Question

Saline hydrides are known to reach with water violently producing fire. Can $C{O_2}$ a well known fire extinguisher be used in this case? Explain.

Answer 1

Hint: We can form saline hydrides by using alkali metals and alkaline earth metals with hydrogen. They are also known as ionic hydride (or) pseudohalides. These are insoluble in solution and are binary compounds. They produce gaseous hydrogen, when they are reacted with water vigorously. They act as reducing agents and powerful dehydrating agents.

Complete step by step answer:
Saline hydrides otherwise named as ionic hydrides are compounds that are formed between hydrogen and most active metal. The active metals are alkali and alkaline-earth metals, which belong to group-1 and group-2.
We have to understand that in saline hydride, hydrogen acts as hydride ion $\left( {{H^ - }} \right).$ The reaction of saline hydride with water gives the product as a base and gaseous hydrogen. We can write the chemical equation as,
$M{H_{\left( s \right)}} + {H_2}{O_{\left( {aq} \right)}}\xrightarrow{{}}MO{H_{\left( {aq} \right)}} + {H_{2\left( g \right)}}$
For example, sodium hydride reacts with water to form sodium hydroxide and gaseous hydrogen.
We can write the chemical reaction as,
$Na{H_{\left( s \right)}} + {H_2}{O_{\left( l \right)}}\xrightarrow{{}}NaO{H_{\left( {aq} \right)}} + {H_{2\left( g \right)}}$
Similarly, we can write the reaction of calcium hydride with water to form calcium hydroxide and gaseous hydrogen. For this reaction, the chemical equation is written as,
$Ca{H_{2(s)}} + 2{H_2}{O_{\left( l \right)}}\xrightarrow{{}}Ca{\left( {OH} \right)_{2\left( {aq} \right)}} + 2{H_{2(g)}}$
In the above reactions, a huge amount of energy is liberated such that fire is caught by hydrogen.
Carbon dioxide could not distinguish fire since it is reduced by hot metal hydride. The above reaction is extremely violent that liberates fire.
We know that carbon dioxide is heavier than oxygen and we could use it as a fire extinguisher since it has the ability to form a blanket over the light that confines the source of oxygen. Hence, it could extinguish fire.
For the given case, carbon dioxide is much heavier than hydrogen and so we can use it to put off the fire.

Note:
Some reactions of saline hydride are extremely exothermic that hydrogen evolved to catch fire. The produced fire cannot be put off by carbon dioxide because it gets reduced by hot metal hydride to form sodium formate. However, we use sand, since it is stable and solid.