NEET Sample Paper NEET Sample Test Paper-7

  • question_answer
    How many grams of \[KCl\]should be added to \[1.0kg\] of water to lower its freezing point to\[-{{8.0}^{o}}C\]? (\[{{K}_{f}}\] for water \[={{1.86}^{o}}C\,kg\,mo{{l}^{-1}}\] )

    A)  \[16.02\text{ }g\]                   

    B)  \[1.602\text{ }g\]

    C)  \[0.1602\,g\]               

    D)  \[160.2\text{ }g\]

    Correct Answer: D

    Solution :

    \[KCl\xrightarrow{{}}{{K}^{+}}+C{{l}^{-}}\] 2 mole of \[KCl\] will give 2 mole particles and \[i=2\]                 \[\Delta T=i{{K}_{f}}m\]                 \[\Delta T=0-(-8.0)={{8}^{o}}C,\,i=2\]                 \[{{K}_{f}}={{1.86}^{o}}C\,kg\,mo{{l}^{-1}}\]                 \[8=2\times 1.86\times m\] \[m=2.15\,mol/kg\] Grams of    \[KCl=2.15\times 74.5=160.2\,g/kg\] Hence \[160.2\text{ }g\] of \[KCl\]should be added to 1 kg of water.


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