NCERT Exemplar Class 12 Chemistry Solutions Chapter 6 Principles and Processes of isolation of elements

Question 1. In the extraction of chlorine by electrolysis of brine ____________.
(i) oxidation of $\text {Cl}^{-}$ ion to chlorine gas occurs.
(ii) reduction of $\text {Cl}^{-}$ ion to chlorine gas occurs.
(iii) For the overall reaction, $\Delta \text {G}^{\ominus }$ has a negative value.
(iv) A displacement reaction takes place.

Answer:

The answer is option (i).

The oxidation reaction of $\text {Cl}^{-}$ ion is responsible for the extraction of chlorine from brine
$2H_{2}O(l)+2Cl^{-}(aq)\rightarrow H_{2}(g)+Cl_{2}(g)+2OH^{-}(aq)$
The $\Delta G^{0}$ for this reaction is $+422\; kJ$
$\Delta G^{0}=-nFE^{0}$
$E^{0}=\frac{\Delta G^{0}}{nF}=-2.2 V$

Question 2. When copper ore is mixed with silica, in a reverberatory furnace copper matte is produced. The copper matte contains ____________.
(i) sulphides of copper (II) and iron (II)
(ii) sulphides of copper (II) and iron (III)
(iii) sulphides of copper (I) and iron (II)
(iv) sulphides of copper (I) and iron (III)

Answer:

The answer is option (iii).

On mixing copper ore with silica in a reverberatory furnace, iron silicate comes off as slag producing copper in the form of copper matte containing copper sulphide $[Cu_{2}S(I)]$ and some iron sulphide $[FeS(II)].$

Question 3. Which of the following reactions is an example of autoreduction ?
(i) $\text {Fe}_{3}\text {O}_{4}+\text {4CO}\rightarrow \text {3Fe}+\text {4CO}_{2}$
(ii) $\text {Cu}_{2}\text {O}+\text {C}\rightarrow \text {2Cu}+\text {CO}$
(iii) $\text {Cu}^{2+}(aq)+Fe (s)\rightarrow \text {Cu (s)}+Fe^{2+}(aq)$
(iv) $\text {Cu}_{2}\text {O}+\frac{1}{2}\text {Cu}_{2}\text {S}\rightarrow \text {3Cu }+\frac{1}{2}\text {SO}_{2}$

Answer:

$\text {Cu}_{2}\text {O}+\frac{1}{2}\text {Cu}_{2}\text {S}\rightarrow \text {3Cu }+\frac{1}{2}\text {SO}_{2}$
In this reaction reduction of copper (I) oxide by copper (I) sulphide takes place. Since, copper is reduced by itself, this process is known as auto-reduction and the solidified copper so, obtained is known as blister copper. We get the copper metal on reaction of sulphide ore of copper with its oxide.

Question 4. A number of elements are available in earth’s crust but most abundant elements are ____________.
(i) $\text {Al and Fe}$
(ii) $\text {Al and Cu}$
(iii) $\text {Fe and Cu}$
(iv) $\text {Cu and Ag}$

Answer:

The answer is option (i).

Several elements are available in the earth’s crust but the most abundant elements in the earth’s crust include $\text {Al and Fe}$.

Question 5. Zone refining is based on the principle that ___________.
(i) Impurities of low-boiling metals can be separated by distillation.
(ii) Impurities are more soluble in molten metal than in solid metal.
(iii) Different components of a mixture are differently adsorbed on an absorbent.
(iv) Vapours of the volatile compound can be decomposed in pure metal.

Answer:

The answer is option (ii).

The basic principle of zone refining method is that impurities are more soluble in molten metal compared to the solid state of the metal.

Question 6. In the extraction of copper from its sulphide ore, the metal is formed by the reduction of $Cu_{2}O$ with
$(i) \; FeS$
$(ii) \; CO$
$(iii) \; Cu_{2}S$
$(iv) \; SO_{2}$

Answer:

The answer is option (iii).

In the process of extraction of copper from its sulphide ore, the metal is formed by the reduction of $Cu_{2}O$ with $Cu_{2}S$
Since, copper is reduced by itself the process is known as autoreduction.
Chemical reaction occuring in this reaction is $Cu_2 O+\frac{1}{2} Cu_2 S\rightarrow 3Cu+\frac{1}{2} SO_2$
In this process, copper appears as blister copper.

