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Which of the ores mentioned in Table 6.1. could be concentrated by magnetic separation method?
Table 6.1 Principal ores of some important metal.
What is the significance of leaching in the extraction of aluminium?
The reaction.
Cr2O3 + 2Al → Al2O3 + 2Cr (ΔG° = – 421 kJ)
is thermodyanmically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?
At room temperature, all reactants and products of the given reaction are in the solid state. As a result, equilibrium does not exist between the reactants and the products. Hence, the reaction does not take place at room temperature.Certain amount of activation energy is essential even for such reactions which are thermodynamically feasible.
Is it true that under certain conditions. Mg can reduce Al2O3 and Al can reduce MgO? What are those conditions?
The role of depressant in froth floatation process is to prevent certain type of materials from forming the froth with bubbles. For example, to separate two sulphide ores (ZnS and Pbs), NaCN is used as a depressant which selectively allows PbS to come with froth, but prevents ZnS from coming to froth. This happens because NaCN reacts with ZnS to form Na2[Zn(CN)4].
4NaCN+ZnS → Na2[Zn(CN)4] + Na2S
Titanium is a metal of modern times. It is obtained as oxide. Why it could not be extracted earlier despite its wide occurence?
Name the common elements present in the anode mud in electrolytic refining of copper. Why are they so present?
State the role of silica in the metallurgy of copper.
What criterion is followed for the selection of the stationary phase in chromatography?
The stationary phase is immobile and immiscible (like the Al2O3 column in column chromatography)
The stationary phase have different adsorptivity for each component of mixture. It should be thermally stable.
What is the role of cryolite in the metallurgy of aluminium?
The role of cryolite in the metallurgy of aluminium:
(i)To lower the melting point of Al2O3
(ii)To dissolve Al2O3
(iii)To increase electrical conductivity of Al2O3.
Why is zinc not extracted from zinc oxide through reduction using CO?
Out of C and CO, which is a better reducing agent for ZnO?
CO is a better reducing agent for ZnO.
What is the role of graphite rod in the electrometallurgy of aluminium?
Predict conditions under which Al might be expected to reduce MgO.
Define the term gangue or matrix.
The impurities present in the ore such as sand, rocks etc are known as gangue.
Define the term flux.
Flux is a substance which combines with gangue to produce an easily fusible mass called slag.
Deine the term slag.
During metallurgy 'Flux’ is added which combines with ‘gangue’ to form ‘slag’. Slag separates more easily from the ore than the gangue. Slag is fusible mass, which usually floats over molten metal, obtained by the reaction of the flux with impurities present in the concentrated ore.
CaO + SiO2 → CaSiO3
gangue flux slag
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Why magnesium oxide is used for the lining in steel making furnance?
Magnesium oxide is used to make linings for blast furnaces because it is resistant to heat. Magnesium oxide due to its high melting point of around 2500-2800 degree Celsius is resistant to the high temperature in a blast furnace. Its melting point is too high because of the strong ionic bonds between the small Mg2+ and O2- ions.
Which process is generally used for the benefication of sulphide ores?
Froth floatation process.
An iron ore has impurities which are attracted by magnet. Suggest process for its benefication.
Magnetic separation
Give one example where hydro-metallurgy is used for metal extraction.
Extraction of silver from its ore.
How does NaCN act as a depressant in preventive ZnS from forming the froth?
NaCN forms a layer of Zinc complex, Na2Zn(CN)4 on the surface of ZnS and thereby prevents it from the formation of froth.
Levigation is a process of removing the lighter impurities by allowing the water to flow through the powdered cake.
What is the major role of fluorospar (CaF2) which is added in small quantities in the electrolytic reduction of alumina dissolved in fused cryolite?
the major role of fluorospar is to lower the temperature of the melt.
Name the oxide ores of (a) iron (b) zinc, (c) manganese (d) aluminium.
Ultra pure silicon is needed by electronic industry. By which method of refining, such a high purity silicon is obtained?
Sulphide ores usually concentrated by froth flotation process. Why?
Why is the formation of sulphate in calcination sometimes advantageous?
Sulphates are usually water soluble and the gangue remains insoluble. Therefore, the desired metal is leached away as soluble sulphate from insoluble gangue.
Carbon is a cheaper reducing agent than aluminium. Why is then aluminium used for reduction in some cases?
Aluminum is used as a reducing agent in those cases where the metal oxide is of a comparatively more reactive than zinc, etc,. Which cannot be satisfactory reduced by carbon. This is because a more reactive metal like aluminum can displace a comparatively less reactive metal from its metal oxide to give free metal.
Why does carbon reduce copper oxide but not calcium oxide?
What is wrought iron?
Wrought iron is the purest form of iron with 99.5%. Fe and 0.5% impurities (mostly c) composition.
What is pig iron? What is its composition?
How is the cast iron obtained?
Cast iron is obtained by igniting pig iron with scrap iron and coke in special furnances by a blast of hot air.
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What is composition of cast iron?
Composition of Cast iron is, it contains Fe 97%, Carbon 3%.
Why roasting of copper pyrites is done?
It is done to remove moisture and volatile impurities as well as to decompose pyrites into FeS and Cu2S. In this process free sulphur is also oxidised.
In electrorefining of copper, where are the Ag and Au found?
These are found in the anodic mud.
Write the names of materials mixed before the calcined ore is subjected for smelting in the extraction of iron.
Coke and limestone.
Which reducing agent for the ore is used in the extraction of iron in the blast furnance ace?
Carbon monoxide is used as reducing agent in the extraction of iron in the blast furnance ace.
Write the name of the iron obtained from the blast furnance?
Pig iron obtained from the blast furnance.
Why is ferric chloride preferred over potassium chloride in case of cut leading to bleeding?
Lime stone is used in the manufacture of pig iron from haematite. Why?
Haematite contains SiO2 as main impurity and thus use of lime stone is made to remove SiO2 in form of slag.
Name any two ores of magnesium.
Give reason for the following: Although aluminium is above hydrogen in the electro-chemical series, it is stable in air and water.
An ore example of galena (PbS) is contaminated with zinc blende (ZnS). Name one chemical which can be used to concentrate galena selectively by froth floatation method.
NaCN can be used to concentrate galena selectively by froth floatation process.
Out of C and CO, which is better reducing agent at 673 K?
CO is a better reducing agent at 673 K
Why copper matte is put in silica lined converter?
Suggest a condition under which magnesium could reduce alumina.
Why reduction of a metal oxide becomes easier if the metal formed is in liquid state at the temperature of reduction?
If at any site, low grade copper ores are available and zinc and iron scraps are also available. Which of the two scraps would be more suitable for reducing the leached copper ore and why?
Copper can be extracted by hydrometallurgy but not zinc. Explain.
Why is the extraction of copper from pyrites difficult than from its oxide ore through reduction.
In the graph of ΔrG° Vs T for the formation of oxides, the Cu2O line is almost at the top. So it is quite easier to reduce oxide ores of copper directly to the metal by heating with coke (both the lines of C, CO and C, CO2 are at much lower positions in the graph particularly after 500-600 K).
However sulphide ores are roasted/smelted to give oxides.
2Cu2S + 3O2 → 2Cu2O + 2SO2
The oxide can then be easily reduced to metallic copper using coke.
Cu2O + C → 2Cu + CO
Explain: (i) Zone refining (ii) Column chromatography.
Write down the reactions taking place in different Zones in the blast furnance during the extraction of Iron.
The higher temperature range, depend on the points of corresponding intersections in the ΔrG0 vs T plots. (Given in ncert book)
These reactions are as follows:
At 500 – 800 K (lower temperature range in the blast furnace)–
3Fe2O3 + CO → 2Fe3O4 + CO2
Fe3O4 + 4CO → 3Fe + 4 CO2
Fe2O3 + CO → 2FeO + CO2
At 900 – 1500 K (higher temperature range in the blast furnace):
C + CO2 → 2CO
FeO + CO → Fe + CO2
The silicate impurity of the ore is removed as slag by calcium oxide (CaO), which is formed by the decomposition of limestone (CaCO3).
