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NEET AIPMT SOLVED PAPER SCREENING 2011

  • question_answer
    The freezing point depression constant for water is \[-{{1.86}^{o}}C\,{{m}^{-1}}.\]If 5.00 g \[N{{a}_{2}}S{{O}_{4}}\]is dissolved in \[45.0g\,{{H}_{2}}O,\] the freezing point is changed by -3.82°C. Calculate the van't Hoff factor for \[N{{a}_{2}}S{{O}_{4}}.\]

    A)  2.63                                      

    B)  3.11                      

    C)         0.381                   

    D)         2.05

    Correct Answer: A

    Solution :

                    \[\Delta {{T}_{f}}=i\times {{K}_{f}}\cdot m\] or            \[i=\frac{\Delta {{T}_{f}}\times {{W}_{solvent}}}{{{K}_{f}}\times {{n}_{solute}}\times 1000}\]                 \[=\frac{3.82\times 45}{1.86\times \left( \frac{5}{142} \right)\times 1000}\]                                 \[=2.63\]


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