Question 7. Brine is electrolysed by using inert electrodes. The reaction at anode is ________.
(i) $Cl^{-}(aq.)\rightarrow \frac{1}{2}Cl_{2}(g)+e^{-};E^{o}cell=1.36 \; V$
(ii) $2H_{2}O(l)\rightarrow O_{2}(g)+4H^{+}+4e^{-};E^{o}cell=1.23 \; V$
(iii) $Na^{+}(aq)+e^{-}\rightarrow Na (s);E^{0}cell=2.71\; V$
(iv) $H^{+}(aq)+e^{-}\rightarrow \frac{1}{2}H_{2} (g);E^{0}cell=0.00\; V$

Answer:

The answer is option (i).

Electrolysis of brine solution is a process of decomposition of $NaCl$ solution using the electric current. The anode is positive; therefore, it attracts negative hydroxide and chlorine ions. Chloride ions get oxidized by electron loss to chlorine molecules.

Question 8. In the metallurgy of aluminium ________________.
(i) $Al^{3+}$ is oxidised to $Al (s)$.
(ii) graphite anode is oxidised to carbon monoxide and carbon dioxide.
(iii) The oxidation state of oxygen changes in the reaction at the anode.
(iv) The oxidation state of oxygen changes in the overall reaction involved in the process

Answer:

The answer is option (ii).

The graphite anode is oxidised to carbon monoxide $(CO)$ and carbon dioxide $(CO_{2})$ in the process of metallurgy of aluminium.
$C(s)+O^{2-}(melt)\rightarrow CO(g)+2e^{-}$
$C(s)+2O^{2-}(melt)\rightarrow CO_{2}(g)+4e^{-}$

Question 9. Electrolytic refining is used to purify which of the following metals?
$(i) \; Cu \; and\; Zn$
$(ii) \; Ge \; and \; Si$
$(iii)\; Zr \; and\; Ti$
$(iv) \; Zn \; and\; Hg$

Answer:

The answer is option (i).

Copper and zinc can be purified by using the electrolyte refining method. In this process, impure metal acts as anode and a strip of pure metal is used as a cathode. Impurities from the blister copper or impure zinc deposit are used as anode mud. The electrolytic refining of copper and zinc is done to get high-grade metals.

Question 10 Extraction of gold and silver involves leaching the metal with $CN^-$ ion. The metal is recovered by ________________.
(i) displacement of metal by some other metal from the complex ion.
(ii) Roasting of the metal complex.
(iii) Calcination followed by roasting.
(iv) thermal decomposition of the metal complex.
Answer:

The answer is option (i).

Extraction of gold and silver involves leaching with $CN-$ ion. The metal in the cyanide process is recovered by displacement of metal by some other metal from the complex ion. The reaction taking place is as:
$4M+8CN^{-}+2H_{2}O+O_{2}\rightarrow 4[M(CN)_{2}]^{-}+4OH^{-}$
$2[M(CN)_{2}]^{-}+Zn\rightarrow [Zn(CN)_{4}]^{2-}+2M$

Question 11 Answer the questions 11-13 on the basis of Fig. 6.1.

Choose the correct option of temperature at which carbon reduces $\text {FeO}$ to iron and produces $\text {CO}$.
(i) Below temperature at point A.
(ii) Approximately at the temperature corresponding to point A.
(iii) Above the temperature at point A but below a temperature at point D.
(iv) The above temperature at point A.

Answer:

The answer is option (iv).

$\text {FeO+C}\rightarrow \text {Fe+CO}$
It can be seen as a couple of two simpler reactions
$\text {FeO}\rightarrow \text {Fe+}\frac{1}{2}\text {O}_{2}(\Delta \text {G}^{0}_{FeO.Fe})$
$\text {C+}\frac{1}{2}\text {O}_{2}\rightarrow \text {CO}(\Delta \text {G}^{0}_{C.CO})$
Total Gibbs energy change becomes $\Delta \text {G}^{0}_{C.CO}+\Delta\text {G}_{FeO.Fe}^{0}$
In $\Delta \text {G}^{0}$ versus T plot, the plot $\text {Fe}$ to $\text {FeO}$ goes upward and the plot for $\text {C}$ to $\text {CO}$ goes downwards.
At temperature above point A, the $\text {C}$ to $\text {CO}$ lines comes below $\text {Fe}$ to $\text {FeO}$ and $\Delta \text {G}^{0}_{C,CO} < \Delta \text {G}^{0}_{Fe, FeO}$
So in this range, $\text {C}$ will reduce $\text {FeO}$ to $\text {Fe}$ and itself be oxidised to $\text {CO}$.

