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NEET Sample Paper NEET Sample Test Paper-79

  • question_answer
    The degree of dissociation of \[Ca{{\left( N{{O}_{3}} \right)}_{2}}\] in dilute aqueous solution, containing 7g of the salt per 100 g of water at \[100{}^\circ C is 70%\]. If the vapour pressure of water at \[100{}^\circ C\] is 760 mm Hg, the vapour pressure of the solution is

    A)  746.3 mm Hg   

    B)  1492.6 mm Hg        

    C)  373.2 mm Hg   

    D)  74.63 mm Hg

    Correct Answer: A

    Solution :

    Total mole of \[\operatorname{Ca} {{\left( N{{O}_{3}} \right)}_{2}}\] \[N=(1+2\,\alpha )\frac{7}{164}\] \[=\,\,\,\left( 1+2\times 0.7 \right)\times \,\,\frac{7}{164}\,\,=\,\,0.1\] Molecular weight of \[Ca{{\left( N{{O}_{3}} \right)}_{2}}=164\] \[\operatorname{Mole} of solvent \left( {{H}_{2}}O \right)\,\,=\,\,\frac{100}{18}\] From Raoult?s law, \[\frac{{{p}^{{}^\circ }}-{{p}_{s}}}{{{p}^{{}^\circ }}}\,\,=\,\,\frac{n}{n+N}\] \[\frac{760-{{p}_{s}}}{760}\,\,=\,\,\frac{0.1}{0.1+\frac{100}{18}}\] \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,\,{{p}_{s}} =746.3 mm Hg\]


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