CaCO3 → CaO +CO2
CaO +SiO2 → CaSiO3
flux impurtiy (slag)
Write chemical reactions taking place in the extraction of zinc from zinc blende.
Anode: Zn → Zn2+ +2e-
Cathode: Zn2+ +2e- → Zn
Describe a method for refining nickel.
Nickel is refined by Mond's process. Nickel when heated in a stream of carbon monoxide forms volatile nickel carbonyl Ni(CO)4. The carbonyl vapour when subjected to still higher temperature undergoes thermal decomposition giving pure metal.
How can you separate alumina from silica in a baxuite ore associated with silica? Give equations, if any.
Aluminium bauxite is carried out by digesting the powdered ore with a concentrated solution of NaOH at 473 – 523 K and 35 – 36 bar pressure.
Al2O3(s)+2NaOH(aq) +3H2O(l)→ 2Na[Al(OH)4(aq)
The aluminate in solution is neutralised by passing CO2 gas and hydrated Al2O3 is precipitated:
2Na[Al(OH)4](aq) + CO2(g) → Al2O3.xH2O(s) + 2NaHCO3(aq)
The sodium silicate remains in the solution and hydrated alumina is filtered, dried and heated to give back pure Al2O3.
Giving examples differentiate between 'roasting' and 'calcium'.
|
Roasting |
Calcination |
|
1. It is a process of heating the ore in presence of excess of air. |
1. It is a process of heating strongly in the absence of air. |
|
2. It is used to convert the sulphides ore into oxide ore. 2ZnS(s) + 3O2(g) →2ZnO(s) + 2SO2 (g) |
2. It is used to convert the carbonate or hydrated oxide ores to oxide ore. ZnCO3 (s) →ZnO(s) + CO2 (g) |
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Cast iron |
Pig iron |
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1.It is obtained by melting pig iron with scrap iron and coke using hot air blast. It contains about 3% carbon. |
1. It is obtained from the blast furnace. It contains about 4% carbon and other impurities like S, P, Si, and Mn. |
|
2. It has a slightly lower melting point than pig iron. |
2. It has slightly higher melting point than cast iron. |
How is leaching carried out in case of low grade copper ores?
Name the processes from which chlorine is obtained as a bye-product. What will happen if an aqueous solution of NaCl is subjected to electrolysis?
Chlorine is obtained as a bye-product in Castner-Kallner process.
NaCl → Na+ + Cl–
Electrolysis of an aqueous solution of sodium chloride:
In aqueous solution, sodium chloride ionises
as:
NaCl(aq) → Na+(aq) + Cl– (aq)
When electricity is passed through the solution, the following reactions take place at the respective electrodes.
At Cathode: The reduction of H2O molecules take place in preference to the reduction of Na+ ions as:
2H2O + 2e– → 2OH– (aq) + H2(g)
At Anode : Cl– ions are preferentially liberated at the anode giving Cl2 gas.
The overall reaction representing electrolysis of aqueous solution of sodium chloride is
Outline the principles of refining of metals by the following methods:
(i) Zone refining.
(ii) Electrolytic refining.
(iii) Vapour phase refining.
(i) Zone refining: The method is based on the principle that the impurities are more soluble in the melt than the pure metal. A circular mobile heater is fixed at one end of a rod of the impure metal. The heater is slowly moved forward. The melted zone moves along with the heater. As the heater moves forward the pure metal crystallizes out of the melt while the impuri-ties pass into the adjacent molten zone. The process is repeated a number of times until the desired state of purity is reached. The end of the rod where the impurities finally get concentrated is cut off.
(ii) Electrolytic refining: The impure metal is made the anode and a pure strip of the same metal the cathode in a suitable electrolytic both.
Anode : M → Mn+ + ne–
Cathode: Mn+ + ne– → M
The net result is the transfer of pure metal from the anode to the cathode. The applied voltage is such that more electropositive metals (impurity) remain as ions in the bath whereas the less electropositive metals (impurities) remain unionized and fall done as anode mud.
(iii) Vapour phase refining:
(a) Mond Process: Nickel when heated in a stream of carbon monoxide forms volatile nickel carbonyl, Ni(CO)4. The carbonyl vapour when subjected to still higher temperature undergoes thermal decomposition giving pure metal.
(b) Van Arkel Process: Zirconium (or titanium) is heated in iodine vapour at about 870 K to form volatile Znl4. The latter when heated over a tungsten filament at 2075 K decomposes to give pure zirconium.
The choice of a reducing agent in a particular case depends on thermodynamic factor. How far do you agree with this statement? Support your opinion with two examples.
Thermodynamic factor helps us in choosing a suitable reducing agent for the reduction of particular metal oxide to the metallic state. From , it is evident that metal oxides for which the standard free energy of formation of their oxides is more negative can reduce those metal oxides for which the standard free energy of formation of their respective oxides is less negative. In other words, any metal will reduce the oxides of other metals which lie above it in the Ellingham diagram because the standard free energy change G0 of the combined redox reaction will be negative by an amount equal to the difference in G0 of the two metal oxides. Hence, both Al, Zn can reduce FeO to Fe but cannot reduce Al2O3 to Al and ZnO. Similarly, C can reduce ZnO but not CO.
Carbon monoxide is more effective agent that carbon below 983 K but above this temperature the reverse is true. How would you explain this?
In the production of iron from its oxide ore, the mixture of ore, coke and limestone is heated with a blast of air in furnace. Below 983K oxides of iron are reduced by carbon monoxide to iron.
Fe2O3 +CO → 2FeO +CO2
FeO +CO → Fe + CO2
Above 983K, Fe2O3 undergoes reduction by hot coke to iron. This region is called fusion zone
Fe2O3 +3C → 2Fe +3CO +Heat
Thus carbon monoxide is more effective agent than carbon below 983K.
The value of ΔrG° for formation of Cr2O3 is – 540 kJmol–1 and that of Al2O3 is – 827 kJ mol-1. Is the reduction of Cr2O3 possible with Al?
Predict the modes of occurrence of the following three types of metals:
(i) Highly reactive (e.g., Na)
(ii) Moderately reactive (e.g., Fe)
(iii) Noble metal (e.g., Au)
(i) Sodium being highly reactive in nature, it does not occur in free state. It occurs as : NaCl, NaNO3, Na2SO4 and Na2B4O7.10H2O.
(ii) Iron being moderately reactive in nature, it does not occur in free state. In combined state it occurs as : Fe2O3, Fe3O4, FeCO3, FeS2 and CuFeS2.
(iii) Noble metal like gold being non-reactive do not occur free in nature.
How do non-metals occur in nature? How are they extracted/isolated from their natural resources?
Some non-metals like inert gases (He, Ne, Ar, Kr, Xe) occur free in nature, whereas some occur in both free and combined states e.g., oxygen, hydrogen, nitrogen, halogens and carbon etc.
Non-metals in general are extracted from their
natural resources by any of the following methods:
(i) By the reduction of oxides and halides.
(ii) By electrolyte reduction of salts, e.g., Cl2 by electrolytic reduction of conc. NaCl solution.
(iii) By the thermal decomposition of their hydrides.
Name the chief ores of tin, iron and aluminium. What methods are employed for the concentration/purification of their ores?
(i) The chief ore of tin is cassiterite (SnO2). It is crushed and then concentrated by hydraulic washing. Tungstate of iron and manganese present are removed by magnetic process.
(ii) The chief ore of iron is haematite (Fe2O3). It is crushed and then concentrated by hydraulic washing.
(iii) The chief ore of aluminium is bauxite AlOx(OH)3-2x [where 0 < x < 1] . It is concentrated by leaching method.
Name three ores which are concentrated by froth-floatation process. What is meant by depressant?
The three ores which are concentrated by froth-floatation process are:
(i) Copper pyrites (CuFeS2)
(ii) Zinc Sulphide (ZnS)
(iii) Silver glance (Ag2S).
Depressants are used to prevent certain types of particles from forming the froth with bubbles.
Example: NaCN is used as a depressant in the separation of ZnS and PbS ore. NaCN forms a layer of Zinc complex Na2 Zn(CN)4 on the surface of ZnS and thereby prevents it from formation of froth.
