Principles of Metallurgical Operations

AISECT TUTORIALS : CHEMISTRY : SET-10

CHAPTER - 1

Principles of Metallurgical Operations (Sodium, Aluminium, Iron, Copper, Silver, Zinc and Lead) usually found in the company of rock or alluvial impurities like clay, sand, etc. Sometimes lumps of almost pure metals (nuggets) are also found.

1. Occurrence of Metals. A few metals particularly noble metals (e.g. Ag, Au, Pt, etc.) having least electropositive character occur in nature in free (native) state. Sometimes lumps of almost pure metals (nuggets) are also found. However, most of the metals occur in nature as their compounds. These metallic compounds occur in the earth’s crust along with a number of rocky and other impurities and are known as minerals. The impurities present are known as gangue or matrix.

(ii) Oxidised ores. These ores consist of oxides or oxysalts (e.g., carbonates, phosphates and silicates) of the metals. Important oxide ores are haematite (Fe2O3), bauxite (Al2O3.2H2O), tinstone or cassiterite (SnO2), zincite (ZnO), pyrolusite (Mn2O3), etc. Important carbonate ores are limestone (CaCO3), dolomite (CaCO3. M g C O3), magnesite (MgCO3) , calamine (ZnCO3) malachite [CuCO3. Cu(OH)2], etc.

Thus the compound of a metal found in nature is called a mineral. A mineral may be a single compound or a complex mixture.

Important sulphate ores are gypsum (CaSO4.2H2O), barytes (BaSO4) , an d anglesite (PbSO4).

Those minerals from which metal can be economically extracted are called ores. Thus all ores are minerals but all minerals are not ores. For example, copper occurs in nature in the form of several minerals like cuprite (Cu2O), copper glance (Cu2S), copper pyrites (CuFeS2) and malachite [CuCO3. C u ( O H )2], copper pyrites is considered as the most economical mineral for the extraction of the metal. Hence copper pyrites is the chief ore of copper.

(iii) Sulphurised ores. These ores consist of sulphides of the metals like iron, lead, mercury, copper, zinc, etc. Important sulphide ores are iron pyrites (FeS2), g a l e n a ( P b S ) , c o p p e r py r i ti es (CuFeS2), zinc blende (ZnS) and cinnabar (HgS). (iv) Halide ores. Metallic halides are very few in nature. However, among the halide ores, chlorides are the most common. Important halide ores are sodium chloride. (NaCl), horn silver (AgCl), carnallite

1.1 Ores may be divided into four groups. (i)

Native ores. These ores contain the metal in free or metallic state, e.g., silver, gold and platinum. These are (1)


(KCl.MgCl2.6H2O), fluorspar (CaF2) and cryolite (AlF3.3NaF).

(iii) Felspar, KAI Si3O8

2.1 Ores of Few Important Metals. Commercially important ores of few of the metals are summarised below. 1. Magnesium (i) Magnesite,

MgCO3

(ii) Dolomite,

MgCO3. CaCO3

(iii) Epsomite (Epsom salt),

MgSO4. 7H2O

(iv) Carnallite,

MgCl2.KCl. 6H2O

(v) Asbestose,

CaMg3 (SiO3)4

(vi) Talc

Mg2 (Si2O5)2 Mg(OH)2 CuFeS2 or Cu2S. Fe2S3

(ii) Cuprite (Ruby copper)

Cu2O

Cu(OH)2. CuCO3

(v) Azurite,

Cu(OH)2 . 2CuCO3 Ag2S

(ii) Horn silver,

AgCl

(iii) Ruby silver (Pyrargyrite),

3 Ag2S Sb2S3

(vi) Corundum,

Al2O3

(vii) Diaspore,

Al2O3.H2O SnO2

(i) Galena,

PbS

(ii) Anglesite,

PbSO4

(iii) Cerussite,

PbCO3

(iv) Lanarkite,

PbO. PbSO4

8. Iron (i) Haematite Fe2O3 (Red haematite) (ii) Limonite 2Fe2O3. 3H2O (Brown haematite) (iii) Magnetite,

Fe3O4

(iv) Siderite FeCO3 (Spathic iron ore), (v) Iron pyrites

FeS2

(vi) Copper pyrites, CuFeS2

3. Metallurgy Metallurgy is the branch of chemistry which deals with the method of extraction of metals from their ores and preparation of alloys. The extraction of metals cannot be carried out by any universal. method because extraction of each metal requires different procedure of extraction which depends upon the nature and properties of the metal. In general, noble metals such as Au, Ag etc. are usually extracted by amalgamation or cyanide process. Active metals, such as Na, K, Ca, Mg, Al etc. are usually obtained by electrolysis of their chlorides, oxides or hydroxides. Heavy

4. Zinc (i) Zinc blende,

ZnS

(ii) Calamine,

ZnCO3

(iii) Zincite ZnO (Red zinc oxide), (iv) Willemite

Zn2SiO4

5. Aluminium (i) Bauxite,

K2O.3Al2O3.6SiO2. 2H2O

7. Lead

3. Silver (i) Argentite (Silver glance),

(v) Mica,

(i) Cassiterite (Tin stone)

(iii) Copper glance, Cu2S (iv) Malachite,

Al2O3.2 SiO2. 2H2O

6. Tin

2. Copper (i) Copper pyrites

(iv) Kaolinite,

Al2O3

(ii) Cryolite, Na3AIF3 (2)


metals, e.g., Cu, Zn. Fe, Pb, Sn etc. are extracted by making use of roasting and smelting methods.

Graphite is one of the best material for the manufacture of electrodes and crucibles because it neither melts nor softens even at the highest temperature of the furnace.

4. REFRACTORY MATERIALS.

Metals such as platinum, thorium, tungsten and their oxides are suitable for refractory material. Silicon carbide or carborundum (SiC) is used as refractory for special purposes. Silica resists temperatures upto 1750oC, bauxite bricks upto 1800oC, alumina (Al2O3) upto 2000oC and magnesia and chromite bricks upto 2200oC.

The substances which are capable of withstanding very high temperatures without melting or becoming soft are called refractory materials. They are thus used in the form of bricks for the internal lining of furnaces, fluxes and hotter parts of chimney and also for the lining of laddles and converters.

5. Various Type of Furnaces.

The refractory materials are generally metals, metal oxides or mixture of metal oxides and sometimes carbides also. A suitable refractory material : (a) Does not melt or soften to an appreciable extent on exposure to intense heat. (b) Resists sudden variations of temperature. (c) Does not crumble at high temperature and pressure. (d) Can withstand the corrosive action of slags which are rich in iron and other metallic oxides.

(i)

Reverberatory furnace. In this type of furnace, the charge is placed on the hearth and heated by the flames deflected from its concave roof. Air supply can be controlled by vents and direct blast. In reverberatory furnace since the fuel does not come in direct contact with the charge, it can be used for reduction as well as oxidation process. For reduction the material is mixed with a reducing agent like coke and heated while for oxidation it is heated in a current of air. The calcination and r o a s t i n g a r e u s u a l l y d on e in a reverberatory furnace. It has been used in case of copper, tin, lead and wrought iron.

Refractory materials are generally of three types- Acidic, basic and neutral refractories. Acidic refractories are those which react with bases. Examples are silica in the form of ganister (a silicious rock containing 92% SiO2) and 2.7% Al2O3, silicious sandstones etc. Basic refractories are those which react with acids. Examples are magnesite (MgCO3) , d o l o m i te ( Mg CO3.CaCO3), l i m e s t o n e ( Ca CO3) et c . Neutral refractories are those which neither react with acids nor with bases. Examples are graphite, chromite etc. Some semi neutral refractories are also known. For example, fire clay consisting of 50-60% SiO2 and 20-35% Al2O3 (alumina) is an example of semi neutral refractory material.

(ii)

Blast furnace. It has double cup and cone arrangement at the top to prevent the exit of hot gases during the addition of charge. The maximum temprature attained is 1500oC near the tuyers. It has three zones : zone of combustion (bottom), zone of fusion (middle) and zone of reduction (upper). The temperature range decreases from the bottom i.e. at the tuyers to the top. In other words the zone of combustion

(3)


present at the bottom has the maximum temperature of about 1500oC, while the zone of reduction present at the top has the minimum temperature of about 200-300oC.

6. ORE DRESSING The process of removing gangue or matrix (non-metallic and rocky materials, such as quartz mica, felspars and other silicates) from the meatel is called ore dressing, which may be accomplished by the following meathods.

The charge is introduced through a h o p p e r a n d a c u p - a n d - c on e arrangement provided at the top. Air, heated by combustion of waste gases, is blown into the furnace under pressure through 8-20 nozzles called tuyers. Thus the downcoming charge meets the upward moving hot air blast. Blast furnaces are used for the extraction of iron and copper. (iii) Electric furnaces. In such furnaces electrical energy is converted into heat energy. These furnaces are largely used where a cheap power is available and very high temperatures are required, and also for electrolytic reduction. (iv) Regenerative furnaces. I n t he s e furnaces, the heat carried away by fuel gases is not allowed to be wasted. Refractory materials. Substances which resist high temperatures and do not become soft are called refractory materials. Acidic refractories are SiO2 and gannister (SiO2 + Al2O3); basic refractories are CaO and MgO; neutral refractories are graphite, chromite and carborundum (SiC).

(i)

Hand Picking - The gross lumps of the rocks may be removed from the ore by simple hand picking and these are then broken away with the hammer. The stony impurties from the iron ore haematite are removed by this method.

(ii)

Hydraulic Washing or Levigation This method is based on the difference in the densities of the gangue and the mineral particles. The ore after grinding, is washed with a running stream of water as a result of which the lighter gangue particles are washed away and the heavier ore particle settle down rapidly. Gravity separation is usually carried out by using. Wilfley table or hydraulic clasifier.

(iii) Froath Floatation- This process is especially suitable for the concentration of low grade ores and sulphide ores. The process is based on the different wetting characteristics of the ore and gangue particles with water and oil. The ore is preferentially wetted by oil and the gangue particles by water. The crushed sulphide ore is treated with water to form a pulp or paste or slurry. This is introduced in a tank and water is added. Now a frother or foaming agent such as pine, oil, together with a little lime or Na2CO3 is added to the floatation tank. Now another substance, (called c o l l e c t o r ) s u c h a s po ta s s iu m ethylxanthate or amyl xanthate is added. The contents of the tank are

Refractory material should not combine with the ore or metal and must be able to protect the furnace from high temperatures.

Fig. 1 (4)


agitated with a mechanical stirrer and air, under pressure, is blown in. The ore particles selectively become attached to air bubbles produced in the aqueous pulp of the ground ore and float on the surface, from where they can be skimmed off. The gangue particles, which are strongly attracted to water, do not attach themselves to foam bubbles (not affected by the floatation reagent) and hence sink to the bottom of the tank and are separately withdrawn. The froath is removed and suitably treated to get concentrated ore. The ores like copper pyrites (CuFeS2) galena (PbS) and zinc blende (ZnS) are purified by this method.

e l e c t r o ma gn et ic r o ll er , th e non-magnetic ore falls off and the magnetic impurities are held and travel round the magnetic roller so long as they are attracted by it. When the magnetic force of attraction disappears, the impurities fall down into a separate heap (collector). The tinstone ore is separated from magnetic impurity, wolframite (FeWO4) by this method. (B) Extraction of Crude Metal - The following chemical reactions are commonly used. (i)

Calcination - Calcination is the process in which the ore is subjected to the action of heat at high temperature in the absence of air but below its melting point. The process of calcination is carried out in the case of carbonate and hydrated ores. As a result of calcination (a) The moisture is removed (b) Gases m a y b e e x p e ll ed ( c) V o la t il e impurities are removed (d) The mass becomes porous (e) Thermal decomposition of the ore takes place. For example. CaCO3 (limestone) →CaO +CO2 ↑ ; MgCO 3 ; (Magnesite)

Fig. 2

MgO +CO2 ↑

(iv) Magnetic Concentration. T h is p r o c es s i s us e d i n c a s e o f ferromagnetic ores such as iron, tinstone, associated with wolfram and in the processing of monazite sand etc. Hence the process is used when the mineral is attracted by a magnet, but not the gangue.

