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J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    25 g of a solute of molar mass \[250\,g\,mo{{l}^{-1}}\] is dissolved in 10 mL of water to obtain a solution whose density is \[1.25\,g{{(mL)}^{-1}}.\] The molarity and molality of the solution are respectively

    A)  0.75 M and 1 m

    B)  0.8 M and 1 m

    C)  1 M and 0.8 m 

    D)  1 M and 0.75 m

    E)  None of These

    Correct Answer: E

    Solution :

     Molarity \[=\frac{\text{weight}\,\text{of}\,\text{solute}\,\text{ }\!\!\times\!\!\text{ 1000}}{\text{mol}\text{.wt}\text{.of}\,\text{solute}\,\text{ }\!\!\times\!\!\text{ volume}\,\text{of}\,\text{solution}}\] \[=\frac{25\times 1000}{250\times 100}\][\[\because \]density of water \[=1g{{(mL)}^{-1}}\]] \[=1\,M\] \[\text{Molality}\,\text{=}\,\frac{\text{weight}\,\text{of}\,\text{solute}\,\text{ }\!\!\times\!\!\text{ 1000}}{\text{mol}\text{.wt}\text{.of}\,\text{solute}\,\text{ }\!\!\times\!\!\text{ }\,\text{wt}\text{.of}\,\text{solvent}}\] \[=\frac{25\times 1000}{250\times 100}=1m.\]


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