12th Class Chemistry Solutions / विलयन Question Bank MCQs - Solutions

  • question_answer
    A 5% solution (w/W) of cane sugar (molar mass\[=\text{ }342\text{ }g\text{ }mo{{l}^{-1}}\]) has freezing point 271 K. What will be the freezing point of 5% glucose (molar mass\[=180\text{ }g\text{ }mo{{l}^{-1}}\]) in water if freezing point of pure water is 273.15 K?

    A) 273.07 K

    B) 269.07 K

    C) 273.15 K

    D) 260.09 K

    Correct Answer: B

    Solution :

    \[\Delta {{T}_{f}}=\frac{{{K}_{f}}\times {{W}_{B}}}{{{M}_{B}}\times {{W}_{A}}}\] For cane sugar solution, 2.15 K=\[\frac{{{K}_{f}}\times 5}{342\times 0.095}\] (95 g of water = 0.095 kg) For glucose solution, \[\Delta {{T}_{f}}=\frac{{{K}_{f}}\times 5}{180\times 0.095}\] \[\frac{\Delta {{T}_{f}}}{2.15}=\frac{{{K}_{f}}\times 5}{180\times 0.095}\times \frac{342\times 0.095}{{{K}_{f}}\times 5}\] \[\Delta {{T}_{f}}=\frac{342}{180}\times 2.15=4.085K\] Freezing point of glucose solution = 273.15 - 4.085 = 269.07 K


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