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(a) What are silicones ? States the uses of silicones (b) What are boranes ? Give chemical equation for the preparation of diborane. |
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Answer» Solution :(a) SILICONES are a group of organosilicon polymers, which have `(R_(2)SiO)` as a repeating unit. These may be lineart silicones, cyclic silicones and cross-liked silicones. These are prepared by the hydrolysis of alkyl or aryl derivatives of `SiCl_(4)`, like `RSiCl_(3),R_(2)SiCl_(2) and R_(3)SiCl` and polymerisation of alkyl or aryl hydroxy dervatives obtained by hydrolysis.  Uses These are used as sealant, greases, electrical unsulators and for water proofing of fabrics. These are ALSO used in sugrical adn cosmetic plants (b) Boron forms a number of covalent hydrides with general formulae `B_(n) H_(n+4) and B_(n) H_(n+6)`. These are called BORANES `B_(2)H_(6) and B_(4)H_(10)` are the representative compounds of the two series respectively. Preparation of Diborane It is prepared by treating boron trifluoride with `LiAlH_(4)` in diethyl ether `4BF_(3)+3LiAlH_(4)rarr2B_(2)H_(6)+3LiF+3AlF_(3)` On industrial scale it is prepared by the reaction of `BF_(3)` with sodium hydride `2BF_(3)+6NaH overset(450K)(rarr)B_(2)H_(6)+6NaF`. |
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