General Principles and Processes of Isolation of Elements Test - 9

The Iron metals can be used for sharp casting.

Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Iron is the best metal amongst the given options for sharp casting.

The method of extraction of silver by cyano complex formation followed by metal displacement is called as MacArthur-Forest method. Cyanide process is used for the extraction of Ag which is also called as MacArthur-Forest process.

Reactions involved in the extraction of silver are as follows:

\(\mathrm{Ag}_{2} \mathrm{~S}+4 \mathrm{NaCN} \rightarrow 2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]+\mathrm{Na}_{2} \mathrm{~S}\) (reversible reaction)

\(2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]+\mathrm{Zn} \rightarrow \mathrm{Na}_{2}\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]+2 \mathrm{Ag}\)

Hence, the correct option is (B).

Electrolytic reduction is used in the manufacture of aluminium from bauxite.

Highly electropositive elements like \(\mathrm{Na}, \mathrm{K}, \mathrm{Al}, \mathrm{Mg}, \mathrm{Ca}, \mathrm{Al}\) can't be reduced by Carbon at moderate temperature. At high temperature, the metal combines with carbon to form carbide. So, these metals are extracted by electrolysis of their oxides and this process is called electrolytic reduction.

Hence, the correct option is (C).

Platinum generally occurs in free state.

Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Since it is noble metal it is found in free state.

Hence, the correct option is (B).

Aluminium is commonly used as a reducing agent in metallurgical operations, It is used in those cases where the metal oxide is of a comparatively more reactive metal than zinc which cannot be satisfactorily reduced by carbon.

Oxides of \(\mathrm{Mn}\) and \(\mathrm{Cr}\) are not satisfactorily reduced by carbon. So, these metals are extracted by the reduction of their oxides with Aluminium powder.

\(3 \mathrm{MnO}_{2}(s)+4 \mathrm{Al}(s) \longrightarrow 3 \mathrm{Mn}+2 \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s})+\mathrm{Heat}\)

Hence, the correct option is (A).

Zone refining is a method to obtain Ultra pure metals.

Zone refining is based upon fractional crystallization as the impurity prefers to stay in the melt and on solidification only pure metals solidifies on the surface of melt. 

In this process solubility of the impurities in the metal in molten and solid states is different. This process is known as ultra-purification because it results in impurity level decreasing to ppm level.

Hence, the correct option is (C).

Zone refining is a method of purification used for semiconductors like Si, Ge and Ga.

Zone refining process is used to get the purest form of elements. It is a technique for the purification of a crystalline material and especially a metal in which a molten region travels through the material to be refined, picks up impurities at its advancing edge, and then allows the purified part to recrystallize at its opposite edge.

Hence, the correct option is (D).

"Aluminium" is used in making planes.

"Aluminium" is most widely used in making planes. They have a low density and they do not corrode. Aluminum is a soft and lightweight metal. It has a dull silvery appearance, because of a thin layer of oxidation that forms quickly when it is exposed to air.

Hence, the correct option is (C).

An ore of tin containing FeCrO₄ is concentrated by magnetic separation.

An ore of tin-containing FeCrO₄ is concentrated by magnetic separation as FeCrO₄ is ferromagnetic in nature. Magnetic separation based on differences in magnetic properties of the ore components. Iron ores are attracted towards the magnet, hence, non-magnetic impurities can be separated from them using magnetic separation.

Hence, the correct option is (B).

Impurity of lead is removed by liquation.

It is used for the refining of metals having low melting point and are associated with high melting impurities. Example, Pb, sn, sb, Bi and Hg. The impure metal is heated on the sloping hearth of a furnace. The pure metal flows down leaving behind the non-fusible material on the hearth.

Hence, the correct option is (C).

\(\mathrm{CO}_{2}\) is less stable than \(\mathrm{CO}\) at more than \(983 \mathrm{~K}\). 

At these temperatures, the \(\Delta \mathrm{G}\) (change in free energy) value of formation of \(\mathrm{CO}\) is more negative than the \(\Delta \mathrm{G}\) value of formation of \(\mathrm{CO}_{2}\). More negative, the value of \(\Delta \mathrm{G}\), the greater is the tendency of the element to combine with oxygen.

Hence, the correct option is (C).

Ag can be obtained from purified Zn-Ag alloy by distillation.

Lead contains impurities such as cu, Ag, \(\mathrm{Bi}\), sb and \(\mathrm{sn}\). Silver is removed by parke's process where motten zinc is added to motten impure lead, The former is inmiscible with the latter. Siver is more soluble in motten zinc than in molten lead. Zinc - silver alloy solidifies earlier then molten lead and thus can be separated.

