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NEET Chemistry Solutions / विलयन Question Bank Self Evaluation Test - Solutions

  • question_answer
    The difference between the boiling point and freezing point of an aqueous solution containing sucrose (molecular \[wt=342g\text{ }mol{{e}^{-1}}\]) in 100 g of water is \[105{}^\circ C\]. If \[{{K}_{f}}\] and \[{{K}_{b}}\] of water are 1.86 and \[0.51K\text{ }kg\text{ }mo{{l}^{-1}}\] respectively, the weight of sucrose in the solution is about

    A) 34.2 g              

    B) 342 g

    C) 7.2 g                

    D) 72 g

    Correct Answer: D

    Solution :

    [d] \[(100+\Delta {{T}_{b}})-(0-\Delta {{T}_{f}})=105\] \[\Delta {{T}_{b}}+\Delta {{T}_{f}}=5\] \[m\left( {{K}_{b}}+{{K}_{f}} \right)=5\] \[m=\frac{5}{2.37}\] i.e., \[\frac{5}{2.37}\] moles in 1000 g water (or) \[\frac{5}{2.37\times 10}\]  moles in 100 g water \[\therefore \] Wt. of sucrose\[=\frac{5}{2.37\times 10}\times 342=72g\]


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