Question

The Chloride of a metal contains about \[\text{71}%\] of chlorine by weight and vapor density is 50 The atomic mass of Metal will be (Valency of the Metal is 2).
A.29
B.58
C.35.5
D.71

Answer 1

Hint: The valency is \[+\text{2}\] for alkaline earth Metal, Ba, Mg, Ca etc. So the possible compound is $\text{BaC}{{\text{l}}_{\text{2}}}\text{,MgC}{{\text{l}}_{\text{2}}}\text{,CaC}{{\text{l}}_{\text{2}}}$, etc. Atomic mass is defined as the sum of the number proton and electron.
Atomic mass = number of protons + number of electrons

Complete answer:
Molecular weight of the compound
$\begin{align}
  & =2\times \text{vapor}\,\text{density}\,100\text{g}/\text{mol} \\
 & =(2\times 50)\text{g}/\text{mol} \\
 & =100\text{g}/\text{mol} \\
\end{align}$
So, 100g of compound containing the 71g of Cl (as it is given in our statement), so remaining metal = \[\text{1}00-\text{71 }=\text{ 29g}\]
Valency of metal = 2
So that 71g of metal corresponds to 2 moles
So, the atomic mass of the metal is 29g.

Therefore, the correct option is (A).

Additional information:
Alkaline earth metals:- The alkaline earth metals are arranged in a second group. They are termed as s- block elements as last electrons enter into the s subshell. They exhibit +2 valency. They are also termed as heavy metals. In alkaline earth metal contains six metals as beryllium, magnesium, calcium strontium, barium and radium. The general electronic configuration is $ns_2$.
Alkaline earth metals have similar properties. They all have shiny silver white color. They are reactive at standard temperature and pressure.
Vapour density :- Vapour density is defined as being mass of a certain volume of substance divided by the same volume of hydrogen.
Atomic mass:- Atomic mass is defined as the sum of the number of protons and number of electrons.
Atomic mass = number of proton + number of electrons
Valency :- Valency is defined as the number of gaining and losing an electron from the outermost shell.
Transition elements exhibit variable valency.

Note: The valency of each group must be known and how the valency is calculated should also be known, ex- Na having the Valency \[+\text{1}\], because it is losing 1 electron to attain the stability. Valency determines the number of electrons present in the outermost shell. Vapor density is half of molecular weight as it is the ratio of the molecular weight of the compound to that of the molecular weight of hydrogen. It tells us about the combining capacity of an atom of the element with another atom. Valency does not have any positive or negative sign.