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RAJASTHAN PMT Rajasthan - PMT Solved Paper-2005

  • question_answer
    By dissolving \[5\,\,g\] substance in \[50\,\,g\] of water, the decrease in freezing point is \[{{1.2}^{o}}C\]. The\[g\] molal depression is\[{{185}^{o}}C\]. The molecular weight of substance is:

    A) \[105.4\]                             

    B) \[118.2\]

    C) \[137.2\]             

    D)        \[154.2\]

    Correct Answer: D

    Solution :

    We know that\[m=\frac{100{{k}_{f}}\times w}{\Delta TW}\] Here,\[\Delta T={{1.2}^{o}},\,\,{{K}_{f}}={{1.85}^{o}}\] \[w=5\,\,g,\,\,W=50\,\,g\] \[\therefore \]  \[m=\frac{1000\times 1.85\times 5}{1.2\times 50}=154.2\]


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