1. Tardigrade
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  3. Chemistry
  4. If 20 g of a solute was dissolved in 500 mL of water and osmotic pressure of the solution was found to be 600 mm of Hg at 15oC , then molecular weight of the solute is

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Q. If 20 g of a solute was dissolved in 500 mL of water and osmotic pressure of the solution was found to be 600 mm of Hg at $ {{15}^{o}}C $ , then molecular weight of the solute is

BVP MedicalBVP Medical 2007

Solution:

Key Idea: Osmotic pressure is colligative property. Use the formula $ \pi V=nRT $ to solve problem. $ \pi V=nRT $ or $ \pi =\frac{n}{V}RT=\frac{m\,RT}{MV} $ where $ \pi $ = osmotic presure = 600 mm of Hg $ =600/760\text{ }atm $ m = mass of solute = 20 g M = molecular mass of solute R = 0.0821 L atm $ mo{{l}^{-1}}\text{ }{{K}^{-1}} $ $ T={{15}^{o}}C=15+273=288\text{ }K $ $ V=500mL=0.5L $ $ \frac{600}{760}=\frac{20\times 0.0821\times 288}{M\times 0.5} $ or $ M=1200 $ $ \therefore $ Molecular mass of solute is 1200.