Q. By dissolving 5g substance in 50 g of water, the decrease in freezing point is $1.2℃.\$ The gram molal depression is$1.85℃$. The molecular weight of substance is
A) 105.4
B) 118.2
C) 137.2
D) 154.2
Explanation
(d)
We know that m=$\frac{1000k_{f} \times w}{\mathrm{\Delta}TW}$
Hence, $\mathrm{\Delta}T = 1.2℃,k_{f} = 1.85{^\circ}$
w=5 g, W =50 g
$\therefore$ m=$\frac{1000 \times 1.85 \times 5}{1.2 \times 50} = 154.2$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.