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(a) What are the special featured of str...

(a) What are the special featured of structures of boron ?
(b) Which alloy of aluminium is used in air-carft industry ?
( c) When finely powdered `Al` is suddenly exposed to air, at cataches fire. Why ?
(d) Write a balanced equation for the preparation of elemental boron by reduction of `BBr_(3)` with dihydrogen.

Text Solution

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(a) Boron is a symmetrical solid with icosahedral sahpe. There are `20` faces (equilateral triangle). The faces meet as `12` corners. Each icosahedran consists of `12` boron aroms, `6` of them are bonded by a three-conre two-electron `(3c, 2e)` bond `(2.02 Å)` in separated icosahedra.
(b) An alloy of aluminium which is used in air-craft industry is duralumin. Its composition is `95 % Al, 4 % Cu, 0.5 % Mn` and `0.5 % Mg`.
( c) Finely powdered aluminium, when suddenly exposed to air, reacts vigorosly with aerial oxygen, `O_(2)`. The reaction is highly exothermic and therefore `Al` catches fire.
`4Al_((s)) + 3O_(2(g)) rarr 2Al_(2) O_(3(s)) Delta H = -310 kJ mol^-1`
(d) `2BBr_(3(g)) + 3H_(2(g)) rarr 2B_((s)) + 6HBr_((g))`.
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