NEET Sample Paper NEET Sample Test Paper-39

  • question_answer 88) 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 \[45.0\,g\,{{H}_{2}}O,\]the freezing point is changed by \[-3.82{{\,}^{o}}C,\] Calculate the van't Hoff factor for \[N{{a}_{2}}S{{O}_{4}}.\]

    A)  0.381         

    B)  2.63

    C)  2.05          

    D)  3.11

    Correct Answer: B

    Solution :

     \[\Delta T=\frac{100\times {{K}_{f}}\times w}{m.W}\times i\] \[\Delta \Tau =0-(-3.82)=3.82{{\,}^{o}}C\] \[3.82=\frac{1000\times 1.86\times 5\times i}{142\times 45}\] \[i=2.63\]

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