Ag can be thus oftained from Zn - Ag alloy by distillation process.

Hence, the correct option is (A).

In the extraction of some metals from their ores, coke can be used as reducing agent.

Metals below carbon in the reactivity series can be extracted using carbon. Carbon reduces the metal oxides that are extracted when heated. 

For example, the common ores of iron are both iron oxides, and these can be reduced to iron by heating them with carbon in the form of coke. 

Hence, the correct option is (B).

Halogens have a strong tendency to accept electrons. The substances that accept electrons from others are termed oxidizing agents. Thus, halogens act as good oxidizing agents.

The oxidizing powers of halogens are measured in terms of their electrode potentials. The electrode potential is the potential difference developed between the electrode and the electrolyte.

The electrode potentials of halogens decrease in the order:

\(F_{2}(+2.87 \mathrm{~V})>\mathrm{Cl}_{2}(+1.36 \mathrm{~V})>\mathrm{Br}_{2}(+1.09 \mathrm{~V})>\mathrm{I}_{2}(+0.54 \mathrm{~V})\)

Same is the order of their oxidizing powers.

\(\mathrm{HCl}\) is a weak reducing agent than \(\mathrm{HBr}\) and \(\mathrm{Br}_{2}\) is a stronger oxidizing agent than \(\mathrm{I}_{2}\). 

The oxidation state of Sulphur in sodium thiosulphate \(\left(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\right)\) is a whole number \((+2)\), while that in sodium tetrathionate \(\left(\mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}\right)\) it is a fraction (+2.5).

Corrosion is not a step in the extraction of ore. 

The metals extracted from Earth's crust endure the process of concentration to remove impurities from the ore. Several processes, different for each metal like roasting and reduction are done to get the pure metal from it's combined state like sulphides or oxides. 

Hence, the correct option is (D).

The process of leaching, alumina using sodium carbonate is called Hall's process.

Bauxite is concentrated through Hall’s process, in which sodium aluminate is prepared using sodium carbonate in bauxite. When excess carbon dioxide is passed through sodium aluminate in the presence of water, it forms aluminium hydroxide along with sodium carbonate. When dried aluminium hydroxide is ignited, alumina is formed.

Hence, the correct option is (D).

During the decomposition of an oxide into oxygen and metal vapour entropy increases as gas is produced in the reaction.

Decomposition of an oxide is an endothermic change. This is because it is reverse of combustion reaction and all combustion reactions are exothermic in nature.

Since, both ΔH  and  ΔS are positive, the temperature should be high enough so that TΔS>ΔH,

Thus, all are correct answers.

Hence, the correct option is (D).

In the cyanide process for extraction of gold and silver from ores, the cyanide solution acts as a leaching agent to bring the gold and silver into solution as cyanide complexes and thus separate these metals from the ores.

Silver and gold are extracted by the cyanide process (Mac Arthur - Forrest process). After the preliminary crushing and concentration by froth floatation process, the ore (crushed auriferous rocks in the case of gold) is leached with dilute (0.4 - 7%) solution of sodium cyanide made alkaline by adding lime kept agitated by a current of air. Silver (or gold) pass into solution as argentocyanide (or aurocyanide).

It is based on the fact that gold/silver dissolves in dilute solution of sodium cyanide in presence of atmospheric oxygen with the formation of complex cyanide.

Reaction:

\(\mathrm{Ag}_{2} \mathrm{S}+4 \mathrm{NaCN} \rightarrow 2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]+\mathrm{Na}_{2} \mathrm{S}\)

Silver is obtained by reaction with Zn:

\(2 \mathrm{Na} \mathrm{Ag}(\mathrm{CN})_{2}+\mathrm{Zn} \rightarrow \mathrm{Na}_{2} \operatorname{Zn}(\mathrm{CN})_{4}+2 \mathrm{Ag}\)

Both assertion and reason are true and reason is the correct explanation of assertion.

Liquation process is based on the difference in fusibility of the metal and impurities. When the impurities are less fusible than the metal itself, the process is employed. Lead, tin, and bismuth possess a low melting point and the refining of such metals is carried out through the process of liquidation as their melting point is lower than the impurities. 

Hence, the correct option is (A).

The oil used in the froth floatation method for the purification of ore is Pine oil.

Froth Floatation process is suitable for sulphide ores. The process is based on different wetting characteristics of the ore and gangue particles with water and pine oil. 

The ore is wetted by oil and impurities are wetted by water. Ore particles are adsorbed on potassium or sodium ethyl xanthate (as a collector) and come at the surface along with the froth. Froth stabiliser (cresols, aniline) stabilise the froth. 

