Q. The empirical formula of a non-electrolyte is ${CH}_{2}O$ . A solution containing 6g of the compound exerts the same osmotic pressure as that of 0.05 M glucose solution at the same temperature. The molecular formula of the compound is
A) $C_{2}H_{4}O_{2}$
B) $\ C_{3}H_{6}O_{3}$
C) $C_{5}H_{10}O_{5}$
D) $C_{4}H_{5}O_{4}$
Explanation
(d)
Solutions having same osmotic pressure, at a given temperature, have same concentration.
Concentration of compound = concentration of glucose
$\frac{6}{M \times 1} = 0.05$
M$= \frac{6}{0.05} = 120$
Empirical formula mass ($CH_{2}O$)= 12+2+16
=30
$n = \frac{molecular\ mass\ }{empirical\ formula\ mass\ }$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{120}{30} = 4\$
Hence, molecular formula = (${CH_{2}O)}_{4}\$ =$\ C_{4}H_{8}O_{4}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.