Question

$X$ and $Y$ both are soluble in given solvent. Molar mass of the polymer $Y$ is

• A. $210\, g \,mol ^{-1}$
• B. $50\, g \,mol ^{-1}$
• C. $205\, g \,mol ^{-1}$
• D. $100\, g \,mol ^{-1}$

Answer 1

Answer: (B)

From $I$ and $II$,

$\left(\Delta T_{b}\right)_{x}=\frac{1000 K_{b} w_{1}}{m_{1} w_{2}}$

$5^{\circ}=K_{b}$ (molality)

$\therefore K_{b}($ solvent $)=5^{\circ} \,mol ^{-1} \,kg$

From $I$ and $III$,

$\left(\Delta T_{b}\right)_{ y }=10^{\circ} $

$\therefore \left(\Delta T_{b}\right)_{y}=\frac{1000 K_{b} w_{1}}{m_{1} w_{2}}$

$ \therefore m _{1}( Y ) =\frac{1000 \,K_{b} w_{1}}{\left(\Delta T_{b}\right)_{y} w_{2}}$

$=\frac{1000 \times 5 \times 10}{10 \times 100} $

$=50 \,g \,mol ^{-1} $