Question 12. Below point ‘A’ $\text {FeO}$ can ______________.
(i) be reduced by carbon monoxide only.
(ii) be reduced by both carbon monoxide and carbon.
(iii) be reduced by carbon only.
(iv) not be reduced by both carbon and carbon monoxide.

Answer:

The answer is option (i).

Below point A, $\text {FeO}$ can be reduced by carbon monoxide only.

Question 13. For the reduction of $\text {FeO}$ at the temperature corresponding to point D, which of the following statements is correct?
(i) $\Delta \text {G}$ value for the overall reduction reaction with carbon monoxide is zero.
(ii) $\Delta \text {G}$ value for the overall reduction reaction with a mixture of 1 mol carbon and 1 mol oxygen is positive.
(iii) $\Delta \text {G}$ value for the overall reduction reaction with a mixture of 2 mol carbon and 1 mol oxygen will be positive.
(iv) $\Delta \text {G}$ value for the overall reduction reaction with carbon monoxide is negative.

Answer:

The answer is option (i).

At point D, the curves of oxidation of iron and oxidation of $\text {CO}$ intersect each other.
Thus, $\Delta \text {G}^{0}$ for the reaction $\text {FeO+CO}\rightarrow \text {Fe+CO}_{2}$ is zero.
$\text {2FeO+O}_{2}\rightarrow \text {2FeO};\Delta \text {G}^{0}=-280$
$\text {2CO+O}_{2}\rightarrow \text {2CO};\Delta \text {G}^{0}=-280$
Resulting in $\text {2FeO+2CO}_{2}\rightarrow \text {2Fe+2CO}_{2}$
$\Delta \text {G}^{0}= (-280+280)=0$

Question 15. Which of the following option are correct?
(i) Cast iron is obtained by remelting pig iron with scrap iron and coke using a hot air blast.
(ii) In the extraction of silver, silver is extracted as a cationic complex.
(iii) Nickel is purified by zone refining.
(iv) $\text {Zr and Ti}$ and are purified by van Arkel method

Answer:

The answer is option (i, iv).

Iron obtained from blast containing about 4% carbon and many impurities such as Mn, P, Si, etc, is called pig iron. It is remelted with scrap iron to obtain cast iron which has slightly less carbon content (3%) compared to pig iron and is extremely hard and brittle.
For refining of $\text {Zr and Ti}$ Van Arkel method, based on the thermal decomposition of metal component is used. In this method, the impurities i.e. oxygen and nitrogen, are removed by heating the metal in an evacuated vessel with iodine.
$\text {Zr (s)}+\text {2 I}_{2}\overset{\text {280 k}}{\longrightarrow}\text {ZrI}_{4}\text {(g)} \overset{\text {2075 k}}{\longrightarrow}\text {Zr (s)}\text {(pure)}+\text {2 I}_{2}$

$\text {Ti}+\text {2I}_{2}\overset{\text {530 k}}{\longrightarrow}\text {TI}_{4}\overset{\text {1700 k}}{\rightarrow}\text {Ti}+\text {2I}_{2}$
Zone refining is used for semiconductors like Ge, Si. For the purification of Nickel, Mond’s process is used.

Question 16. In the extraction of aluminium by Hall-Heroult process, purified $\text {Al}_{2}\text {O}_{3}$ is mixed with $\text {CaF}_{2}$ to
(i) lower the melting point of $\text {Al}_{2}\text {O}_{3}$
(ii) increase the conductivity of the molten mixture.
(iii) reduce $\text {Al}^{3+}$ into Al(s).
(iv) acts as a catalyst

Answer:

The answer is option (i, ii).

