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)
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Solution:
- Moles of $CO _2$ can be calculated using ideal gas equation as :
$$ n=\frac{p V}{R T}=\left(\frac{700}{760}\right)\left(\frac{1336}{1000}\right) \times \frac{1}{0.082 \times 300}=0.05 $$
Also, the decomposition reaction is :
$$ \begin{aligned} & M CO _3 \ & 0.05 mol \end{aligned} \longrightarrow \underset{M}{M O}+CO _2 $$
$\because \quad 0.05$ mole $M CO _3=4.215 g$
$\therefore \quad 1.0$ mole $M CO _3=\frac{4.215}{0.05}=84.3 g$ (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
$$ =\frac{\text { Molecular weight }}{2}=12.15 $$
