Class 12 Chemistry · 49 questions · 49 with answers
In the extraction of chlorine by electrolysis of brine ____________. –
(iii) For overall reaction ∆G has negative value.
When copper ore is mixed with silica, in a reverberatory furnace copper matte is produced. The copper matte contains ____________.
(iii) sulphides of copper (I) and iron (II)
Which of the following reactions is an example of autoreduction?
(iv) Cu2O + Cu2S → 3Cu + SO2 2 2
A number of elements are available in earth’s crust but most abundant elements are ____________.
(i) Al and Fe
Zone refining is based on the principle that ___________.
(ii) impurities are more soluble in molten metal than in solid metal.
In the extraction of copper from its sulphide ore, the metal is formed by the reduction of Cu2O with
(iii) Cu2S
Brine is electrolysed by using inert electrodes. The reaction at anode is ________. – 1 V
(i) Cl (aq.) → Cl (g) + e– ; ECell = 1.36V 2 2 + V
In the metallurgy of aluminium ________________. 3+
(ii) graphide anode is oxidised to carbon monoxide and carbon dioxide.
Electrolytic refining is used to purify which of the following metals?
(i) Cu and Zn
Extraction of gold and silver involves leaching the metal with CN ion. The metal is recovered by ________________.
This question refers to a figure in the original PDF.
(i) displacement of metal by some other metal from the complex ion.
Choose the correct option of temperature at which carbon reduces FeO to iron and produces CO.
(iv) Above temperature at point A. 79 General Principles and Processes of Isolation of Elements
Below point ‘A’ FeO can ______________.
(i) be reduced by carbon monoxide only.
For the reduction of FeO at the temperature corresponding to point D, which of the following statements is correct?
(i) ∆G value for the overall reduction reaction with carbon monoxide is zero.
At the temperature corresponding to which of the points in Fig.6.1, FeO will be reduced to Fe by coupling the reaction 2FeO → 2Fe + O2 with all of the following reactions? (a) C + O2 → CO2 (b) 2C + O2 → 2CO and (c) 2CO + O2 → 2 CO2
This question refers to a figure in the original PDF.
(ii) Point B
(iv) Point E
Which of the following options are correct?
(i) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.
(iv) Zr and Ti are purified by van Arkel method.
In the extraction of aluminium by Hall-Heroult process, purified Al2O3 is mixed with CaF2 to
(i) lower the melting point of Al2O3.
(ii) increase the conductivity of molten mixture.
Which of the following statements is correct about the role of substances added in the froth floation process?
(i) Collectors enhance the non-wettability of the mineral particles.
(iii) By using depressants in the process two sulphide ores can be separated.
In the Froth Floatation process, zinc sulphide and lead sulphide can be separated by ______________.
(ii) adjusting the proportion of oil to water.
(iii) using depressant.
Common impurities present in bauxite are ____________.
(iii) Fe2O3
(iv) SiO2
Which of the following ores are concentrated by froth floation?
(ii) Galena
(iii) Copper pyrites
Which of the following reactions occur during calcination?
(i) CaCO3 → CaO + CO2
(iii) Al2O3.x H2O → Al2O3 + x H2O
For the metallurgical process of which of the ores calcined ore can be reduced by carbon?
(i) haematite
(ii) calamine
The main reactions occurring in blast furnace during extraction of iron from haematite are ________.
(i) Fe2O3 + 3CO → 2Fe + 3CO2
(iv) CaO + SiO2 → CaSiO3
In which of the following method of purification, metal is converted to its volatile compound which is decomposed to give pure metal?
(i) heating with stream of carbon monoxide.
(ii) heating with iodine.
Which of the following statements are correct?
(i) A depressant prevents certain type of particle to come to the froth.
(iii) The solidified copper obtained from reverberatory furnace has blistered appearance due to evolution of SO2 during the extraction.
In the extraction of chlorine from brine _____________.
(ii) ∆G for the overall reaction is positive.
(iii) E for overall reaction has negative value.
Why is an external emf of more than 2.2V required for the extraction of Cl2 from brine?
For the reaction – – 2Cl (aq) + 2H 2 O (l) → 2OH (aq)+H2 (g)+Cl 2 (g) V V V V Value of ∆G is + 422kJ. Using the equation ∆G = – nFE the value of E comes out to be –2.2V. Therefore extraction of Cl2 from brine will require an external emf of greater than 2.2V.
At temperatures above 1073K coke can be used to reduce FeO to Fe. How can you justify this reduction with Ellingham diagram?
As per Ellingham diagram at temperatures greater than 1073 K ∆G (C, CO) < ∆G (Fe, FeO). Hence coke can reduce FeO to Fe.
Wrought iron is the purest form of iron. Write a reaction used for the preparation of wrought iron from cast iron. How can the impurities of sulphur, silicon and phosphorus be removed from cast iron?
Fe2O3 + 3C → 2Fe + 3CO Limestone is added as flux and sulphur, silicon and phosphorus change to their oxides and pass into the slag.
How is copper extracted from low grade copper ores?
