Solutions Question 386
Question: A 5% solution of cane sugar (molar mass 342) is isotonic with 1% of a solution of an unknown solute. The molar mass of unknown solute in g /mol is
Options:
A) 136.2
B) 171.2
C) 68.4
D) 34.2
Show Answer
Answer:
Correct Answer: C
Solution:
Two solutions are isotonic if their osmotic pressure are equal $ {\pi_1}={\pi_2} $ $ M_1ST_1=M_2ST_2 $ ( $ M_1 $ and $ M_2 $ are molarities)
At a given temperature, $ M_1=M_2 $ $ \underset{Conesugar}{\mathop{\frac{1000,w_1}{m_1v_1}}},=\underset{Unknown}{\mathop{\frac{1000,w_2}{m_2v_2}}}, $
$ (V_1=V_2,100,mL) $
$ \therefore $ $ \frac{w_1}{m_1}=\frac{w_2}{m_2} $ $ \frac{5}{342}=\frac{1}{m_2} $ $ m_2=\frac{342}{5}=68.4,g,mo{l^{-1}} $