MgCO3 CaCO3 (Dolomite) → MgO +CaO +2CO2 ↑ CuCO3.Cu(OH) 2 (Malachite) → 2CuO +H2O +CO2 ↑ ZnCO3 (Calamine) →ZnO +CO2 ↑ ; 2Fe2O3.3H2O(Limonite) →2Fe2O3 +3H2O ↑

(v) Electromagnetic Separation - This method is used for separating ore from magnetic impurities. The crushed or powdered ore is dropped over a belt moving over two rollers, one of which is magnetic. As the mass passes over the

The name calcination originated from the o r e c a l c i t e , w h i c h o n t h er m a l d e c o m p o s i t i o n g i v e s q u ic k li m e . Calcination is usually carried out in reverberatory furnace. (5)


(ii)

2CuFeS2 +O2 →Cu2S +2FeS +SO2 ; 2Cu2S +3O2 →2Cu2S +2SO2

Roasting - In the process of roasting, the ore either alone or with the addition of suitable material, is subjected to the action of heat in excess of air at temperatures below its melting point. Roasting is usually carried out in a reverberatory furnace or in a blast furnace. During roasting (a) Volatile impurities like S, As, Sb etc. get oxidised and escape out as volatile gases SO2, As2O3 and Sb2O3 (b) The sulphide ores de-compose to their oxid es evolving SO2 ( c ) T h e moisture is removed (d) Mass becomes porous and thus it can easily be reduced. Roasting may be of many types.

2FeS +3O2 →2FeO +2SO2 (d) Sulphating Roasting - In this type of roasting, the sulphide is not converted to an oxide, but to a soluble sulphate. For example, CuS to CuSO4 or ZnS to ZnSO4. The resulting soluble salt is then leached with water. PbS +2O2 →PbSO 4 ; CuS +2O2 →CuSO 4 ; ZnS +2O2 →znSO 4 (e) Chlorodising Roasting - I n th is process, the metal or its ore is converted into a chloride by heating the ores with NaCl in presence of air. For example,

(a) Oxidising Roasting - In this type of roasting S, As and Sb impurities are removed in the form of their volatile oxides as SO2, As2O3 and Sb2O3 etc. due to combined action of heat and air. The ore is simultaneously converted into its oxides. This type of roasting is used for copper pyrites, zinc blende and lead ores (PbS) etc.

Ag2S +2NaCl →2AgCl +Na2S AgCl +2Hg →AgHg +HgCl (iii) Smelting - It is the process used for all o p e r a t i o n s w h e r e th e m et al is separated by fusion from the ore. The process of smelting is that in which ore is melted with a flux and often with a reducing agent, and it involves, calcination, roasting and reduction. In general, the process of separation of a metal or its sulphide mixture from its ore is fused state is called smelting. Smelting is generally carried out in a blast furnace and high temperature is produced by buring coal or by using electric energy.

2ZnS +3O2 →2ZnO +2SO2 2PbS +3O2 →2PbS +2SO2 (b) Blast Roasting - In this, the oxidation is carried out by a blast of hot air. This process is applied for galena and copper pyrites. (c) Reducing Roasting - In this process, the oxidis ed metallic mineral is subjected to the action of reducing agents (e.g., active hydrogen, carbon or m e t a l l i c s u l p h id es e tc . ) at a temperature below the point of fusion. For example, in the extraction of Cu or Pb, iron sulphide acts are reducing agent.

In smelting, the roasted or calcined ore is mixed with coke and then heated in a furnace. As a result, carbon and CO p r o d u c e d by th e in c om pl et e combustion of carbon reduce the oxide to the metal. For example, in the extraction of iron, haematite ore (Fe2O3) is smelted with coke and (6)


li me s to ne ( fl ux ) . As a res ult of reduction, iron is obtained in fused or molten state.

(c) Reduction with Coke or Carbon Monoxide - The reduction of an oxide ore using carbon (coke) or CO is a clean cut method. The calcined or roasted ore is mixed with coke and heated in a suitable furnace. Carbon and CO (formed by incomplete combustion of carbon) reduce the oxide to the metal. For example,

Fe2O3 +3C →2Fe +3CO Fe2O3 +3CO →2Fe +3CO2 CaCO3 →CaO +CO2 CaO +SiO2 →CaSiO3 Flux Gangue Slag Similarly, in the extraction of copper from copper pyrites, the ore is mixed with coke and heated in blast furnace (smelted). Infusible impurity FeO is converted to FeSiO3 (slag) and is removed. A mixture containing sulphide of copper and iron, called matte is formed in the molten state.

(1) SnO2 +2C →Sn +2CO (2) Fe2O3 +3CO →2Fe +3CO2 (3) CaCO3 →CaO +CO2 Flux

(4) ZnO +C →Zn +CO (5) FeO +CO →Fe +CO2

Other exmple FeO +SiO2 →FeSiO3 Gangue Flux

(6) CaO +SiO2 →CaSiO3

Slag

Flux

ZnO +C →Zn +CO ; SnO 2 +2C →Sn +2CO

Impurity Slag

(1) The concentrated cassiterite (SnO2) is reduced to metallic tin by heating with coke in a reverberatory or blast furnace. (2) The oxide of zinc is reduced by carbon to metallic zinc. (3) The oxides of iron are reduced to spongy iron by CO. (4) Same as (3). (5) Flux limestone is decomposed into CaO and CO2 and in the middle of the furnace at about 1275 K, slag is formed. (6) In the lower part of the blast furnace at 1575 K, the spongy iron undergoes melting and sinks at the bottom and forms a layer below the slag. It is removed periodically and called pig iron or cast iron and contains about 5% carbon.

MnO2 +2C →Mn +2CO (iv) Reduction - Extraction of metals from their ore generally means reduction. It can be carried out in a number of ways. (a) Reduction with Hydrogen - T h e oxides of certain metals such as WO3, NiO, Co2O3, In2O3 may be conveniently reduced by means of hydrogen to the corresponding metal. In2O3 +3H2 →2In +3H2O Co2O3 +6H →3H2O NiO +2H →Ni +H2O WO3 +6H →3H2O +W

(d) Reduction by Heating In Air - Metals whose oxides are unstable towards heat (e.g., less active metals such as Hg, Pb, Cu Sb etc.) are extracted by air reduction. For example, roasting of sulphide or of mercury (cinnabar) yields the metal and not the oxide. Mercury

This method is suitable for metals which are heavier than manganese. (b) R e d u c t i o n w i t h M a g n e si u m Reduction of an oxide of a metal can also be carried out by means of magnesium. Rb2O3 +3Mg →3MgO +2Rb (7)


vapours are allowed to condense the condensing chamber.

possibility of formation of their carbides. Aluminothermic process is used for welding together the broken pieces of rails, machinery, parts of ships etc., without removing them from their position.

2HgS +3O2 →2HgO +2SO2 ; 2HgO →2Hg +O2

2HgO +HgS →3Hg +SO2 Similarly, self reduction takes place in the extraction of copper from sulphide ore.

(f)

Cu2S +2Cu2O →6Cu +SO2 (e) Reduction by Aluminium - Certain metal oxides, such as Cr2O3, Mn3O4 etc. cannot be reduced effectively with carbon or carbon monoxide. In such cases aluminium is used as reducing a g e n t b e c a us e A l i s m o r e electropositive than Cr and Mn. The oxides of all refractory metals are commercially reduced by aluminium a n d t h e p r o c e s s i s k n ow n as Goldschmidt alumino thermite process. A mixture of iron oxide (Fe2O3) and aluminium powder in the ratio of 3 : 1 is called thermite. The thermite is taken in a graphite crucible a n d c o v e r e d wi th a m ix t ur e o f a l u mi ni um p ow de r a nd ba r iu m peroxide. A piece of magnesium ribbon is placed in the mixture. When the ribbon is lighted, the ignition mixture catches fire and burns. The reaction is higly exothermic. The much heat is produced, which is sufficient to melt the metal. This process is called thermite welding in which iron oxide is reduced by aluminium.

Auto Reduction Method - This method does not involve any additional reduc ing method and similar to reduction by heating in air. In this method, sulphide is heated in air until a part is converted into oxide. On further heating in the air, the unchanged sulphide reduces the oxide to metal. For example, 2PbS +3O2 →2PbO +2SO2 2PbO +PbS →3Pb +SO2

(g) Reduction with Na or Ca - Certain metal halides are also reduced with Na or Ca in a closed vessel by heating. TiCl4 +4Na →Ti +4NaCl (h) Reduction with Silicon, Calcium carbide etc. - For example, MnO. FeO +Si +FeO →MnSiO3 +2Fe ; MgCl2 +CaC2 →Mg +2C +CaCl2 (i)

R e d u c t i o n w i t h W at e r G a s (CO +H2) − Both CO and H2 present in water gas act as reducing agents. For example, NiO +CO →Ni +CO2

;

NiO +H2 →Ni +H2O (j)

Fe2O3 +2Al →Al 2O3 +2Fe +185 k.cals (3000º C)

Fe is obtained in molten state, because the reaction is exothermic, Similarly.

Reduction of Complex Salts - Metals, like gold, silver etc. can be precipitated from the complex salt solutions by more electropositive zinc metal. 2NaAg(CN) 2 +Zn →Na2Zn(CN) 4 +2Ag ;

Cr2O3 +2Al →Al2O3 +2Cr +Heat ;

2KAu(CN) 2 +Zn →K2Zn(CN) 4 +2Au

3Mn3O4 +8Al →4Al2O3 +9Mn +Heat

Metals such as Ti, Zr, Ta etc. are obtained by reducing their complex salts with alkali metals or Al.

Coke can not be used for extracting the above metals because of the (8)


K2TiF6 +4K →6KF +Ti ;

elements such as alkali metals and alkaline earth metals and metals with high negative oxidation potentials can not be obtained by above chemical methods. These metals can also not be obtained by reducing their oxides, with carbon, because oxides of these metals are very stable and have to the heated very strongly with carbon to reduce them to metals. Moreover, they are expected to form metal carbides with carbon at such a higher temperature. These metals are, therefore, extracted by electrolytic reduction.

K2ZrF6 +2Al →2AlF3 +2K +Zr (k) Am algam ation Process - T h is process consists of formation of an amalgam of the crushed ore with mercury. The metal amalgam thus formed is distilled to get the metal and mercury vapours are condensed and recovered. The process is usually employed in the extraction of noble metals, like gold, silver etc. Some amalgams, such as sodium amalgam and zinc amalgam have also been used for the separation of metals from their solutions. For example.

Alkali metals, usually occur in nature as chlorides e.g. NaCl, MgCl2.KCl.6H2O (carnallite). Calcium, strontium and barium (alkaline earth metals) occur as carbonates, which can readily be converted into the halides. Metals such as Li, Na, K, Rb, Cs, Ca, Sr, Ba etc. are best obtained by electrolysis of their fused salts (chlorides). In general, electrolytic reduction is carried out by the electrolysis of fused salts (such as chlorides or hydroxides) under an inert atmosphere using a cathode and anode separated by a diaphragm in order to avoid recombination of the products formed at the anode and cathode.

2Ti3++3Zn ⁄ Hg →3Zn2++2Ti ⁄ Hg; 2In3+ +3zn ⁄ Hg →3zn2+ +2In ⁄ Hg In fact, above reactions are known as displacement reactions, in which one metal is displaced by the other in the amalgam. A metal can be displaced from its solution by another whose position is higher than it in the electrochemical series. Usually a more expensive metal is displaced from its solution by a cheap metal. For example, in the electro refining of zinc, the liquid in the vats is rich in Cd. This metal can be recovered by precipitating it by adding zinc.

