

Sol. Answer (2) Calcination process is heating of hydrated oxides, carbonate to convert them into oxides, in the absence of oxygen ∆ Fe 2O 3 ⋅ XH2O(s)  → Fe 2O 3 (s) + xH 2O ↑

4.

Which of the following is not a concentration technique? (1) Levigation

(2)

Froth- flotation

(3)

Leaching

(4)

Calcination

Sol. Answer (4) Calcination is not a method of concentration of ore. It is used for the conversion of carbonate, hydroxides, hydrated oxides into corresponding oxide. 5.

The ores that are concentrated by Froth flotation method are (1) Carbonate

(2)

Sulphides

(3)

Oxides

(4)

Phosphates

(4)

Lime stone

Sol. Answer (2) Froath floatation process is used for the concentration of sulphide ores. 6.

In blast furnace, iron oxide is reduced by (1) Silica

(2)

CO


(3)

H2S




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Sol. Answer (2) In blast furnace iron oxide is reduced by carbon monoxide Fe 3O 4 + CO FeO + CO

7.

 →

 →

3FeO + CO 2

Fe + CO 2

The silver complex formed during cyanide process is (1) Na2[Ag(CN)]

(2)

Na[AgCN]

(3)

Na2[Ag(CN)2]

(4)

Na[Ag(CN)2]

Sol. Answer (4) During cyanide process Na[Ag(CN) 2] is formed

→ 4Na [ Ag ( CN) 2 ] + 4NaOH 4Ag + 8NaCN + 2H 2O + O 2  8.

Zincite and calamine respectively are (1) Oxide and carbonate ore of Zn

(2)

Carbonate and oxide ore of Zn

(3) Oxide and sulphate ore of Zn

(4)

Sulphate and sulphite ore of Zn

(3)

KMgCl3.6H2O

Sol. Answer (1)

→ ZnO (zinc Oxide) Zincite  Calamine  → ZnCO 3 (zinc Carbonate) 9.

Which of the following is chalcopyrite? (1) CuFeS2

(2)

FeS2

(4)

Al2O3.2H2O

(4)

Hg, Ag and Sb

Sol. Answer (1) CuFeS2 is called chalcopyrites. Also known as copper pyrites and Fool's gold. 10. The alloy used in dental filling contains (1) Ag and Sn

(2)

Ag and Sb

(3)

Hg, Ag and Sn

Sol. Answer (3) In dental filling, the alloy used consist of (50%) Hg, Ag (22.23%) and Sn (~ 14%). 11. What is the slag formed from P2O5 impurity in metallurgy of iron? (1) Ca3(PO4)2

(2)

CaSiO3

(3)

Fe3(PO4)2

(4)

FeSiO3

Fe2O3

(4)

Ag2O

Sol. Answer (1) In the metallurgy of iron, slag formed P 2O5 is Ca3(PO4)2 P2O 5 + 3CaO

 →

(

Ca 3 PO 4

)

2

12. Which of the following oxide is thermally least stable? (1) CaO

(2)

Al2O3

(3)

Sol. Answer (4) Due to small size of Ag 2+, it has very small size. This small size of Ag 2+ gives Ag2O more covalent character than CaO, Al2O3 and Fe2O3. Since covalent oxides are thermally stable than ionic oxides, Ag 2O is thermally least stable. Aakash Educational Services Pvt. Ltd. -


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13. Thomas slag is (1) Calcium silicate

(2)

Anode mud

(3)

FeSiO3

(4)

Calcium phosphate

(4)

Both (1) & (2)

Sol. Answer (4) Thomas slag is Ca 3(PO4)2, a by-product of steel industry. (Electrochemical principles of metallurgy) 14. Which of the following metal can be extracted without using reducing agent? (1) Sn

(2)

Pb

(3)

Fe

Sol. Answer (2) Oxides of less reactive metals like Pb can undergo auto reduction and the metal can be extracted without using reducing agent. 15. Which of the following metal is extracted by using coke and carbon monoxide as reducing agent? (1) Na

(2)

Cu

(3)

Fe

(4)

Al

(4)

Ag

Sol. Answer (3) Fe 2O 3 + C

 →

3CO + Fe

Fe 2O 4 + C

 →

3FeO + CO 2

FeO + CO

 →

Fe + CO 2

Fe can be extracted by using coke and carbon monoxide. 16. Which of the following metal is extracted by the use of cyanide solution? (1) Pb

