Question

Alane is chemically
A. $Al{H_3}$
B. ${\left( {Al{H_3}} \right)_n}$
C. $LiAl{H_4}$
D. None

Answer 1

Hint : Aluminium hydride is an inorganic compound with a chemical formula $Al{H_3}$. It is white solid and appears as tinted grey when particle size and impurity level is decreased. It is also known as alane or alumnae and its surface may be passivated with a thin layer of aluminium hydroxide or aluminium oxide depending upon synthesis conditions.

Complete Step By Step Answer:
Alane is basically a polymer with chemical formula ${\left( {Al{H_3}} \right)_n}$ and it forms various forms of polymorphs that are named as $\alpha - $ alane, $\beta - $ alane, $\gamma - $ alane, $\delta - $ alane, $\varepsilon - $ alane and $\zeta - $ alane. Among these polymorphs, $\alpha - $ alane is the most thermally stable polymorph which is formed on the heating of $\beta - $ alane and $\gamma - $ alane.
$\alpha - $ alane consist of a cubic or rhombohedral crystal system and in its structure, aluminium atoms are surrounded by six hydrogen atoms which bridge with other six aluminium atoms and all $Al - H$ distances are equivalent i.e., $172pm$ and angle between $Al - H - Al$ bond is ${141^o}$. $\alpha - $ alane is produced by the hydrogenation reaction of aluminium metal under specific conditions. In the reaction, liquified hydrogen reacts with aluminium to form $\alpha - $ alane which can be recovered under ambient conditions.
Alane is an active species in its passivated form and can be used for storing hydrogen, efficient power generation which consists of fuel cell applications and other lightweight power applications. Alane is considered as an excellent rocket fuel in its unpassivated form.
Hence, alane is chemically ${\left( {Al{H_3}} \right)_n}$. So, option (B) is the correct answer.

Note :
Remember alane is not spontaneously flammable and it should be handled in a way similar to other reducing agents like lithium aluminium hydride because the reactivity of alane is similar to $LiAl{H_4}$ and acts as a reducing agent in many organic reactions.