What is the role of graphite rod in the electrometallurgy of aluminium?
In the electrometallurgy of aluminium, oxygen gas is evolved at anode. O2 reacts with graphite or carbon (graphite electrodes) to form carbon monoxide and carbon dioxide. In case if some other metal electrodes is used as anode, then oxygen will react with aluminium formed during the process to form aluminium oxide(Al2O3) which will pass into the reaction mixture resulting into wastage of Al. Since graphite is cheaper than aluminium, its wastage or can be tolerated.
Extraction of gold and silver involves leaching the metal with CN+ ion. The metal is recovered by
(a) displacement of metal by some other metal from the complex ion
(b) roasting of metal complex
(c) calcinations followed by roasting
(d) thermal decomposition of metal complex
Which of the following statements are correct?
(a) A depressant prevents certain type of particle to come to the froth.
(b) Copper matte contains Cu2S and ZnS.
(c) The solidified copper obtained from reverberatory furnace has blistered appearance due to evolution of SO2 during the extraction.
(d) Zinc can be extracted by self-reduction.
t the temperature corresponding to which of the points in figure of Q. 11-13, FeO will be reduced to Fe by coupling the reaction 2FeO —> 2Fe + 02 with all of the following reactions?
The main reactions occurring in blast furnace during extraction of iron from haematite are
Assertion (A): Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.
Reason (R): Copper is extracted by hydrometallurgy.
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 a slag of iron silicate and copper is produced in the form of copper matte.
Assertion (A): Zirconium can be purified by van Arkel method.
Reason (R): ZrI4 is volatile and decomposes at 1800 K.
The purest form of iron is prepared by oxidizing impurities from cast iron in a reverberatory furnace. Which iron ore is used to line the furnace? Explain by giving reaction.
Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.
Assertion (A): Sulphide ores are concentrated by froth floatation method. Reason (R): Cresols stabilize the froth in froth floatation method.
Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?
The value of ΔfG ° for formation of Cr2O3 is – 540 kJ mol-1 and that of Al203 is – 827 kJ mol-1 . Is the reduction of Cr2O3 possible with Al?
In the extraction of aluminium by Hall-Heroult process, purified A1203 is mixed with CaF2 to
(a) lower the melting point of A1203.
(b) increase the conductivity of molten mixture.
(c) reduce Al+3 into Al(s).
(d) acts as catalyst.
Which of the following statements are correct about the role of substances added in the froth floatation process?
(a) Collectors enhance the non-wettability of the mineral particles.
(b) Collectors enhance the wettability of gangue particles.
(c) By using depressants in the process two sulphide ores can be separated.
(d) Froth stabilizers decrease wettability of gangue.
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?
Assertion (A): Zone refining method is very useful for producing semiconductors.
Reason (R): Semiconductors are of high purity.
Which of the following options are correct?
(a) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.
(b) In extraction of silver, silver is extracted as cationic complex.
(c) Nickel is purified by zone refining.
(d) Zr and Ti are purified by van Arkel method.
Why is an external emf of the more than 2.2 V required for the extraction of Cl2 from brine?
In the froth floatation process, zinc sulphide and lead sulphide can be separated by
(a) using collectors
(b) adjusting the proportion of oil to water
(c) using depressant
(d) using froth stabilisers
Choose the correct option of temperature at which carbon reduces FeO to iron and produces CO.
(a) Below temperature at point A
(b) Approximately at the temperature corresponding to point A
(c) Above temperature at point A but below temperature at point D
(d) Above temperature at point A
For the metallurgical process of which of the ores, calcined ore can be reduced by carbon?
(a) Haematite (b) Calamine (c) Iron pyrites (d) Sphalerite
Write two basic requirements for refining of a metal by Mond's process and by van Arkel method.Why?
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.
Name the processes from which chlorine is obtained as a by-product What will happen if an aqueous solution of NaCl is subjected to electrolysis?
Outline the principles of refining of metals by the following methods:
(i) Zone refining
(ii) Electrolytic refining
(iii) Vapour phase refining