For example, electrolysis of fused sodium chloride using iron cathode and graphite anode gives sodium metal.

Cd2+ +Zn →Zn2+ +Cd

NaCl ⇒ Na+ +Cl−

Similarly, the sulphide ore with low copper content, when exposed to air, copper sulphide is formed which is leached with excess of water. The scrap iron is then added to the leached solution to precipitate Cu.

At cathode

Na+ +e− →Na

At Anode 2Cl− −2e− →Cl2 Similarly, magnesium is prepared by the electrolysis of fused carnallite.

Cu2+ +Fe →Cu +Fe2+

MgCl2 ⇒. Mg2+ +2Cl−

(1) Electrolytic Reduction - Chemically active and highly electropositive

At cathode Mg2++2e−→Mg (9)


At Anode 2Cl− −2e− →Cl2

The process consists in heating the impure metal in a retort as a result of which pure metal distils over and c o l l e c t s in th e r e c ei v er , wh il e non-volatile impurities are left behind. The volatile compounds are further separated by distillation to get the pure metal.

Aluminium i s o b t a i ne d b y th e electrolysis of fused aluminium oxide. Since fused aluminium oxide (alumina) is not an electrolyte, it is made an electrolyte by dissolving in fused cryolite and then electrolysed using carbon electrodes. Molten aluminium collects at the cathode.

(iv) Fractional Crystallisation - This is another method of purification of metals. For example, the method has been used for the separation of p l a t i n u m a n d i r i d i u m t hr o ug h ammonium hexachloroplatinate and irridate.

2Al2O3 →4Al +3O2 (C) Purification of Metals- A metal obtained by the above methods is not pure. Hence the metal obtained by above methods require adequate refining method, however, depends upon the use to which a metal has to be put.

(v) Cage-Zone Melting Technique- This method is capable of reducing the concentration of impurities to less than one part per billion parts and is based on the principle that an impure metal on solidification will deposit crystals of the pure metal and the impurities will be left behind in the molten part of the metal. Ge, Si, Ga etc. used as semi conductors are refined by this method.

(A) PHYSICAL METHODS (i)

(ii)

Fusion Method - This method is especially employed when the metal is associated with adsorbed gases. For example, fusion method is used to remove dissolved oxygen from silver and dissolved SO2 gas from copper metal.

(vi) Vacuum Arc Sublimation Method This method consists in compressing the impure metal to an electrode. The electrode is then allowed to melt progressively under vacuum in an electric furnace. As a result, volatile impurities are given off. The molten metal is chilled in an externally cooled copper crucible when an ingot of pure metal is obtained. Refractory metals such as Te, Zr, Mo etc. are refined by this this method.

Liquation - This method is used when the melting point of metal is less than that of impurities. For example, zinc is separated from lead by liquation. The impure lead is heated on the sloping hearth of a furnace, when lead melts at a much lower temperature than many of the impurities and flows down the slope. The impurities remain sticking to the hearth at the temperature which is slightly greater than the m.p. of lead. Hg, Sn, Bi etc. are also purified by liquation.

(B) CHEMICAL METHODS (i)

(iii) Distillation - Low boiling point metals, such as Hg, Cd and Zn (volatile metal) etc. are refined by distillation method. (10)

Pyrometallurgical Oxidation - In this process impurities are oxidised in a suitable manner. The oxidation may be


electrolyte. On passing an electric current through the solution pure metal dissolves from the oxidation of anode. The insoluble impurities either dissolve in the electrolyte or fall at the bottom and collect as anode mud.

carried out by poling or farnace refining, cupellation or electrolytic refining. (a) P o li n g o r F u r n ac e Re f in i n g Impurities of reducible oxides from the metals are removed by poling. For example, blister copper containing traces of cuprous oxide as impurity is refined by melting the impure metal on the hearth of a reverberatory furnace. The melt is stirred with green logs of wood. As a result, cuprous oxide is reduced to copper metal by the hydrocarbons produced from the green wood and reducing gases, such as SO2, As2O3 etc. are given off. The reoxidation of copper metal by air is prevented by covering the molten copper surface with a layer of charcoal powder. Tin is also refined by poling.

For example, in the refining of copper, impurities like Fe and Zn dissolve in the electrolyte, while Au, Ag and Pt are left behind as anode mud. (d) Thermal Decomposition Methods Thermal methods include methods as carbonyl method, decomposition of hydrides etc. The carbonyl method is used for the refining of metals like Ni and Fe. For example, in case of nickel, the impure metal is heated with CO. The nickel carbonyl thus formed is then decomposed (after distilling off the impurities) to get pure nickel metal and CO. The process is known as Mond’s process.

(b) Cupellation - This method is used to purify silver containing lead as impurity and depends upon the selective oxidation of lead over silver. The impure silver is smelted in a cupel made of bo ne as h in a blast of air in a reverberatory furnace. The lead is oxidised to lead oxide. (PbO, litharge) which is partly blown away from the crucible by blast of air. The remaining part melts and is absorbed by the bone ash cupel. The completion of the purification process is indicated by a flash produced by the pure molten silver in the cupel.

Ni +4CO →Ni(CO) 4 →Ni +4CO

7. Extraction of Iron Iron occurs in the free state as meteorites which also contain 20 to 30% nickel. In the combined state, iron occurs in the following mineralsMagnetite. Fe3O4 Haematite. Fe2O3 Limonite. 3Fe2O3 . 3H2O Spathic iron ore. Fe Co3

(c) Electrolytic Refining - This is one of the most convenient and important method of refining and gives a metal of high purity. This method is applicable to many metals such as Cu, Ag, Pb, Au, Ni, Sn, Zn etc. The blocks of impure metal form the anode and thin sheets of metal form the cathode. A solution of a salt of the metal is taken as an

Iron pyrites, FeS2 Copper pyrites, CuFeS2 Iron and tin may be extracted by the carbon reduction method. Extraction : Iron is extracted from its p r i n c ip al o r e, h ae ma ti te , A ft er th e preliminary washing, concentration and (11)


roasting, the ore is smelted in the presence of coke and limestone in a blast furnace.

(present as impurity, gangue) to form calcium silicate (fusible slag). CaCO3 →CaO +CO2

Roasted ore (8 parts) with desulphurized coke (4 parts) and limestone pieces (1 part) is fed into the blast furnace from the top. P r e h e at ed a ir i s bl ow n i n t hr o ug h water-jacketed pipes called tuyeres fixed in the lower part of the furnace. There is a temperature gradient as we move from the bottom (temperature about 2000 K) of the blast furnace. The blast furnace may be broadly divided into three main parts as described in the following-

CaO +SiO2 →CaSiO3 (3) Zone of reduction - The upper portion (675 K-975 K) where iron oxide is reduced to spongy iron by carbon monoxide rising up the furnace. Fe2O3 +3CO →2Fe +3CO2 The reduction is believed to take place in stage : 3Fe2O3 +CO →2Fe3O4 +CO2

(1) Zone of fusion - The lower portion where coke burns and produce carbon dioxide and a lot of heating is known as zone of fusion.

Fe3O4 +CO →3FeO +CO2 FeO +CO →Fe +CO2

C +O2 →CO2; ∆H = −406 kJ mol−1

At the bottom of the furnace the molten iron sinks down while above this floats the fusible slag which protects the molten iron from oxidation. These two can be removed from different holes. Waste gases escaping at the top consists of about 30% CO, 10% CO2 and the rest nitrogen.

Here the temperature is about 1775 K. A little above this, where temperature is about 1475 K - 1575 K, iron coming from above melts. (2) Zone of heat absorption - The middle portion (temperature 1075 K-1275 K), CO2 rising up is reduced to CO w ith the absorption of heat.

Iron obtained from the blast furnace is known as pig iron.

CO2 +C →2CO; ∆H = 163 kJ mol−1

Pig iron contains about 2 - 5% carbon as well as other impurities (usually Si, Mn, S and P). Pig iron is converted into cast iron by remelting in a vertical furnace heated by coke. Cast iron expands on solidification and is used for casting various articles. Wrought iron, which is the purest form of iron can be o b t a in ed b y h ea ti ng c a s t i r on in a reverberatory furnace lined with iron oxide. Wrought iron contains about 0.2% carbon.

8. Extraction of Copper. Copper occurs in the native state as well as in the compounds form. The natural ores of copper are.

Fig.3 In this portion, limestone coming from above is decomposed and the resultant lime (CaO) which acts as flux, combines with silica

Copper pyrites, CuFeS2 Malachite, Cu (OH)2 .CuCO3 (12)


The molten matte is finally transferred to bessemer converter. A blast of sand and air is blown in the converter through tuyeres which are situated a little above the bottom. This causes removal of S and As as oxides and ferrous oxide as slag [reaction (iv)]. At the same time Cu2S is oxidized mostly into Cu2O [reaction (ii)] and partly into CuO and CuSO4. All these react with Cu2S giving copper. The reactions are.

Cuprite or ruby copper, Cu2O Azurite, Cu(OH)2 2CuCO3 Copper glance, Cu2S Copper and lead may be extracted by Self-reduction method. Extraction : Copper is mainly extracted from copper pyrites. After the concentration of its ore froth flotation process, the ore is roasted in a current of air to remove arsenic, antimony and much of sulphur. The reactions occurring are.

2Cu2S +3O2 →2Cu2O +2SO2 ↑ 2Cu2S +5O2 →2CuSO4 +2CuO

(i) 2CuFeS 2 +O2 →Cu 2S +2FeS +SO2 ↑

2Cu2O +Cu2S →6Cu +SO2 ↑

(major reaction)

CuSO4 +Cu2S →3Cu +2SO2 ↑

(ii) 2Cu2S +3O2 →2Cu2O +2SO2

Cu2S +2CuO →4Cu +SO2 ↑

(iii) 2FeS +3O2 →2FeO +2SO2

F i n a l l y , c o p p e r m a y b e r e fi ne d electrolytically (electrolyte; copper sulphate; anode; impure copper and cathode; pure copper).

(minor reaction) The ore is then mixed with a little coke and sand and smelted in a water-jacketed blast furnace. The minor reactions that occurred during roasting continue here. Ferrous oxide combines with sand to form a fusible slag. Cuprous oxide formed combines with ferrous sulphide to give ferrous oxide and cuprous sulphide. This is because iron has more affinity for oxygen than copper.

9. Extraction of Lead Lead is widely distributed in nature. It is the stable end product of all natural radioactive elements. It occurs in traces in the native form. In the combined form, it occurs as

(iv) FeO +SiO2 →FeSiO3

Galena, PbS

(v) Cu2O +FeS →Cu2S +FeO

Cerussite, PbCO3 Anglesite, PbSO4

Molten mass collected from the bottom of furnace contains largely cuprous sulphide and a little ferrous sulphide. This molten mass is known as matte.

Wulfenite, PbMnO4 Stolzite, PbWO4 Extraction : Lead is mainly extracted from galena. After the concentration of the ore by froth flotation process. the ore is roasted in a reverberatory furnace for about six hours at a moderate temperature in a current of air. Part of galena is converted into lead oxide and lead sulphate. After this, the supply of air is stopped and small quantities of carbon, quicklime and cheap iron ore are added along with increase of temperature. At this

Fig. 4 (13)


stage, unreacted sulphide reacts with the lead oxide and sulphate giving metallic lead.

Aluminium is the third most abundant element of earth’s crust.

PbS +2PbO →3Pb +2SO2

Extraction : Aluminium is isolated from the electrolysis of bauxite Al2O3 . 2H2O. Since it is difficult to purify aluminium, bauxite ore is purified either by baeyer’s process (or hall’s process) or serpek’s process depending upon the impurity present in the ore.

PbS +PbSO4 →2Pb +2SO2 The obtained lead contains impurities such as Cu, Ag, Bi, Sb and Sn. Silver is removed by Parke’s process where molten zinc is added to molten impure lead. The former is immiscible with the latter. Silver is more soluble in molten zinc than in molten lead. Zinc-silver alloy solidifies earlier than molten lead and thus can be separated. After this, crude lead is refined electrolytically (electrolyte; lead silicofluoride PbSiF6 and hydrofluosilicic acid H2SiF6 with a little gelatine, anode; crude lead and cathode; pure lead).

