MOST COMMON QUESTIONS METALLURGY-II 1MARK QUESTIONS 1. Name the process used for desilverisation of lead • Ans: Parke’s process 2. Write the reaction which occurs in the zone of combustion of blast furnace during the extraction of iron
ANS: CO2 (g)+ C(s) ื 2CO(g)‐163kJ This reaction is endothermic. Therefore the temperature decreases gradually from bottom(15000C) towards the top(4000C) 3. Write the equation for the chemical reaction taking place at 600oC in the extraction of iron by blast furnace. • Coke produces “CO” which acts as reducing agent Fe2O3 +3CO ื 2Fe +3CO2 4. Define partition coefficient Ans: “At a constant temperature, a solute distribute itself between two immiscible solvents in such a way that the ratio of its concentration in two solvents is a constant”(distribution ratio or partition co‐efficient)
For example; Silver is 300 times more soluble in molten zinc than in molten lead at 800oC Conc. of silver in molten Zinc 300 partition co - efficient = = = 300 Conc. of silver in molten lead 1
2 MARKS QUESTIONS 1.Metal oxides are unstable at high temperature. Explain using Ellingham diagram OR 7.Draw Ellingham diagram for the formation of HgO. With the help of Ellingham diagram suggest a method for the reduction of HgO
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Ans: Change in std.free energy change v/s Temperature curves for the oxidation of Ag & Hg crosses zero line & their change in std. free energy become +ve even at lower temperature
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So these oxides become unstable & readily decompose on heating
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2.What is the function of lime stone and coke in the smelting of haematite?
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Ans: Lime stone(CaCO3 )decomposes to CaO which acts as “flux
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CaCO3 ื CaO + CO2
CaO + SiO2 ื CaSiO3 (flux) (gangue) (slag)
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Coke produces “CO” which acts as reducing agent Fe2O3 +3CO ื 2Fe +3CO2
3.With the help of Ellingham diagrams explain why aluminium is used as reducing agent in the manufacture of chromium from chromic oxide.
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Ans: Std. Change in free energy value for the formation of Al2O3 is always less than that of Cr2O3.
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Al2O3 is more stable
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Hence “Al” is used to reduce Cr2O3(Chromic oxide)
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This process is called “Goldschmidt alumino thermic” process
Cr2O3+2Alื Al2O3 +2Cr 4. Give the composition of the following a) Limonite b) Magnetite
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Ans: Magnetite‐ Fe3O4
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Limonite ‐2Fe2O3.3H2O
5. With the help of Ellingham diagrams explain why carbon monoxide acts as reducing agent in the production of cast iron from haematite •
Ans: Below 7100C, std.change in free energy for the formation of Fe2O3 is more than that of formation of CO2 form “CO”. Therefore “CO” is better reducing agent for Fe2O3 below 7100C.
Fe2O3 +3CO ื 2Fe +3CO2
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Above 7100C, the std .change in free energy value for the formation of Fe2O3 is more than that of CO formation from Carbon(Coke)
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Hence above 7100C, coke (carbon ) is better reducing agent for Fe2O3.
Fe2O3 +3C ื 2Fe +3CO
3 OR 4 MARKS QUESTIONS 1.Draw a neat labeled diagram of blast furnace used in the extraction of cast iron .Give the chemical reactions that take place in the different zones of the furnace
Ans: Important Minerals of Iron •
Haematite ‐Fe2O3
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Magnetite‐ Fe3O4
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Limonite ‐2Fe2O3.3H2O
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Siderite ‐FeCO3
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Iron Pyrites‐ FeS2
1.CONCENTRATION •
Haematite ore is concentrated by washing with a current of water
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The concentrated ore is subjected to “calcination”
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Volatile impurities are removed.
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If there is any traces FeO, it is oxidised to Fe2O3.
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The ore become porous.
2. SMELTING
A mixture of haematite Ore +lime stone+ Coke (8:1:4) is introduced in to a tall cylindrical blast furnace by means of cup & double cone at the top of the furnace. The widest portion of the furnace is called as “Boshes” Hot air is blasted into the furnace just below the boshes using “tuyers” I. Zone of combustion (15000C) C (S)+ O2(g) ื CO2(g)+406kJ Due to this exothermic reaction, the temperature raises to 15000C at the combustion zone. •
As the CO2 raises up the furnace,coke combines with CO2 to form CO
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CO2 (g)+ C(s) ื 2CO(g)‐163kJ
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This reaction is endothermic. Therefore the temperature decreases gradually from bottom(15000C) towards the top(4000C)
II.Zone of reduction (below 7100C OR at 6000C ) •
At about 6000C, Fe2O3 is reduced by “CO” to give spongy iron
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Fe2O3 +3CO 2Fe +3CO2
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Spongy iron collects at the bottom of the furnace called pig iron or “cast iron”
III.Zone of slag formation: (at 9000C) CaCO3 ื CaO + CO2 CaO + SiO2 ื CaSiO3 (flux) (gangue) (slag)
2. Describe the Parkes process for desilverisation of argentiferrous lead
Ans: Parke’s process is based on the following facts(Principle): *Argentiferrous lead contains up to 2% silver * Molten zinc & molten lead can become immiscible liquid mixture * According to distribution law at 8000C ,Silver 300 times more soluble in the “ molten Zn” layer compared to that of molten lead * Zn‐Ag alloy solidifies more readily compared to that of molten lead ,when cooled.
