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Chemistry Question on Solutions

A solution containing 10 g10\,g per dm3dm^{ 3} of urea (molecular mass = 60 g mol−1)60\,g\, mol^{-1}) is isotonic with a 5%5\% solution of a non-volatile solute. The molecular mass of this non-volatile solute is :

A

200 g mol−1200\, g\, mol^{-1}

B

300 g mol−1300 \,g \,mol^{-1}

C

400 g mol−1400 \,g \,mol^{-1}

D

500 g mol−1500\, g\, mol^{-1}

Answer

300 g mol−1300 \,g \,mol^{-1}

Explanation

Solution

For isotonic solution π1=π2\pi_{1}=\pi_{2}
or, C1=C2C _{1}= C _{2} (conc. in mol/lit.)
(Urea solution) (unknown solution)
1060=5×1000mw×100\frac{10}{60}=\frac{5 \times 1000}{ m _{ w } \times 100}
mw=300 gm mol−1m _{ w }=300 \,gm\, mol ^{-1}

So, the correct option is (B): 300 g mol−1300 \,g \,mol^{-1}