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JEE Main & Advanced Sample Paper JEE Main Sample Paper-47

  • question_answer
    In a polymer sample, 30% molecules have a molecular mass of 20000, 40% have 30000and rest have 60000. The number average \[({{\overline{M}}_{n}})\] and weight average \[({{\overline{M}}_{w}})\] molecular weights are respectively

    A)  110000 and 10538       

    B)  36000 and 43333

    C)  140000 and 156000 

    D)  228000 and 56000

    Correct Answer: B

    Solution :

     \[{{\overline{M}}_{n}}\] (number average molecular mass) \[=\frac{30\times 20000+40\times 30000+30\times 60000}{(30+40+30)}\]\[=36000\] \[{{\overline{M}}_{w}}\]  (weight average molecular mass) \[30\times {{(20000)}^{2}}+40\times {{(30000)}^{2}}\] \[=\frac{+30\times {{(60000)}^{2}}}{30\times 20000+40\times 30000+30\times 60000}\]\[=43333\]


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