General Elements

GENERAL PRINCIPLES AND PROCESSES OF ISOLATION OF ELEMENTS

Metallurgy: The science and technology of isolation or extraction of pure metals from their ores and preparing them for practical use is called metallurgy.

Minerals: Most of the metals are found in nature in the form of solid inorganic compounds in combined state.  These compounds are called minerals.  The naming of minerals is based on the location of their discovery and the person who discovered them and on some characteristics of the minerals.

Ores:  The minerals from which metal can be conveniently and economically extracted are called ores.  Since all the ores are minerals but all minerals are not ores.  Ores may be divided into following types.  

1. Oxides: Haematite (Fe₂O₃), Magnetite ore, Load stone (Fe₃O₄), Bauxite (Al₂O₃.2H₂O), Cassiterite (SnO₂), Corundum (Al₂O₃), Diospar (Al₂O₃.H₂O), Pyrolusite (MnO₂), Zincite (ZnO), Rutile (TiO₂), Cuprite or Ruby copper (Cu₂O).

2. Carbonates: Magnesite (MgCO₃), Dolomite (CaCO₃.MgCO₃), Cerusite (PbCO₃), Calamine (ZnCO₃), Siderite (FeCO₃), Malachite or Basic copper carbonate (CuCO₃), Cu(OH)₂, Azurize (2CuCO₃.Cu(OH)₂, Limestone or calcite, marble chalk (CaCO₃).

3. Sulphites: Iron Pyrites (FeS₂), Galena (PbS), Zinc blende (ZnS), Cinnabar (HgS), Copper pyrite (CuFeS₂), Copper glance (Cu₂S), Silver glance (Ag₂S), Pentlandite (Ni, Fe)S.

4. Halides: Syllvine (KCl), Carnallite (KCl. MgCl₂.6H₂O), Rocksalt (NaCl), Cryolite (Na₃AlF₆), Horn silver (AgCl), Fluorspar (Fluorite) (CaF₂).

5. Sulphates: Awglesite (PbSO₄), Gypsum (CaSO₄.2H₂O), Barytes (BaSO₄), Epsom salt or Epsomite (MgSO₄.7H₂O).

6. Silicates: Talc (Mg₂(Si₂O₅)₂.M(OH)₂, Asbestos – Mg₂(Si₂O₅)₂.(OH)₄, Willemite – Zn₂SiO₄, Felspar – KAlSi₃O₈, Mica – K₂O.3Al₂O₃.6H₂O.2H₂O.

Concentration or dressing or Beneficiation of Ores:

1. The process such as hand picking, grinding, crushing or pulverizing, which gives the ore in such a physical form that gangne can be easily removed from it, is called dressing of ore.

2. The various process which help in the removal of gangne or matrix from the dressed ore, there by increasing percentage of metal in the ore, is called concentration of ore.

3. The dressed ore is generally concentrated by the following methods.

1) Levigation or gravity separation:

This is the process of separating the lighter gangue particles from the heavier ore particles from pulverized ore by washing in a current of water. This process is also known as hydraulic washing and generally used for oxide ores and carbonate ores.  This method is based on the difference in densities of ore particles and impurities.

2) Electromagnetic separation:

The electromagnetic separation for the concentration of ore is employed.
(a) When ore is magnetic in nature such as iron ore.
(b) Ore is non-magnetic, but gangue or matrix is magnetic in nature.
Examples:  Electromagnetic separation is used

(a) in the concentration of aluminium ore which contains ferric oxide as magnetic gangue.
(b) In the concentration of tin ore i.e. tine stone or cassiterite (SnO₂) which contains ferrous tungstate (woefranite – FeNO₄) as magnetic gangue.
Similarly chromate (FeCr₂O₄) an ore of chromium, magnetic (Fe₃O₄) an ore of iron and pyrolusite (MnO₂) an ore of manganese all being magnetic are separated from non-magnetic gangue by this process.
Rulite (TiO₂-magnetic) and chlorapatite (3 Ca₃(PO₄)₂. CaCO₂-nonmagnetic) are also separated by this method.