Purified $\text {Al}_{2}\text {O}_{3}$ is mixed with $\text {CaF}_{2}$ in Hall-Heroult process to lower the melting point of $\text {Al}_{2}\text {O}_{3}$ and increase the conductivity of the molten mixture. Hence, options a and b are correct.

Question 17. Which of the following statements is correct about the role of substances added in the froth floatation process?
(i) Collectors enhance the non-wettability of the mineral particles.
(ii) Collectors enhance the wettability of gangue particles.
(iii) By using depressants in the process, two sulphide ores can be separated.
(iv) Froth stabilisers decrease the wettability of gangue.

Answer:

The answer is option (i, iii).

To enhance the non-wettability of mineral particles as well as froth stabilisers, collectors like sodium ethyl xanthate are used.
For example, sodium cyanide acts as a depressant for zinc sulphide in the process of concentration of galena ore. Depressants can be used for the separation of two sulphide ores.
Froth stabilisers are used to stabilise the froth in the process.

Question 18. In the Froth Floatation process, zinc sulphide and lead sulphide can be separated by ______________.
(i) using collectors.
(ii) adjusting the proportion of oil to water.
(iii) using a depressant.
(iv) using froth stabilisers.

Answer:

The answer is option (ii, iii).

The froth flotation method is used in the extraction of metal from sulphide ore. The two sulphide ores can be separated by using a depressant and adjusting the proportion of oil to water in the froth flotation process. Depressant used in the separation of zinc sulphide and lead sulphide is $NaCN$. It is utilised in the selective prevention of $ZnS$ from coming to the froth.

Question 19. Common impurities present in bauxite are ____________.
(i) $\text {CuO}$
(ii) $\text {ZnO}$
(iii) $\text {Fe}_{2}\text {O}_{3}$
(iv) $\text {SiO}_{2}$

Answer:

The answer is option (iii, iv).

Bauxite is an ore of aluminium which contain $\text {Fe}_{2}\text {O}_{3}$ and $\text {SiO}_{2}$ as common impurities. Also some of the major impurities in bauxite are iron oxides (goethite and hematite), silicon dioxide, kaolinite and small amounts of anatase.

Question 20. Which of the following ores are concentrated by froth flotation?
(i) Haematite
(ii) Galena
(iii) Copper pyrites
(iv) Magnetite

Answer:

The answer is option (ii, iii).

Sulphide ores are concentrated by the froth flotation process as pine oil selectively wets the sulphide ore. Galena and copper pyrite, being sulphide ores are concentrated by the froth flotation process.

Question 21. Which of the following reactions occur during calcination?
(i) $\text {CaCO}_{3}\rightarrow \text {CaO}+ \text {CO}_{2}$
(ii) $\text {2FeS}_{2}+\frac{11}{2}\text {O}_{2}\rightarrow \text {Fe}_{2}\text {O}_{3}+ \text {4SO}_{2}$
(iii) $\text {Al}_{2}\text {O}_{3}.x\text {H}_{2}\text {O}\rightarrow \text {Al}_{2}\text {O}_{3}+ x \text {H}_{2}\text {O}$
(iv) $\text {ZnS}+\frac{3}{\text {2}}O_{2}\rightarrow \text {ZnO}+\text {SO}_{2}$

Answer:

The answer is option (i, iii).

In the process of calcination, heating of the ore below its melting in a limited supply of air takes place. Ores that contain oxygen like oxide, hydroxides or carbonates are calcined. The reaction that takes place is:
$\text {CaCO}_{3}\overset{\Delta }{\rightarrow}\text {CaO}+\text {CO}_{2}$
$\text {Al}_{2}\text {O}_{3}.\text {xH}_{2}\text {O}\overset{\Delta }{\rightarrow}\text {Al}_{2}\text {O}_{3}+ \text {xH}_{2}\text {O}$

Question 22. For the metallurgical process of which of the ores calcined ore can be reduced by carbon?
(i) haematite
(ii) calamine
(iii) iron pyrites
(iv) sphalerite

Answer:

The answer is option (i, ii).

Oxide reduction can be done by using carbon. Haematite (Iron ore - $\text {Fe}_{2}\text {O}_{3}$ ) and calamine $\text {ZnCO}_{3}\rightarrow \text {ZnO}+\text {CO}_{2}$ contain oxygen, so they can be reduced by carbon.
Sulphide ores cannot be reduced by carbon. Iron pyrite and sphalerite are sulphide ores of iron and zinc, respectively.

