Question

When a metal $\mathrm{X}$ is treated with cold water, it gives a basic salt $\mathrm{Y}$ with molecular formula $\mathrm{XOH}$ (Molecular mass $=40$) and liberates a gas $\mathrm{Z}$ which easily catches fire. Identify $\mathrm{X},\mathrm{Y}$ and $\mathrm{Z}$ and also write the reaction involved.

Answer 1

Chemical reaction:

• “The reaction in which change in chemical properties takes place is called a chemical reaction.”

Identification of $\mathrm{X},\mathrm{Y}$ and $\mathrm{Z}$:

• As the molecular mass of $\mathrm{XOH}$ is $40$, therefore, the sum of the molecular masses of all elements is given as

$$\begin{gathered} \mathrm{X}+\mathrm{O}+\mathrm{H}=40 \\ \mathrm{X}+16+1=40 \\ \mathrm{X}=40-17 \\ \mathrm{X}=23 \end{gathered}$$

• The molecular mass of $\mathrm{X}$is $23$, therefore, the metal $\mathrm{X}$ is $\mathrm{Na}$.
• As $\mathrm{X}$ is $\mathrm{Na}$, therefore, the salt $\mathrm{Y}$ is $\mathrm{NaOH}$.
• The reaction of Sodium with cold water takes place as

$\underset{\left(\mathrm{Sodium}\right)}{2\mathrm{Na}\mathrm{(}\mathrm{s}\mathrm{)}}+\underset{\left(\mathrm{Water}\right)}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\left(\mathrm{Sodium}\mathrm{hydroxide}\right)}{2\mathrm{NaOH}\left(\mathrm{l}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

• In this reaction, hydrogen gas is evolved which also catches fire easily, therefore, the gas $\mathrm{Z}$ is ${\mathrm{H}}_2$.