3) Electrostatic separation: This method is used for the separation of lead sulphide.  Lead sulphide is a good conductor and is charged immediately in an electrostatic field and is thrown away (separate) from the roller from zinc sulphide (poor conductor) which is not charged and hence drop vertically from the roller.

4) Froth floatation process: This method is employed for the concentration of sulphide ores only.
Principle: It has been found that when the finely divided sulphide ores containing gangue are immersed in a mixture of water and oil (i.e. pine oil, eucalyptus oil or camphor oil), then oil wets only the sulphide ore where as water wets the gangue particles.  When a strong current of air is passed to agitate the ore and mixture of oil and water Due to this agitation oil forms, foam with water.  As a result, the ore particles become light and cling to pine oil foam and hence rise up with the foam while the gangue particles become heavy and settle down in the tank.

5) Chemical Leaching: This is the process in which the ore is concentrated by chemical reaction with suitable reagent which dissolves the ore but not the impurities.
Eg. bauxite is leached with a hot concentrated solution of NaOH to dissolved aluminium while other oxides (Fe₂O₃.TiO₂, SiO₂) remains undissolved and noble metals (Ag and Au) are leached with dilute aqueous solution of NaCN or KCN in presence of air.

${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}+2\mathrm{NaOH}⟶2{\mathrm{NaAIO}}_2+3{\mathrm{H}}_2\mathrm{O}$

${\mathrm{Na}}_3{\mathrm{AlO}}_2+3{\mathrm{H}}_2\mathrm{O}⟶3\mathrm{NaOH}+\mathrm{Al}(\mathrm{OH}{)}_3$

$\mathrm{Al}(\mathrm{OH}{)}_3\to {\mathrm{Al}}_2{\mathrm{O}}_3+3{\mathrm{H}}_2\mathrm{O}$

${\mathrm{Ag}}_2\mathrm{S}+4\mathrm{NaCN}⟶\underset{(\mathrm{soda} \mathrm{argentocyanide})}{2\mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN}{)}_2\right]+{\mathrm{Na}}_2\mathrm{S}}$

$4\mathrm{Au}+8\mathrm{KCN}+2{\mathrm{H}}_2\mathrm{O}+\left[\mathrm{O}\right]⟶4 \mathrm{K}\left[\mathrm{Au}(\mathrm{CN}{)}_2\right]+4\mathrm{KOH}$

 II. Roasting: Roasting is the process in which the ore is heated strongly below its melting point, in presence of excess of air. This process is used for the conversion of sulphide ores to their respective oxides (de-electronation of ores) and to expel the moisture and impurities of non-metals (P, As, S) as their volatile oxides. Hence the ore become porous and easily workable.
2ZnS + 3O₂ → 2ZnO + 2SO₂
2MoS₂ + 7O₂ → 2MoO₃ + 4SO₂

III. Calcination: Calcination is the process in which the ore is heated strongly below its melting point, either in absence of air or in a limited supply of air.   This process is used for the conversion of the carbonates and hydrated oxides ores to their respective oxide. Beside this, during the process, moisture is driven out, volatile impurities of P, As and S are removed and the ore becomes porous and hence easily workable in the subsequent steps.

$\begin{array}{l}{\mathrm{CaCO}}_3⟶\mathrm{CaO}+{\mathrm{CO}}_2\\ {\mathrm{Al}}_2{\mathrm{O}}_3\cdot 2{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{Al}}_2{\mathrm{O}}_3+2{\mathrm{H}}_2\mathrm{O}\end{array}$

Both calcination and roasting are carried out in various types of furnaces such as reverberatory furnace, blast furnace, electric furnace, regenerative furnaces, the most important of these is reverberatory furnace.  These furnaces employ refractory materials which resist high temperatures and donot become soft.
Acidic refractories – SiO₂ and Al₂O_{3  ;}   Basic refractories – CaO and MgO

