NCERT Solutions for Class 12 Chemistry Chemistry I Chapter 6 General Principles And Processes Of Isolation Of Elements

Which of the ores mentioned in Table 6.1. could be concentrated by magnetic separation method?
Table 6.1 Principal ores of some important metal.

What is the significance of leaching in the extraction of aluminium?

The reaction.
Cr₂O₃ + 2Al → Al₂O₃ + 2Cr                  (ΔG° = – 421 kJ)
is thermodyanmically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?

Is it true that under certain conditions. Mg can reduce Al₂O₃ and Al can reduce MgO? What are those conditions?

Titanium is a metal of modern times. It is obtained as oxide. Why it could not be extracted earlier despite its wide occurence?

Name the common elements present in the anode mud in electrolytic refining of copper. Why are they so present?

State the role of silica in the metallurgy of copper.

What criterion is followed for the selection of the stationary phase in chromatography?

What is the role of cryolite in the metallurgy of aluminium?

Why is zinc not extracted from zinc oxide through reduction using CO?

Out of C and CO, which is a better reducing agent for ZnO?

What is the role of graphite rod in the electrometallurgy of aluminium?

Predict conditions under which Al might be expected to reduce MgO.

Define the term gangue or matrix.

Define the term flux.

Deine the term slag.

Why magnesium oxide is used for the lining in steel making furnance?

Which process is generally used for the benefication of sulphide ores?

An iron ore has impurities which are attracted by magnet. Suggest process for its benefication.

Which method of metal refining is generally used when a metal of high degree of purity is needed?

Give one example where hydro-metallurgy is used for metal extraction.

How does NaCN act as a depressant in preventive ZnS from forming the froth?

What is the major role of fluorospar (CaF₂) which is added in small quantities in the electrolytic reduction of alumina dissolved in fused cryolite?

Name the oxide ores of (a) iron  (b)  zinc,  (c) manganese  (d) aluminium.

Which process is used for the concentration of Bauxite (Al₂O₃.2H₂O)?

Ultra pure silicon is needed by electronic industry. By which method of refining, such a high purity silicon is obtained?

Sulphide ores usually concentrated by froth flotation process. Why?

Why is the formation of sulphate in calcination sometimes advantageous?

Carbon is a cheaper reducing agent than aluminium. Why is then aluminium used for reduction in some cases?

Why does carbon reduce copper oxide but not calcium oxide?

What types of ores are roasted?

Which metal is refined by Van Arkel Method?

What are the chief ores of iron?

What is wrought iron?

What is pig iron? What is its composition?

How is the cast iron obtained?

What is composition of cast iron?

Name the two volatile metals.

Why roasting of copper pyrites is done?

In electrorefining of copper, where are the Ag and Au found?

How much pure is Blister Copper?

Write the names of materials mixed before the calcined ore is subjected for smelting in the extraction of iron. 

Which reducing agent for the ore is used in the extraction of iron in the blast furnance ace?

Write the name of the iron obtained from the blast furnance?

Why is ferric chloride preferred over potassium chloride in case of cut leading to bleeding?

Lime stone is used in the manufacture of pig iron from haematite. Why?

Name any two ores of magnesium.

Give reason for the following: Although aluminium is above hydrogen in the electro-chemical series, it is stable in air and water.

An ore example of galena (PbS) is contaminated with zinc blende (ZnS). Name one chemical which can be used to concentrate galena selectively by froth floatation method.

Out of C and CO, which is better reducing agent at 673 K?

Why copper matte is put in silica lined converter?

Suggest a condition under which magnesium could reduce alumina.

Why reduction of a metal oxide becomes easier if the metal formed is in liquid state at the temperature of reduction?

If at any site, low grade copper ores are available and zinc and iron scraps are also available. Which of the two scraps would be more suitable for reducing the leached copper ore and why?

Copper can be extracted by hydrometallurgy but not zinc. Explain.

Why is the extraction of copper from pyrites difficult than from its oxide ore through reduction.

Explain: (i) Zone refining     (ii) Column chromatography. 

Write down the reactions taking place in different Zones in the blast furnance during the extraction of Iron. 

