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KVPY Sample Paper KVPY Stream-SX Model Paper-25

  • question_answer
    Liquids A and B form an ideal solution in the entire composition range. At 350 K, the vapour pressures of pure A and pure B are \[7\times {{10}^{3}}\] and \[12\times {{10}^{3}}\] Pa, respectively. The composition of the vapour in equilibrium with a solution containing 40 mole per cent of A at this temperature is:

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

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

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

    D) \[{{x}_{A}}=0.76;6{{x}_{B}}=0.24\]

    Correct Answer: B

    Solution :

    \[{{P}_{A}}={{\chi }_{A}}P_{A}^{0}={{Y}_{A}}{{P}_{T}}\]
    \[{{P}_{T}}={{\chi }_{A}}P_{A}^{0}+{{\chi }_{B}}P_{B}^{0}\]
    \[=0.4\times 7\times {{10}^{3}}+0.6\times 12\times {{10}^{3}}={{10}^{4}}\]
    \[0.4\times 7\times {{10}^{3}}={{Y}_{A}}\times {{10}^{4}}\]
    \[{{Y}_{A}}=0.28\]
                \[{{Y}_{B}}=1-0.28=0.72.\]


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