IV) Reduction: After calcinations or roasting, the metal oxides are reduced to metallic state by the following methods.
i) Reduction by carbon (smelting): In this process calcinated or roasted ore is heated with powdered coke in presence of a flux. During this process the oxides are reduced to their respective metals (in molten state) by carbon or CO.
e.g.    SnO₂ + C → Sn + 2CO
          ZnO + C → Zn + CO
          Fe₂O₃ + 3CO → 2Fe + 3CO₂

ii) Reduction by Aluminium: (Goldschmidt aluminothermic process):
This process involves the reduction of oxides such as Fe₂O₃, Cr₂O₃, Mn₃O₄ etc by aluminium.
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
Cr₂O₃ + 2Al → Al₂O₃ + 2Cr
The mixture of metallic oxide such as Fe₂O₃ and aluminium, powder in the ratio of 3:1 is known as thermite.  A magnesium ribbon (which acts as a fuse) is embedded in a mixture of Al powder and BaO₂, (called ignition mixture).  It is lighted and in turn causes burning of the mixture.
iii) Reduction by precipitation (Hydrometallurgy or Amalgamation): This is the process of dissolving the metals or its ore by the action of a suitable chemical reagent followed by recovery of the metal either by electrolysis or by the use of a suitable precipitating agent (displacement method)
e.g.
_{$\begin{array}{l}4\mathrm{Au}+8\mathrm{KCN}+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2⟶4\mathrm{K}\left[\mathrm{Au}\right(\mathrm{CN}{)}_2]+4\mathrm{KOH}\\ \\ 2\mathrm{K}\left[\mathrm{Au}\right(\mathrm{CN}{)}_2]+\mathrm{Zn}⟶2\mathrm{Au}+{\mathrm{K}}_2\left[\mathrm{Zn}\right(\mathrm{CN}{)}_4]\\ \\ 2\mathrm{Na}\left[\mathrm{Ag}\right(\mathrm{CN}{)}_2]+2\mathrm{n}⟶{\mathrm{Na}}_2\left[\mathrm{Zn}\right(\mathrm{CN}{)}_4]+2\mathrm{Ag}\end{array}$}

iv) Reduction by Mg (Kroll’s process): This method is appreciable for the reduction of TiCl₄.
TiCl₄ + 2Mg → 2MgCl₂ + Ti.

v) Reduction by heating in air – (Auto reduction or self electronation): When the sulphide ores of some of the electropositive metals like Hg, Cu, Pb, Sb etc are heated in air, a part of the sulphides is oxidized to their respective oxides which further react with more of the sulphides to yield the metals.
e.g       2HgS + 3O₂ → 3HgO + 2SO₂ :   2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
            2HgO + HgS → 3 Hg + SO₂    :      2Cu₂O + Cu₂S → 6 Cu + SO₂

vi) Electrolytic reduction (Electrometallurgy): This is the process of extracting highly electropositive metals (active) such as Na, K, Ca, Mg, Al etc by electrolysis of fused NaCl in Down’s cell and Al by the electrolysis of fused Al₂O₃. The metal is liberated at cathode.
e.g. NaCl (fused) → 2Na⁺ + Cl^–
At anode (+)          $\begin{array}{l}2{\mathrm{Cl}}^{-}{\stackrel{–2{\mathrm{Cl}}^{–}}{\to }\mathrm{Cl}}_2\\ \end{array}$ 
At cathode (-)       $2{\mathrm{Na}}^{+}+2{\mathrm{e}}^{-}\stackrel{2e^{–}}{\to }2\mathrm{Na}$ 

Note: Reduction and slagging take place together.  For the removal of acidic impurities (i.e. SiO₂, P₂O₅) basic flux is added and for the removal of basic impurities (i.e. MnO₂) acidic flux is added.

Illustration 1: The process of converting hydrated alumina into anhydrous alumina is called
(A) roasting                  (B) smelting                  (C) dressing                  (D) calcination
Solution: The process of converting hydrated alumina into anhydrous alumina is called calcination.
Illustration 2: A process used for the concentration of ore is
(A) froth floatation

(B) roasting

(C) electrolysis

(D) bessemerization
Solution: A process which is used for the concentration of ore is froth floatation.