If the bauxite contains iron oxide as the impurity, one can use baeyer’s or hall’s process as described below. 10.1 Baeyer’s process - Finally ground ore is roasted to convert ferrous oxide to ferric oxide and then digested with concentrated caustic soda solution at 423 K. Al2O3 dissolves while Fe2O3 remains undisolved. The latter is filtered off and from the solution Al(OH)3 is precipitated by adding a weak acid. The ignition of Al(OH)3 gives Al2O3.

10. Extraction of Aluminium

Al2O3 +2OH− +3H2O →2Al (OH) −4 aluminate ion dissolves

Aluminium also does not occur free in nature. In the combined state, it occurs in the following forms-

Al(OH) −4 +H+→Al(OH) 3 +H2O precipitates

Oxides : Corundum, Al2O3

heat

2Al(OH) 3 −−−> Al2O3 +3H2O

Diaspore. Al2O3 . H2O

10.2 Hall’s process - In this process, the ore is fused with sodium carbonate when soluble meta-aluminate (NaAlO2) is produced. This is extracted with water leaving behind iron oxide. Carbon dioxide at 323-333 K is passed through water extract to get Al(OH)3 which on heating gives Al2O3.

Bauxite. Al2O3 . 2H2O Fluorides : Cryolite. Na3AlF6 Silicates : Feldspar, KAlSi3O8, Mica. (KAlSi3O10 (OH)2)

fused Al 2O3 +Na2CO3 −−−−−> 2NaAlO 2 +CO2

Kaolinite. (Al(OH)4, Si2O5) Basic sulphates :

extracted with water

Alunite or Alumstone, K2SO4 . Al2 (SO4)3 . 4Al(OH)3

2NaAlO 2 +3H2O +CO2 →2Al (OH) 3 +Na2CO3

heat 2Al(OH) 3 −−−−−> Al2O3 +3H2O

Basic Phosphates : Turquoise. AlPO4 . Al(OH)3 . H2O

If the impurity is silica, the serpek’s process is used to purify bauxite.

Aluminates : Aluminates of Mg, Fe and Mn.

(14)


Serpek’s process - The powdered ore is mixed with coke and heated to 2075 K in a current of nitrogen. Silica present is reduced to silicon which volatilizes off and alumina gives aluminium nitride. The hydrolysis of the latter gives Al(OH)3. heating of which gives Al2O3.

Silver in the native form is associated with copper and gold. The main ores of silver are Argentite or silver glance, Ag2 S Pyrargyrite, 3A2 S . Sb2 S3 Proustite, 3Ag2 S . As2 S3 Horn silver, AgCl

SiO2 +2C →Si +2CO2

Extraction : Silver is extracted from its ore by the cyanide process (MacArthur-Forrest process). After the preliminary crushing and concentration by froth floatation process, the ore is leached with 0.4 -7% solution of sodium cyanide kept agitated by a current of a i r . S i lv e r pa s s es i nt o s ol ut io n as argentocyanide :

Al2O3 +3C +N2 →2AlN +3CO AlN +3H2O →Al(OH) 3 +NH3 2Al(OH) 3 −−−−> Al2O3 +3H2O heat After obtaining pure Al2O3. it is dissolved in fused cryolite Na3AlF6 with a little fluorspar CaF2, and is electrolysed in an iron tank lined with blocks of carbon which serve as the cathode. The anode consists of a number of graphite rods suspended verticaly inside the tank.

Ag2 S +4NaCN →2Na[Ag(CN) 2] +Na2S The air blown in remove Na2 S as Na2S2 O3 and Na2SO4 causing the above reaction to proceed to completion. 2Na2S +2O2 +H2 O →Na2S2O3 +2NaOH Na2S2O3 +2 NaOH +2O2 →2Na2SO4 +H2O The solution obtained above is filtered and treated with scrap iron or zinc when silver gets precipitated. 2Ag(CN) −2 +Zn →Zn (CN) −42 +2Ag The obtained silver is purified electrolytically (electrolyte : silver nitrate solution containing 1% nitric acid, anode : impure silver and cathode : pure silver). The impurities like zinc and copper pass into the solution while gold falls down as anode mud.

Fig. 5 Aluminium gets settled at the bottom of the tank and can be removed. The reactions occurring at the electrodes are Cathode : Al3++3e−→Al

12. PROPERTIES OF METALS

Anode : 2 O−22 →O2 +4e−

12.1 Sodium and Potassium

C +O2 →CO2 Anode is replaced periodically because of its consumption.

Sodium and potassium are the members of group 1. Their electronic configurations are

11. Extraction of Silver

11

(15)

Na : 1s2 , 2s22p6 , 3s1

AISECT TUTORIALS : CHEMISTRY : SET-10 19K

: 1s2 , 2s2 2p6 , 3s23p6 , 4s1

12.2 Aluminium

Only one electron per atom is available for the metallic bonding, therefore, these metals are soft and low melting. These have low ionization energy and thus are good reducing agents. These metals can be detected by flame photometry as the electronic excitation requires radiation in the vis ible region (sodium : yellow and potassium : lilac). Potassium (also caesium) is used in photoelectric cells as this element emits electrons when irradiated with light. Both sodium and potassium (and also other a l k a l i m e t a l s e x c e p t l i t h i u m a t lo w temperature) crystallize in the body-centred cubic lattice. Sodium and potassium are the sixth and seventh most abundant elements in the earth’s crust. Being the strongest reducing agents, these metals are not prepared by reducing oxides. These are usually obtained by the electrolysis of fused halides with impurity added to lower the melting point.

Aluminium belongs to group 3. Its electronic configuration is 13Al

: 1S2 , 2s22p6 , 3s23p1

It is a silvery white metal, nontoxic and capable of taking high polish. It has a high thermal and electrical conductivity, excellent corrosion resistance and good malleability and ductility. Aluminium is a self - protective metal. This is due to the formation of protective layer of aluminium oxide. At high temperature, aluminium reacts with nitrogen and chlorine giving nitride and chloride. Pure water has almost no action on aluminium when cold. Salt water corrodes it rapidly especially when it is hot. Aluminium dissolves rapidly in hydrochloric acid liberating hydrogen. The reaction is vigorous if the acid is hot and concentrated. Dilute sulphuric acid does not attack aluminium. Hot concentrated sulphuric acid reacts with aluminium liberating SO2.

Chemically, these elements are very reactive and tarnish rapidly in air to form the oxide. With oxygen, sodium forms peroxide (Na2O2) whereas potassium forms superoxide (KO2) . Both react with hydrogen, nitrogen, halogens, sulphur and phosphorus to form corresponding hydride, nitride, halides, suplhide and phosphide, respectively.

+ − SO2− 4 +4H +2e →SO2 +2H2O] × 3

Al →Al 3+ +3e−] × 2 + 3+ 2Al +3SO2− 4 +12H →2Al +3SO2 +6H2O

Nitric acid both dilute and concentrated does not attack aluminium because the latter becomes passive due the formation of oxide layer.

Both react with water to form hydroxide and hydrogen; potassium catches fire when it reacts with water and the reaction of sodium with water is less violent.

Strong alkalis react with metal producing meta aluminates. 2Al +6OH−+6H2O →2[Al (OH) 6] 3− +3H2

Both sodium and potassium dissolve in very high concentration in liquid ammonia. These solutions conduct electricity very similar to the pure metals. This is due to presence of solvated electrons along with solvated metal ions. The colour of the solution is dark blue.

Aluminium has great affinity for oxygen and is, therefore, good reducing agent. It reduces many other metallic oxides. Fe2O3 +2Al →2Fe +Al2 O3

(16)


(ii) NO−3 +2H+ +e− →NO2 +H2 O] × 2

In the above reaction, a lot of heat is generated and forms the basis of aluminothermit process.

Pb →Pb 2++2e− Pb +2NO−3 +4H+→Pb 2+ +2NO2 +2H2 O

12.3 Lead

(concentrated )

With concentrated HCl, Pb forms H2PbCl4.

Lead is member of group 14. Its electronic c o n f i g ur a ti on is 82Pb

Pb +2HCl →PbCl2 +H2

: [Xe] 4f14, 5d10, 6s2 6p2

PbCl2 +2HCl →H2 PbCl4 chlorplumbic acid

Lead is a soft, bluish grey metal. It is highly malleable.

With concentrated sulphuric acid, Pb forms PbSO4 liberating SO2.

Dry air has no action on lead but in moist air a protective coating of basic carbonate is formed and protects it from further oxidation. When heated in air, it forms litharge which at very high temperature is converted to red lead. 6pb +3O2 →6PbO litharge

O2 T > 725 K

Pb +2H2 SO4 →PbSO4 +2H2 O +SO2 In caustic alkali, lead dissolves slowly forming plumbite and hydrogen Pb +2NaOH →Na2bo2 +H2 On heating, lead also combines with Cl2 and S forming PbCl4 and PbS, respectively.

2Pb 3 O4 red lead

12.4 Iron

Lead is rapidly corroded by water containing dissolved oxygen to form loose deposit of lead hydroxide which is soluble in water rendering it poisonous. This solvent action of water is known as plumbo solvency. The presence of nitrates, ammonium salts and organic matter in water accelerates this dissolution whereas bicarbonates. sulphates and phosphate retard the dissolution due to the formation of protective layer.

Iron belongs to group 8 of the periodic table. Its electronic c o n f i g u r a t i on is 1s2 , 2s22p6 , 3s23p63d6, 4s2. Pure iron is a silvery white metal. It combines with a number of nonmetals (e.g. oxygen, halogens, sulphur, nitrogen and carbon) on heating. Dry air has no affect on iron. However moist air results in the rusting of iron - and electrochemical process in which iron is converted into Fe(OH) 3 or FeO(OH) .

Hydrochloric acid and sulphuric acid have little effect on lead but nitric acid reacts vigorously. With dilute nitric acid. NO is evolved while with concentrated nitric acid, NO2 is evolved.

Red hot iron combines with steam resulting in the formation of magnetic oxide of iron (Fe3O4) and releasing hydrogen.

(i) NO−3 +4H+ +3e− →NO +2H2 O] × 2 Pb →Pb2+ +2e− ] × 3 3Pb

+2NO−3

3Fe +4H2O →Fe3O4 +4H2

+

+8H →2NO +4H2O (dilute)

Dilute HCl and H2SO4 displaces H2 when reacted with iron.

(17)


Fe +2H+→Fe2++H2

Iron is available in different forms e.g. pig iron cast iron, wrought iron and steel. Of these, wrought iron is the purest form of iron containing 0.1 to 0.25% of carbon and less than 0.25% of other impurities like S, Si, P and Mn.

Dilute HNO3 forms ferrous nitrate and ammonium nitrate. Fe +2H+→Fe2++H2 Dilute HNO3 forms ferrous nitrate and ammonium nitrate.

The most important form of commercial iron is steel which contains 0.15 - 2.0% of carbon and traces of S and P. Increasing the carbon content results into harder steel.

Fe →Fe2++2e−] × 4 NO−3 +10H++8e−→NH+4 +3H2O 4Fe +NO−3 +10H+→4Fe2++NH+4 +3H2O

Steel alloy contains special constituents such as tungsten, chromium, nickel, cobalt, vanadium, molybdenum and manganese which impart desired properties to steel. Some of them are as follows -

Hot concentrated H2SO4 acid liberates SO2 and a mixture of ferrous and ferric sulphates. Fe +2H2SO4 →FeSO4 +SO2 +2H2 O

Stainless steel : Fe (73), Cr(18), Ni(8) and C(1)

2FeSO4 +2H2SO4 →Fe2(SO4) 3 +SO2 +2H2 O

Moderately conc entrated nitric acid dissolves iron giving ferric nitrate and librates oxides of nitrogen. With fuming nitric acid, the reaction does not occur as the metal becomes passive.

