Question

When a metal ${\text{X}}$ is treated with cold water, it gives a basic salt ${\text{Y}}$ with molecular formula ${\text{XOH}}$ (molecular mass $ = {\text{40}}$) and liberate a gas ${\text{Z}}$ which easily catches fire. Identify ${\text{X}}$, ${\text{Y}}$ and ${\text{Z}}$.
A.${\text{Y}}$ is ${\text{NaOH}}$, ${\text{Z}}$ is ${{\text{H}}_{\text{2}}}$
B.${\text{Y}}$ is ${\text{NaOH}}$, ${\text{Z}}$ is ${\text{C}}{{\text{O}}_{\text{2}}}$
C.${\text{Y}}$ is ${\text{KOH}}$, ${\text{Z}}$ is ${{\text{H}}_{\text{2}}}$
D.${\text{Y}}$ is ${\text{KOH}}$, ${\text{Z}}$ is ${\text{C}}{{\text{O}}_{\text{2}}}$

Answer 1

Hint:The sum of masses of all the atoms in the molecular formula of the molecule is known as the molecular mass. The unit of molar mass is ${\text{g mo}}{{\text{l}}^{ - 1}}$or ${\text{kg mo}}{{\text{l}}^{ - 1}}$.

Complete step by step answer:
Determine the atomic mass of ${\text{X}}$ in the molecular formula of the basic salt ${\text{XOH}}$ as follows:
The molecular formula of the basic salt formed is ${\text{XOH}}$. It has a molecular mass $ = {\text{40}}$.
${\text{Molecular mass of XOH}} = {\text{Mass of X}} + {\text{Mass of O}} + {\text{Mass of H}}$
${\text{Mass of X}} = {\text{Molecular mass of XOH}} - {\text{Mass of O}} - {\text{Mass of H}}$
Substitute ${\text{40}}$ for the molecular mass of ${\text{XOH}}$, ${\text{16}}$ for the atomic mass of ${\text{O}}$, ${\text{1}}$ for the atomic mass of ${\text{H}}$. Thus,
${\text{Mass of X}} = {\text{40}} - {\text{16}} - {\text{1}}$
${\text{Mass of X}} = 23$
Thus, the atomic mass of ${\text{X}}$ in the molecular formula of the basic salt ${\text{XOH}}$ is ${\text{23}}$.
Determine the formula of basic salt ${\text{Y}}$ formed as follows:
The metal with atomic mass ${\text{23}}$ is sodium $\left( {{\text{Na}}} \right)$. Thus, a metal ${\text{X}}$ is ${\text{Na}}$.
Thus, the formula of basic salt ${\text{Y}}$ formed is ${\text{NaOH}}$. Thus, ${\text{Y}}$ is ${\text{NaOH}}$.
Determine the formula of the gas ${\text{Z}}$ formed as follows:
The reaction of a metal ${\text{X}}$ with cold water gives basic salt ${\text{Y}}$ and the gas ${\text{Z}}$ is liberated.
Thus, the reaction of metal ${\text{Na}}$ with cold water gives basic salt ${\text{NaOH}}$ and the gas ${\text{Z}}$ is liberated.
Thus, the reaction is as follows:
${\text{2Na}} + 2{{\text{H}}_2}{\text{O}} \to 2{\text{NaOH}} + {\text{Z}}$
The ${\text{Z}}$ in the reaction is ${{\text{H}}_{\text{2}}}$. Thus, ${\text{Z}}$ is ${{\text{H}}_{\text{2}}}$.
Thus, ${\text{Y}}$ is ${\text{NaOH}}$, ${\text{Z}}$ is ${{\text{H}}_{\text{2}}}$.
Thus, the correct option is option (A).

Note:
Hydrogen is very flammable gas. Also, hydrogen in contact with chlorine, oxygen is very explosive. Hydrogen generally burns with invisible flame. Whereas carbon dioxide is non-flammable gas. Carbon dioxide is very stable chemically and inert. Instead carbon dioxide is used to cease fire. It is generally used in fire extinguishers.