Refining: The refining of metals in the pure state from crude metals is done by employing following methods.

Liquation: This method is used for the refining of such metals which are readily fusible (having low M.P.) such as (Sn, Pb, Si and Hg) as compared to impurities less fusible). i.e. impurities present must be less fusible than the metal to the purified.
The curd metal is placed on the slopping hearth of reverberatory furnace at a temperature just above the melting point of the metal.
The pure metals flow down the slopping heath leaving behind infusible material called dross on the hearth.

ii) Distillation: This method is employed for the refining of such metals which have low boiling points such as Zn, Cd, Hg, etc and impurities are non-

iii) Zone refining (Fractional crystallization): 
This method is based upon the principle of fractional crystallization i.e. difference in solubilities of impurities in molten and solid state of metal.
In this method impure metal rod is heated with the help of circular heater at one end.  The melted molten get solidified on cooling while the impurities pass on into the molten zone and the method is repeated twice or thrice to get the pure metal.  Hence metals of very high purity are obtained by this method.  Semiconductors, like silicon, germanium and gallium are purified by this method.

iv) Polling:
This method is employed when the impure metal contain impurities of its own oxide.  In this method molten metal is stirred with green poles of wood, which liberates gas like methane.  The hydrocarbon gas reduces any oxide present in the metal.  e.g. i) CuO in the blister copper is reduced to copper.

v) Electrolytic refining:
Metals like Cu, Ag, Au, Cr, Zn, Ni, Sn are purified by this method.
In this method the blocks of impure metal form anode and pure metal (rod) form the cathode.
Aqueous solution of appropriate salt is used as electrolyte.
On electrolysis at a suitable voltage the pure metal is deposited at cathode        
At anode M – ne^– → Mⁿ⁺
At cathode: Mⁿ⁺ + ne^– → M (metals)

vi) Cupellation: This method is used for refining of such metals which contains impurities of other metals which form volatile oxides.
e.g. Last trace of lead are removed from silver by this method.  In this process impure silver is heated in a shallow (cupel) made of bone ash under blast of air.  Lead is easily oxidized and carried away by blast air.

vii) Vapour phase refining: Metal is removed as volatile compound which is then decomposed by heating to get pure metal.
E.g. a) Mond’s process: Ni is purified by this process.

$\mathrm{Ni}\left(\mathrm{s}\right)+4\mathrm{CO}\left(\mathrm{g}\right)\stackrel{27–77°\mathrm{C}}{⟶}\mathrm{Ni}\left(\mathrm{CO}{)}_4\right( \mathrm{g})$

$\mathrm{Ni}\left(\mathrm{CO}{)}_4\right( \mathrm{g})\stackrel{177–197°\mathrm{C}}{⟶}\mathrm{Ni}+4\mathrm{CO}(\mathrm{g})$

Van Arkel process: Here decomposition temperature of metal iodide should be less than the mp of the metal.
Further Th and U are also purified by this method.
Metals require in space technology are also purified by van arkel process.

De-silverication of lead:
Lead is obtained from galena (PbS) contains impurities of silver, removal of which is called de-silverisation.
The process employed are

a) Parke’s process: In this method lead (containing Ag) is melted in iron pots and 1% Zn is added then allowed to cool. Zn-Ag alloy solidifies and being lighter, floats over molten lead and removed.
(Pb + Ag) + zn → Zn – Ag (alloy) + Pb.

(b) Pattison’s process: Pb containing less than 2.5% at Ag metals at lower temperature.
When as alloy of Pb-Ag containing more lead, it is melted and allowed to cool slowly, pure Pb separates.

Illustration 3: The common method of extraction of metals from oxide ore is

(A) reduction with carbon

(B) reduction with hydrogen

(C) I reduction with aluminium

(D) electrolytic method

Solution: The common method of extraction of metals from oxide ore is reduction with carbon.

Illustration 4: The process of zone refining is used in purification of

(A) Si                 (B) Al                 (C) Ag                 (D) Cu

Solution: The process of zone refining is used in purification of silicon.