Why is it advantageous to roast a sulphide ore to the oxide before reduction?
Sulphide ore is roast to the oxide before reduction because metal oxides can be reduced to metal by carbon and hydrogen much more easily than sulphides.
Discuss some of the factors which need consideration before deciding on the method of extraction of metal from its ore.
Some of the factors which need consideration before deciding on the method of extraction of metal from its ore are:
Type of impurity present in the ore.
(i) Hand picking: When the ore and impurities differ in the size and the shapes of the particles.
(ii) Gravity separation: When the gangue impurities are lighter than the ore.This can be achieved by washing with a stream of running water.
(iii) Froth floatation process: This is used for sulphide ores.
(iv) Magnetic process: This is used in those cases where the impurities of ore are of magnetic nature.
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You are provided with samples of some impure metals such as zinc, copper and germanium. Which methods could you recommend for the purification of each of these metals?
Zinc: The metal may be purified by
(i) Fractional distillation
(ii) Electrolytic refining.
Copper: The metal may be purified by
(i) Poling
(ii) Electrolytic refining.
Germanium: The metal may be purified by
(i) zone refining.
Name the chief forms of the occurrence of the following in the earth crust:
(a) aluminium, (b) calcium, (c) sodium, (d) lead.
(a) Aluminium: Oxides:
(i) CorundumAl2O3
(ii) DiasporeAl2O3.H2O
(iii) Bauxite Al2O3.2H2O
Halides: Cryolite Na3AlF6
Silicates:
(i) Feldspar KAlS3O8
(ii) Mica KAlSi3O10 (OH)2
(b) Calcium:Carbonate: Lime stone (CaCO3) marble, chalk, calcite and dolomite Sulphate : Gypsum, CaSO4 2H2O and anhydrite, CaSO4 Fluoride: Fluorspar, CaF2, Fluorapatite 3Ca3(PO4)2CaF2 Phosphate : Phosphorite, Ca3(PO4)2
(c) Sodium: Sodium chloride, NaCl
Sodium nitrate or chile salt petre NaNO3
Sodium carbonate Na2CO3 Borax Na2B4O7,10H2O.
(d) Lead: Anglesite, PbSO4 Cerussite PbCO3 Lanarkite, PbO, PbSO4.
Sodium metal cannot be obtained by the electrolysis of aqueous sodium chloride solution.
The reduction potential values of sodium and water - 2.71 V and - 0.83 V respectively.
Na+(aq) + e → Na(s) E° = –2.71V
2H2O(l) + 2e → H2(g) + 20H– E° = – 0.83 V
Thus Na+ has less tendency to change into a metal compared to H2O which has greater tendency to change into H2 gas. Therefore, H2O accepts electrons preferentially than Na+ in the electrolysis of aqueous chloride. Therefore, metal is not produced.
Write the chemical reactions involved in the extraction of metallic silver from argentite.
In the metallurgy of silver metal is leached with a dilute solution of NaCN or KCN in the presence of
air (for O2) from which the metal is obtained later by replacement:
ii) The high abundance of iron on earth is due to its very high nuclear binding energy which makes it highly stable. On other hand, the element with higher atomic numbers have relatively low nuclear binding energy and hence are relatively unstable and have rare abundance.
Silver ores and native gold have to be leached with metal cyanides. Suggest a reason for this.
Describe the principle of froth floatations process. What is the role of stabilizer and of a depressant? Give one example of each.
This method is based on the fact that more electropositive metal can displace less electropositive metal from its salt solution. The concentrated ore is bleached with aqueous solution of suitable reagent (NaCN solution of Cl2in the presence of water) to extract the metal salt in complex salts solution in water. The salt solution is then either electrolyzed or precipitated by adding more electropositive metal. This method also known as complex salt formation method.
Ag2S +4NaCN → 2Na[Ag(CN)2] +Na2S
2Na[Ag(CN)2] +Zn → 2Ag +Na2[Zn(CN)4]
Differentiate between 'minerals' and 'ores'.
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Minerals |
Ores |
|
1. The natural materials in which the metals or their compounds are found in earth are called minerals. 2. All the ores are minerals. |
1. Those minerals from which the metals can be extracted conveniently and profitably are called ore. 2. All the minerals are not ores. |
State briefly the principles which serve as basis for the following operations in metallurgy:
(i) Froth floation process.
(ii) Zone refinnting.
(iii) Refining by liquation.
What chemical principle is involved in choosing a reducing agent for gettting the metal from its oxide ore? Consider the metal oxides, Al2O3 and Fe2O3 and justify the choice of reducing agent in each case.
Highly electropositive elements are obtained by the electrolysis of their oxides, hydroxides or chlorides in fused state.
Extraction of less electropositive metals say Cr, Mn, Cu, Ca, Ni etc. can be done by heating their oxides with strong reducing agent e.g., CO + H2, Na, Al, Mg etc. The oxides of less electropositive metals like Pb, Fe, Zn, Sb and Cu are reduced by strongly heating with coal or coke.
Al2O3 is mixed with Na3AlF6 which lowers the melting point of the mix and brings conductivity. The fused Al2O3 is electrolysed steel cathode and graphite anode are used.
Explain different methods of reduction of the roasted/calcined ore to the metallic form.
Various reduction process are described under the following main categories, viz.,
(a) Chemical reduction
(b) Auto-reduction
(c) Displacement method
(d) Electrolytic reduction.
(a) Chemical reduction:
(i) Carbon as a reducing agent. Carbon and carbon monoxide reduces many metal oxides into the respective metals. Examples,
(ii) Hydrogen as a reducing agent. Because of its inflammable nature, it is used in a very few case
e.g.,
(iii) Aluminium as a reducing agent. The oxides of chromium and manganese are reduced by aluminothermic reduction process/or Goldschmidt thermic process.
Cr2O3 + 2Al Al2O3 + 2Cr 3M3O4 + 8Al → 4Al2O3 + 9Mn
(iv) Other metals as reducing agents. Sodium and magnesium metals are used in certain cases such as titanium oxide TiO2. Thus,
TiO2 + 2Mg → Ti + 2MgO or TiO2 + 4Na → Ti + 2Na2O
(b) Auto-reduction: In certain cases no reducing agent is required. The metal is obtained either by simple roasting or by the reduction of its partly oxidized form. Thus, mercury is directly obtained by roasting its ore cinnabar (HgS) in air.
(c) Displacement method: Some metals are reduced by displacement by more reactive metal, from their complexes. Siver and gold, for example, are obtained from their complex cyanides when more reactive zinc metal displaces them.
2M(CN)2 + Zn → Zn(CN)42– + 2M
(where M = Ag or Au).
(d) Electrolytic reduction: Highly electropositive elements of groups 1 and 2 are reduced by electrolytic method. These metals which occur as chlorides or oxo-salts are converted into their chlorides. When electric current is passed through a fused chloride the Mn+ ions are discharged at cathode and deposited. In the electrolysis of brine (NaCl) using Hg cathodes, Na+ is discharged at cathode and forms an amalgam. This takes place in preference to the liberation of H2 due to high H2 over voltage at Hg cathode.
The crude metal is refined by one or more of the following techniques:
(i) Liquation: Easily fusible metals like Hg, Sn, etc. are heated in a sloping hearth of a reverberatory furnace. The fusible metal melts and flows down in pure form, leaving behind the infusible impurities called drop.
(ii) Fractional distillation: Volatile metals like Hg, Zn etc. are submitted to distillation when pure metal distills over, leaving behind non-volatile impurities.
(iii) Polling: It is a process of stirring the hot molten anode metal with green logs of wood. The wood gases like methane and other hydrocarbons produced from green logs reduce metal oxide impurity to the metallic form. Moreover, during stirring large quantity of air is absorbed by the molten metal, oxidises easily oxidisable impurities. The oxidised impurities escape either as vapour or form scum over molten metal, which can be scooped out by perferated ladle.
