Haryana PMT Haryana PMT Solved Paper-2009

  • question_answer
    \[0.2\text{ }molal\]acid HX ionises \[20%\].  \[{{k}_{f}}\]for acid is \[1.86\]\[molalit{{y}^{-1}}\]. Freezing point is

    A)  \[-0.45\]             

    B)  \[-0.50\]

    C)  \[-0.31\]                             

    D)  \[-0.53\]

    Correct Answer: A

    Solution :

                    Since HX is 20% ionised, vants Hoff factor, \[i=1+(y-1)\alpha \] [\[\because \] \[y=2\], as two particles are produced]                   \[=1+(2-1)0.2\]                 \[=1.2\]                 \[\Delta {{T}_{f}}=i{{k}_{f}}.m\]                 \[=1.2\times 1.86\times 0.2\]                 \[={{0.45}^{o}}C\]                 \[\Delta {{T}_{f}}={{T}_{1}}-{{T}_{2}}\]                 \[{{T}_{2}}={{0}^{o}}C-{{0.45}^{o}}C\]                 \[=-{{0.45}^{o}}C\]


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