Question

${\text{Be}}{{\text{H}}_2}$ is prepared by the reaction of:
A. ${\text{2}}\,{\text{BeC}}{{\text{l}}_2}\, + \,{\text{LiAl}}{{\text{H}}_4}\mathop \to \limits^{{\text{ether}}} {\text{2Be}}{{\text{H}}_{\text{2}}}{\text{ + AlC}}{{\text{l}}_{\text{3}}}{\text{ + LiCl}}$
B.${\text{Be}}\,{\text{ + }}\,{{\text{H}}_2}\, \to \,\,{\text{Be}}{{\text{H}}_2}$
C. Both A and B
D. None of these

Answer 1

The oxidation potential of beryllium is very low. Beryllium is not able to give electrons to hydrogen. All the alkaline earth metal hydrides are prepared by the direct reaction of metal with hydrogen except beryllium.

Complete answer:
In the reaction of alkali metals with hydrogen metal gets oxidized and hydrogen gets reduced. Alkaline earth metal has higher oxidation potential than hydrogen, so alkaline earth metal gets oxidized and hydrogen gets reduced. The reaction of metal with hydrogen is as follows:
${\text{M}}\,{\text{ + }}\,{{\text{H}}_2}\, \to \,\,{\text{M}}{{\text{H}}_2}$
Here, M is the alkaline earth metals except beryllium.
The hydride of beryllium is prepared by the reaction of beryllium chloride with lithium hydride in presence of ether which gives beryllium hydride, aluminium chloride and lithium chloride.
The reaction of formation of beryllium hydride is as follows:
${\text{2}}\,{\text{BeC}}{{\text{l}}_2}\, + \,{\text{LiAl}}{{\text{H}}_4}\mathop \to \limits^{{\text{ether}}} {\text{2Be}}{{\text{H}}_{\text{2}}}{\text{ + AlC}}{{\text{l}}_{\text{3}}}{\text{ + LiCl}}$
So, option (A) is correct.
Beryllium does not react with hydrogen directly because its oxidation potential is very low, so it is not able to get oxidized and donate electrons to hydrogen so hydrogen cannot get reduced hydrogen by beryllium.
So, option (B) is incorrect.

Therefore, option (A) is correct.

Note: Beryllium shows the diagonal relationship with aluminum because the size of beryllium and aluminum is the same, so the chemical and physical properties of beryllium matched with aluminum. Aluminum does not react directly with hydrogen due to the small reduction potential. The oxidation potential of alkaline earth metals except beryllium is higher than hydrogen and the oxidation potential of hydrogen is higher than beryllium.