(2)

Zn

(3)

Mn

Sol. Answer (4) Ag can be extracted by using solution of cyanide ion –

→ 4 [ AgCN 2 ] ( aq) + 4OH – 4Ag(s) + 8CN (–aq) + 2H 2O ( aq) + O 2 ( g)  –

2–

→ 2Ag(s) + [ Zn ( CN) 4 ]( aq) Zn(s) + 2 [ Ag ( CN) 2 ]( aq)  17. Electrolytic reduction method is used for extraction of (1) Highly electronegative elements

(2)

Transition metals

(3) Highly electropositive elements

(4)

Metalloids

Sol. Answer (3) Electrolytic reduction method is used for extraction of highly electropositive elements because they are highly reactive and very difficult to extract from other processes. 18. Which of the following metals cannot be extracted by carbon reduction process? (1) Pb

(2)

Al

(3)

Hg

(4)

Zn

Sol. Answer (2) Aluminium cannot be extracted by carbon reduction process because reduction of oxides of aluminium with carbon requires a very high temperature of about 2000°C as shown in Ellingham diagram. 19. What will happen, if anode is made of nickel instead of graphite in the extraction of aluminium from AlCl 3? (1) Nickel will be affected by high temperature

(2)

Nickel will combine with Cl 2

(3) Nickel is insulator

(4)

All of these





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Sol. Answer (2) Nickel combines with Cl 2 2AlCl3 + 3Ni

 →

2Al + 3NiCl 2

At cathode, Al 3+ (melt ) + 3e –  → Al(l) At anode, Ni(s) + 2Cl –  → NiCl 2 + 2e – 20. When molten NaCl is electrolysed by using inert electrode, the product obtained at cathode is (1) Na

(2)

Cl2

(3)

H2

(4)

Na-Hg amalgam

Sol. Answer (1) When molten NaCl is used in electrolysis, the product obtained at cathode is sodium (Na) At cathode, Na (melt) + e  → Na(l) +

–

21. Which of the following give respective metal by self reduction? (1) Galena PbS

(2)

HgS

(3)

ZnS

(4)

Both (1) & (2)

Sol. Answer (4) Both PbS and HgS on roasting undergo auto reduction to give respective metal ∆ ∆ → PbO + PbS  → Pb + SO 2 PbS + O 2  –SO 2

∆

∆ → HgO + HgS  → Hg + SO 2 HgS + O 2  –SO 2

22. Which of the following statement is incorrect? (1) Al2O3 cannot be reduced into Al by Cr 2O3

(2)

Ca is stronger reducing agent than Mg

(3) At 673 K, CO is poor reducing agent than carbon

(4)

All of these

(1) Electrolytic reduction

(2)

Roasting followed by reduction with carbon

(3) Calcination followed by reduction with carbon

(4)

Roasting followed by self reduction

(3)

Poling

Sol. Answer (3) At higher temperature Al2O3 can be reduced by Cr. 23. By which process zinc is extracted from zinc blende?

Sol. Answer (2) Roasting followed by reduction with carbon ∆ → 2ZnO + 2SO 2 (Roasting) 2ZnS + 3O 2  1400°C → Zn + CO (Reduction with CO ) ZnO + C 

(Refining) 24. Which of the following is not a refining process? (1) Mond’s process

(2)

Van-Arkel process


(4)

Leaching


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Sol. Answer (4) Leaching is a method of extraction of metal. Mond's process, Van-Arkel process and poling are used for refining of metals. 25. From gold amalgam, gold may be recovered by (1) Distillation

(2)

Oxidation

(3) Electrolytic refining

(4)

Dissolving in HNO3

Sol. Answer (1) From gold amalgam, gold may be recovered by distillation process since Hg is as metal with low BP, it will boil first and will separate out from gold. SECTION - C

Previous Years Questions 1.

Extraction of gold and silver involves leaching with CN– ion. Silver is later recovered by (1) Liquation

(2)

Distillation

(3)

Zone refining

(4)

[NEET-2017]

Displacement with Zn

Sol. Answer (4) Zn being more reactive than Ag and Au, displaces them. From Native ore, 4Ag + 8NaCN + 2H 2O + O2

Leaching →

+ 4NaOH

4Na[Ag(CN)2 ] Soluble Sodium dicyanoargentate(I)

2Na[Ag(CN)2] + Zn 2.