Nickel steel : Fe(96 - 98), Ni(2 - 4)

Rusting of iron - It is due to the formation of local electrochemical cells on the surface of

Permalloy : Fe(21), Ni(78), C(1)

Tungsten steel : Fe (94), W(5), C(1) Invar : Fe(64), Ni(34) Alnico : Fe(63), Al(12), Ni(20), Co(5) Manganese steel : Fe(86), Mn(13), C(1)

metal. In case of iron, Fe is oxidized to Fe2+ at one spot which acts as an anode. Electrons released from this spot move to another spot where oxygen in the presence

12.5 Copper and Silver Copper and silver belong to group 11. Their electronic configurations are

of H+(which is believed to be available by the absorption of Co2 into moisture) is reduced to oxide in the form of water. The two reactions are as follows -

Cu : [Ar] 3d10 , 4s1 Ag : [Kr] 4d10 , 5s1 Both Cu and Ag are malleable and ductile, Next to silver, copper is the best conductor of heat and electricity.

Anode (oxidation) : Fe(s) →Fe2+ (aq) +2e−

Dry air and pure water have no affect on Cu and Ag. In moist air, Cu slowly reacts forming a coating of green basic carbonate, CuCO3 Cu(OH) 2. In thermosphere of SO2. a similar coating of basic sulphate, CuSO4 3Cu(OH) 2 is formed. At high temperature, Cu reacts with oxygen (or air) forming cupric and cuprous oxides.

Cathode (reduction) : O2(g) +4H+ (aq) +4e−→2H2O(l) The electrolytic solution is moisture on the surface of iron. If the water present is saline, it will help in increasing the speed of corrosion. (18)


2Cu +O2 −−−−−−→2CuO

1 2Ag +H2O + O2 →2Ag+ +2OH− 2

Below1370 K

4Cu +O2 −−−−−−→ 2Cu2O

+

−

−

Ag +2CN →[Ag(CN) 2] × 2 1 − − − 2Ag +H2O + O2 +2CN →2[Ag(CN) 2] 2OH 2

Above 1370 K

Dilute HCl and H2SO4 have no action on Cu and Ag. In the presence of air, however, Cu reacts as follows.

Copper forms a number of alloys. A few important alloys of copper are as follows-

2Cu +2H2SO4 +O2 →2CuSO4 +2H2O

Brass : Cu(60.8) , Zn(20.4)

2Cu +4HCl +O2 →2CuCl2 +2H2O

Bronze : Cu(75.9), Sn(10.25)

Hot concentrated H2SO4 liberates SO2 with both Cu and Ag.

Aluminium bronze : Cu(90) , Al(10)

+ 2+ Cu +SO2− 4 +4H →Cu +SO2 +2H2O

Monel metal : Cu(30) , Ni(67) , Fe +Mn(3%)

+ + 2Ag +SO2− 4 +4H →2Ag +SO2 +2H2O

Bell metal : Cu(80) , Sn(20)

Dilute nitric acid produces NO whereas concentrated nitric acid produces NO2 both with Cu and Al

Gun Metal : Cu(87) , Sn(10) , Zn(3) German silver : Cu(50) , Zn(25) , Ni(25) Nickel coin : Cu(75) , Ni(25)

3Cu +2NO−3 +8H+→3Cu 2++2NO +4H2O (dilute)

14 Carat gold : Au (58) , Ag (14.3) , Cu(12.28)

3Ag +NO−3 +4H+→3Ag++NO +2H2O (dilute)

Zinc

Cu +2NO−3 +4H+→Cu 2++2NO2 +2H2O (concentrated)

Zinc belongs to group 12. Its electronic

Ag +NO−3 +2H+→Ag++NO2 +H2O (concentrated)

Metallic zinc is bluish-white in colour, It is brittle at room temperature but becomes malleable and ductile between 370 K and 420 K.

configuration is [Ar] 3d10, 4s2.

Heating with Cl2 and S both Cu and Ag react forming halides and sulphides.

Dry air has no action on zinc, However, in moist air, a protective layer of basic zinc carbonate is formed. In the atmosphere of O2, zinc reacts at higher temperature forming zinc oxide.

Copper dissolves in concentrated HBr and HI forming H2[Cu2Br4] and H2[Cu2I4]. In presence of air, copper dissolves in an aqueous ammonium hydroxide solution.

P u r e wa te r h as n o a c ti on on z in c . Zinc-copper couple decomposes water l i be r at in g hy d r og en . Im pu r e z i nc decomposes boiling water slowly.

1 Cu +H2O + O2 →Cu2++2OH− 2 Cu2++4NH3 →Cu(NH3) 2+ 4

Dilute HCl and H2SO4 liberates H2 and SO2, respectively with impure zinc.

Silver dissolves in the solution of an alkali cyanide in the presence of oxygen forming the complex argentocyanide ion.

Zn +2Hcl →ZnCl2 +H2 (19)


Zn +2H2SO4 →ZnSO4 +SO2 +2H2O

Caustic alkalies react with zinc forming soluble zincate and liberate hydrogen.

With nitric acid, the following reactions occur-

Zn +2OH− →ZnO2− 2 +H2

4Zn +2NO−3 +10H+ →4Zn 2++N2O +5H2O (dilute)

Zinc combines with halogens and sulphur forming halides and sulphides. Zn is fairly electropositive element. It replaces Cu, Ag, Au and Pb form their salt solutions.

4Zn +NO−3 +10H+ →4Zn 2++NH+4 +3H2O (very dilute) Zn +2NO−3 +4H+→Zn2++2NO2 +2H2O (concentrated)

(20)


13. SYNOPSIS & EXPLANATORY NOTES metals are either black or dark grey in colour.

General Properties of Metals A metal may be defined as a substance which is a good conductor of heat and electricity and which possesses a bright appearance called metallic clustre. Certain mechanical properties such as high tensile strength, malleability and ductility are usually associated with metallic state,

Most of the metals have white silvery colour and are non-transparent, since nearly all of them absorb long range and short wavelength of light spectrum to the same extent. Caesium and gold are yellow, while copper is yellow-red. Metals are classified as light metals and dense metals in terms of their density. Light metals have a density of less than 5g/cm3 (Li, K, Ca, Al etc). Heavy metals are those which have a density of more than 5g/cm3. Examples of heavy metals are Sn, Pb, Hg, Fe etc.

Pure metals in solid state are crystals in which the particles are arranged in definite geometrical order to form crystal lattices, also called space lattices. The lattice points are occupied by positively charged ions and neutral atoms, and in the space between them free electrons move. Atoms in the crystal lattices of metals are arranged very close to one another and their valence electrons may move not only ground their own atoms, but also around neighbouring atoms. Thus the valence electrons move freely within the whole metal forming the so called electron gas or electron sea. The presence of free electrons in metals is confirmed by the fact that metals possess high electrical conductivity and emit free electrons on heating.

Lithium (density 0.53g/cm3) is th e lightest and osmium (density 22.5 g/cm3) is the heaviest metal. Metals are classified as low melting and high melting in terms of melting point. Metals having m.p. 350ºC or below are called low melting. Examples are : Pb (327ºC), Sn (232ºC), Na(98ºC), K(63ºC), calcium (28ºC) etc. Metals having m.p. above 350ºC are classified as high melting. Examples are : Fe(1539ºC), Cr (1875ºC). Metal with the highest melting point is tungsten (3380ºC).

All metals, except mercury are solid under ordinary conditions.

Two important physical properties of metals are electrical and thermal conductivity which are due to the presence of free electrons in all metals. The best conductor of electricity is silver followed by copper, gold, chromium, aluminium and magnesium.

In the compact form, that is, in the form of plates and slabs metals possess shining, lustrous appearance. This is due to the reflection of light from their surfaces. In finely powdered form only magnesium and aluminium do retain their metallic lustre, while the powders of the other

Among the mechanical properties, m a l l e a b i l i t y a n d d u c t i l it y ar e characteristic of metals. Malleability is a (21)


is +3, while in those with sulphur, it is +2. Compounds of metals with carbon are called carbides.

property of metals by virtue of which they can be hammered or pressed into new shapes (beaten into sheets) at a temperature below the m.p. of the metal. Ductility is the capacity of metals to be drawn into wires. Metals with low ductility are fragile and those having high ductility are strong enough to be ruptured. Gold has the highest malleability and ductility.

Ca +2C →CaC2 Me ta ls r e ac t wi th ph os p horus at 600-1200ºC and form compounds known as phosphides. 3Li +P →Li 3P ;

3Zn +2P →Zn 3P2

Alkali and alkaline earth metals can react directly with hydrogen to give hydrides.

The common chemical property of metals is their ability to donate electrons and to be transformed into positively charged ions. The ability to give up electrons varies from metals to metal.

2Li +H2 →2Li +H−; Ca +H2 →Ca2+H−2 Metals react with silicon to form silicates. 2Mg +Si →Mg2Si

Whether electrons in atoms are strongly or loosely held is measured by the ionisation energy.

Metals have been arranged in a series called series of standard reduction electrode potentials or electrochemical series or activity series, according to the ability to donate electrons in solutions. Hydrogen has also been placed in this series, because it is the only non-metal which can, like metals, exist in aqueous

Alkali metals have the lowest ionisation energies and therefore they are strong reducing agents. The reducing properties of metals account for their ability to enter into reaction with various oxidising agents such as non-metals, acids and salts of less active metals. The names of all compounds of metals with non-metals end in-ide. For example, oxide, chloride, nitride, sulphide, etc. Metals react with non-metals. (a) Most metals easily react with oxygen to form oxides.

solution as positive ions (H3O+) . Metals have been arranged in the series of standard reduction electrode potentials in order of their decreasing reducing properties in solution or in order of the increasing oxidising properties of their ions in solution. Any metal in the series can displace the metals placed below it from their salt solutions. Metals arranged above hydrogen replace the latter from dilute acids, except HNO3. Alkali and alkaline earth metals replace hydrogen. even from water. The series of standard reduction electrode potentials is valid for redox processes which take place only in aqueous media. Important chemical properties of metals are reflected in their relation to water, acid solutions, alkalies and slats.

2Mg +O2 →2MgO (b) They readily add halogens to form halides. 2Fe +3Cl2 →2Fed3 (c) Metals react with nitrogen to yield nitrides. 3Ba +N2 →Ba3N2 ( d ) M e t a l s r e a c t u n d e r c er t ai n c on di tions with s ulphur to for m sulphides. 2AI +3S →Al2S3 The more electronegative the element, the stronger it oxidises a metal. For example, in compounds formed by iron and chlorine, the oxidation number of Fe (22)


Increase in oxidising properties follows the order : Li+, K+, Ca2+, Na+ , Mg2+, Al3+, Mn2+, Zn2+, Cr3+, Fe2+, Ni2+, Sn2+, Pb2+,

Sulphide ores are concentrated by froath floatation method. Liquation process is used for the concentration of oresQ‘ which are having lesser melting point than impurities.

2H+, Cu2+, Hg2+ 2, + t2+ 3+ Ag , P , Au . Decrease in reducing properties follows the order Li, K, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Ni, Sn, Pb, H2, Cu, Ag, Pt, Au. Thus lithium is most powerful reducing agent and Au is least powerful reducing agent.

Tinstone (SnO2) containing Wolframite (FeWO4) can be c o nc e nt r at ed by e le c tr o ma gn etic separation. The process of heating the ore to a high temperature below its melting point in called calcination. The process of strong heating of the ore below its melting point in the presence of air is called roasting. Sulphide ore is generally roasted in air. Carbonate ores are generally calcined. The high temperature reduction process in which the metal is obtained in molten state is called smelting.

Alkali and alkaline earth metals dissolve in water to form hydroxides known as alkalies. A number of heavy metals react with water on heating to yield oxides. (Steam )

3Fe +4H2O

→

Fe3O4 +4H2

Alkalies react only with those metals which exhibit amphoteric properties.