Write chemical reactions taking place in the extraction of zinc from zinc blende.

Describe a method for refining nickel.

How can you separate alumina from silica in a baxuite ore associated with silica? Give equations, if any.

Giving examples differentiate between 'roasting' and 'calcium'.

How is leaching carried out in case of low grade copper ores?

Name the processes from which chlorine is obtained as a bye-product. What will happen if an aqueous solution of NaCl is subjected to electrolysis?

Outline the principles of refining of metals by the following methods:
(i) Zone refining.
(ii) Electrolytic refining.
(iii) Vapour phase refining.

The choice of a reducing agent in a particular case depends on thermodynamic factor. How far do you agree with this statement? Support your opinion with two examples.

Carbon monoxide is more effective agent that carbon below 983 K but above this temperature the reverse is true. How would you explain this?

The value of Δ_rG° for formation of Cr₂O₃ is – 540 kJmol^–1 and that of Al₂O₃ is – 827 kJ mol^-1. Is the reduction of Cr₂O₃ possible with Al?

Predict the modes of occurrence of the following three types of metals:

(i) Highly reactive (e.g., Na)
(ii) Moderately reactive (e.g., Fe)
(iii) Noble metal (e.g., Au)

How do non-metals occur in nature? How are they extracted/isolated from their natural resources?

Name the chief ores of tin, iron and aluminium. What methods are employed for the concentration/purification of their ores?

Name three ores which are concentrated by froth-floatation process. What is meant by depressant?

Why is it advantageous to roast a sulphide ore to the oxide before reduction?

Discuss some of the factors which need consideration before deciding on the method of extraction of metal from its ore.

You are provided with samples of some impure metals such as zinc, copper and germanium. Which methods could you recommend for the purification of each of these metals?

Name the chief forms of the occurrence of the following in the earth crust:
(a) aluminium,           (b) calcium,    (c) sodium,          (d) lead.

Sodium metal cannot be obtained by the electrolysis of aqueous sodium chloride solution.

Write the chemical reactions involved in the extraction of metallic silver from argentite.

Silver ores and native gold have to be leached with metal cyanides. Suggest a reason for this.

Describe the principle of froth floatations process. What is the role of stabilizer and of a depressant? Give one example of each. 

Differentiate between 'minerals' and 'ores'.

State briefly the principles which serve as basis for the following operations in metallurgy:
(i) Froth floation process.
(ii) Zone refinnting.
(iii) Refining by liquation.

What chemical principle is involved in choosing a reducing agent for gettting the metal from its oxide ore? Consider the metal oxides, Al₂O₃ and Fe₂O₃ and justify the choice of reducing agent in each case. 

Explain different methods of reduction of the roasted/calcined ore to the metallic form.

The impurities present in minerals are called ______________.

Cassiterite is an ore of ___________.

Calamine is an ore of ________.

Aluminium is obtained from Al₂O₃ by_________reduction.

In the metallurgical process for the electrorefining of the metal the anode is made of _________ metal.

In the Bessemer converter during the extraction of copper, the substance responsible for forming blister is  ___________.

During the extraction, the metallic silver is precipitated by the addition of __________ to ________

__________ acts as a reducing agent during the extraction of iron from the pyrites ore.

Bauxite is used to extract ___________.

Sulphide ores are extracted by __________.

A.

B.

C.

D.

E.

A.

B.

C.

D.

The ores that are concentrated by floatation method are

• Carbonates

• Sulphides

• Oxides

• Phosphates

In blast furnance, iron oxide is reduced by

• Silica

• CO

• C

• Limestone

Which of the following metal is obtained by leaching its ore with dilute cyanide solution

• Silver

• Titanium

• Vanadium

• Zinc

Which method of purification is represented by the following equation?${\mathrm{T}}_{\mathrm{i}} + 2{\mathrm{I}}_2 \stackrel{\mathrm{\pi }3}{\to } {\mathrm{I}}_{\mathrm{i}} {\mathrm{I}}_4 \stackrel{1675\mathrm{K}}{\to } {\mathrm{T}}_{\mathrm{i}} + 2{\mathrm{I}}_2$