(iv) Electrolytic refining: In this method, large block of impure metal is made anode in an electrolytic cell and a thin sheet of pure metal is made the cathode. Suitable metal salt solution is made an electrolyte. On passing current, pure metal deposits on the thin cathode sheet. While the more electropositive pure metal deposits on the thin cathode sheet while the more electropositive metallic impurities are left in solution and noble metal impurities settle below the anode as anode mud. Most of the metals are refined by this method.
Fig. Electrolytic purification of metal.
(v) Zone refining: This method is used when highly pure metal is required for the purpose as semi-conductors in transistors and solar batteries.
It is based on the fact that melting point of a substance is lowered when impurities are present. Consequently, when an impure molten metal is cooled, crystals of pure metal are solidified and the impurities remains in molten metal.
The process consists in casting the impure metal in the form of a bar. A circular heater is fitted around this bar and the circular heater is moved slowly longitudinally from one end to the other. At the heated zone, the bar melts and as the heater moves on, pure metal crystallizes, while impurities pass into the adjacent molten part.
In this way, the impurities are swept from one end of the bar to the other. By repeating the process, ultra pure metal of silicon, germanium etc. are obtained.
Fig. Zone Refining.
During the extraction, the metallic silver is precipitated by the addition of __________ to ________
zinc
,sodium argentocyanide
A.
Sodium is found in the native state.B.
Metals can be recovered from their ores by chemical methods.C.
Metallic sodium is obtained by electrolysis of molten sodium chloride.D.
In calcination, the ore is heated with calcium.E.
In electrolytic refining of copper, pure copper is taken as anode.A.
The presence of carbon in pig iron makes it very soft and malleable.B.
Azurite is an ore of aluminium.C.
Aluminium is extracted by heating aluminium oxide with coke in furnace.D.
The reducing agent used in the blast furnace to reduce Fe2O3 to Fe is lime stone.Zinc refining is a method to obtain
Very high temperature
Ultra pure Al
C.
Ultra pure Germaniuminfusible impurities to fusible material
soluble impurities to insoluble impurities
A.
infusible impurities to fusible material
The method of zone refining of metals is based on the principle of
higher melting point of impurity than that of the pure metal
greater noble character of the solid metal than that of the impurity
greater solubility of the impurity in the molten state than in the solid.
greater mobility of the pure metal than that of the impurity.
C.
greater solubility of the impurity in the molten state than in the solid.
Sulphide ore of:
i) Lead is Pbs (galena)
ii)Copper is Cu2S (Chalcocite)
iii) Silver is Ag2S (silver glance)
What type of ores are dressed up by magnetic separation method?
Iron ore is dressed up by magnetic separtion method.
Name two metals which occurs native(free) in nature.
Gold and silver are occur native in nature.
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Define the term mineral.
Minerals are the building blocks of rocks. A mineral may be defined as any naturally occurring inorganic solid that has a definite chemical composition (that can vary only within specified limits) and possesses a crystalline structure.
Name the process and the chemical by which sodium is extracted on large scale?
Explain the froth floatation of concentrating ores.
In this method gangue is remove from sulphide ores. In this process, a suspension of the powdered ore is made with water. Suitable collectors and froth stabilizer are added. Collectors (e.g. pine oils, fatty acid, xanthates, etc) enhance non-wettability of the mineral particles and froth stabilize (e.g., cresols, aniline) stabilize the forth. The mineral particles wet by oils while the gangue particles by water. A rotating paddle agitates the mixture and draws air in it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for recovery of the ore particles.
What type of ores are roasted?
In roasting ore is heated in the presence of excess of oxygen or air. This method is employed for sulphide ores. Example: ZnS (sphalerite) and Cu2S (chalcocite).
Write a chemical equation for the roasting of an ore of each type.
In roasting ore is heated in the presence of excess of oxygen or air. This method is employed for sulphide ores. Example: ZnS (sphalerite) and Cu2S (chalcocite)
The chemical equation:
2ZnS +3O2 → 2ZnO + 2SO2
2Cu2S +3O2 → 2Cu2O + 2SO2
Explain the following:
Coke and flux are used in the smelting.
The phenomenon in which ore is mixed with suitable flux and coke and is heated to fusion is known as smelting. Oxide of matter obtained from nature or by calcination or roasting is reduced by a coke through smelting.
MO +C --> M + CO
During smelting the impurities are also removed. This is done by the addition of a suitable external substance known as flux. Flux reacts with impurities and forms slag which floats over the molten metal and removed.
Explain the following:
Partial roasting of sulphide ore is done in the metallurgy of copper.
Partial reduction of sulphide ores give copper oxide which further reacts with copper sulphide to show auto reduction.
2CuS +3O2 -> 2CuO + 2SO2
How will you differentiate between:
Gangue and flux
Gangue is the waste rock or materials overlying an ore or mineral body that are displaced during mining without being processed or simply rocky impurities.
Flux is any substance introduced in the smelting of ores to promate fluidity and to remove objectionable impurities.
How will you differentiate between:
Flux and slag
Flux is any substance introduced in the smelting of ores to promate fluidity and to remove objectionable impurities.
Slag Waste content of metal ores that floats on the surface during the process of extracting or refining metal. Slag containing mainly sillicates, sulfates, and phosphates of calcium.
How will you differentiate between:
Concentration and refining
Concentration: concentration is the abundance of a constituent divided by the total volume of a mixture.
Refining: it is process of removing impurities from the ore of metal or non- metal. For example aluminium can be refine by electrolysis.
Give a brief account of the following processes as used in extraction of metals:
(a) Smelting
(b) Magnetic separation
a) Smelting is a process in which the oxide of metal is reduced to the metal and the metal is obtained in a molten form. In smelting reduction is done at high temperatures.
Two different ways are used to employ smelting;
1: carbon reduction process: Oxide of matter obtained from nature or by calcination or roasting is reduced by a coke through smelting.
MO +C -->M + CO
During smelting the impurities are also removed. This is done by the addition of a suitable external substance known as flux. Flux reacts with impurities and forms slag which floats over the molten metal and removed.
2: using reduction agent other than carbon: They are many oxides ores which cannot be reduced by carbon. Therefore the powerful reducing agent like aluminum, sodium or magnesium are required. For example, oxides of chromium and manganese etc., are to reduce with aluminum;
Cr2O3 + 2Al --> 2Cr + Al2O3
3MnO2 +4Al --> 3Mn + 2Al2O3
b) Magnetic separation : This method is used when either ores or gangues have strong ferromagnetic nature. Strong ferromagnetic ores e.g. iron, tin or ferromagnetic impurities are thrown in between magnetic poles which attracts ores on poles. E.g. wolframite(FeWO4) a magnetic ore is separated from the non-magnetic ore.
What is electro-refining? Explain with one example.
In electrolytic the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in soluble salt of the same metal. The more basic metal remains in solution and less basic go to the anode mud.
Anode : M → Mn+ + ne-
Cathode : Mn+ + ne- → M
For example copper is refine using this method. Anodes are of impure copper and pure copper strips are taken as cathode. The electrolyte is acidified solution of copper sulphate and the net result of electrolysis is the transfer of copper in the pure form from the anode to the cathode:
Anode: Cu → Cu2+ +2e-
Cathode : Cu2+ + 2e-→ Cu
Describe Van Arkel method to obtain metals of high purity.
Van arkel developed a method is based on the thermal decomposition and is used for getting pure metal. In this method, the metal is converted into a volatile compound, while impurities remain unaffected during compound formation. The resulting compound is then decomposed to get pure metal. for example this method is used for refining Zirconium or Titanium:
For example
Ti + 2I2 → TiI4(gas) + heat → Ti +2I2
impure compound pure
Explain how, electrolytic refining purifies a metal?
Electrolytic refining :
In electrolytic refining method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic go to the anode mud. This can be explained by using electrode potential.
Anode: M → Mn+ + ne-
Cathode : Mn+ + ne- → M
for example copper is refined using an electrolytic method. Anodes are of impure copper and pure copper strips are taken as cathode. The electrolyte is acidified solution of copper sulphate and the net result of electrolysis is the transfer of copper in pure form from the anode to the cathode:
Anode: Cu → Cu2+ + 2 e-
Cathode: Cu2+ + 2 e- → Cu
Impurities from the blister copper deposit as anode mud which contains antimony, selenium, tellurium, silver, gold and platinum.
