Question

Question 42
When a metal X is treated with cold water, it gives a base Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z, which easily catches fire. Identify X, Y and Z and also write the reaction involved.

Answer 1

Molecular mass of $\text{X + O + H}=40$
$\to \text{X}+16+1=40$
$\to \text{X}=23$
Only Na has the molecular mass of 23. Therefore, X is sodium and Y is sodium hydroxide as it has molecular mass 40.

Sodium on reaction with cold water gives out sodium hydroxide, hydrogen gas and heat energy. The reaction occurs as follows:

$2\text{Na(s)}+2{\text{H}}_2\text{O(cold)}\to 2\text{NaOH(aq)}+{\text{H}}_2\text{(g)}+\text{Heat energy}$

Hydrogen gas easily catches fire. Therefore, Z is hydrogen gas.