PROCESS; •
Argentiferrous lead is melted to 800oC.It is mixed with molten zinc
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As silver 300 times more soluble in molten zinc ,most of the “Ag” moves in to the “Zn” layer.
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On cooling ,the upper “Zn‐Ag” alloy solidifies first. It is skimmed off.
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The “Zn‐Ag” alloy is distilled in retort to separate zinc from silver
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The traces of lead impurity is removed by “Cupellation”
INDUSTRIAL IMPORTANT COMPOUNDS 1MARK QUESTIONS 1.Name the catalyst used in the Contact process ANS: V2O5 2. Name the gas liberated at anode during the manufacture of caustic soda using Nelson cell ANS: Cl2
3. Name the chromium compound formed when K2Cr2O7 solution is treated with KOH Ans: potassium chromate 4. How does con.H2SO4 react with PCl5? •
H2SO4 + PCl5 SO3H‐Cl + POCl3 + HCl chlorosulphonic acid is formed
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H2SO4 + 2PCl5 SO2Cl2 + 2POCl3 +2HCl With excess of PCl5 ,sulphuryl chloride is formed
5. Write the molecular formula of Chromyl chloride
CrO2Cl2 2 MARKS QUESTIONS 1.How does conc.H2SO4 react with oxalic acid crystals ? Give equation Ans: H2C2O4 +Conc.H2SO4 ื CO + CO2+[H2SO4.H2O] Oxalic acid undergoes dehydration 2.H2S can not be dried with conH2SO4. Give reason •
Conc.H2SO4 oxidizes H2S to S
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H2S +ConH2SO4 ื SO2 +2H2O +S
3. How does conc.H2SO4 react with formic acid ? Give equation Ans: formic acid undergo dehydration HCOOH Con.H2SO4 ื CO + [H2SO4.H2O] 4. .How does conc.H2SO4 react with a mixture of NaCl and K2Cr2O7 crystals ? Give equation Ans: K2Cr2O7 +4 KCl +6H2SO4 ื 6KHSO4+2CrO2Cl2 +3H2O When a mixture of potassium dichromate crystals and a water soluble chloride is heated with Con.sulphuric acid, red vapours of chromyl chloride is evolved
3 OR 4 MARKS QUESTIONS 1.How ammonia is manufactured by Haber’s process ? •
ANS: Haber’s process involves the direct combination of N2 & H2
N2+ 3H2 ֞ 2NH3 + Heat •
According to Le Chatelier’s principle ,The following favorable conditions give better yield of ammonia;
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i)Finely divided “Fe” catalyst ii)a promoter like Mo or K2O or Al2O3.
iii)a moderate temperature of 773K (5000C)
iv)A high pressure of 200atm
Step‐I; Compression;A mixture of N2&H2 in the ratio of 1:3 by volume is compressed to a pressure of 200 atm Step‐II: Conversion;*The compressed gaseous mixture is passed over heated “Fe‐catalyst” in presence of “Mo” as promoter
*The catalytic converter is maintained at 450‐5000C *Only about 15‐20% of the mixture is converted in to ammonia N2+ 3H2 ֞ 2NH3+Heat STEP‐III COOLING; •
The gaseous mixture is passed through cooling pipes. Only NH3 liquefies
Step‐IV: Recycling •
The unreacted gases are collected & recycled
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NH3 gas is dried over CaO to get liquor ammonia
2. Describe the manufacture of sodium hydroxide (caustic soda) using Nelson cell. Principle: NaCl ื Na+ + Cl‐ : H2O ֞ H+ + OH‐ •
A solution of sodium chloride in water contains Na+, Cl‐, H+ and OH‐
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During electrolysis, only H+ ion reduced to H2 at
cathode .Similarly only Cl‐ is oxidized to Cl2 at anode •
The solution become richer in Na+ & OH‐ ions PROCESS; Nelson cell consists of a rectangular steel tank. A perforated U‐tube is suspended in the tank. It is made to act as Cathode.
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The steel U‐tube is lined inside with asbestos which act as diaphragm
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A saturated solution of NaCl in water (Brine) is taken in the cell.
