Method used for obtaining highly pure silicon used as a semiconductor material, is [1994, 96]
Si obtained by reduction of SiCl4 with H2 is further purified by zone refining method to get Si of very high purity. Silicon is purified by zone-refining process because the impurities present in it are more soluble in the liquid phase than in the solid phase.
The method of zone refining of metals is based on the principle of 
Zone refining is based on the difference in solubility of impurities in molten and solid state of the metal. This method is used for obtaining metals of very high purity.
Which of the following statements, about the advantage of roasting of sulphideore before reduction is not true? 
The sulphide ore is roasted to oxide before reduction because the ΔGof of most of the sulphides are greater than those of CS2 and H2S, therefore neither C nor H can reduce metal sulphide to metal. Further, the standard free energies of formation of oxide are much less than those of SO2. Hence oxidation of metal sulphides to metal oxide is thermodynamically favourable.
Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offer an exception and its concentrated by chemical leaching? 
Leaching is the selective dissolution of the desired mineral leaving behind the impurities in a suitable dissolving agent eg Argentitie or Silver glance, Ag2S is an ore of silver. Silver is extracted from argentite by the mac-Arthur and Forest process (leaching process).
Which of the following elements is present as the impurity to the maximum extent in the pigiron ?
Pigironor castiron contains 3 – 5% carbon and varying amounts of Mn, Si, P and S which makes the iron hard and brittle.
Which of the following pairs of metals is purified by van Arkel method ? 
Zr and Ti are purified by van Arkel method.
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. [2011 M]
In blast furnace at about 1270 K, calcium carbonate is almost completely decomposed to give CaO which acts as a flux and combines with SiO2 present as impurity (gangue) in the ore to form calcium silicate (fusible slag)
Which one of the following is a mineral of iron? 
[Fe3O4 ⇒ Magnetite]
[CuCO3 Cu(OH)2 – Malachite]
Pyrolusite – MnO2 Cassiterite – SnO2.
In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with : 
Cuprous oxide formed during roasting of cuprous sulphide is mixed with few amount of cuprous sulphide and heated in a reverberatory furnace to get metallic copper.
Identify the alloy containing a non-metal as a constituent in it. 
Invar is a nickel iron alloy, Bell metal is an alloy of about 80% copper and 20% tin, Bronze is also an alloy of copper and tin.
Steel : It always have few % of carbon.
The metal oxide which cannot be reduced to metal by carbon is [NEET Kar. 2013]
Al2O3 cannot be reduced by carbon.