Important minerals of some metals and non–metals and main methods of extraction:

1.	Li	Spodumene (LiAl(SiO3)2.  It is extracted by electrolysis of fused LiCl with KCl
2.	Na	Rock salt, common salt (NaCl), chile salt petre (NaNO3), Borax or sodium borate (Na2B4O7.10H2O) sodium carbonate (Na2CO3).  It is extracted by electrolysis of fused NaCl with CaCl2 (added to it)
3.	K	Carnallit (KCl, MgCl2.6H2O), Karnite (KCl.MgSO4.3H2O), Sylvine (KCl), Nitre (KNO3), Felspar (K2O.Al2O3.6SiO2).  It is extracted by electrolysis of fused KCl with CaCl2 (added to it)
4.	Be	Beryl (3BeO.Al2O3.6SiO2), Chrysoberyl (BeO.Al2O3), It is extracted by electrolysis of fused BeF2 with NaF (added to it)
5.	Mg	Carnallite (KCl. MglCl2.6H2O), Magnesite (MgCO3), Dolamite (MgCO3.CaCO3), Kieserite (MgSO4.H2O), Epsom salt (MgSO4.7H2O).  It is extracted by electrolysis of fused MgCl2 with KCl (added to it)
6.	Ca	Limestone, marble, chalk, calcite (CaCO3), Gypsum (CaSO4.2H2O), Dolamite (CaCO3.Mg.CO3), Fluospar (CaF2), Phsophorite (Ca3(PO4)2).  It is extracted by electrolysis of CaCl2 and CaF2 mixture.
7.	Ba	Witherite (BaCO3), Barytes (BaSO4).  It is extracted by electrolysis of fused BaCl2.
8.	Al	Bauxite (Al2O3.2H2O), Corundum (Al2O3), Cryolite (Na3AlF6), Potash feldspar (K2O.Al2O3.6SiO3), It is extracted by electrolysis of Al2O3 with molten Na3AlF6.
9.	C	Free as diamond, and graphite (also known as plumbago i.e. black lead).
10.	Si	Silica (SiO2), Clay, talc (2MgSi2O5.Mg(OH)2 or Mg3Si4O8), Asbestos (CaMg3Si4O12), beryl (Be3Al2Si6O18), Mica (K2O.3Al2O3.6SiO2.2H2O)
11.	Sn	Cassiterite or Tin stone (SnO2) stannite (Cu2S.FeS.SnS2).  It is extracted by reduction of SnO2 with C. e.g, SnO2 + 2C → Sn + 2CO.
12.	Pb	Galena (PbS), Cerussite PbCO3, Anglesite (PbSO4).  It is extracted by reduction of PbO with C. PbO → Pb + CO.
13.	N	Free an air, Ammonia, Chile salt petre, nitrate.
14.	P	Phosphorite (Ca3(PO4)2), Chlorapatite (3Ca3(PO4)2.CaCl2, Fluorapatite (3Ca3(PO4)2.CaF2).
15.	Sb	Stibnite (Sb3S3)
16.	Bi	Native, Bismithglance – (Bi2S3), Bismuthite (Bi2O3) Reduction of Bi2O3 with carbon Bi2O3 + 3C → 2Bi + 3CO.
17.	S	Native, Gypsum (CaSO4.2H2O), Celestone (SrSO4), Galena (PbS), Zinc blend (ZnS), Copper pyrites (Cu2S.Fe2S3) and Iron pyrite (FeS2).