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A graphite rod dipped in the solution is made to act as Anode
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At Cathode;(Reduction)
2H+ +2e‐ ื H2
2Cl‐ ื 2e‐ + Cl2
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* At anode :(Oxidation)
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The solution becomes richer in NaOH.It collects in the catch basin at the bottom
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The steam is circulated ,to keep the electrolyte warm & to keep the pores clean and clear
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Purification: The 98% pure NaOH is further purified by dissolving in alcohol
3. How is pure K2Cr2O7 manufactured from chromite ore?
ANS: Step‐I:Concentration of Chromite ore ; •
Chromite ore(FeoCr2O3 or FeCr2O4)
is concentrated by Gravity separation method. Step‐II:Roasting of concentrated ore’. •
The concentrated ore is roasted with Na2CO3 in a reverberatory furnace in presence of excess of air to obtain Sodium chromate (Na2CrO4)
4FeO.Cr2O3 +8Na2CO3 + 7O2 ื 8Na2CrO4 +2Fe2O3 +8CO2 •
Na2CrO4 is treated with calculated amount of conc.H2SO4 to get sodium dichromate (Na2Cr2O7)
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2Na2CrO4 +H2SO4 ื Na2Cr2O7 +Na2SO4 + H2O
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The less soluble Na2SO4 crystals are removed by filtration.
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Hot & concentrated solution of Na2Cr2O7 is treated with calculated amount of KCl
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Na2Cr2O7 +KCl ื K2Cr2O7 +2Na
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The solution is concentrated ,less soluble K2Cr2O7 separates out. The crystals are removed by filtration.
4. How is con H2SO4 is manufactured by Contact process? •
SO2(g)+O2 (g) ֞ 2SO3(g) + 188kj
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According to Le Chatelier’s principle, the following favorable conditions are maintained;
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i)Catalyst like V2O5 or
Platinized asbestos or Fe2O3. •
ii)Temperature=723K or 5000C
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iii)Pressure ;2 to 3 atm
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Mixture of SO2 & O2 is purified by passing through a series of Chambers; •
1)Dust chamber: Steam is passed. Steam condenses on the dust particles which settle at the bottom
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2)Cooler: The hot gases are cooled by passing through cooling pipes
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3)Scrubber: Water is sprayed from the top of the tower. Water soluble impurities are removed.
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5)Drier: The gaseous mixture is dried by spraying Con.H2SO4.
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6)Arsenic purifier: As2O3 impurity is removed by using Fe(OH)3 ppt.
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7)Tyndall box: Pure & dry gas is passed through a “Tyndall box” to detect the presence of colloidal impurities CONVERSION:
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The gaseous mixture is pre‐heated to 3000C & passed in to the converter.
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The converter is packed with “V2O5” or “Pt” catalyst & maintained at 5000C.
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2SO2(g)+O2(g) ֞ 2SO3(g)+188kj
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SO3 gas is absorbed by using Con.H2SO4 (98%) in the absorption tower to get OLEUM or Fuming sulphuric acid.
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SO3 + H2SO4 ื H2S2O7
Oleum is carefully diluted with calculated amount of water to obtain 98% H2SO4. •
H2S2O7 + H2O ื 2H2SO4.
D-BLOCK ELEMENTS 1 MARK & 2 MARKS QUESTIONS 1.Mention two reasons for the formation of co‐ordination compounds by transition metals (2m) Ans:a)Presence of vacant d‐orbitals b)High charge /size ratio i.e high polarization power
2.Why are transition elements &their compounds good catalyst? Explain (2m) Ans: a)They exhibit variable oxidation states b)Presence of vacant d‐orbitals using which unstable intermediate compounds can be formed which decompose giving products c)In their finely divided form they can produce large surface area for adsorption 3.Which among Cu+ &Cu+2 salts is coloured? (1m) •
Ans: Cu2+ is paramagnetic & coloured, because it has unpaired electron
E.C of Cu2+ :[Ar]3d9 4s0 ‐ one unpaired electron
E.C of Cu+ :[Ar]3d10 4s0 ‐ No unpaired electron
4.Among Sc3+(Z=21) &Cr3+(Z=24),which is coloured. Why?
(2m)
Ans: E.C of Sc3+ is [Ar]3d0 In Sc3+,there are no unpaired electron. Therefore it is colourless
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E.C of Cr3+ is [Ar]3d3 4s0 There are three unpaired electrons in 3d‐ orbitals. Hence it should be paramagnetic & coloured
7.Name the transition metal in 3d series which shows maximum oxidation state (1m) •
Ans: Manganese(Mn) shows maximum oxidation state of +7
K+1 Mn+7O4‐2
8.Why Fe3+ ion is more stable than Fe2+ion? Ans:Presence of half filled d‐orbitals
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OR
Smaller the size higher the stability
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OR
Higher the oxidation state ,more is the stability