• Cupellation

• Polling

• Van Arkel

• Zone refining

Van Arkel method of purification of metals involves converting the metal to a

• volatile stable compound

• volatile unstable compound

• non-volatile stable compound

• None of the above

Zinc refining is a method to obtain

• Very high temperature

• Ultra pure Al

• Ultra pure Germanium
• Ultra pure oxides

Electrochemical process (electrolysis of fused salt) is employed to extract:

• iron

• lead

• sodium

• silver

In electro refining of metals, the pure metal is made the anode and a strip of pure metal the cathode during the electrolysis of an aqueous solution of a complex metal salt. This method cannot be used for refining of

• Silver

• Copper

• Aluminium

• Zinc

• infusible impurities to fusible material

• soluble impurities to insoluble impurities

   
• fusible impurities to infusible impurities
• mineral into silicate

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

• higher melting point of impurity than that of the pure metal

• greater noble character of the solid metal than that of the impurity

• greater solubility of the impurity in the molten state than in the solid.

• greater mobility of the pure metal than that of the impurity.

Name a method to get titanium metal in the pure state.

What type of ores are dressed up by magnetic separation method?

Name two metals which occurs native(free) in nature.

Define the term mineral.

Name the process and the chemical by which sodium is extracted on large scale?

Which method of metal refining is generally used when a metal of high degree of purity is needed?

Name the two volatile metals. 

Explain the froth floatation of concentrating ores.

What type of ores are roasted?

Write a chemical equation for the roasting of an ore of each type.

Explain the following:
Coke and flux are used in the smelting. 

Explain the following:
Partial roasting of sulphide ore is done in the metallurgy of copper.

How will you differentiate between:
Gangue and flux

How will you differentiate between:
Flux and slag

How will you differentiate between:
Concentration and refining

Give a brief account of the following processes as used in extraction of metals:
(a) Smelting
(b) Magnetic separation

What is electro-refining? Explain with one example.

Describe Van Arkel method to obtain metals of high purity.

Explain how, electrolytic refining purifies a metal?

What do you understand by the following terms: (i) Roasting, (ii) Calcination, (iii) Smelting?

Describe mainly with balanced chemical equations.
(a) Copper from copper pyrites by self reduction.
(b) Zinc from zinc blende by carbon reduction.
(c) Silver from silver glance by cyanide process.

(a) How is aluminium extracted from alumina?
(b) Give balanced equations for the extraction of aluminium from bauxite by electrolysis.
(c) What is the function of cryolite in the extraction of Al from Al₂O₃.

Describe the methods used to obtain concentrated ores.

What is meant by the term 'chromatography'?

Give reasons for the following observations:

Leather gets hardened after tanning

Give reasons for the following observations:

Lyophilic sol is more stable than a lyophobic sol.

Indicate the principle behind the method used for the refining of zinc.

What is the role of silica in the extraction of copper?

Which form of the iron is the purest form of commercial iron?

Which reducing agent is employed to get copper from the leached low-grade copper ore?

Outline the principles behind the refining of metals by the following methods:

Zone refining method

Outline the principles behind the refining of metals by the following methods:

Chromatographic method 

Name the method used for the refining of Nickel metal?

Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver? 

Out of C and CO, which is a better reducing agent at the lower temperature range in the blast furnace to extract iron from the oxide ore?

What is the role of graphite in the electrometallurgy of aluminium?

Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.

(ii) Column chromatography for purification of rare elements.

Define electrophoresis ? 

Explain how the phenomenon of adsorption finds application in each of the following processes:

(i) Production of vacuum

(ii) Heterogeneous catalysis

(iii)Froth Floatation process

Describe the principle behind each of the following processes:

(i)Vapour phase refining of a metal.

(ii)Electrolytic refining of a metal.

(iii)Recovery of silver after silver ore was leached with NaCN.

(i) What is the principle behind the zone refining of metals?

(ii) What is the role of silica in the extraction of copper?

(iii) How is 'cast iron' different from 'pig iron'?

Name the method used for refining of copper metal.

Outline the principles of refining of metals by the following methods: 

(i) Zone refining

(ii) Vapour phase refining

How is copper extracted from a low-grade ore of it?

