In general stability of Complexes is directly proportional to the magnitude of charge on central metal atom. Thus Complexes of Ni +2 are more stable than Ni0
[Ni(CN)4]4- < [Ni(CN)4]2-
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Wednesday, April 13, 2022
d3s Hybrization and it's examples.
d3s Hybridization or dxy+dyz+dxz+s possess tetrahedral geometry and bond angle 109'28'. And examples are as CrO2Cl2, CrO42-, MnO41-, MnO42-
VO43-, Cr2O72-
Chemical methods of purification/refining of metals:
These methods include the following methods :
(1) OXIDATIVE REFINING :
The method is used when the impurities present in the metal have a greater affinity for oxygen and are more readily oxidized than the metal. Then these oxides may be removed as follows
(A) These oxide may form a scum on the surface of the metal. This scum can easily be removed by
skimming.
(B) If the oxides are volatile, they escape from the mouth of the furnace.
(C) The oxides may form a slag with the lining on the inside surface of the furnace and may thus be removed. In the formation of the slag, the lining acts as a flux.This method is usually employed for refining metals like Pb, Ag, Cu, Fe, etc. In this method the molten impure metal is subjected to oxidation by various ways.
Pudding process : Used for the manufacture of wrought iron from cast iron:
This process is used for the manufacture of wrought iron from cast iron. We know that cast iron contains the impurities of C, S, Si, Mn and P. When these impurities are removed from cast iron, we get wrought iron. In this process the impurities are oxidised to their oxides not by blast of air but by the haematite (Fe2O3) lining of the furnace.
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Vapour phase refining : Van Arkel–De Boer process :
Small amounts of very pure metals (Ti, Zr, or Bi) can be produced by this method. This process is based on the fact that iodides are the least stable of the halides. The impure element is heated with iodine, producing a volatile iodide, TiI4, ZrI4, or BiI3. These are decomposed by passing the gas over an electrically heated filament of tungsten or tantalum that is white hot. The element is deposited on the filament and the iodine is recycled. As more metal is deposited on the filament, it conducts electricity better. Thus, more electric current must be passed to keep it white hot. Thus the filament grows fatter and eventually the metal is recovered. The tungsten core is distilled out of the center and a small amount
of high purity metal is obtained.
Impure Ti + 2I2 (50–250ºC)-->TiI4 Tungsten filament(1400ºC)-->Ti+ 2I2
The method is very expensive and is employed for the preparation of very pure metal for specific use.
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