Displacement  → Na2[Zn(CN)4] + 2Ag↓

Match items of Column I with the items of Column II and assign the correct option: Column I

[NEET-2016]

Column II

(a) Cyanide process

(i)

Ultrapure Ge

(b) Froth floatation process

(ii)

Dressing of ZnS

(c) Electrolytic reduction

(iii) Extraction of Al

(d) Zone refining

(iv) Extraction of Au (v) Purification of Ni

(1) a(iii), b(iv), c(v), d(i)

(2)

a(iv), b(ii), c(iii), d(i)

(3)

a(ii), b(iii), c(i), d(v)

(4)

a(i), b(ii), c(iii), d(iv)

Sol. Answer (2) Fact. 3.

Aluminium is extracted from alumina (Al 2O3) by electrolysis of a molten mixture of (1) Al2O3 + Na3AIF6 + CaF2

(2)

Al2O3 + KF + Na3AIF6

(3) Al2O3 + HF + NaAIF 4

(4)

Al2O3 + CaF2 + NaAIF4

[AIPMT (Prelims)-2012]

Sol. Answer (1) During extraction of aluminium by electrolysis, a molten mixture of Al 2O3, Na3AlF6, CaF2 is used. CaF2 is used as flux and Na 3AlF6 is the main electrolyte. The overall reaction is

2Al 2O 3 + 3C


 →

4Al + 3CO 2



4.


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In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with [AIPMT (Prelims)-2012] (1) Iron sulphide (FeS)

(2)

Carbon monoxide (CO)

(3) Copper (Ι) sulphide (Cu2S)

(4)

Sulphur dioxide (SO2)

Sol. Answer (3) In the final step of extraction of copper, Cu 2O is reduced with the help of Cu 2S. CU2S + 2Cu 2O

5.

 →

6Cu + SO 2

. [AIPMT (Prelims)-2012]

Identify the alloy containing a non-metal as a constituent in it (1) Bell metal

(2)

Bronze

(3)

Invar

(4)

Steel

Sol. Answer (4) 6.


Which one of the following is a mineral of iron ? (1) Pyrolusite

(2)

Magnetite

(3)

Malachite

(4)

Cassiterite

Sol. Answer (2) Magnetite (Fe3O4) is a mineral of iron. 7.


Which of the following pairs of metals is purified by Van Arkel method? (1)

Ni and Fe

(2)

Ga and In

(3)

Zr and Ti

(4)

Ag and Au

Sol. Answer (3) Van Arkel method is used to collect ultra pure titanium and zirconium by using I 2 as specific reagent. 8.

Which of the following elements is present as the impurity to the maximum extent in the pig iron? [AIPMT (Prelims)-2011] (1) Phosphorus

(2)

Manganese

(3)

Carbon

(4)

Silicon

Sol. Answer (3) Carbon is the major impurity in the pig iron. Pig iron contains about 4% carbon. 9.

The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction [AIPMT (Mains)-2011] pertaining to the formation of the slag (1) CaO(s) + SiO2(s) → CaSiO3(s)

(2)

2C(s) + O2(g) → 2CO(g)

(3) Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)

(4)

CaCO3(s) → CaO(s) + CO 2(g)

Sol. Answer (1) In the blast furnace during the extraction of iron SiO 2 is present as impurity and CaO is used as flux to remove SiO2 in the form of CaSiO3 (slag). 10. Match List-I (substances) with List-II (process) employed in the manufacture of the substances and select the correct option List - I (Substances)

List - II (Processes)

a.

Sulphuric acid

(i)

Haber's process

b.

Steel

(ii) Bessemer's process

c. Sodium hydroxide

(iii) Leblanc process

d.

(iv) Contact process

Ammonia

(1) a(i), b(iv), c(ii), d(iii)

(2)

a(i), b(ii), c(iii), d(iv)

(3)

[AIPMT (Mains)-2010] a(iv), b(iii), c(ii), d(i) (4)

a(iv), b(ii), c(iii), d(i)

Sol. Answer (4) Aakash Educational Services Pvt. Ltd. -


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11.