Question 23. The main reactions occurring in the blast furnace during the extraction of iron from haematite are ________.
(i) $\text {Fe}_{2}\text {O}_{3}+\text {3CO}\rightarrow \text {2Fe}+\text {3CO}_{2}$
(ii) $\text {FeO}+\text {SiO}_{2}\rightarrow \text {FeSiO}_{3}$
(iii) $\text {Fe}_{2}\text {O}_{3}+\text {3C}\rightarrow \text {2Fe}+\text {3CO}$
(iv) $\text {CaO}+\text {SiO}_{2}\rightarrow \text {CaSiO}_{3}$

Answer:

The answer is the option (i, iv).

The 2 main reactions taking place in the blast furnace during the extraction of iron are:
(i) Reduction of $\text {Fe}_{2}\text {O}_{3}+\text {CO}\rightarrow \text {2FeO}+\text {CO}_{2}$
$\text {2FeO}+\text {2CO}\rightarrow \text {2Fe}+\text {2CO}_{2}$
$\text {Fe}_{2}\text {O}_{3}+\text {3CO}\rightarrow \text {2Fe}+\text {3CO}_{2}$
(ii) Slag formation $\text {CaO}+\text {SiO}_{2}\rightarrow \text {CaSiO}_{3} \; \text {Fusible slag}$

Question 24. In which of the following method of purification, metal is converted to its volatile compound which is decomposed to give pure metal?
(i) heating with a stream of carbon monoxide.
(ii) heating with iodine.
(iii) liquation.
(iv) distillation.

Answer:

The answer is option (i,ii)

(i) Heating of Nickel with Carbon Monoxide (Mond's Process):

$$
\mathrm{Ni}+4 \mathrm{CO} \rightarrow \mathrm{Ni}(\mathrm{CO})_4 \xrightarrow{450-470 \mathrm{~K}} \mathrm{Ni}+4 \mathrm{CO}
$$

(ii) Heating with lodine (Van Arkel Method for Zirconium):

$$
\mathrm{Zr}+2 \mathrm{I}_2 \xrightarrow{870 \mathrm{~K}} \mathrm{ZrI}_4 \xrightarrow[\text { (Tungsten filament) }]{2075 \mathrm{~K}} \mathrm{Zr}+2 \mathrm{I}_2
$$

Question 25. Which of the following statements are correct?
(i) A depressant prevents a certain type of particle to come to the froth.
(ii) Copper matte contains $\text {Cu}_{2}\text {S}$ and $\text {ZnS}$
(iii) The solidified copper obtained from the reverberatory furnace has blistered appearance due to evolution of $\text {SO}_{2}$ during the extraction.
(iv) Zinc can be extracted by self-reduction.

Answer:

The answer is option (i, iii).

Frothing of a particular sulphide can be prevented by depressants. The solidified copper that we get in the reverberatory furnace has a blistered appearance due to evolution of $\text {SO}_{2}$ during extraction. Hence, it is called blister copper.

Question 26. In the extraction of chlorine from brine _____________.
(i) $\Delta \text {G}^{0}$ for the overall reaction is negative.
(ii) $\Delta \text {G}^{0}$ for the overall reaction is positive.
(iii) $\text {E}^{0}$ for the overall reaction has negative value.
(iv) $\text {E}^{0}$ for the overall reaction has positive value.

Answer:

The answer is option (ii,iii).

$3Cl^{-}+2H_{2}O\rightarrow 2OH^{-}+H_{2}+Cl_{2}$
$\Delta G^{0}$ for the reaction is $+422\; kJ$
Using $\Delta G^{0}=-nFE^{0},$ we get

$E^{0}=-2.2\; V$

Question 28. At temperatures above 1073K coke can be used to reduce $FeO\; to \; Fe$. How can you justify this reduction with the Ellingham diagram?