Copper is extracted by hydrometallurgy from low grade copper ores. It is leached out using acid or bacteria. The solution containing Cu2+ is treated with scrap iron, Zn or H2. 2+ + Cu (aq) + H2 (g) → Cu(s)+ 2H (aq) 2+ 2+ Cu + Fe(s) → Fe (aq)+ Cu(s)
Write two basic requirements for refining of a metal by Mond process and by Van Arkel Method.
Basic requirements for both processes are : (i) The metal should form a volatile compound with an available reagent. (ii) The volatile compound should be easily decomposable, so that recovery of metal is easy.
Although carbon and hydrogen are better reducing agents but they are not used to reduce metallic oxides at high temperatures. Why?
It is because at high temperature carbon and hydrogen react with metals to form carbides and hydrides respectively. 87 General Principles and Processes of Isolation of Elements
How do we separate two sulphide ores by Froth Floatation Method? Explain with an example.
Two sulphide ores can be separated by adjusting proportion of oil to water or by using depressants. For example, in the case of an ore containing ZnS and PbS, the depressant NaCN is used. It forms complex with ZnS and prevents it from coming with froth but PbS remains with froth.
The purest form of iron is prepared by oxidising impurities from cast iron in a reverberatory furnace. Which iron ore is used to line the furnace? Explain by giving reaction.
Haematite Fe2O3 + 3C → 2Fe + 3CO
The mixture of compounds A and B is passed through a column of Al2O3 by using alcohol as eluant. Compound A is eluted in preference to compound B. Which of the compounds A or B, is more readily adsorbed on the column?
Since compound ‘A’ comes out before compound ‘B’, the compound ‘B’ is more readily adsorbed on column.
Why is sulphide ore of copper heated in a furnace after mixing with silica?
Iron oxide present as impurity in sulphide ore of copper forms slag which is iron silicate and copper is produced in the form of copper matte. FeO + SiO2 → FeSiO3
Why are sulphide ores converted to oxide before reduction?
Sulphides are not reduced easily but oxides are easily reduced.
Which method is used for refining Zr and Ti? Explain with equation.
van Arkel method is used for refining Zr and Ti. In this method crude metal is heated with iodine. Zr + 2I2 → ZrI4 1800K ZrI4 → Zr + 2I2
What should be the considerations during the extraction of metals by electrochemical method?
Generally two things are considered so that proper precautions can be taken. (i) reactivity of metal produced. (ii) suitability of electrodes.
What is the role of flux in metallurgical processes?
Flux is used for making the molten mass more conducting.
How are metals used as semiconductors refined? What is the principle of the method used?
Semiconducting metal is produced by zone refining method which is based on the principle that the impurities are more soluble in melt than in the solid state of metals.
Write down the reactions taking place in Blast furnace related to the metallurgy of iron in the temperature range 500-800 K.
3Fe2O3 + CO → 2Fe3O4 + CO2 Fe3O4 + 4CO → 3Fe + 4CO2 Fe2O3 + CO → 2FeO + CO2
Give two requirements for vapour phase refining.
(i) The metal should form a volatile compound with available reagent. (ii) The volatile compound should be easily decomposable so that the recovery is easy. – – –
Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.
4Au (s) + 8CN (aq) + 2H2O (aq) + O2 (g) → 4 [Au (CN)2] (aq) + 4OH (aq) – 2[Au(CN)2] (aq) + Zn(s) → 2Au(s) + [Zn (CN)4]2– (aq) In this reaction zinc acts as a reducing agent. IV. Matching Type
Match the items of Column I with items of Column II and assign the correct code: Column I Column II (A) Pendulum (1) Chrome steel (B) Malachite (2) Nickel steel (C) Calamine (3) Na3AlF6 (D) Cryolite (4) CuCO3.Cu (OH)2 (5) ZnCO3 Code :
(ii) A (2) B (4) C (5) D (3)
Match the items of Column I with the items of Column II and assign the correct code : Column I Column II (A) Coloured bands (1) Zone refining (B) Impure metal to volatile complex (2) Fractional distillation (C) Purification of Ge and Si (3) Mond Process (D) Purification of mercury (4) Chromatography (5) Liquation Code :
(ii) A (4) B (3) C (1) D (2)
Match items of Column I with the items of Column 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 Code :
(i) A (4) B (2) C (3) D (1)
Match the items of Column I with the items of Column II and assign the correct code : Column I Column II (A) Sapphire (1) Al2O3 (B) Sphalerite (2) NaCN (C) Depressant (3) Co (D) Corundum (4) ZnS (5) Fe2O3 Code :
(i) A (3) B (4) C (2) D (1)
Match the items of Column I with items of Column II and assign the correct code : Column I Column II (A) Blisterred Cu (1) Aluminium (B) Blast furnace (2) 2Cu2O + Cu2S → 6Cu + SO2 (C) Reverberatory furnace (3) Iron (D) Hall-Heroult process (4) FeO + SiO2 → FeSiO3 (5) 2Cu2S + 3O2→ 2Cu2O + 2SO2 Code :
(i) A (2) B (3) C (4) D (1)