Which of the following statements, about the advantage of roasting sulphide ore before reduction is not true? [AIPMT (Prelims)-2007] (1) Roasting of the sulphide to the oxide is thermodynamically feasible (2) Carbon and hydrogen are suitable reducing agents for metal sulphides (3) The ∆f G° of the sulphide is greater than those for CS 2 and H2S (4) The ∆f G° is negative for roasting of sulphide ore to oxide

Sol. Answer (2) 12. Sulphides ores of metals are usually concentrated by Froth Floatation process. Which one of the following [AIPMT (Prelims)-2007]

sulphides ores offers an exception and is concentrated by chemical leaching ? (1) Sphalerite

(2)

Argentite

(3)

Galena

(4)

Copper pyrite

Sol. Answer (2) 13. The mass of carbon anode consumed (giving only carbondioxide) in the production of 270 kg of aluminium metal [AIPMT (Prelims)-2005]

from bauxite by the Hall process is (Atomic mass Al= 27) (1) 180 kg

(2)

270 kg

(3)

540 kg

(4)

90 kg

Sol. Answer (4) 14. In which of the following process fused sodium chloride is electrolysed for extraction of sodium? (1) Castner process

(2)

Cyanide process

(3)

Down's process

(4)

Both (2) & (3)

Sol. Answer (3) Na is extracted by the electrolysis of fused sodium chloride by Down's process in which Na is collected at cathode. 15. Which of the following does not contain aluminium? (1) Cryolite

(2)

Fluorspar

(3)

Feldspar

(4)

Mica

(4)

Carnalite

(4)

SiC

Sol. Answer (2) Fluorspar is CaF2. Also known as fluorite and does not contain aluminium. 16. Which of the following does not contain Mg? (1) Magnetite

(2)

Asbestos

(3)

Magnesite

Sol. Answer (1) Magnetite is Fe3O4, an are of iron and it does not contain magnesium. 17. Carborundum is (1) CaC2

(2)

CaCO3

(3)

Fe3C

Sol. Answer (4) Carborundum is SiC, silicon carbide. It is a very hard substance which is used as abrasive. 18. Bessemer converter is used for manufacture of (1) Steel

(2)

Wrought iron

(3)

Pig iron

(4)

Cast iron

Sol. Answer (1) Steel is commonly prepared in Bessemer converter. Steel contains 0.1 to 1.7% carbon. 19. Mond's process is used for (1) Ni

(2)

Al


(3)

Fe

(4)

Cu




63

Sol. Answer (1) Mond's process is used for refining of Ni Ni

330–350 K  →

+ 4CO

Ni ( CO) 4

Impure

Volatile

Ni ( CO) 4

 → 450–470 K

NI + 4CO Pure

20. Which process of purification is represented by following scheme? Ti

250ºC + 2I2  →

(Impure)

TiI4

1400ºC  → Ti + 2I2 (Pure)

(1) Poling

(2)

Electro refining

(3)

Zone refining

(4)

van Arkel process

Sol. Answer (4) In Van Arkel process titanium and zirconium are purified by using I 2 as specific reagent. 21. Which of the following sulphides when heated strongly in air gives the corresponding metal? (1) CuS

(2)

Fe2S3

(3)

FeS

(4)

HgS

(4)

All of these

(4)

None of these

Sol. Answer (4) HgS undergo auto reduction and gives the Hg metal on strong heating. O 2 / ∆

∆ → HgO + HgS  → Hg + SO 2 HgS  –SO 2

22. Most important ore of tin is (1) Cassiterite

(2)

Cryolite

(3)

Malachite

Sol. Answer (1) The most important ore of tin is cassiterite (SnO 2). 23. Heating of ore in presence of air to remove sulphur impurities is called (1) Calcination

(2)

Roasting

(3)

Smelting

Sol. Answer (2) Heating of sulphide ore in presence of air to get corresponding oxide is called roasting For example,

2ZnS + 3O 2

∆  →

2ZnO + 2SO 2 .

