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CMC Medical CMC-Medical VELLORE Solved Paper-2014

  • question_answer
    How many gram of sucrose (mol. wt. = 342) should be dissolved in 100 g water in order to produce a solution with a \[105.0{}^\circ C\] difference between the freezing point and boiling temperature? \[[{{k}_{f}}=1.860{}^\circ C\text{/}m,\,{{k}_{b}}=0.151{}^\circ C\text{/}m]\]

    A)  34.2 g                  

    B)  72 g  

    C)  342 g                    

    D)  460 g

    Correct Answer: B

    Solution :

              Boiling point \[({{T}_{b}})=100+\Delta {{T}_{b}}=100+{{k}_{b}}m\] Freezing point \[({{T}_{f}})=0-\Delta {{T}_{f}}=-{{k}_{f}}m\] \[{{T}_{b}}-{{T}_{f}}=(100+{{k}_{b}}m)-(-{{k}_{f}}m)\] \[105=100+0.51\,m+1.86\,m\] \[2.37\,m=5\] or      \[m=\frac{5}{2.37}\]               \[=2.11\] \[\therefore \]Weight of sucrose to be dissolved in 100g water \[=\frac{2.11\times 342}{1000}\times 100\] \[=72\,g\]


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