Question

What happens when ionic hydrides of s-block elements in molten states are electrolyzed?
(A) hydride ion migrates to the cathode
(B) dihydrogen is liberated at the cathode
(C) hydride ion reforms metal hydride
(D) dihydrogen is liberated at the anode

Answer 1

The term hydride is commonly named after binary compounds that hydrogen forms with other elements in the periodic table. Depending on the physical and chemical properties of hydrides in s-block elements are classified into three categories, which are ionic, metallic, and covalent hydrides. Due to the hydrogen bonding, these hydrides are a high ionic character of the compounds.

Complete step by step solution:
In s-block elements, the general formula of hydrides $M{{H}_{X}}$, where M is the elements of alkali and alkali earth elements and X is the number of hydrogen atoms. Hydride is a negative charge ion, ${{H}^{-}}$ is called a hydride ion.
Based on the hydrogen bond forms with metals or the basis of chemical bonding, ionic, covalent, metallic are the three types of hydrides.
Ionic hydrides:
These hydrides form only with highly electropositive metals in s-block elements like alkali and alkali earth metals.
$A(s)+{{H}_{2}}(g)\to 2AH(s)$
In liquid state or molten states, ionic hydrides are electrolyzed and conduct electricity by liberating hydrogen gas at the anode.
For example, consider calcium hydride hydrolysis,
$Ca{{H}_{2}}\to C{{a}^{+2}}+2{{H}^{-}}$
At anode: $2{{H}^{-}}\to {{H}_{2}}\uparrow +2{{e}^{-}}$
At cathode: $C{{a}^{2+}}+2{{e}^{-}}\to Ca$
Hence, when ionic hydrides of s-block elements in molten states are electrolyzed, hydrogen is liberated at the anode.

So, the correct answer is option D.

Note: Ionic hydride does not dissolve in conventional solvents and is mostly used as a base or reducing agents (due to hydride ion) in organic synthesis. This electrolysis of ionic hydrides indicates the presence of hydrogen in the compound. These ionic hydrides are also known as saline hydrides and usually binary compounds that are insoluble in solutions.