Amineral from which a metal can be profitably extracted is called an ore.

T h e i m p o r t a n t f u r n a c e s us e d i n metallurgy are blast furnace, open hearth furnace, Bessemer converter and reverberatory furnace. Open hearth furnace is called heat regenerative furnace and it is an special type of reverberatory furnace. Calcination and roasting are carried out in reverberatory furnace. The metals are generally refined b y li qu at io n, d is t il la ti on , p ol in g, cupellation and electrolysis. Smelting is carried out in blast furnace.

The process of removing gangue from the ore is called concentration.

An alloy is a solid solution of two or more elements with metallic property.

The earthy impurities like sand, rock and clay associated with the ore are called gangue or matrix.

The substances which can withstand very high temperature with out melting or becoming soft are called refractory materials. Alloys of mercury are called amalgams. Coating or alloying of metals like Fe with zinc is called galvanising. Coatings or alloying of metal with tin is called tinning. Alloying of a metal with Hg is known as amalgamation. Thomas slag is Ca3(PO4) 2. It is used as fertilizer.

2A1 +2NaOH +2H2O →2NaA1O2 +3H2 More active metals replace the less active metals from their salt solutions. Fe +CuSO4 →FeSO4 +Cu The process of extraction of metals from their ores is known as metallurgy. The metal compound occurring in earth crust is called mineral.

A substance added to convert the gangue into fusible mass is called flux. Gangue + Flux →Slag (Fusible mass). O x i d e a n d c ar b on at e o r es a r e concentrated by gravitational method.

(23)


In alumino thermite process, Al is used as reducing agent.

The slow cooling of red hot steel is called annealing.

Some metals like Al, Mg, Na are prepared by electrolysis of their fused halides or oxides.

In quenching or hardening, the steel article is heated to a temperature which is above 920ºC and then suddenly cooled to normal temperature by dipping in a bath of oil or water.

Copper is obtained by auto reduction. Metals like Ag and Au are prepared by hydrometallurgy.

Heating of steel in contact with charcoal is called cast hardening.

The principal ores of copper are malachite [Cu(OH) 2. CuCO3] and copper pyrites (CuFeS2) .

Heating steel in presence of an atmosphere of NH3 is called nitriding. Iron rusts in presence of oxygen and moisture. The rusting metal always acts as anode. Rusting in moist air involves loss of electrons by Fe. Rusting is oxidation. Rust is brown layer of hydrated ferric oxide. Composition of rust is Fe2 O3 +Fe (OH) 2 or Fe2O3. xH2O. Rusting is prevented by applying grease. painting, tinning and galvanising etc, Rusting of iron is chemical combination reaction.

Matte is a mixture of Cu2S containing little FeS. 98% pure copper formed at the end of Bessemerisation process of copper pyrites is called blister copper. Spelter is 97-98% pure zinc. Formation of alloy (a) Increases the intensity of colour (b) Increases the hardness (c) Decreases the conductivity ( d ) D e c r e a s e s t h e c or r o s io n ( e ) Decreases the melting point (f) Increases the good casting.

(24)


Objective Questions Principle of Metallurgical Operations (Na, Al, Fe, Cu, Ag, Zn & Pb) 1.

The most abundant element on earth crust is

(d) They do not require replacement 6.

(a) Hydrogen

(b) Oxygen

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

(c) Silicon

(d) Carbon

[MP PMT; NCERT; CPMT; MLNR]

[MP PMT; Delhi PMT]

2.

(a) They are light

Naturally occuring substances from which a metal can be profitably (or economically) extracted are called.

(b) Their surface is not easily wetted by water (c) They bear electrostatic charge

[CPMT; MP PET]

3.

(a) Minerals

(b) Ores

(c) Gangue

(d) Salts

Sulphide ores concentrated by

are

(d) They are insoluble 7.

g e n e r a l ly

Whic h of the following metal is sometimes found native in nature. [CPMT; MP PET]

[CPMT; EAMCET; MNR; Delhi PMT; KCET] (a) Froth floatation process

8.

(b) Magnetic separation

(a) Oxide ores

(b) Silicate

(c) Sulphide ores

(d) Carbonate ores

Heating of pyrites in air for oxidation of sulphur is called

(c) Gravity separation

[CPMT; Delhi PMT]

(d) By hand picking 4.

Froth floatation process is used for the concentration of

9.

[NCERT; CPMT; MP PMT; EAMCET; AMU; Delhi PMT; BHU]

5.

(a) Roasting

(b) Calcination

(c) Smelting

(d) Slagging

A substance which reacts with gangue to form fusible material is called [MP PMT; Kurukshetra CEE]

(a) Oxide ores

(b) Sulphide ores

(a) Flux

(b) Catalyst

(c) Chloride ores

(d) Amalgams

(c) Ore

(d) Slag

Refractory materials are generally used in furnaces because

10. Magnetic separation is used for in c r ea s in g c o nc e ntr ation of the following

[MNR; MP PMT] (a) They possess great structural strength

[MP PET]

(b) They can withstand high temperature

(a) Horn silver

(b) Calcite

(c) They are chemically inert

(c) Haematite

(d) Magnesite

(25)


11. Purpose of smelting of an ore is

(c) Metal can be extracted profitably from it

[MP PMT; Kurukshetra CEE]

(d) Metal cannot be extracted from it.

(a) To oxidise it

18. In blast furnace iron oxide is reduced by

(b) To reduce it

[MP PMT]

(c) To remove vaporisable impurities (d) To obtain an alloy 12. Titanium containing mineral found in our country is

(a) Silica

(b) CO

(c) Carbon

(d) Lime stone

19. Inner layer of blast furnace is made of

[NCERT]

[MP PMT]

(a) Bauxite

(b) Bolomite

(a) Graphite bricks (b) Silica bricks

(c) Chalcopyrites

(d) Elmanite

(c) Fire - clay bricks (d) Basic bricks

13. General method for the extraction of metal from oxide ore is

20. Carnellite is a mineral of [CBSE; Delhi PMT]

[CPMT] (a) Carbon reduction (b) Reduction by hydrogen

(a) Ca

(b) Na

(c) Mg

(d) Zn

21. The most abundant metal in the earth crust is

(c) Reduction by aluminium (d) Electrolytic reduction

[BHU, CPMT; MP PMT]

14. Froth floatation process is used for concentration of [MLNR; IIT] (a) Chalcopyrite

(b) Bauxite

(c) Haematite

(d) Calamine

(b) Mg

(c) Al

(d) Fe

22. Formula of carnellite is [MP PET; EAMCET] (a) KCl. MgCl2. 6H2O

15. Which ore is metalloid

(b) K2SO4. MgCl2. 6H2O [MP PMT]

(a) As

(b) Na

(c) Au

(d) Fe

(c) K2SO4. MgSO4. 6H2O (d) K2SO4. MgSO4. CaSO4. 6H2O 23. Metal which can be extracted from all the three dolomite, magnesite and carnellite.

16. When lime stone is heated strongly, it gives off CO2. In metallurgy this process is known as

[MP PET]

[MP PET/PMT] (a) Calcination

(a) Na

(b) Roasting

(c) Smelting (d) Ore dressing

(a) Na

(b) K

(c) Mg

(d) Ca

24. ‘Lapis-Lazuli’ is a blue coloured precious stone. It is mineral of the class

17. A mineral is called an ore if [MP PMT]

[NCERT; AIIMS; BHU]

(a) Metal present in mineral is precious

(a) Sodium - alumino silicate

(b) Metal can be extracted from it

(b) Zinc cobaltate (26)


(c) Basic copper carbonate

31. Which of the following substances consists of only one element

(d) Prussian blue

[MP PET]

25. Which of the following metal is obtained by leaching out process using a solution of NaCN and then precipitating the metal by addition of zinc dust. (b) Silver

(c) Nickel

(d) Iron

(b) Sand

(c) Diamond

(d) Glass

32. A and B are two allotropes of an element. One gram of A will differ from one gram of B in

[NCERT; AIIMS; CBSE] (a) Copper

(a) Marble

[NCERT]

26. Cinnabar is an ore of

(a) Oxidation number (b) Chemical composition

[NCERT] (a) Hg

(b) Cu

(c) Total number of atoms

(c) Pb

(d) Zn

(d) Atomic arrangement

27. Smelting is termed to the process in which [MP PMT] (a) The ore is heated in the absence of air

33. The phenomenon in which white transparent crystals change into white powder is known as [EAMCET]

(b) Ore is cold (c) The ore is heated in the presence of air

(a) Sublimation

(b) Allotropy

(d) Ore is melted

(c) Efflorescence

(d) Deliquescence

28. The substance added in water in the froth floatation process is

34. Which of the following substance can be used for drying gases

[EAMCET]

[EAMCET; MP PET]

(a) Soap powder

(b) Pine oil

(a) CaCO3

(b) Na2 CO3

(c) Coconut oil

(d) None of the above

(c) NaHCO3

(d) CaO

35. The electrolytic method of reduction is employed for the preparation of metals that

29. The substance used in the thermite process of reducing metal ores is [MP PET] (a) Aluminium

[MP PMT; NCERT; CPMT]

(b) Thorium

(a) Are weakly electropositive

(c) Heated Pt gauge (d) Carbon

(b) Are moderately electropositive

30. Cassiterite is concentrated by

(c) Are strongly electropositive

[EAMCET]

(d) Form oxides

(a) Levigation

36. Fr oth floatation process for the concentration of ores is an illustration of the practical application of

(b) Electromagnetic separation (c) Floatation (d) Liquifaction

[NCERT] (a) Adsorption (27)

(b) Absorption


(c) Coagulation

(d) Sedimentation

37. Cupellation process is used in the metallugry of

44. The metallurgical process in which a metal is obtained in a fused state is called

[CPMT; MP PET]

[IIT; MP PET]

(a) Copper

(b) Silver

(a) Smelting(b) Roasting

(c) Aluminium

(d) Iron

(c) Calcination

(d) Froth floatation

45. Of the following, which cannot be obtained by electrolysis of the aqueous solution of their salts

38. An alloy is [MP PMT] (a) Intermetallic compound

[IIT]

(b) A solid substance containing two or more metallic elements (c) A solid which contains one non-metal (d) A solid which contains more than one nonmetal 39. Metals are

(a) Ag

(b) Mg and Al

(c) Cu

(d) Cr

46. One of the following metals forms a volatile compound and this property is taken advantage for its extraction. This metal is

[MADT Bihar]

[NCERT]

(a) Electropositive

(a) Iron

(b) Nickel

(b) Electronegative

(c) Cobalt

(d) Tungsten

(c) Acceptor of electrons

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

(d) None of these 40. The cyanide process is used for obtaining

[BHU]

[Delhi PMT; CPMT; MNR; MP PET/PMT]

(a) Volatile stable compound

(a) Na

(b) Ag

(b) Volatile unstable compound

(c) Cu

(d) Zn

(c) Non volatile stable compound

41. Alloy is an example of

(d) None of the above

[Delhi PMT; CPMT] (a) Gel

(b) Aerosol

(c) Solid sol

(d) Emulsion

48. Which one of the following metals is e x t r a c t e d by th er m al r ed uc t io n process? [EAMCET]

42. An example of halide ore is [MP PMT] (a) Galena

(b) Bauxite

(c) Cinnabar

(d) Cryolite

(a) Copper

(b) Iron

(c) Aluminium

(d) Magnesium

49. Bauxite ore is concentrated by [MP PET]

43. Which of the following is not an ore (a) Froth flotation

[IIT] (a) Bauxite

(b) Malachite

(b) Electromagnetic separation

(c) Zinc blende

(d) Pig iron

(c) Chemical separation (28)


(d) Hydraulic separation

(b) Sodium bicarbonate

50. Chemical reduction is not suitable for converting

(c) Sodium carbonate (d) Calcium carbonate

[MP PET]