What do you understand by the following terms: (i) Roasting, (ii) Calcination, (iii) Smelting?
i) Roasting: In roasting, the ore is heated in aregular supply of air in a furnace at a temperature below the melting point of the metal. For example:
2ZnS + 3O2 → 2ZnO + 2SO2
2PbS + 3O2 → 2PbO + 2SO2
2Cu2S + 3O2 → 2Cu2O + 2SO2
ii) Calcination: Calcination involves simple decomposition of ore on heating below its melting point usually in absence of air to produce new compounds having higher percentage of metal.
Fe2O3.xH2O(s)+heat → Fe2O3 (s) + xH2O(g)
ZnCO3 (s) +heat → ZnO(s) + CO2(g)
Describe mainly with balanced chemical equations.
(a) Copper from copper pyrites by self reduction.
(b) Zinc from zinc blende by carbon reduction.
(c) Silver from silver glance by cyanide process.
a) copper pyrites is first converted into cuprous sulphide.
2CuFeS2 + O2 → Cu2S + 2FeS + SO2
Cuprous sulphide and ferrous sulphide are further oxidized into their oxides.
2Cu2S + 3O2 → 2Cu2O + 2SO2
2FeS + 3O2 → 2FeO + 2SO2
Copper is extracted from the molten matte through bessmerization. The matte is introduced in to Bessemer. The air is blown through the molten matte. Blast of air convert Cu2s partly into Cu2O which react with remaining Cu2S to give molten copper.
2Cu2 S + 3O2 → 2Cu2 O + 2SO2
2Cu2O + Cu2 S → 6Cu + SO2
This is self-reduction
b) Zinc blende is concentrated by floath floatation process. The concentrated ore is heated in excess supply of air above 900o C on the hearth furnace. During roasting. Zinc sulphide is converted to zinc oxide
2ZnS + 3O2 → 2ZnO + 2SO2
The reduction of zinc oxide is done using coke. The temperature in this case is higher than that in case of copper. For the purpose of heating, the oxide is made into brickettes with coke and clay.
ZnO + C Zn + CO
The metal is distilled off and collected by rapid chilling.
c) Extraction of silver by cyanide process: silver is extracted from argentite ore. The powdered ore is agitated with a dilute solution of NaCN while a current of O2 is constantly passed. The metallic sliver from the ore dissolves and forms sodium argentocynide.
2Ag2S +8NaCN +O2 +H2O → 4Na[Ag(CN)2] +2NaOH +2S
This complex is treated with zinc dust when silver gets precipitated as a dark amorphous mass.
4Na[Ag(CN)2] +Zn → Na[Zn(CN)4] + 2Ag
Thus, impure Ag is obtained which is purified by electrolysis of a solution of AgNO3 containing dil HNO3 using impure Ag as the anode and a strip of pure Ag as the cathode.
(a) How is aluminium extracted from alumina?
(b) Give balanced equations for the extraction of aluminium from bauxite by electrolysis.
(c) What is the function of cryolite in the extraction of Al from Al2O3.
a) it is extracted by electrolysis. The ore is first converted into pure aluminium oxide by the Bayer Process, and this is then electrolysed in solution in molten cryolite - another aluminium compound.
The alumina is dissolved in a mixture of molten cryolite and fluorspar which lowers the melting point. It is then electrolysed in a rectangular steel tank with carbon lining, which serves as cathode. Anode is set of thick carbon rods suspended from the top into the fused Al2O3. The temperature is maintained between 1200 and 1310k. Oxygen is evolved at the anode.
Al2O3 -------> 2Al3+ + 3O2-
At cathode: 2Al3+ + 6 e- -------> 2Al
At cathode: 3O2- --------> 1/5O2 + 6e-
Aluminium formed at the cathode gets collected at the bottom of the electrolytic cell from where it is removed periodically.
b) In the Baeyer's process, the bauxite ore is heated with concentrated NaOH solution under pressure alumina dissolves as sodium meta aluminate. The other materials present in the ore are left as insoluble part. This solution is filtered in ore are left as insoluble part. This solution is filtered off. From the solution Al(OH)3 is precipitated by adding freshly prepared Al(OH)3 to the cold dilute solution and agitating.
Al2O3 + 2NaOH -------> 2NaAlO2 + H2O
NaAlO2 + 2H2O -------> NaOH + Al(OH)3
The precipitated Al(OH)3 is dried and ignited to get pure alumina.
2Al(OH)3 --------> Al2O3 + 3H2O
c) Cryolite is added as an impurity to the electrolyte. The cryolite, lowers the melting point of alluminium oxide to 980. The rule is as it is for all impurities they lower the melting point and raise the boiling point, so the reduction of the melting point allows the alluminium to melt at lower temperatures, making electrolysis work at lower temperatures, hence requires lesser energy, making the process cheaper, and more cost effective.
Describe the methods used to obtain concentrated ores.
Method used to obtain concentration:
Hydraulic washing : This method is based on the difference in gravities of the ore and the gangue particles. It is therefore a type of gravity separation. In one such process an upward stream of running water is used to wash the powdered ore. The lighter gangue particles are wasted away and the heavier ores are left behind.
Magnetic separation : this method is based on differences in magnetic properties of the ore components. If either the ore or the gangue is capable of being attracted by a magnetic field, then such separation are carried out. The ground ore is carried on a conveyer belt which passes over a magnetic roller.
Froth floatation method: This method based on removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water. To it, collectors and froth stabilisers are added. Collectors (e. g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilisers (e. g., cresols, aniline) stabilise the froth.
What is meant by the term 'chromatography'?
Give reasons for the following observations:
Leather gets hardened after tanning
Animal skin (hide) is colloidal in nature and has positively charged particles, whereas tanning consists of negatively charged colloidal particles. When a hide is soaked in tanning, mutual coagulation takes place and as a result, leather gets hardened.
Give reasons for the following observations:
Lyophilic sol is more stable than a lyophobic sol.
The stability of lyophilic sols is a result of two factors, the presence of a charge and the solvation of colloidal particles. On the other hand, the stability of lyophobic sols is only because of the presence of a charge. Thus, the lyophilic sol is more stable than lyophobic sol due to the extensive solvation.
Indicate the principle behind the method used for the refining of zinc.
Zinc is refined using electrolytic refining process. In this process, pure zinc is transported to cathode from the impure sample at the anode. The more basic metal remains in the electrolytic solution and the less basic metals, present as impurities, precipitate as anode mud.
|
Electrode |
Chemical Reaction |
|
Anode |
Zn Zn2+ +2e - |
|
Cathode |
Zn2+ 2e- + Zn |
What is the role of silica in the extraction of copper?
Ores of copper contain iron oxide as an impurity. Silica reacts with iron oxide and forms iron silicate, which is removed as slag. In the smelting process such chemical reactions are taking place:
1) Oxidizing of the copper pyrite: 2 CuFeS2 (s) + 3 O2 (g) → 2 FeO (s) + 2 CuS (l) + 2 SO2 (g)
2) Conversion of iron oxides and sulfides into molten slag:
FeO (s) + SiO2 (s) → FeSiO3 (l)
2 FeS (s) + 3O2 (g) + 2 SiO2 (s) → 2 FeSiO3 (l) + 2SO2 (g)
Which form of the iron is the purest form of commercial iron?
Wrought iron is the purest form of commercial iron.
Which reducing agent is employed to get copper from the leached low-grade copper ore?
Copper can be obtained from low-grade ore through the process of leaching using acid or bacteria (leaching is a process in which ore is treated with a suitable reagent that dissolves ore but not the impurities).
The solution containing copper can be reduced with the help of reducing agents such as scrap iron or H2 to get copper metal.
Cu2+(aq) + Fe Cu(s) + Fe2+(aq)
Cu2+ (aq) + H2(g) Cu(s) + 2 H+(aq)
Outline the principles behind the refining of metals by the following methods:
Zone refining method
Zone Refining Method:
Zone refining method is based on the principle that impurities are more soluble in the molten state than in the solid state of a metal. This method is used in the purification of elements like Germanium(Ge), Silicon(Si), Indium (In) etc.