Explain the role of each of the following:

(i) NaCN in the extraction of silver

(ii) SiO₂ in the extraction of copper

(i) Name the method of refining of metals such as Germanium.
(ii)In the extraction of Al, impure Al₂O₃ is dissolved in conc. NaOH to form sodium aluminate and leaving impurities behind. What is the name of this process?
(iii)What is the role of coke in the extraction of iron from its oxides?

What type of ores can be concentrated by magnetic separation method?

Describe the principle controlling each of the following processes:

(i) Preparation of cast iron form pig iron.

What is the role of zinc metal in the extraction of silver?

Explain the principle of the method of electrolytic refining of metals. Give one example.

Write the principle of the method used for the refining of germanium.

Out of PbS and PbCO3 (ores of lead), which one is concentrated by froth flotation process preferably?

What is the significance of leaching in the extraction of aluminium?

Write the chemical reactions involved in the process of extraction of Gold. Explain the role of dilute NaCN and Zn in this process

Which one of the following ores is best concentrated by froth flotation method?

• Siderite

• Galena

• Malachite

• Magnetite

In the context of the Hall-Heroult process for the extraction of Al, which of the following statements is false?

• CO and CO₂ are produced in this process

• Al₂O₃ is mixed with CaF₂ which lowers the melting point of the mixture and brings conductivity

• Al³⁺ is reduced at the cathode to form Al

• Na₃AlF₆ serves as the electrolyte

The metal that cannot be obtained by electrolysis of an aqueous solution of its salts is

• Ag

• Ca

• Cu

• Cr

Which series of reactions correctly represents chemical relations related to iron and its compound?

Which method of purification is represented by the following equation

• zone refining

• cupellation

• Polling

• Van-Arkel

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?

• Metal sulphides are thermodynamically more stable than CS₂

• CO₂ is thermodynamically more stable than CS₂

• Metal sulphides are less stable than the corresponding oxides

• CO₂ is more volatile than CS₂

During the process of electrolytic refining of copper, some metals present as impurity settle as ‘anode mud’ These are

• Sn and Ag

• Pb and Zn

• Ag and Au

• Fe and Ni

Heating mixture of Cu₂O and Cu₂S will give

• Cu + SO₂

• Cu + SO₃

• CuO + CuS

• Cu₂SO₃

Which one of the following ores is best concentrated by froth – floatation method?

• Magnetite

• Malachite

• Galena

• Cassiterite

Excess of KI reacts with CuSO₄ solution and then Na₂S₂O₃ solution is added to it. Which of the statements is incorrect for this reaction?

• Cu₂I₂ is reduced

• Evolved I₂ is reduced

• Na₂S₂O₃ is oxidized

• CuI₂ is formed

Match items of Columns I with the items of Columns II and assign the correct code.

• A

  B

  C

  D

    2       3     1     5

• A

  B

  C

  D

    1      2      3     4

• A

  B

  C

  D

     3     4      5     1

• A

  B

  C

  D

     4      2     3     1

"Metals are usually not found as nitrates in their ores"
Out of the following two (a and b) reasons which isare/are true for the above observation?
I. Metal nitrates are highly unstable.
II.Metal nitrates are highly soluble in water.

• I and II are true

• I and II are false

• I is false but II is true

• I is true but II is false

Roasting of sulphides gives the gas X as a by-product. This is a colourless gas with the 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 has never been isolated. The gas X is

• H₂S

• SO₂

• CO₂

• H₂SO₃

Aluminium is extracted from alumina (Al₂O₃) by electrolysis of a molten mixture of 

• Al₂O₃ +HF +NaAlF₄

• Al₂O₃ + CaF₂ +NaAlF₄

• Al₂O₃ +Na₃AlF₆ +CaF₂

• Al₂O₃ +KF +Na₃AlF₆

Which one of the following is a mineral of iron?

• Malachite

• Cassiterite

• Pyrolusite

• Magnetite

In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with

• Copper (I) sulphide (Cu₂S)

• sulphur dioxide (SO₂)

• Iron sulphide (FeS)

• Carbon monoxide (CO)

Identify the alloy containing a non-metal as a constituent in it.

• Invar

• Steel

• Bell metal

• Bronze