57. Washing soda is

(a) Bauxite into aluminium

[CPMT; Delhi PMT; CBSE; MP PMT]

(b) Cuprite into copper

(a) Na2CO3. 10H2O

(c) Haematite into iron

(b) Na2CO3. H2O

(d) Zinc oxide into zinc

(c) Na2CO3. 5H2O

51. Reverberatory furnace is employed in the metallurgical process mainly for

(d) Na2CO3 58. The main salt soluble in sea water is

[MP PMT]

[MP PMT]

(a) Reduction of oxide ores (b) Smelting of sulphide ores (c) Conversion of chloride to sulphate

(a) MgCl2

(b) NaCl

(c) MgSO4

(d) CaSO4

59. The metallic lustre exhibited by sodium is explained by

(d) Getting magnetic materials 52. Globar salt is

[IIT]

[BHU; CPMT; IIT] (a) MgSO4. 7H2O

(b) CuSO4. 5H2O

(c) FeSO4. 7H2O

(d) Na2SO4. 10H2O

(a) Diffusion of sodium ions (b) Oscillation of loose electrons (c) Excitation of free protons

53. The colour given to the flame by sodium salts is

(d) Existence of body centred cubic lattice 60. Electrolysis of molten sodium chloride leads to the formation of

[CPMT; MP PET] (a) Light red(b) Golden yellow (c) Green

[KCET]

(d) Pink

54. Sodium when heated in a current of dry ammonia gives (b) Sodium hydride

(c) Sodium amide

(d) Sodium azide [CPMT] (b) Sodium

(c) Bromine

(d) Magnesium

(c) H2 and O2

(d) Na and Cl2

[IIT]

55. Chile saltpetre is an ore of (a) Iodine

(b) Na and O2

61. A solution of sodium metal in liquid ammonia is strongly reducing due to the presence of

[NCERT] (a) Sodium nitrite

(a) Na and H2

(a) Sodium atoms

(b) Sodium hydride

(c) Sodium amide

(d) Solvated electron

62. Causticization process is used for the preparation of

56. Solvay’s process is used for the preparation of

[CPMT; BHU]

[CPMT; AIIMS] (a) Ammonia

63. (29)

(a) Caustic soda

(b) Caustic potash

(c) Baryta

(d) Slaked lime


NaOH is manufactured by electrolysis of brine solution. The products of the reaction are

[CPMT; Delhi PMT; Bihar CEE; MNR] (a) Reduce silver bromide to metallic silver (b) Convert metallic silver to silver salt

[Karnataka CET 1990] (a) Cl2 and H2

(b) Cl2 and Na−Hg

(c) Remove undecomposed AgBr as a soluble silver thiosulphate complex

(c) Cl2 and Na

(d) Cl2 and O2

(d) Remove unreduced silver

64. Sodium carbonate is manufactured by Solvay process, the products that are recycled are

70. Microcosmic salt is [CPMT; BHU] (a) Na2HPO42H2O

[Karnataka CET 1993] (a) CO2 and NH3

(b) CO2 and NH4Cl

(c) NaCl. CaO

(d) CaCl2, CaO

(b) Na(NH4) HPO44H2O (c) (NH4) 2HPO42H2O (d) None of the above

65. In the preparation of sodium carbonate, which of the following is used

71. In the manufacture of metallic sodium by the fused salt electrolysis (Down’s process) a small amount of calcium chloride is added to

[AFMC 1992] (a) Slaked lime

(b) Quick lime

(c) Lime stone

(d) NaOH

[MP PET; MP PMT]

66. Sodium carbonate reacts with SO2 in aqueous medium to give

(a) Improve the electrical conduction (b) Increase the temperature of electrolysis

[MP PMT] (a) NaHSO3

(b) Na2SO3

(c) NaHSO4

(d) Na2SO4

(c) Bring down the melt temperature (d) Stabilize the metallic sodium 72. In alumino-thermite process, aluminium is used as

67. Soda lime is [Karnataka CET] (a) NaOH

[IIT; DPMT; MP PMT; MP PET/PMT; NCERT]

(b) CaO

(a) Oxidising agent (b) Flux

(c) NaOH and CaO (d) Na2CO3

(c) Reducing agent (d) Solder

68. Molten sodium is used in nuclear reactors to

73. Which of the following ore is used for industrial extraction of aluminium in India

[Karnataka CET] (a) Absorb neutrons in order to control the chain reaction

[MP PET]

(b) Slow down the fast neutrons

(a) Corundum

(b) Keolin

(c) Absorb the heat generated by nuclear fission

(c) Cryolite

(d) Bauxite

(d) Extract radio-isotopes produced in the reactor 69. Sodium thiosulphate (Na2S2O35H2O) is used in photography to

74. Which metal is extracted by electrolytic reduction method [CPMT; MP PET] (a) Cu

(30)

(b) Al


(c) Fe

(d) Ag

(c) Magnesium, Manganese and Copper

75. Bauxite is an oxide ore of

(d) Magnesium, Nickel and Manganese 82. Bauxite containing impurities of iron oxide is purified by

[CPMT; BHU; AFMC; Kurukshetra CEE] (a) Barium

(b) Boron

(c) Bismuth

(d) Aluminium

[CPMT; AIIMS] (a) Hoop’s process

76. Which metal is protected by a layer of its own oxide

(b) Serpeck’s process (c) Baeyer’s process

[NCERT; Delhi PMT; BHU] (a) Al

(b) Ag

(d) Electrolytic process

(c) Au

(d) Fe

83. Thermite is the mixture of

77. Hoop’s pr oces s is used for the purification of the metal

[BHU]

[MP PET] (a) Al

(b) Zn

(c) Ag

(d) Cu

(a) Fe2O3 +Al

(b) Cu +Mg

(c) Zn +Mg

(d) Fe +Al

84. Corundum is [CPMT; DPMT; MP PAT]

78. Cryolite is [AMU] (a) Magnesium silicate

(a) SrO2

(b) Al2O3

(c) CaCl2

(d) Cu2Cl2

85. Hydrogen gas will not reduce

(b) Sodium borofluoride

[IIT]

(c) Sodium aluminium fluoride

(a) Heated cupric oxide

(d) Magnesium silicate

(b) Heated ferric oxide

79. Purification of aluminium done by electrolytic refining is known as

(c) Heated stannic oxide (d) Heated aluminium oxide

[CPMT; CBSE]

86. Anhydrous AlCl3 is obtained from

(a) Serpeck’s process

[BHU; CPMT]

(b) Hall’s process

(a) HCl and aluminium metal

(c) Baeyer’s process

(b) Aluminium and chlorine gas

(d) Hoop’s process

(c) Hydrogen chloride gas and aluminium metal

80. Main ore of aluminium is [CPMT; Raj. PMT] (a) Bauxite

(b) Corundum

(c) Cryolite

(d) Magnetite

(d) None of the above 87. A lu mi ni um is p r ep ar e d i n l ar ge quantities by

81. In duralumin, which metals are alloyed with aluminium

[KCET] (a) Heating cryolite in a limited quantity of air

[CPMT; Delhi PMT] (a) Nickel

(b) Reducing aluminium oxide with coke

(b) Magnesium and Nickel (31)


(c) Reducing aluminium oxide with sodium

[Karnataka CET; IIT] (a) As a catalyst

(d) Electrolysing aluminium oxide dissolved in fused electrolyte

(b) To lower the temperature of the melt and to make the fused mixture very conducting

88. Sapphire is mineral of (a) Cu

(b) Zn

(c) To decrease the rate of oxidation of carbon at the anode

(c) Al

(d) Mg

(d) None of the above.

[BHU]

94. Whic h technique is used in the manufacture of aluminium from bauxite

89. Alum is used by dyers [CPMT; MP PMT]

[NCERT]

(a) For fire-proofing fabrics

(a) Reduction with magnesium

(b) As first-aid for cuts

(b) Reduction with coke

(c) For softening hard water

(c) Electrolytic reduction

(d) As mordant

(d) Reduction with iron

[MP PAT]

95. When Al is added to KOH solution

90. Which is not a mineral of aluminium

[NCERT; CPMT]

[BHU; MLNR]

(a) No action takes place

(a) Anhydrite

(b) Bauxite

(c) Corundum

(d) Diaspore

(b Oxygen is evolved (c) Water is produced

91. Which of the following mineral does not contain Al

(d) Hydrogen is evolved 96. Aluminium is more reactive than iron. But aluminium is less easily corroded than iron because

[IIT Screening] (a) Cryolite

(b) Mica

(c) Feldspar

(d) Fluorspar

[Karnataka CET]

92. In the extraction of aluminium the electrolyte is

(a) Aluminium is a noble metal (b) Oxygen forms a protective oxide layer

[CBSE]

(c) Iron undergoes reaction easily with water

(a) Fused cryolite with felspar (b) Fused cryolite with fluorspar

(d) Iron forms mono and divalent ions

(c) Pure alumina in molten cryolite (d) Pure alumina with bauxite and molten cryolite

97. Aluminium vessels should not be washed with materials containing washing soda since. [Karnataka CET] (a) Washing soda is expensive

93. The function of fluorspar in the electrolytic reduction of alumina dissolved in fused cryolite (Na3AlF6) is

(b) Washing soda is easily decomposed (c) Washing soda reacts with aluminium to form soluble aluminate (32)


(d) Washing soda reacts with aluminium to form insoluble aluminium oxide

(d) On heating it melts in its water of crystallization

98. Which of the following processes does not involve a catalyst

103. An important oxide ore of iron is [MP PAT; MP PET/PMT; MP PET; MP PMT]

[Karnataka CET] (a) Haber’s process

(a) Haematite

(b) Siderite

(b) Thermite process

(c) Pyrites

(d) Malachite

(c) Ostwald process

104. In the manufacture of iron lime stone added to the blast furnace, the calcium ion ends in the form

(d) Contact process 99. W h i c h o f t h e s ta te me nt s ab ou t anhydrous aluminium chloride is correct

[MP PMT; CPMT; KCET; IIT; MADT Bihar]

[IIT] (a) It exists as AlCl3 molecule

(a) Slag

(b) Gangue

(c) Calcium metal

(d) CaCO3

105. Stainless steel is an alloy steel of the following metals

(b) It is not easily hydrolysed (c) It sublimes at 100ºc under vacuum

[MP PET]

(d) It is a strong Lewis base 100. Common alum is [DPMT; CPMT; AMU]

(a) Fe only

(b) Cr and Ni

(c) W and Cr

(d) Ni and Fe

106. Steel becomes soft and pliable by

(a) K2SO4Al2(SO4) 3 . 24H2O

[MP PET]

(b) K2SO4.Cr2(SO4) 3 . 24H2O (c) K2SO4.Fe2(SO4) 3.24H2O (d) (NH4) 2SO4.FeSO4.6H2O

(a) Annealing

(b) Nitriding

(c) Tempering

(d) Case hardening

107. Most stable oxidation state of iron is

101. Which of the following is called alum

[AFMC; CPMT]

[CPMT; Delhi PMT; AIIMS] (a) Aluminium NaAlO2 (b) Na2SO4.Al2(SO4) 3.24H2O

(a) + 2

(b) + 3

(c) - 2

(d) - 3

108. Nickel steel contain % of Ni

(c) KCl.MgCl2.6H2O

[MP PMT/PET]

(d) FeSO4.(NH4) 2SO4.6H2O 102. Which of the following is not true about potash alum

(a) 1 - 5%

(b) 3 - 5%

(c) 6 - 5%

(d) 8 - 5%

109. Permanent magnet is made from

[MLNR]

[MP PMT / PET; MP PMT]

(a) Its empirical formula is KAl(SO4) 2.12H2O (b) Its aqueous solution is basic

(a) Cast iron

(b) Steel

(c) Wrought Iron

(d) All the above.

