Q. At $25^{\circ}C\$a 5% aqueous solution of glucose (molecular weight = 180 g $mol^{- 1}$) is isotonic with 2% aqueous solution containing an unknown solute. What is the molecular weight of the unknown solute.
A) 60
B) 80
C) 72
D) 63
Explanation
(c)
Solutions having same osmotic pressure are called isotonic solutions. $\pi\ gloucose = \pi\ unknown\ solute\$
$\ \ \ \frac{5}{180} = \frac{2}{M}\ \ \ \ or\ \ \ \ \ \ \ \ \ \ \ \ M = \frac{180 \times 2}{5} = 72$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.