Outline the principles behind the refining of metals by the following methods:
Chromatographic method
Chromatography method:
Chromatography is the technique used for separation of the components of a mixture that are soluble in the same solvent and are differently adsorbed on an adsorbent. This technique was first used for separation of colours and hence, the name. There are two phases in chromatography - the stationary phase and the mobile phase. The components of the mixture are absorbed differently in the stationary phase, thus leading to their separation. There are many different types of chromatography - paper chromatography, thin-layer chromatography, gas chromatography etc.
Name the method used for the refining of Nickel metal?
Nickel is refined by mond’s process .In this process, nickel is heated in the presence of carbon monoxide to form nickel tetracarbonyl, which is a volatile complex.
Then, the obtained nickel tetracarbonyl is decomposed by subjecting it to a higher temperature (450-470) to obtain nickel metal.
Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver?
Dilute solution of NaCN and KCN is used for leaching of silver metal in the presence of air in the metallurgy of silver, for example in the following reaction
AgS + 4NaCN ⇌ 2Na[Ag(CN)2] + Na2SAgS + 4NaCN ⇌ 2Na[Ag(CN)2] + Na2S
The solution of sodium Argento cyanide combines with zinc dust and forms sodium tetra cyanozicate and precipitated silver. This precipitated silver is called spongy silver.
Zn+2Na[Ag(CN)2] → Na2[Zn(CN)4] + 2AgZn + 2Na[Ag(CN)2] → Na2[Zn(CN)4] + 2Ag
The spongy silver is fused with potassium nitrate to obtain pure silver. Then the silver obtained is purified by an electrolytic process.
Out of C and CO, which is a better reducing agent at the lower temperature range in the blast furnace to extract iron from the oxide ore?
Out of C and CO, CO is a better reducing agent at the lower temperature range because 
. So, CO will reduce FeO, and will itself be oxidized to CO2.
What is the role of graphite in the electrometallurgy of aluminium?
In the metallurgy of aluminium, steel cathode and graphite anode are used. The graphite anode is useful for the reduction of Al2O3 into Al.
2Al2O3 + 3C ---> 4Al + 3CO2
(graphite)
Describe the principle involved in each of the following processes.
(i) Mond process for refining of Nickel.
(ii) Column chromatography for purification of rare elements.
Mond process for refining of Nickel is based on the principle that nickel is heated in the presence of carbon monoxide to form nickel tetracarbonyl, which is a volatile complex.
Ni + 4CO 
Ni(CO)4
(Nickel tetracarbonyl)
Then, the obtained nickel tetracarbonyl is decomposed by subjecting it to a higher temperature (450 - 470 K) to obtain pure nickel metal.
Ni(CO)4 
Ni + 4CO
(Nickel tetracarbonyl) nickel
(ii) Column chromatography is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. In it, there are two phases: mobile phase and stationary phase. The stationary phase is immobile and immiscible example Silica gel(SiO2) , Alumina gel(Al2O3) . Al2O3 column is usually used as the stationary phase in column chromatography. The mobile phase may be a gas, liquid, or supercritical fluid in which the sample extract is dissolved.
Then, the mobile phase is forced to move through the stationary phase. The component that is more strongly adsorbed on the column takes a longer time to travel through it than the component that is weakly adsorbed. The adsorbed components are then removed (eluted) using a suitable solvent (eluent).
Define electrophoresis ?
1. The migration of charged colloidal particles or molecules through a solution under the influence of an applied electric field usually provided by immersed electrodes. Also called ionophoresis, phoresis.
2. A method of separating substances, especially proteins, and analyzing molecular structure based on the rate of movement of each component in a colloidal suspension while under the influence of an electric field.
Explain how the phenomenon of adsorption finds application in each of the following processes:
(i) Production of vacuum
(ii) Heterogeneous catalysis
(iii)Froth Floatation process
i) Production of high vacuum: Traces of air can be adsorbed by charcoal from a vessel, evacuated by a vacuum pump to give a very high vacuum.
(ii) Heterogeneous catalysis: heterogeneous catalysis refers to the form of catalysis where the phase of the catalyst differs from that of the reactants. Phase here refers not only to solid, liquid, or gas, but also immiscible liquids, e.g. oil and water
For example: N2(g) + 3H2(g) 
2NH3(g)
(iii) Froth floatation process: This process is used to remove gangue from sulphide ores. The basic principle involved in this process is adsorption. In this process, a mixture of water and pine oil is taken in the tank. The impure powdered sulphide ore is dropped in through hopper and the compressed air is blown in through the agitator. The agitator is rotated several times. As a result, the froth is formed and the sulphide ores get adsorbed in the froth. The impurities settled down and are let out through an outlet at the bottom. The froth formed is collected in froth collector tank. After sometime, the ore particles in the froth collecting tank start settling gradually, which are then used for further metallurgical operations.
Describe the principle behind each of the following processes:
(i)Vapour phase refining of a metal.
(ii)Electrolytic refining of a metal.
(iii)Recovery of silver after silver ore was leached with NaCN.
(i) Vapour phase refining
Vapour phase refining is the process of refining metal by converting it into its volatile compound and then, decomposing it to obtain a pure metal. The basic principles involved in this process are:
(a) The metal should form a volatile compound with an available reagent, and
(b) The volatile compound should be easily decomposable so that the metal can be easily recovered.
Nickel, zirconium, and titanium are refined using this method.
(ii) Electrolytic refining is the process of refining impure metals by using electricity. In this process, impure metal is made the anode and a strip of pure metal is made the cathode. A solution of a soluble salt of the same metal is taken as the electrolyte. When an electric current is passed, metal ions from the electrolyte are deposited at the cathode as a pure metal and the impure metal from the anode dissolves into the electrolyte in the form of ions. The impurities present in the impure metal gets collected below the anode. This is known as anode mud.
(iii) In the process of leaching, the finely divided silver is treated with a dilute solution of sodium cyanide while a current of air is continuously passed. As a result, silver passes into the solution.
forming sodium dicyanoargenate (I) while the impurities remain unaffected which are filtered off.
Ag2S + 4NaCN ---> 2Na [Ag(CN2)] + Na2S
Sodium dicyanoargenate (I)
(i) What is the principle behind the zone refining of metals?
(ii) What is the role of silica in the extraction of copper?
(iii) How is 'cast iron' different from 'pig iron'?
(i) The technique of zone refining is based on the principle that the impurities are more soluble in the molten state of metal than in the solid state. Silicon , boron gallium , indium etc. can purify by this process.
(ii) Ores of copper contain iron oxide as an impurity. Silica reacts with iron oxide and forms iron silicate, which is removed as slag.
FeO + SiO2 -------> FeSiO3
Iron oxide silica iron silicate (slag)
(iii) The iron obtained from the blast furnace is known as pig iron. It contains around 4% carbon and many impurities, such as S, P, Si, Mn, in smaller amounts.
Cast iron is obtained by melting pig iron and coke using a hot air blast. It contains a lower amount of carbon (about 3%) than pig iron. Unlike pig iron, cast iron is extremely hard and brittle.
Name the method used for refining of copper metal.
The electrolytic method is used for refining copper metal.
Outline the principles of refining of metals by the following methods:
(i) Zone refining
(ii) Vapour phase refining
Principles of refining of metals by:
(i) Zone refining: The impurities are more soluble in the melt than in the solid state of the metal. Hence, the pure metal crystallises out of the melt and impurities pass on into the adjacent molten zone and like this at one end impurities get concentrated. Silicon, indium, boron, gallium etc. can be purified by this process.
(ii) Vapour phase refining: Vapour phase refining is the process of refining metal by converting it into its volatile compound and then, then decomposing it to obtain a pure to carry out this process
(a) The metal should form a volatile compound with an available reagent.
(b) The volatile compound should be easily decomposable so that the metal can be easily recovered.
Nickel, Zirconium, and titanium are using this method.How is copper extracted from a low-grade ore of it?
Copper can be obtained from low grade from low through the process of leaching using acid or bacteria (leaching processes in which ore is treated with a suitable reagent which dissolves ore but not the impurities).
