Question

Metal hydride on treatment with water gives ________
A.${{H}_{2}}{{O}_{2}}$
B.${{H}_{2}}O$
C.Acid
D.Hydrogen

Answer 1

Hint: Metal hydrides are formed from the metal belonging to the s, d, and f block of the periodic table. In this, the metal atom is bonded to the Hydrogen atom through a covalent bond or an ionic bond. Usually, the hydrolysis of metal hydride results in the formation of a strong base with the liberation of hydrogen gas.

Complete answer:
Metal hydrides are reducing agents. They donate their Hydrogen ions. The hydrogen atom separated from the metal hydride forms the bimolecular hydrogen gas.
The hydride group (H-) leaves the metal hydride, so it is also termed the ‘leaving group’.
Let us understand the reaction equation by an example:
When Calcium hydride reacts with water it forms calcium hydroxide and hydrogen gas is liberated. The resultant metal hydroxide is a strong base.
The balanced reaction equation is as follows:
$Ca{{H}_{2}}\text{ + 2}{{\text{H}}_{2}}O\text{ }\to \text{ }Ca{{(OH)}_{2}}\text{ + 2}{{\text{H}}_{2}}$
Now, let’s see one more example of a metal hydride from Group 1 of the periodic table.
When Lithium hydride is hydrolyzed it results in the formation of Lithium hydroxide and hydrogen is formed. Lithium is an alkali metal as it forms alkalis when it comes in contact with water.
$LiH\text{ + 2}{{\text{H}}_{2}}O\text{ }\to \text{ Li}(OH)\text{ + 2}{{\text{H}}_{2}}$
Thus, the reaction between a metal hydride and water forms metal hydroxide, and hydrogen gas is liberated.
The correct answer is Option D: Hydrogen.

Note:
Some metal hydrides are highly reactive and react vigorously when they come in contact with water. For example, Sodium hydride is very reactive. The resultant compound is a very strong base. It can deprotonate an acid to form the metal derivative of alcohols and phenols.