18.	F	Fluorspar (CaF2), Cryolite (Na3AlF6), Fluorapatite (3Ca3(PO4)2.CaF2).
19.	Cl	Sea water, rock salt (NaCl), Carnallite (KCl, MgCl2.6H2O)
20.	Br	Sea water as MgBr2, Carnallite (KCl.MgCl2.6H2O) contains 0.01 to 0.1% as MgBr2.
21.	I	Sea weeds as NaI, caliche (Chilesaltpetre NaNO3) as NaIO3
22.	Ti	Rutile (TiO2), Ilmenite (TiO2.FeO).  Extracted by reduction of TiCl4 with Mg or Na TiCl4 + 2Mg → Ti + 2MgCl2
23.	Cr	Chromite (FeO.Cr2O3), Chrome ochre (Cr2O3) Reduction of Cr2O3 with Al. Cr2O3 + 2Al ® 2Cr + Al2O3
24.	Mn	Pyrolusite (MnO2), Braunite (Mn2O3), Manganite (Mn2O3.H2O) Reduction of oxide with Al or C. 3Mn3O4 + 8Al → 9Mn + 4Al2O3
25.	Fe	Haematite (Fe2O3), Magnetite (Fe3O4), Limestone (2Fe2O3.3H2O), Iron pyrite (FeS2), Siderite spathic iron ore (FeCO3), Copper pyrites (CuFeS2) Reduction of oxides with CO Fe2O3 + 3CO → 2Fe + 3CO2
26.	Co	Smaltite (CoNiFe)As2, Cobaltite (CoAsS).
27.	Ni	Millerite (NiS), Reduction of NiO with CO              NiO + CO → Ni + CO2
28.	Pt	Native, Speryllite (PtAs2).  Obtained by thermal decomposition of (NH4)2PtCl6. (NH4)2PtCl6 → Pt + 2NH4Cl + 2Cl2.
29.	Cu	Native, Copper pyrites or chalcopyrites (CuFeS2 or Cu2SfeS3) (main source) (Cuprite Cu2O), Azurite (2CuCO3.Cu(OH)2), Malachite (Cu(OH)2.CuCO3, Copper glance (Cu2S).
30.	Ag	Native, Argentite or silver glance (Ag2S), Horn silver or chloragyrite (AgCl), Ruby silver or pyragyrite (Ag3SbS3) It is extracted as 4NaCN + Ag2S → 2Na[Ag(CN)2] + Na2S, 2Na[Ag(CN)2] → 2Ag + Na2[Zn(CN)4]
31	Au	Native, Bismuth aurite (BiAu), Sylvanite (Au, Ag) Te2. It is extracted by cyanide process. 4Au + 8KCN 2K[Au(CN)2] + Zn → K2 [Zn(CN)4] + 2Au.
32.	Zn	Zinc blende (ZnS), Calamine (ZnCO3), Zincite (znO), willemite (Zn2SiO4) Obtained by reduction of ZnO with C or electrolysis of ZnSO4. ZnO + C → Zn + CO.
33.	Mg	Cinnabar (HgS) obtained by direct reduction of HgS(by heating alone) HgS + O2 $\stackrel{∆}{\to }$ Hg + SO2
34.	U	Pitch blende or Uraninite (U3O8) or UO2.2UO3, carnotite (K2O.2UO3, V2O5.3H2O) Antunite (UO2.PO4.2H2O) Obtained by reduction of U3O8 by C. U3O8 + 8C → 3Cl + 8CO 98 to 99 to pure U is obtained by reducing U3O8 by Mg, Ca or Al. 3U3O8 + 16 Al → 9 U + 8Al2O3.

