JEE Main & Advanced Sample Paper JEE Main Sample Paper-38

  • question_answer 19) The vapour pressure of benzene at a certain temperature \[640\text{ }mm\] of Hg. A non-volatile and non-electrolyte solid weighing \[2.175\text{ }g\] is added to \[39.08\text{ }g\] of benzene. If the vapour pressure of the solution is \[600mm\] of Hg, what is the molecular weight of solid substance?                

    A)  \[49.50\]                 

    B)  \[59.60\]

    C)  \[69.60\]                 

    D)  \[79.87\]

    Correct Answer: C

    Solution :

     \[\frac{{{P}^{o}}-{{P}_{S}}}{{{P}^{o}}}=\frac{w/m}{W/M};(640-600)/640=wM/mW\] \[40/640=2.175\times 78/m\times 39.08\] \[m=2.175\times 78\times 640/39.08\times 40=69.458\cong 69.60\]

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