Answer:

As per the Ellingham diagram at temperatures greater than 1073 K, $\Delta G^{0}$ for the formation $FeO$ is less negative than $\Delta G^{0}$ for the formation of carbon monoxide from carbon.
Thus, above 1073 K, carbon can reduce $FeO$, i.e., $\Delta_{r} G^{0}$ for the reaction

$\mathrm{FeO}+\mathrm{C} \xrightarrow{>1073 \mathrm{~K}} \mathrm{Fe}+\mathrm{CO} \quad \Delta G<0$

Question 29. Wrought iron is the purest form of iron. Write a reaction used for the preparation of wrought iron from cast iron. How can the impurities of sulphur, silicon and phosphorus be removed from cast iron?

Answer:

Wrought iron is an alloy with a very low carbon content (less than 0.08%).
The reaction is:
$Fe_{2}O_{3}+3C\rightarrow 2Fe+3CO$

In the extraction of cast iron from haematite ore, on the addition of limestone as flux, the impurities of sulphur, silicon and phosphorus pass into slag on changing to their oxides.

Question 30. How is copper extracted from low-grade copper ores?

Answer:

Copper is extracted from low-grade ores by the process of hydrometallurgy. Acid or bacteria is used in its leaching process. In the process, ore is treated with a suitable regent that dissolves ore but not the impurities. Scrap iron, zinc or $H_{2}$ is used to treat the solution containing copper ions $(Cu^{+2})$ and the reactions are as:
$Cu^{2+} (aq)+H_{2} (g) \rightarrow Cu(s)+2H^{+} (aq)$
$Cu^{2+} (aq)+Fe (s) \rightarrow Cu(s)+Fe^{2+} (aq)$
In this way, copper, is obtained.

Question 31. Write two basic requirements for refining of metal by Mond process and by Van Arkel Method

Answer:

Mond’s process and van arkel method are used for refining of nickel and zinc, respectively. The basic requirements for both the processes are:
(i) A volatile compound should be formed by the metal on reaction with an available reagent.
(ii) The volatile compound formed should be easily decomposable, enabling the metal to be easily recovered.

Question 32. Although carbon and hydrogen are better-reducing agents they are not used to reduce metallic oxides at high temperatures. Why?

Answer:

Despite being better reducing agents, carbon and hydrogen are not used as carbon and hydrogen form carbides and hydrides, respectively on reaction with metals at high temperature.

Question 33. How do we separate two sulphide ores by Froth Floatation Method? Explain with an example.

Answer:

The separation of two sulphide ores is done by adjusting proportion of oil to water or by using depressants. $NaCN$ is used for an ore containing $ZnS$ and $PbS$. Sodium cyanide forms complex with $ZnS$ and prevents it from coming with froth but lead sulphide remains with froth.
$4NaCN+ZnS\rightarrow Na_{2}Zn(CN)_{4}+Na_{2}S$

Question 34. The purest form of iron is prepared by oxidising impurities from cast iron in a reverberatory furnace. Which iron ore is used to line the furnace? Explain by giving a reaction.

Answer:

Haematite $(Fe_{2}O_{3})$ is used to line the furnace. It supplies the oxygen and oxidises impurities present in the cast iron like carbon, silicon, manganese and phosphorus to $CO, SiO_{2}, MnO$ and $P_{2}O_{5}$.
$Fe_{2}O_{3}+3C\overset{Heat}{\longrightarrow}2Fe+3CO$

$3Si+2Fe_{2} O_3\rightarrow 4Fe+3SiO_2$

$3S+2Fe_2 O_3\rightarrow 3SO_2+4Fe$

$CO$ and $SO_{2}$ escape and $MnO \; and\; SiO_{2}$ combine to form to form manganous silicate $(MnSiO_{3})$ as slag $MnO+SiO_{2}\overset{Heat}{\longrightarrow}MnSiO_{3}$ (Manganous silicate-slag)

Question 35. The mixture of compounds A and B is passed through a column of $Al_{2}O_{3}$ by using alcohol as eluant. Compound A is eluted in preference to compound B. Which of the compounds A or B, is more readily adsorbed on the column?

Answer:

Compound B is more readily adsorbed on the column as compound A is eluted in preference to compound B

Question 36. Why is sulphide ore of copper heated in a furnace after mixing with silica?
Answer:

Iron oxide that is present as impurity in sulphide ore of copper forms an iron silicate slag and copper is produced in the form of copper matte. This is why, sulphide ore of copper is heated in a furnace after mixing with silica.
$FeO+SiO_{2}\rightarrow FeSiO_{3}$

Question 37. Why are sulphide ores converted to oxide before reduction?