Illustration 5: Which of the following is not an ore?

(A) zinc blende                 (B) pitch blende                 (C) bauxite                 (D) cast iron

Solution: Cast iron is not an ore.

Exercise 3:

(i) Among the following groups of oxides, the group that cannot be reduced by carbon to give the respective metal is

(A) CaO, K₂O               (B) Fe₂O₃, ZnO               (C) Cu₂O, SnO₂               (D) PbO, Fe₃O₄

(ii) The chief source of iodine, in which it is present as sodium iodate is

(A) carnallite

(B) sea weeds

(C) caliche

(D) I₂ never exist as sodium iodate

(iii) Pyrodustie is a/an

(A) oxide ore

(B) sulphide ore

(C) carbide ore

(D) carbonate ore

Answer to Exercise

Exercise 1:

(i) B               (ii) C               (iii) C

Exercise 2:

(i) C               (ii) A               (iii) D

Exercise 3:

(i) A               (ii) C               (iii) A

SOLVED PROBLEMS -1

Prob 1. What type of ores are subjected to calcination?

Sol: Calcination process is normally applied to carbonates and bicarbonates.

Prob 2. How is crude Ag refined electrolytically?

Sol: Impure silver is refined by electrolysis.  In this method the impure metal is made the anode and the pure metal is made the cathode.  An acidified solution of the metal salt or molten metal salt is made the electrolyte.  On passing electricity, pure metal is deposited on the cathode.

Prob 3. What are the impurities present in cast iron?

Sol: Cast iron contains nearly 4%C.

Prob 4. What are the changes that take place during roasting?

Sol: During the roasting three types of changes might take place

(i) Oxidising roasting   (ii) sulphatizing roasting   (iii)  chloridizing roasting.

Prob 5. What is the primary product of Bassemerization of Matte?

Sol: Blister copper ($\approx$ 98% pure Cu) is obtained.

Prob 6. Write the a chemical equation between horn silver and sodium cyanide?

Sol: AgCl + 2NaCn $\to$ Na [Ag(CN)₂] + NaCl

Prob 7. Can ‘Al’ be used instead of ‘Zn’ to precipitate ‘Ag’ from sodium argento cyanide? Why?  or why not?

Sol: ‘Al’ can also be used in the reaction because it is more reactive than Ag.  Any metal which is more reactive than Ag can be used for precipitation.

Prob 8. ‘Zn’, Cu are more reactive and Au is less reactive than ‘Ag’ chemically.  How are they elemeinated in the electrolytic refining of Ag?

Sol: The silver metal can be also obtained from argentiferrous lead also.  Two common process adopted for this are.

(a)  Parke’s process and      (b)  Pattinson’s process.

Prob 9. Why the fluorides of Mg, Ba & Na are added to magnesia?  Give your reason.

Sol: Magnesia is a high melting solid.  To lower its mp the fluorides are added and also the reactions are facilitated by fluorides of Mg, Ba & Na.

Prob 10. What is the purpose of porcelain hood in the extraction of Mg from carnalite?

Sol: The collection of chlorine is controlled and the hood prevents the contact between chlorines magnesium vigorous reaction takes place at 970K if they come together.

SOLVED PROBLEMS -2

Prob 1. The most abundant metal in the earth crust is:

(A) Al               (B) Fe               (C) Ca               (D) Na

Sol: (A)  The most abundant metal in the earth crust is aluminium.

Prob 2. Froth floatation process is based on

(A) specific gravity of the ore particles

(B) magnetic properties of the ore particles

(C) wetting properties of the ore particles

(D) electrical properties of the ore particles

Sol: (C) Froth floatation process is based on wetting properties of the ore particles

Prob 3. Complex formation method is used for the extraction of

(A) Zn               (B) Ag               (C) Hg               (D) Cu

Sol: (B)  Complex formation method is used for the extraction of silver.

Prob 4. Gold is extracted by hydrometallurgical process based on its property

(A) of being electropositive

(B) to form complexes which are water soluble

(C) of being less reactive

(D) to form salts which are water soluble

Sol: (A)

Prob 5. Heating of pyrites in presence of air to remove sulphur is called as

(A) roasting               (B) calcination               (C) smelting               (D) fluxing

Sol: (B) Heating of pyrites in presence of air to remove sulphur is called as calcination

Prob 6. Froth floatation process is used for the

(A) oxide ores          (B) sulphide ores          (C) chloride ores          (D) all of these

Sol: (B)  Froth floatation process is used for the sulphide ores.

Prob 7. In the froth floatation process, for the purification of ores, the ore particles float because

(A) they are light

(B) their surface is not easily wetted by water

(C) they bear electrostatic charge

(D) they are insoluble

Sol: (B)  In the froth floatation process, for the purification of ores, the ore particles float because their surface is not easily wetted by water.

Prob 8. Which method of purification is represented by the following equations?

$\mathrm{Ti}+2{\mathrm{l}}_2\stackrel{522\mathrm{K}}{⟶}{\mathrm{Til}}_4\stackrel{1700 \mathrm{K}}{⟶}\mathrm{Ti}+2{\mathrm{l}}_2$

(A) Cupellation               (B) Poling               (C) Van Arkel               (D) zone refining

Sol: (C)  Titanium is purified by Van Arkel method.