24. Sodium is extracted from (1) NaCl(aq)

(2)

NaCl(l)

(3)

NaOH(aq)

(4)

NaNO3(aq)

Sol. Answer (2) Sodium is extracted by electrolysis of molten NaCl. Na metal is collected at cathode and gives Cl 2 at anode. 25. Among the metals, the one that cannot be obtained by reduction of its metal oxide (1) Cr

(2)

Fe

(3)

Mn

(4)

Mg

Sol. Answer (4) In Ellingham diagram, the slope of Mg → MgO lies well below the slope of C → CO. A very high temperature is required for the reduction of Mg. Therefore, Mg cannot be obtained by its reduction. 26. Which of the following is used as depressant in the separation of mixture of PbS and ZnS? (1) NaCN

(2)

NaCl

(3)

AgCl

(4)

All of these

Sol. Answer (1) During the concentration of sulphide ores using froath floatation process, NaCN is used to separate PbS and ZnS. NaCN reacts with ZnS and forms Na 2[Zn(CN)4] therefore, acts as depressants. Aakash Educational Services Pvt. Ltd. -


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27. Which contains both iron and copper? (1) Cuprite

(2)

Chalcocite

(3)

Chalcopyrite

(4)

Malachite

NaCl

(4)

HCl

Pig iron

(4)

Steel

Sol. Answer (3) Chalcopyrite contains both Cu and Fe. Chalcopyrite is CuFeS 2. 28. To dissolve argentite ore which of the following is used? (1) Na[Ag(CN)2]

(2)

NaCN

(3)

Sol. Answer (2) Argentite is dissolved using NaCN

→ Na 2SO 4 + 2Na [ Ag ( CN) 2 ] Ag 2S + 4NaCN + 2O 2  Argentite

29. Iron obtained from blast furnace is (1) Wrought iron

(2)

Cast iron

(3)

Sol. Answer (3) Iron obtained from blast furnace is pig iron. It contains about 4% carbon with many other impurities like S, P, S8, Mn etc. 30. Elements used as semiconductor are purified by (1) Van Arkel method

(2)

Mond process

(3)

Distillation

(4)

Zone refining

Sol. Answer (4) Semiconductor like Si, Ge, Ga etc can be purified by using zone refining method. 31. Which of the following oxide is least stable? (1) CO2

(2)

CO

(3)

MgO

(4)

HgO

(4)

Fireclay bricks

Sol. Answer (4) HgO is least stable oxide because +1 oxidation state of Hg is more stable. 32. The inner layer of a blast furnace is made of (1) Graphite bricks

(2)

Silica bricks

(3)

Basic bricks

Sol. Answer (4) The inner layer of blast furnace is made up of fire clay bricks which can withstand high temperature. 33. Roasting of sulphides gives the gas X as a by- product. This is a colorless gas with choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic acts as a reducing agent and its acid is known only in solution. The gas X is (1) SO2

(2)

CO2

(3)

SO3

(4)

H2S

Sol. Answer (1) Sulphur dioxide is a colourless gas which can cause damage to respiratory organs. Its aqueous solution is acidic SO 2 + H 2O

 →

H 2SO 3

H2SO3 is sulphurous acid and it is known only in solution. 34. Which of the following mineral contains calcium as well as magnesium? (1) Tridymite

(2)

Aragonite

(3)

Dolomite

(4)

Carnalite

Sol. Answer (3) Dolomite is CaCO3⋅MgCO3 which contains Ca as well as Mg. Aakash Educational Services Pvt. Ltd. -




65

SECTION - D

Assertion - Reason Type Questions 1.

A : Cuprite is concentrated by froth floatation process. R : Cuprite is the sulphide ore.

Sol. Answer (4) Assertion is incorrect because sulphide ores are concentrated by froath floatation process and cuprite is not a sulphide ore, Hence reason is also false. 2.

A : Bauxite is purified by leaching process. R : Aluminium oxide reacts with NaOH to form soluble sodium meta aluminate.

Sol. Answer (1) Bauxite (Al2O3⋅2H2O) is purified by leaching process. In this process bauxite is treated with NaOH to form sodium meta aluminate Al 2 O 3 ⋅ 2H 2O + 2NaOH

45% NaOH  → 200–250°C

2NaAlO 2 + 3H 2O Sodium Meta sulphate

Hence, both Assertion and Reason are true. 3.

A : Calamine and Dolomite are the carbonate ores. R : Calamine is ZnCO3 whereas Dolomite is MgCO3.ZnCO3.

Sol. Answer (3) Calamine is ZnCO3 whereas Dolomite is CaCO 3⋅MgCO3. Therefore, Assertion is true but reason is false. 4.