Hence, the correct option is (C).

During the process of electrorefining of \(\mathrm{Cu}\), some metals present as impurity settle as anode mud. These are \(\mathrm{Ag}\) and \(\mathrm{Au}\).

When an electric current is passed through the electrolyte, the anode gradually dissolves and pure copper is deposited on the cathode which gradually grows in size. The impurities like Fe,Zn,Ni, etc, dissolve in the solution as sulphates while gold, silver, platinum settle down below the anode as anode mud.

Hence, the correct option is (C).

The correct match is: I-Z, II-W, III-X, IV-Y

(II) In Downs cell molten \({MgCl}_{2}\) is electrolyzed, the electrolyte used in the cell is a fused mixture of \(4096 {NaCl}\) and \(6096 {CaCl}_{2}\).

(II) In Dow process, \({Mg}({OH})_{2}\) is precipitated from sea-water by slurrying with calcined dolomite and then converting it to \({MgCl}_{2}\) by reacting with \({HCl}\). In Dow sea water process, the electrolyte used is fused \({MgCl}_{2}\).

(III) In the Hall-Heroult process, the electrolyte used is a fused mixture of \({A} {l}_{2} {O}_{3}\) and \({Na}_{3} {AIF}_{6}\).

(IV) In Moissan process, the electrolyte used is fused \({KHF}_{2}\).

Hence, the correct option is (A).

Matrix is defined as the unwanted foreign material present in the ore.

The ore that exists inside our earth contains dust, stone, quartz and other foreign materials. The impurities are called gangue or matrix in the ore. During the concentration process, care is taken to remove the matrix from the ore.

Hence, the correct option is (A).

\(2 \mathrm{Mg}+\mathrm{O}_{2} \rightarrow 2 \mathrm{MgO}\)

In this, Magnesium undergoes oxidation adding 2 electrons from Oxygen while Oxygen undergoes reduction by losing two electrons. Therefore, the reaction has simultaneous oxidation and reduction reaction and called Redox Reaction.

In \(\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}\) there is no change in oxidation state.

In \(\mathrm{CaO}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}\) there is no change in oxidation state.

In \(\mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{BaCl}_{2} \rightarrow \mathrm{BaSO}_{4}+2 \mathrm{NaCl}\) too there is no change in oxidation state.

Hence, the correct option is (C).

Ellingham diagram represents the change in free energy (ΔG) with temperature.

An Ellingham diagram is a graph showing the temperature dependence of the stability for compounds. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulphides. 

The diagrams are useful in predicting the conditions under which an ore will be reduced to its metal. The analysis is thermodynamic in nature and ignores reaction kinetics. Thus, processes that are predicted to be favourable by the Ellingham diagram can still be slow.

Aluminium is extracted by the electrolysis of molten aluminium oxide in fused cryolite.

The ore is first converted into pure aluminium oxide by the Bayer Process and this is then electrolysed in solution in molten cryolite another aluminium compound. The aluminium oxide has too high a melting point to electrolyse on its own. The usual aluminium ore is bauxite.

Hence, the correct option is (D).

The powdered ore is agitated with water or washed with running stream of water. The heavy ore particles and lighter impurities are separated. This method of concentration is known as Gravity separation.

Gravity separation is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical: i.e., the components of the mixture have different specific weight.

Gangue have Sand and soil, Silt and Gravel.

The definition of gangue is worthless rock or mineral in which valuable minerals are found. Gangue are the impurities which are mixed closely with the ores. It is unwanted material which is of no market value and it is waste rock or mineral or sand etc.

Hence, the correct option is (D).

Galena ores is best concentrated by froth-floatation method. 

Froth flotation is a process for selectively separating of hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. This method is used for the concentration of sulphide ores such as galena (PbS ), zinc blende \((\mathrm{ZnS})\) and copper pyrite \(\left(\mathrm{CuF} \mathrm{eS}_{2}\right)\).

In Hall's process, the ore is mixed with Sodium carbonate.

Hall's process is used for the extraction of Aluminum from Alumina.  Bauxite is concentrated through Hall’s process, in which sodium aluminate is prepared using sodium carbonate in bauxite. When excess carbon dioxide is passed through sodium aluminate in the presence of water, it forms aluminum hydroxide along with sodium carbonate. When dried aluminum hydroxide is ignited, alumina is formed.

The reaction involved in Hall's process is as follows:

\({Al}_{2} {O}_{3} .2 {H}_{2} {O}+2 {Na}_{2} {CO}_{3} \rightarrow 2 {NaAlO}_{2}+{CO}_{2}+2 {H}_{2} {O}\)

Hence, the correct option is (D).