Prob 9. Van Arkel method of purification of metals involves converting the metal to a

(A) volatile stable compound

(B) volatile unstable compound

(C) non-volatile stable compound

(D) none of the above

Sol: (A)  Van Arkel method of purification of metals involves converting the metal to a volatile stable compound.

Prob 10. Zone refining is a method to obtain

(A) very high temperautre

(B) ultrapure Al

(C) ultrapure metals

(D) ultrapure oxides

Sol: (C)  Zone refining is a method to obtain ultrapure metals.

FORMULAE AND CONCEPTS AT A GLANCE

1. Metals obtained by electrolytic reduction are Li, Na, K, Mg, Ca, Al, Sr, Ba

2. Metals obtained by reduction of oxides by carbon – Zn from ZnO, Sn from SnO₂.

3. Metals obtained by reduction with water gas – Ni

4. Metals obtained by reduction with CO is Fe.

5. Metals obtained by reduction of oxides b thermite process, alumino thermite process Cr from Cr₂O₃, Mn from Mn₃O₄.

6. Metals obtained by air reduction Hg from HgS, Pb from PbS and Cu.

7. Metals obtained by precipitation method are – Ag, Au.

8. Heavy metals like Sn, Pb, Fe, Cu, Zn are obtained by roasting and smelting process.

9. Hydrometallurgy: It involves the extraction of metals from ores using aqueous solution. It includes (a) leaching (b) reduction.
Ag and Au are extracted by this process.

10. Pyrometallurgy: In this process, the decomposition of the minerals and extraction of the metal is broughabout in dry state at high temperature by the action of heat. It involves the following steps
(a) Calcination   (b) Roasting   (c) Smelting         (d) Refining

11. Thermite: It is a mixture of 3 part Fe₂O₃ and 1 part Al powder when ignited with the help of barium peroxide, Fe₂O₃ is reduced to iron and as enormous amount of heat is produced due to exothermic nature of reaction.
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe+Heat (2500^oC)
The molten mixture is utilized for welding and the process is known as thermit welding known as gold Schmidt alumino thermic process.

12. Amalgamation process:
Ore + Hg → Amalgm $\stackrel{\mathrm{distilled}}{\to }$ Hg + metal
Pt, Ag, Au form amalgam.

13. Electrometallurgy:
In this process metals are obtained through electrolysis.
e.g. the electropositive metals are obtained by this method e.g. Na, Mg etc.

14. Refractory material: The substance capable of with standing very high temperature without undergoing any deformation is called refractory material.
Acidic refractories: Silica, quartz and sand stone.
Basic refractories: Lime, dolomite and magnesite.
Neutral refractories: Chromite, bone ash and graphite.

15. Anodizing: It is a process of forming an oxide coating on metal surface by making it an anode by electrolytic method is called anodizing.

16. Bessemerisation: The oxidation of impurities by passing the hot blast of air through molten metal in Bessemer converter is called bessemerisation.
E.g. Pig iron and copper are purified by this method.

17. Matte or regules: Artficiarly obtained sulphides are known as matter or regulus.
E.g. CH₂S in extraction of copper.

18. Pulverisation: The conversion of large pieces of a substance into small fine piece or powder is known as pulverization.

19. Sulphating roasting: It is partial oxidizing roasting. Roasting of galena gives mixture of lead oxide and lead sulphate.
2PbS + 3O₂ → 2PbO + 2SO₂
PbS + 2O₂ → 2PbSO₄ (Lead sulphate)

20. Chlorinating roasting: Silver ores mixed with common salt when heated in presence of air, the chloride is obtained.
Ag₂S + 2NaCl → 2AgCl + Na₂S

21. Sintering: the conversion of small pieces of a substances into larger one by partial fusion is known sintering.

22. Order of relative abundance of elements in the earth crust by weight is
O > Si > Al > Fe > Ca > Na > K > Mg > H > Ti > Cl > F.