States of Matter - Result Question 95
95. $4.215 g$ of a metallic carbonate was heated in a hard glass tube, the $CO _2$ evolved was found to measure $1336 mL$ at $27^{\circ} C$ and $700 mm$ of $Hg$ pressure. What is the equivalent weight of the metal ?
(1979, 3M)
Show Answer
Solution:
Moles of $CO _2$ can be calculated using ideal gas equation as :
$ n=\dfrac{p V}{R T}=\left(\dfrac{700}{760}\right)\left(\dfrac{1336}{1000}\right) \times \dfrac{1}{0.082 \times 300}=0.05 $
Also, the decomposition reaction is :
$ \hspace{8mm} M CO _3 \hspace{10mm} \longrightarrow \hspace{10mm} MO+CO_2$
$\hspace{8mm} 0.05 {~mol} \hspace{27mm} 0.05 {~mol}$
$\because \quad 0.05$ mole $M CO _3=4.215 ~ g$
$\therefore \quad 1.0$ mole $M CO _3=\dfrac{4.215}{0.05}=84.3 ~ g$ (molar mass)
$\Rightarrow \quad 84.3=$ MW of $M+12+48$
$\Rightarrow$ Molecular weight of metal $=24.3$
$\because \quad$ Metal is bivalent, equivalent weight
$ =\dfrac{\text { Molecular weight }}{2}=12.15 $
BETA
