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BHU PMT BHU PMT Solved Paper-2004

  • question_answer
    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\[15{}^\circ C,\] then molecular weight of the solute is:

    A)  1000                                     

    B)  1200

    C)  1400                                     

    D)  1800

    Correct Answer: B

    Solution :

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


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