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JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    A solution \[\text{of}\]\[4.5\,\,g\] of a pure non-electrolyte in \[100\,\,g\] of water was found to freeze at\[{{0.465}^{o}}C\]. The molecular weight of the solute is closest to\[({{k}_{f}}=1.86)\]:

    A) \[135.0\]                             

    B) \[172.0\]

    C)  \[90.0\]                                              

    D)  \[180.0\]

    Correct Answer: D

    Solution :

    Key Idea: Molecular mass\[=\frac{1000\times {{k}_{f}}\times w}{\Delta {{T}_{f}}\times W}\] Given\[{{k}_{f}}=1.86\]                 \[w=\]mass of solute\[=4.5\,\,g\]                 \[W=\]mass of solvent\[=100\,\,g\] \[\Delta {{T}_{f}}=\]Depression in freezing point\[={{0.465}^{o}}C\] \[\therefore \]Molecular weight of solute                 \[=\frac{1000\times 1.86\times 4.5}{0.465\times 100}\]                 \[=180\]


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