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Question: When a metal \({\text{X}}\) is treated with cold water, it gives a basic salt \({\text{Y}}\) with mo...

When a metal X{\text{X}} is treated with cold water, it gives a basic salt Y{\text{Y}} with molecular formula XOH{\text{XOH}} (molecular mass =40 = {\text{40}}) and liberate a gas Z{\text{Z}} which easily catches fire. Identify X{\text{X}}, Y{\text{Y}} and Z{\text{Z}}.
A.Y{\text{Y}} is NaOH{\text{NaOH}}, Z{\text{Z}} is H2{{\text{H}}_{\text{2}}}
B.Y{\text{Y}} is NaOH{\text{NaOH}}, Z{\text{Z}} is CO2{\text{C}}{{\text{O}}_{\text{2}}}
C.Y{\text{Y}} is KOH{\text{KOH}}, Z{\text{Z}} is H2{{\text{H}}_{\text{2}}}
D.Y{\text{Y}} is KOH{\text{KOH}}, Z{\text{Z}} is CO2{\text{C}}{{\text{O}}_{\text{2}}}

Explanation

Solution

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 g mol−1{\text{g mo}}{{\text{l}}^{ - 1}}or kg mol−1{\text{kg mo}}{{\text{l}}^{ - 1}}.

Complete step by step answer:
Determine the atomic mass of X{\text{X}} in the molecular formula of the basic salt XOH{\text{XOH}} as follows:
The molecular formula of the basic salt formed is XOH{\text{XOH}}. It has a molecular mass =40 = {\text{40}}.
Molecular mass of XOH=Mass of X+Mass of O+Mass of H{\text{Molecular mass of XOH}} = {\text{Mass of X}} + {\text{Mass of O}} + {\text{Mass of H}}
Mass of X=Molecular mass of XOH−Mass of O−Mass of H{\text{Mass of X}} = {\text{Molecular mass of XOH}} - {\text{Mass of O}} - {\text{Mass of H}}
Substitute 40{\text{40}} for the molecular mass of XOH{\text{XOH}}, 16{\text{16}} for the atomic mass of O{\text{O}}, 1{\text{1}} for the atomic mass of H{\text{H}}. Thus,
Mass of X=40−16−1{\text{Mass of X}} = {\text{40}} - {\text{16}} - {\text{1}}
Mass of X=23{\text{Mass of X}} = 23
Thus, the atomic mass of X{\text{X}} in the molecular formula of the basic salt XOH{\text{XOH}} is 23{\text{23}}.
Determine the formula of basic salt Y{\text{Y}} formed as follows:
The metal with atomic mass 23{\text{23}} is sodium (Na)\left( {{\text{Na}}} \right). Thus, a metal X{\text{X}} is Na{\text{Na}}.
Thus, the formula of basic salt Y{\text{Y}} formed is NaOH{\text{NaOH}}. Thus, Y{\text{Y}} is NaOH{\text{NaOH}}.
Determine the formula of the gas Z{\text{Z}} formed as follows:
The reaction of a metal X{\text{X}} with cold water gives basic salt Y{\text{Y}} and the gas Z{\text{Z}} is liberated.
Thus, the reaction of metal Na{\text{Na}} with cold water gives basic salt NaOH{\text{NaOH}} and the gas Z{\text{Z}} is liberated.
Thus, the reaction is as follows:
2Na+2H2O→2NaOH+Z{\text{2Na}} + 2{{\text{H}}_2}{\text{O}} \to 2{\text{NaOH}} + {\text{Z}}
The Z{\text{Z}} in the reaction is H2{{\text{H}}_{\text{2}}}. Thus, Z{\text{Z}} is H2{{\text{H}}_{\text{2}}}.
Thus, Y{\text{Y}} is NaOH{\text{NaOH}}, Z{\text{Z}} is H2{{\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.