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JEE Main & Advanced JEE Main Paper (Held On 10-Jan-2019 Morning)

  • question_answer
    Liquids A and B form an ideal solution in the entire composition range. At 350 K, the vapor pressures of pure A and pure B are \[7\times {{10}^{3}}\]Pa and \[12\times {{10}^{3}}\] Pa, respectively. The  composition  of the  vapor in equilibrium with a solution containing 40 mole percent of A at this temperature is: [JEE Main Online Paper (Held On 10-Jan-2019 Morning]

    A) \[{{x}_{A}}=0.76;\,\,{{x}_{B}}=0.24\]                 

    B)                  \[{{x}_{A}}=0.28;\,\,{{x}_{B}}=0.72\]

    C)                  \[{{x}_{A}}=0.4;\,\,{{x}_{B}}=0.6\]                     

    D)                  \[{{x}_{A}}=0.37;\,\,{{x}_{B}}=0.63\]

    Correct Answer: B

    Solution :

    \[{{Y}_{A}}\,=\,\frac{{{P}_{A}}}{{{P}_{T}}}\,=\,\frac{{{P}^{O}}_{A}{{X}_{A}}}{{{P}^{O}}_{A}{{X}_{A}}+{{P}^{O}}_{B}{{X}_{B}}}\] \[=\frac{7\times {{10}^{3}}\times 0.4}{7\times {{10}^{3}}\times 0.4+12\times {{10}^{3}}\times 0.6}\] = 0.28 \[\therefore \,{{\,}_{Y}}_{B}\,\,=1-0.28=0.72\]


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