JEE Main & Advanced Chemistry Solutions / विलयन Question Bank Critical Thinking Solutions

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    A 0.2 molal aqueous solution of a weak acid (HX) is 20% ionised. The freezing point of this solution is (Given \[{{K}_{f}}={{1.86}^{o}}C/m\] for water)            [IIT 1995]

    A)                 \[-{{0.31}^{o}}C\]            

    B)             \[-{{0.45}^{o}}C\]

    C)                 \[-{{0.53}^{o}}C\]            

    D)                 \[-{{0.90}^{o}}C\]

    Correct Answer: B

    Solution :

             \[\Delta {{T}_{f}}=\text{molality}\times {{K}_{f}}\times (1+\alpha )\]            \[\alpha =0.2\], Molality = 0.2, \[{{K}_{f}}=1.86\]            \[\Delta {{T}_{f}}=0.2\times 1.2\times 1.86={{0.4464}^{o}}\]                 Freezing point = \[-{{0.45}^{o}}C\].


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