Answer:

Sulphides are not reduced easily, unlike the oxides. This is why sulphides are first oxidised and then subjected to reduction.

Question 38. Which method is used for refining $Zr \; and\; Ti$ ? Explain with equation.

Answer:

Van Arkel method is used in refining of $Zr \; and\; Ti$ . The crude metal, on heating with iodine, forms a volatile, unstable compound. Pure metal is then obtained by decomposing the compound.
The equations are :

$\text {Zr (s) (impure)+2I}_{2}\overset{870\; K}{\longrightarrow}\text {ZrI}_{4}$
$\text {ZrI}_{4}\overset{1800\; K}{\longrightarrow}\text {Zr (pure)+2I}_{2}$
$\text {Ti (impure)+2I}_{2}\overset{523\; K}{\longrightarrow}\text {TiI}_{4} \text {(g)}$
$\text {TiI}_{4}\overset{1700\; K}{\longrightarrow}\text {Ti (pure)+2I}_{2}$

Question 39. What should be the considerations during the extraction of metals by electrochemical method?

Answer:

During the extraction of metals by the electrochemical method, we should keep in mind the following factors
(i) Reactivity of the metal.
(ii) Suitability of the electrode.

Question 40. What is the role of flux in metallurgical processes?

Answer:

Flux is a chemical cleaning agent.
The ores contain some gangue even after concentration. Certain substances are mixed with concentrated ore for the purpose of removing the gangue. They combine with the gangue to form a fusible material that is insoluble in molten metal. These substances are called fluxes. Some examples of materials used as flux: Limestone, silica, dolomite, lime, borax etc.
Fluxes are classified as acidic or basic based on the type of impurities they remove.
$SiO_{2}\; (Acidic\; acid)+CaO\; (basic\; impurity)\rightarrow CaSiO_{3}(Slag)$
$MgO\; (basic\; flux)+SiO_{2}\; (Acidic\; impurity)\rightarrow MgSiO_{3}(Slag)$

Question 41. How are metals used as semiconductors refined? What is the principle of the method used?

Answer:

Semiconductor like silicon and germanium is produced by zone refining method and the principle used is that the impurities are more soluble in melt than the corresponding solid state of metals.

Question 42. Write down the reactions taking place in the Blast furnace-related to the metallurgy of iron in the temperature range 500-800K.

Answer:

The reactions that take place in blast furnace during the metallurgy of iron at the temperature range 500-800 K are:
$3Fe_{2}O_{3}+CO\rightarrow 2Fe_{3}O_{4}+CO_{2}$
$Fe_{3}O_{4}+4CO\rightarrow 3Fe+4CO_{2}$
$Fe_{2}O_{3}+CO\rightarrow 2FeO+CO_{2}$

Question 43. Give two requirements for vapour phase refining.

Answer:

The two requirements for vapour phase refining are:
(i) A volatile compound should be formed by the metal on reaction with an available reagent.
(ii) The volatile compound formed should be easily decomposable, enabling the metal to be easily recovered.

Question 44. Write the chemical reactions involved in the extraction of gold by the cyanide process. Also, give the role of zinc in the extraction.

Answer:

In the extraction of gold by the cyanide process, gold particles present in the ore are treated with a dilute solution of $NaCN$ in the presence of atmospheric oxygen. Gold particles dissolve by forming a complex cyanide that is soluble in nature.
$4Au+8NaCN+2H_{2}O+O_{2}\rightarrow 4Na[Au(CN)_{2}]+4NaOH$
On adding an electropositive metal like zinc, Au is recovered from solution.
$2Na [Au(CN)_{2}]+Zn\rightarrow Na_{2}[Zn(CN)_{4}]+2Au$
The process of extraction of gold by cyanide oxidation as well as reduction. Oxidation of gold takes place during the formation of the cyanide complex, whereas reduction takes place during its recovery. $Zn$ acts as a reducing agent.