110. In nitriding process of steel

(c) It is used in dyeing industries

[MP PET/PMT; CBSE] (33)


(a) Steel is heated in an atmosphere of ammonia

(a) CuSO4.5H2O

(b) FeSO4.7H2O

(b) Steel is made red hot and then cooled

(c) CaSO4.2H2O

(d) ZnSO4.7H2O

[Delhi PMT; BHU]

(c) Steel is made red hot and then pluged into oil for cooling (d) None of the above 111. Iron is rendered passive by the action of

(b) Conc. H3PO4

(c) Conc. HCl

(d) Cone. HNO3

[CPMT] (a) Fe2O3

(b) FeS2

(c) FeCO3

(d) Fe3O4

118. The alloy of steel that is used in making automobile parts and utensils

[IIT; MP PET; MP PMT; Delhi PMT; KCET] (a) Conc. H2SO4

117. Formula of magnetite is

[EAMCET; MP PMT]

112. I r o n s h e e t s a r e ga lv a ni z ed by d e p o s i t i n g a c oa ti ng o f or i n galvanisation, iron surface is coated with

(a) Stainless steel

(b) Nickel steel

(c) Tungstun steel

(d) Chromium steel

119. Which of the following has lowest percentage of carbon [Delhi PMT; CPMT] (a) Cast iron

[MP PET; NCERT; Bihar CEE] (a) Zinc

(b) Tin

(b) Wrought iron

(c) Chromium

(d) Nickel

(c) Steel (d) All have same percentage

113. Chemical formula of rust is

120. Which of the following is ferrous alloy

[BHU; MP PET] (a) FeO

(b) Fe3O4

(c) Fe2O3 . xH2O

(d) FeO. xH2O

[Delhi PMT; CPMT]

114. Heating steel to bright redness and then cooling suddenly by plunging it into oil or water, makes it

(a) Invar

(b) Solder

(c) Magnalium

(d) Type metal

121. Galvanisation is the [CPMT; MP PET/PMT]

(a) Hard and pliable

(a) Deposition of Zn on Fe

(b) Soft and pliable

(b) Deposition of Al on Fe

(c) Soft and brittle

(c) Deposition of Sn on Fe

(d) Hard and brittle

(d) Deposition of Cu on Fe

115. Which of the following pairs of elements might form an alloy

122. Best quality of steel is manufactured by [BHU]

[NCERT]

(a) Siemen-Martin’s open hearth process

(a) Zinc and lead

(b) Electrical process

(b) Iron and mercury

(c) Bessemer process

(c) Iron and carbon

(d) Blast furnace

(d) Mercury and platinum

123.

116. Green vitriol is (34)


The chief constituents of stainless steel made in India are

130. Cyanide process is used for obtaining

[MP PMT/PET] (a) Mn and Cr

(b) Al and Zn

(c) V and Co

(d) Ni and Mg

(c) Slag

(d) Gangue

125. Magnetic separation is used for in c r ea s in g c o nc e ntr ation of the following (a) horn silver

(b) calcite

(c) haematite

(d) magnesite

(c) Cu

(d) Zn

(a) PbS

(b) O2

(c) C

(d) A1

132. A common metal that is used for the extraction of some metals from their oxides is

[CPMT; MP PET] (b) Flux

(b) Ag

131. In the extraction of lead by air reduction process, the reducing agent is

124. In the manufacture of iron from haematite, the function of lime stone is as (a) A reducing agent

(a) Cr

(a) Cr

(b) Fe

(c) Mn

(d) Al

133. Whic h method of purification is r e p r e s e n t ed by t he fo ll ow in g equations? 1675k

T : +2I2 −−−−> T : I4 −−−−−> T : +2I2

[M.P. PET] 126.The main function of roasting is (a) To remove the volatile matter

(a) Cupellation

(b) Poling

(c) Van Arkel

(d) Zone refining

134. Zone refining is a method to obtain

(b) Oxidation (c) Reduction

(a) Very high temperature

(d) To make slag

(b) Ultra pure Al (c) Ultra pure metals

(M.P.)

(d) Ultra pure oxide

127. Heating of pyrites in air for oxidation of sulphur is called (a) roasting

(b) smelting

135. In metallurgy, flux is a subtance used to convert

(c) calcination

(d) slagging

(E.A.M.C.E.T.) (a) Infusible impurities to fusible material

(C.P.M.T.; D.P.M.T.)

(b) Soluble impurities to insoluble impurities

128. In blast furnace iron oxide is reduced by (a) silica

(b) CO

(c) C

(d) lime stone

(c) Fusible impurities to infusible impurities

(M.P.P.M.T.)

(d) Mineral into silicate

129. Blast furnace is employed in the smelting of oxide ore with coke and flux in the metallurgy of

136. The lustre of a metal is due to (a) its high density

(a) iron

(b) copper

(b) its high polishing

(c) lead

(d) all the above

(c) its chemical inertness (d) presence of free electrons (35)


137. Which one of the following reactions is a example for calcination process?

144. Bessemer converter is used in the manufacture of

(a) 2Ag +2HCl +(O) →2 AgCl +H2O

[CPMT]

(b) 2Zn +O2 →2

(a) Pig iron

(b) Steel

(c) 2ZnS +3O2 →2ZnO +2SO2

(c) Wrought iron

(d) Cast iron

145. Steel contains

(d) MgCO3 →MgO +CO2 (E.A.M.C.E.T.) 138. Malachite is an ore of (a) iron

(b) copper

(c) mercury

(d) zinc

(b) Ag

(c) Al

(d) Cu

(b) Fe +C +Al

(c) Fe +Mn

(d) Fe +Mn +Cr

146. Mohr’s salt is (a) FeSO4 7H2O (b) Fe(NH4) SO4 6H2O

139. The extraction of which of the following metals involves bessemerisation? (a) Fe

(a) Fe +C +Mn

(c) (NH4) 2SO4 FeSO4 6H2O (d) [Fe(NH4) 2](SO4) 2 6H2O 147. An example of double salt is

(B.H.U.)

[CPMT; CBSE; Roorkee]

140. I n G o l d s c h mi dt a lu mi no th er m ic process, reducing agent used is (C.E.E. Bihar 1995) (a) Coke

(b) Al power

(c) Na

(d) Ca

(b) K4[Fe(CN) 6]

(c) Hypo

(d) Potash alum

148.Malachite is a mineral of [MP PMT; MP PET; MP PET/PMT]

(B.H.U.) 141. Purification of silicon element used in semiconductors is done by

(a) Zn

(b) Fe

(c) Hg

(d) Cu

149. After partial roasting, the sulphide of copper is reduced by

(C.B.S.E.)

[MP PMT]

(a) zone refining

(a) Reduction by carbon

(b) heating

(b) Electrolysis

(c) froth floatation

(c) Self-reduction

(d) heating in vacuum

(d) Cyanide process

142. Purest form of iron is

150. In extraction of copper, we use

[CPMT, DPMT; MP PMT; MP PET) (a) Cast iron

(a) Bleaching powder

[CPMT; MP PMT]

(b) Wrought iron

(a) Cu2S

(c) Hot steel(d) Stainless steel

(b) Pyrites

143. The formula of haematite is

(c) Silver argentocyanide

[MLNR] (a) Fe3O4

(b) Fe2O3

(c) FeCO3

(d) FeS2

(d) CuFeS2 151. Blister copper is [CPMT; DPMT; MP PET; Bihar CEE] (36)


(a) Pure copper

(c) Copper, zinc and tin

(b) Ore of copper

(d) Copper, zinc and silver

(c) Alloy of copper

159. Brass contains

(d) 1% impure copper

[Delhi PMT; CPMT; MLNR; AFMC; EAMCET; MP PMT]

152. The most important oxidation state of copper is [MP PMT] (a) + 1

(b) + 2

(c) + 3

(d) + 4

(a) (Cu + Sn)

(b) (Cu + Ni)

(c) (Cu + Zn)

(d) (Mg + Al)

160. An alloy which does not contain copper is [Delhi PMT]

153. Which of the following property is not expected to be shown by copper [MP PET/PMT; NCERT; MP PET] (a) High thermal conductivity

(a) Solder

(b) Bronze

(c) Brass

(d) Bell metal

161. Percentage of silver in the alloy german silver is

(b) Low electrical conductivity

[CPMT]

(c) Ductility (a) 1.5%

(d) Malleability

(b) 2.5% (c) 10%

(d) 0%

154. One of the constituent of german silver is

162. Reaction between the following pairs will produce H2 except

[IIT; Kurukshetra CEE]

[CPMT; CBSE]

(a) Ag

(b) Cu

(a) Na + ethyl alcohol

(c) Mg

(d) Al

(b) Fe +steam (c) Fe +H2SO4 (aq) .

155. Gun metal is an alloy of

(d) Cu +HCl (aq.)

[MP PMT; CPMT] (a) Cu and Al

(b) Cu, Sn and Zn

(c) Cu, Zn and Ni

(d) Cu and Sn

163. An extremely hot copper wire reacts with steam to give

156. Copper can be extracted from [NCERT; CPMT] (a) Kupfernickel

(b) Dolomite

(c) Galena

(d) Malachite

(c) Sn

(c) Cu2O2

(d) CuO2

[MP PET; CPMT]

[CPMT; DPMT] (b) Mn

(b) Cu2O

164. From a solution of CuSO4 the metal used to recover copper is

157. Which element is alloyed with copper to from bronze (a) Fe

(a) CuO

(a) Sodium

(b) Iron

(c) Silver

(d) Hg

(d) Zn

165. Indicate the mineral from which copper is manufactured

[EAMCET; CPMT; MP PET/PMT]

[NCERT]

158. German silver is an alloy of (a) Copper, zinc and nickel

(a) Galena

(b) Copper and silver

(c) Sphalerite (37)

(b) Cuprite


(d) Chalcopyrite

(b) It reacts with KCl to give Cu2Cl2

166. The slag obtained during the extraction of copper from copper pyrites is composed mainly of

(c) It reacts with NaOH and glucose to give Cu2O (d) It gives CuO on strong heating in air

[MNR; MP PMT] (b) FeSiO3

171. If excess of NH4OH is added to CuSO4 solution, it forms blue coloured complex which is

(c) CuSiO3

[MP PMT; Bihar CEE]

(a) CaSiO3

(a) Cu(NH3) 4SO4

(d) SiO2 167. Copper displaces which of the metal from their salt solutions

(b) Cu(NH3) 2SO4

[CPMT]

(d) Cu(NH4) 2SO4

(c) Cu(NH4) 4SO4

(a) AgNO3

172. Bell metal is an alloy of

(b) ZnSO4

[Delhi PMT; CBSE]

(c) FeSO4

(a) Cu, Zn and Sn

(d) All of the above

(b) Cu, Zn and Ni

168. High purity copper metal is obtained by

(c) Cu and Zn

[MP PMT]

(d) Cu and Sn

(a) Carbon reduction

173. Which composition amongst the following represents the alloy ‘‘german silver’’

(b) Hydrogen reduction (c) Electrolytic reduction

[EAMCET; CPMT; BIT; MNR]

(d) Thermite reduction

(a) Cu(52) , Ni(25) , Zn(18) , Fe(5)

169. Cuprous ion is colourless, while cupric ion is coloured because

(b) Cu(60) , Ni(40)

[EAMCET]

(c) Ni(60) , Fe(25) , Cr(15)

(a) Both have unpaired electrons in d-orbital

(d) Cu(55) , Ni(20) , Zn(25)

(b) Cuprous ion has a completed d-orbital and cupric ion has an incomplete d-orbital

174. The metal commonly present in brass and german silver is [EAMCET]

(c) Both have half-filled p and d-orbintals

(a) Mg

(b) Zn

(d) Cuprous ion has incomplete d-orbital and cupric ion has a completed d-orbital

(c) C

(d) Al

175. Complex is formed in the extraction of [MP PET]

170. Identify the statement which is not correct regarding CuSO4 [MNR; Punjab PMT] (a) It reacts with KI to give iodine (38)

(a) Na

(b) Cu

(c) Ag

(d) Fe

Principles of Metallurgical Operations

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