Explain the role of each of the following:
(i) NaCN in the extraction of silver
(ii) SiO2 in the extraction of copper
(i) The roasted ore of gold is leached with a solution of sodium cyanide in the presence of oxygen for many days. The role of NaCN in this process is to dissolve the gold to form an aurocyanide complex, from which the metal is obtained by displacement.
4Au + 8NaCN + 2H2O + O2 ---> 4 Na [Au(CN)2] + 4KOH
2Na[Au(CN)2] + Zn ---> Na2[Zn(CN)4] + 2Au
(ii) Copper matte contains Cu2S and FeS. In the blast furnace, copper matte is added with powdered coke and silica. The oxidation of ore takes place in this process. As a result, cuprous oxide and ferrous oxide are produced. The role of silica in this process is to remove the iron oxide obtained as ‘slag’. FeO combines with silica (flux) to form iron silicate, FeSiO3(slag).
FeO + SiO2 
FeSiO2
Flux slag
(i) Name the method of refining of metals such as Germanium.
(ii)In the extraction of Al, impure Al2O3 is dissolved in conc. NaOH to form sodium aluminate and leaving impurities behind. What is the name of this process?
(iii)What is the role of coke in the extraction of iron from its oxides?
(i) Zone refining method is the most suitable method for refining metals like germanium (semiconductor).
(ii) In the extraction of aluminium, impure Al2O3 is dissolved in concentrated NaOH to form NaAlO2.
This method is known as leaching of alumina.
(iii) Coke reduces the iron oxide to molten iron metal. Also, coke, when burnt in the blast furnace, supplies the heat required for carrying out the extraction of iron from its oxide.
FeO +C ---> Fe +CO
What type of ores can be concentrated by magnetic separation method?
If the ore or the gangue can be attracted by the magnetic field, then the ore can be concentrated by the process of magnetic separation.
Describe the principle controlling each of the following processes:
(i) Preparation of cast iron form pig iron.
(ii) Preparation of pure alumina (Al2O3) from bauxite ore.(i) The iron obtained from blast furnaces is known as pig iron. It contains around 4%carbon and many impurities such as S, P, Si, and Mn in smaller amounts.
Cast iron is obtained by melting pig iron and coke using a hot air blast. It contains a lower amount of carbon (3%) than pig iron; cast iron is extremely hard and brittle.
(ii) Bauxite usually contains silica, iron oxide, and titanium oxide as impurities. In the process of leaching, alumina is concentrated by digesting the powdered ore with a concentrated solution of NaOH at 473-523 K and 35-36 bar. Under these conditions, alumina (Al2O3) dissolves as sodium meta-aluminate and silica (SiO2) dissolves as sodium silicate leaving the impurities behind.
The impurities are then filtered and the solution is neutralized by passing CO2 gas. In this process, hydrated Al2O3 gets precipitated and sodium silicate remains in the solution. Precipitation is induced by seeding the solution with freshly prepared samples of hydrated Al2O3.
Hydrated alumina thus obtained is filtered, dried, and heated to give back pure alumina (Al2O3).
What is the role of zinc metal in the extraction of silver?
In the extraction of silver, zinc metal act as reducing agent.
2[Ag(CN)2]-(aq.) + Zn(s) --> 2Ag(s) + [Zn(CN)4]2-(aq.)
Explain the principle of the method of electrolytic refining of metals. Give one example.
Electrolytic refining; Electrolytic refining is the process of refining impure metals by using electricity. In this process, impure metal is made the anode and a strip of pure metal is made the cathode. A solution of a soluble salt of the same metal is taken as the electrolyte. When an electric current is passed, metal ions from the electrolyte are deposited at the cathode as a pure metal and the impure metal from the anode dissolves into the electrolyte in the form of ions. The impurities present in the impure metal gets collected below the anode. This is known as anode mud.
Copper refined by the electrolytic refining.
Write the principle of the method used for the refining of germanium.
Zone refining method is used for the refining of germanium. The principle states that the impurities are more soluble in the melt than in the solid state of the metal.
Out of PbS and PbCO3 (ores of lead), which one is concentrated by froth flotation process preferably?
PbS is concentrated by froth flotation process.
What is the significance of leaching in the extraction of aluminium?
Leaching is significant as it helps in removing the impurities like SiO2, Fe2O3 etc.It is the chemical method used for the concentration of ores. Aluminium is generally extracted from bauxite ore, this ore contains SiO2, iron oxides and titanium oxide as impurities. it is concentrated by digesting the powdered ore with a concentrated solution of NaOH at 473-523 K and 35-36 bar pressure when Al2O3 gets leached out as sodium aluminate.The impurities are left behind.
Write the chemical reactions involved in the process of extraction of Gold. Explain the role of dilute NaCN and Zn in this process
The roasted ore of gold is leached with a solution of sodium cyanide in the presence of oxygen for many days. The role of NaCN in this process is to dissolve the gold to form an aurocyanide complex, from which the metal is obtained by displacement.
Which one of the following ores is best concentrated by froth flotation method?
Siderite
Galena
Malachite
Magnetite
B.
Galena
Sulphide ores are concentrated by froth flotation method. e.g. Galena (PbS).
In the context of the Hall-Heroult process for the extraction of Al, which of the following statements is false?
CO and CO2 are produced in this process
Al2O3 is mixed with CaF2 which lowers the melting point of the mixture and brings conductivity
Al3+ is reduced at the cathode to form Al
Na3AlF6 serves as the electrolyte
D.
Na3AlF6 serves as the electrolyte
The metal that cannot be obtained by electrolysis of an aqueous solution of its salts is
Ag
Ca
Cu
Cr
C.
Cu
Higher the position of the element in electrochemical series more difficult is the reduction of its cations.
If Ca2+ (aq) is electrolyzed, water is reduced in preference to it. Hence, It cannot be reduced electrically from their aqueous solution.
Ca2+ (aq) + H2O → Ca2+ +OH- +H2
Which method of purification is represented by the following equation
zone refining
cupellation
Polling
Van-Arkel
D.
Van-Arkel
Van-Arkel (and de-Boiser) process is based on the thermal decomposition of a volatile compound like an iodide, which is first formed by direct combination of metal to be purified and iodine.
The metallic iodide is then decomposed when heated at a higher temperature and thus the metal obtained in the purest form. Titanium and zirconium are purified by this method.
Which of the following factors is of no significance for roasting sulphide ores to the oxides and not subjecting the sulphide ores to carbon reduction directly?
Metal sulphides are thermodynamically more stable than CS2
CO2 is thermodynamically more stable than CS2
Metal sulphides are less stable than the corresponding oxides
CO2 is more volatile than CS2
A.
Metal sulphides are thermodynamically more stable than CS2
Heating mixture of Cu2O and Cu2S will give
Cu + SO2
Cu + SO3
CuO + CuS
Cu2SO3
A.
Cu + SO2
2Cu2O + Cu2S → 6Cu + SO2
Excess of KI reacts with CuSO4 solution and then Na2S2O3 solution is added to it. Which of the statements is incorrect for this reaction?
Cu2I2 is reduced
Evolved I2 is reduced
Na2S2O3 is oxidized
CuI2 is formed
D.
CuI2 is formed
CuSO4 + 2KI → Cul2 + I2
Thus Cul2 is not formed.
Match items of Columns I with the items of Columns II and assign the correct code.
|
Column I |
Column II |
|
A.Cyanide process |
1.Ultrapure Ge |
|
B. Froth floatation process |
2.Dressing of ZnS |
|
C.Electrolytic reduction |
3.Extraction of Al |
|
D.Zone refining |
4.Extraction of Au |
|
|
5.Purification of Ni |
|
A
|
B
|
C
|
D
|
|
A
|
B
|
C
|
D
|
|
A
|
B
|
C
|
D
|
|
A
|
B
|
C
|
D
|
D.
|
A
|
B
|
C
|
D
|
Cyanide process is used for extracting Au (gold) from low-grade ore by converting the Au to the water soluble coordination complex.
Froth flotation process is used for the dressing of sulphide ore such ZnS.