A : Roasting process is involved in the metallurgy of Cu from Malachite ore. R : Roasting is the process of heating the ore in absence of air.

Sol. Answer (4) Roasting process is used for sulphide ores. Malachite is CaCO 3⋅Cu(OH)2 which can be converted into oxide by calcination process. Roasting is done in presence of air. Therefore, both Assertion and Reason are false. 5.

A : Metallurgy of Ag from Argentite is known as hydro-metallurgy. R : Argentite is Ag2S.

Sol. Answer (2) In the extraction of Ag from argentite, leaching is done with the help of NaCN and Zn dust. This process is called hydrometallurgy. Argentite is Ag 2S but this reason is not the correct explanation of Assertion. 6.

A : In the manufacturing of iron from haematite, silicon dioxide is added as flux. R : Lime stone is also used as acidic flux in many case.

Sol. Answer (4) In the metallurgy of Iron CaO is used as flux and SiO 2 is present as impurity. Limestone is not used as acidic flux. Hence, both Assertion and Reason are false. 7.

A : Ultrapure metals are obtained by zone refining. R : Van arkel method is used for purification of titanium.

Sol. Answer (2) Zone refining method is used for purification of semiconductors and this method gives metals of very high purity. Van Arkel method is used for purification titanium. Hence, Reason and Assertion are true but Reason is not the correct explanation. 8.

A : Wrought iron is purest form of iron with respect to other forms. R : It has less than 0.5% carbon.



66



Sol. Answer (1) The percentage of impurities in wrought iron is minimum and it contains less than 5% carbon. Therefore, both Assertion and Reason are true. 9.

A : Magnesium oxide is used for the lining in steel making furnace. R : Magnesium oxides acts as flux.

Sol. Answer (1) In the steel industry, MgO is used for lining the surface of furnace. MgO is a basic oxide and reacts with SiO 2 which is present in the iron ore as impurity to form slag. Hence MgO acts as a flux. Therefore, both Assertion and Reason are true. 10. A : Aluminium metal is used as a reducing agent for the extraction of metals. R : Aluminium has great affinity for oxygen. Sol. Answer (1) Aluminium metal has great affinity for oxygen and it readily combines with oxygen. This property of aluminium makes it a suitable reducing agent for the extraction of other metals. Hence, both assertion and reason are true. 11. A : Zinc but not copper is used for recovery of Ag from the complex [Ag(CN) 2]–. R : Zinc is more powerful reducing agent in comparison to copper. Sol. Answer (1) During the extraction of Ag, Zn is used for the reduction. Cu is a less electropositive metal and less reactive than Zn. Due to high electropositive nature of Zn, zinc dust is used for the recovery of Ag from the complex [Ag(CN)2]–. 12. A : Hydrometallurgy is used for extraction of Ag and Au. R : Hydrometallurgy is different from pyrometallurgy. Sol. Answer (2) Hydrometallurgy is used for the extraction of Ag and Au in which they are treated with NaCN solution. This process is known as leaching. Pyrometallurgy is thermal treatment of minerals and is different from hydrometallurgy. Therefore Reason is not the correct explanation of Assertion. 13. A : Pure silver is obtained by electrolysis of AgNO3 solution. R : In electrolysis impure silver is taken as cathode and pure silver is taken as anode. Sol. Answer (3) Pure silver can be obtained by electrolysis of AgNO 3 solution. During its electrolysis, pure silver is taken as cathode so the impure silver from the anode dissolves and pure silver is deposited at cathode made up of pure silver. Hence Assertion is true, Reason is false. 14. A : Carbon is used in blast furnace for reduction of Fe 2O3. B : This process is called smelting. Sol. Answer (2) Carbon is used as a reducing agent in the blast furnace for the reduction of Fe 2O3 to obtain Fe. This process of reduction is known as smelting. Reason is true but not the correct explanation of Assertion. 15. A : In Hall’s process Aluminium is purified. B : Al2O3 (aq) is used in Hall’s process. Sol. Answer (4) Hall's process is a method of extraction of aluminium not of purification, Also in Hall's process molten Al 2O3 is used. Therefore, both Assertion and Reason are false.  Aakash Educational Services Pvt. Ltd. -

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CLS Aipmt 18 19 XII Che Study Package 6 SET 2 Chapter 6

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