Question 46. Match the items of Column I with the items of Column II and assign the correct code :

(i) A (1) B (2) C (4) D (5)
(ii) A (4) B (3) C (1) D (2)
(iii) A (3) B (4) C (2) D (1)
(iv) A (5) B (4) C (3) D (2)

Answer:

Option (ii) is the answer.

Chromatography shows coloured bands as it separates components based on their movement through a medium. The Mond process involves forming a volatile complex to purify nickel. Zone refining is used to purify semiconductors like germanium and silicon. Mercury is purified by fractional distillation due to its volatility.

Question 47. Match items of Column I with the items of Column II and assign the correct code :

(i) A (4) B (2) C (3) D (1)
(ii) A (2) B (3) C (1) D (5)
(iii) A (1) B (2) C (3) D (4)
(iv) A (3) B (4) C (5) D (1)

Answer:

Option (i) is the answer.

The cyanide process is used for the extraction of gold (Au) by forming soluble complexes. The froth flotation process is used for the concentration (dressing) of zinc sulfide (ZnS) ores. Electrolytic reduction is used in the extraction of reactive metals like aluminium (Al).
Zone refining is used to obtain ultrapure semiconductors like germanium (Ge).

Question 48. Match the items of Column I with the items of Column II and assign the correct code:

(i) A (3) B (4) C (2) D (1)
(ii) A (5) B (4) C (3) D (2)
(iii) A (2) B (3) C (4) D (5)
(iv) A (1) B (2) C (3) D (4)

Answer:

Option (i) is the answer.

Sapphire and corundum are both crystalline forms of aluminium oxide (Al₂O₃). Sphalerite is the mineral name for zinc sulfide (ZnS). In metallurgy, sodium cyanide (NaCN) acts as a depressant by preventing the flotation of certain minerals like zinc sulfide during the extraction of metals like lead.

Question 49. Match the items of Column I with items of Column II and assign the correct code :

(i) A (2) B (3) C (4) D (1)
(ii) A (1) B (2) C (3) D (5)
(iii) A (5) B (4) C (3) D (2)
(iv) A (4) B (5) C (3) D (2)

Answer:

Option (i) is the answer.

Blistered copper forms during the self-reduction of copper ores: $2 C u_2 O+C u_2 S \rightarrow$ $6 C u+S O_2$.
The blast furnace is used for iron extraction, where slag is formed: $\mathrm{FeO}+\mathrm{SiO}_2 \rightarrow$ $\mathrm{FeSiO}_3$.
The reverberatory furnace oxidizes copper(I) sulfide to copper(I) oxide: $2 C u_2 S+$ $3 \mathrm{O}_2 \rightarrow 2 \mathrm{Cu}_2 \mathrm{O}+2 \mathrm{SO}_2$.
The Hall-Héroult process is used to extract aluminium from alumina.

Question 51 In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Zirconium can be purified by Van Arkel method.
Reason: $ZrI_{4}$ is volatile and decomposes at 1800K.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.

Answer:

The answer is option (i).

Zirconium is also purified by Van Arkel method as it forms $ZrI_{4}$ on treating with iodine and is easily decomposed to get pure zirconium.

Question 52. In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Sulphide ores are concentrated by Froth Flotation method.
Reason: Cresols stabilise the froth in the Froth Flotation Method.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.

Answer:

The answer is option (ii).

Sulphide ores, on being wetted by oil, become lighter and rises to the surface along with froths. On the other hand, impurities wetted by water settle down as they get heavier.

Question 53. In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Zone refining method is very useful for producing semiconductors.
Reason: Semiconductors are of high purity.
(i) Both assertion and reason are true and the reason is the correct explanation of assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.

Answer:

The answer is option (ii).

The principle of the zone refining method is that the the impurities of semiconductors are more soluble in the molten zone compared to the solid state and the ultrapure semiconductor crystallizes.

Question 54 In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.
Reason: Copper is extracted by hydrometallurgy.
(i) Both assertion and reason are true and the reason is the correct explanation of the assertion.
(ii) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(iii) The assertion is true but the reason is false.
(iv) The assertion is false but the reason is true.
(v) Assertion and reason both are wrong.

Answer:

The answer is option (ii).

Copper is extracted by a hydrometallurgical process. Suitable solvent like water is used for dissolving salts of metal. They are then reduced by more electropositive element in this process.