JEE Main & Advanced Sample Paper JEE Main - Mock Test - 20

  • question_answer
    If the boiling point of an aqueous solution is\[100.3{}^\circ C\]. Given \[{{l}_{f}}\] and \[{{l}_{v}}\] are 100 and \[500\,cal\,{{g}^{-1}}\]respectively, (\[{{l}_{f}}\]and \[{{l}_{v}}\]are latent heat of fusion and vapourization respectively) Select the CORRECT expression for \[\Delta {{T}_{f}}\].

    A) \[\Delta {{T}_{f}}=\frac{{{(273)}^{2}}\times 1.5}{{{(373)}^{2}}}\]   

    B) \[\Delta {{T}_{f}}=\frac{{{(273)}^{2}}\times 0.5}{{{(373)}^{2}}}\]

    C) \[\Delta {{T}_{f}}=\frac{{{(373)}^{2}}\times 1.5}{{{(273)}^{2}}}\]   

    D) \[\Delta {{T}_{f}}=\frac{{{(373)}^{2}}\times 0.5}{{{(273)}^{2}}}\]

    Correct Answer: A

    Solution :

    [a] \[\Delta {{T}_{b}}={{K}_{b}}\times m\] \[\Delta {{T}_{f}}={{K}_{f}}\times m\] \[\frac{\Delta {{T}_{f}}}{\Delta {{T}_{b}}}\frac{{{K}_{f}}}{{{K}_{b}}}\] \[=\frac{RT_{2}^{f}}{RT_{b}^{2}}\frac{1000{{l}_{v}}}{1000{{l}_{f}}}\] \[=\frac{T_{f}^{2}}{T_{b}^{2}}\frac{{{l}_{v}}}{{{l}_{f}}}\] \[{{T}_{b}}=100+273=373K\] \[{{T}_{f}}=273K\] \[\Delta {{T}_{b}}=100.3-100=0.3{}^\circ C\] \[\frac{\Delta {{T}_{f}}}{0.3}=\frac{{{(272)}^{2}}}{{{(373)}^{2}}}\times \frac{500}{100}\] \[\Delta {{T}_{f}}=\frac{{{(273)}^{2}}\times 1.5}{{{(373)}^{2}}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner