The experimentally determined molar mass of a non-volatile solute, $\mathrm{BaCl}_2$ in water by Cottrell's…
The experimentally determined molar mass of a non-volatile solute, $\mathrm{BaCl}_2$ in water by Cottrell's method, is
equal to the calculated molar mass
more than the calculated molar mass
less than the calculated molar mass
double of the calculated molar mass
Solution
$\mathrm{BaCl}_2$ being ionic in nature, ionises completely to give $\mathrm{Ba}^{2+}$ and $2 \mathrm{Cl}^{-}(1+2=3)$ ions, i.e., number of particles increases in the solution.
$\therefore \quad i=\frac{3}{1}=3=\frac{M_c}{M_o}$
(where, $M_c=$ calculated molar mass and $M_o=$ observed molar mass)
$\begin{array}{ll} & 3=\frac{M_c}{M_o} \\ \text { or } & M_o=\frac{M_c}{3} \\ \text { i.e., } \quad & M_o < M_c\end{array}$
or observed molecular mass of $\mathrm{BaCl}_2$ is less than the calculated molecular mass.