Electrolytic reduction is used for the extraction of Al. The extraction of aluminium is carried out in a steel tank lined inside with graphite. Here graphite used serves as a cathode.
Zone refining is used for ultra pure Ge element. An ingot of Ge is first purified by zone refining. Then a small amount of antimony is placed in the molten zone which is passed through the pure Ge with the proper choice of rate of heating and other variables.
"Metals are usually not found as nitrates in their ores"
Out of the following two (a and b) reasons which isare/are true for the above observation?
I. Metal nitrates are highly unstable.
II.Metal nitrates are highly soluble in water.
I and II are true
I and II are false
I is false but II is true
I is true but II is false
C.
I is false but II is true
Metals are usually not found as nitrates in their ores, because metal nitrates are highly soluble in water. For example, KNO3 (salt peter) would be classified as completely soluble. Thus, KNO3 could be expected to dissociate completely in aqueous solution into K+ and NO3- ions.
The nitrate anion has three equivalent oxygen surrounding a central nitrogen atom. This tends to spread the single negative charge and make it easier for water to separate the ions in solution.
Roasting of sulphides gives the gas X as a by-product. This is a colourless gas with the choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic acts as a reducing agent and its acid has never been isolated. The gas X is
H2S
SO2
CO2
H2SO3
B.
SO2
SO2 gas is obtained when any sulphide ore is roasted.
This gas (x) SO2 exhibits all the characteristics given in the equation.
Aluminium is extracted from alumina (Al2O3) by electrolysis of a molten mixture of
Al2O3 +HF +NaAlF4
Al2O3 + CaF2 +NaAlF4
Al2O3 +Na3AlF6 +CaF2
Al2O3 +KF +Na3AlF6
C.
Al2O3 +Na3AlF6 +CaF2
Alumina, Al2O3, is a bad conductor of electricity and has a very high melting point, so before subjecting to electrolysis, it is mixed with fluorspar (CaF2) and cryolite (Na3AlF6), which lower its melting point and make it more conducting.
Which one of the following is a mineral of iron?
Malachite
Cassiterite
Pyrolusite
Magnetite
D.
Magnetite
|
Mineral |
Chemical composition |
|
Malachite |
CuCO3.Cu(OH)2 |
|
Cassiterite |
SnO2 |
|
Pyrolusite |
MnO2 |
|
Magnetite |
Fe3O4 |
In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with
Copper (I) sulphide (Cu2S)
sulphur dioxide (SO2)
Iron sulphide (FeS)
Carbon monoxide (CO)
A.
Copper (I) sulphide (Cu2S)
In the extraction of copper from its sulphide ore, when ore is subjected to roasting, some of it is oxidised to Cu2O which reacts with the remaining Cu2S (sulphide ore) to give copper metal.
Cu2S +2Cu2O → 6Cu +SO2 ↑
In this process, Cu2S behaves as reducing agent.
Identify the alloy containing a non-metal as a constituent in it.
Invar
Steel
Bell metal
Bronze
B.
Steel
|
Alloy |
Constituents |
|
Invar |
Fe + Ni |
|
Steel |
Fe + C |
|
Bell metal |
Cu (80%) +Sn (20%) |
|
Bronze |
Cu (75,90%) +Sn (10.25%) |
Which of the following elements is present as the impurity to the maximum extent in the big iron?
Carbon
Silicon
Phosphorus
Manganese
A.
Carbon
Pig iron contains about 4% carbon (major impurity) and other impurities (S, P, Si, Mn) in trace amount.
Which of the following pairs of metals is purified by van Arkel method?
Zr and Ti
Ag and Au
Ni and Fe
Ga and In
A.
Zr and Ti
Zr and Ti are purified by van Arkel method.
In the extraction of copper from its sulphide ore, the metal finally obtained by the reduction of cuprous oxide with
Iron (II) sulphide
Carbon monoxide
Copper (I) sulphide
Sulphur dioxide
C.
Copper (I) sulphide
Reduction of Copper oxide done with Copper (I) sulphide.
Cu2S + 2Cu2O → 6Cu +SO2 ↑
Which of the following statements in incorrect?
pure sodium metal dissolves in liquid ammonia to give blue solution
NaOH reacts with glass to give sodium silicate
Aluminium reacts with excess NaOH to give Al(OH)3
NaHCO3 on heating gives Na2CO3
C.
Aluminium reacts with excess NaOH to give Al(OH)3
Aluminium being amphoteric reacts with aqueous alkalies with the evolution of H2 gas.
2 Al (s) + 2NaOH (aq) + 6H2O (l) --> 2Na+[Al(OH)4]- (aq) +3 H2 ↑
The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction pertaining to the formation of the slag.
Fe2O3 (s) + 3CO (g) → 2 Fe (l) +3CO2 (g)
CaCO3 (s) → CaO (s) + CO2 (g)
CaO (s) +SiO2 → CaSiO3 (s)
2C (s) + O2 (g) → 2 CO(g)
C.
CaO (s) +SiO2 → CaSiO3 (s)
A slag is an easily fusible material which is formed when gangue still present in the roasted or the calcined ore combines with the flux. For example, in the metallurgy of iron, CaO (flux) combines with silica gangue to form easily fusible calcium silicate (CaSiO3) slag.
CaO + SiO2 → CaSiO3 (slag)
Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?
Carbon and hydrogen are suitable reducing agent for metal sulphides
The ΔfGo of the sulphide is greater than those for CS2 and H2S
The ΔfGo is negative for roasting of sulphide ore to oxide
Roasting of the sulphide to the oxide is thermodynamically feasible
A.
Carbon and hydrogen are suitable reducing agent for metal sulphides
Carbon and hydrogen are not suitable reducing agents for metal sulphides.
Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?
Argentite
Galena
Copper pyrite
Sphalerite
D.
Sphalerite
galena (Pbs), Copper pyrite (CuFeS2) and argentite (Ag2S) are concentrated by froth flotation process but sphalerite (ZnS) is concentrated by chemical leching.
Copper sulphates dissolves in excess of KCN to give:
CuCN
[Cu(CN)4]3-
[Cu(CN)4]2-
Cu(CN)2
B.
[Cu(CN)4]3-
Copper sulphate on reaction with KCN to give cupric cyanide precipitates firstly which reduce into Cu2CN2 and dissolve in excess of KCN to give soluble K3[Cu(CN)4] complex salt
[CuSO4 + 2KCN →Cu(CN)2 + K2SO4] x 2
2Cu(CN2) → Cu2(CN)2 + NC - CN
Cu2(CN)2 + 6KCN → 2K3[Cu(CN)4]
_______________________________________
2CuSO4 + 10 KCN → 2K3[Cu(CN)4 + 2K2SO4 + (CN)2]
Al2O3 can be converted to anhydrous AlCl3 by heating:
Al2O3 with HCl gas
Al2O3 with NaCl in solid state
a mixture of Al2O3 and carbon in dry Cl2 gas
Al2O3 with Cl2 gas
C.
a mixture of Al2O3 and carbon in dry Cl2 gas
Al2O3 may be converted to anhydrous AlCl3 by heating of mixture of Al2O3 and carbon in dry chlorine
Considering the Ellingham diagram, which of the following metals can be used to reduce alumina?
Fe
Zn
Cu
Mg
D.
Mg
The metal which is more reactive than 'Al' can reduce alumina. Also, according to the Ellingham diagram, Mg has more –ΔG value then alumina. Metals which has more –ΔG value can reduce those metals oxide which has less –ΔG value.
In cyanide extraction process of silver from argentite ore, the oxidising and reducing agents are respectively.
O2 and CO2
O2 and Zn dust
HNO3 and Zn dust
HNO3 and CO
B.
O2 and Zn dust
The extraction of silver involves in cyanide process are:
Thus, in equation (i) O2 act as oxidising agent (Oxidise sulphide to SO2) and in (ii) Zn act as reducing agent (reduce Ag+ to Ag).
Flux is used to
remove all type of impurities
reduce metal oxide
remove carbonate and sulphate
remove silica and undesirable metal oxides
D.
remove silica and undesirable metal oxides
Flux removes silica and undesirable metal oxides as silicates etc.
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