JEE Main & Advanced JEE Main Paper (Held On 22 April 2013)

  • question_answer A molecule M associates in given solvent according to the equation \[\operatorname{M}\underset{{}}{\overset{{}}{\longleftrightarrow}}{{(\operatorname{M})}_{\operatorname{n}.}}\] For a certain concentration of  M, The van? t Hoff factor was found to 0.9 and the fraction of associated molecules was 0.2 The value of n is:     JEE Main  Online Paper (Held On 22 April 2013)

    A)  3                                            

    B)  5

    C)  2                                            

    D)  4

    Correct Answer: C

    Solution :

     van't Hoff factor (i) and the degree of association are related as below: \[i=1-\alpha \left( 1-\frac{1}{n} \right)\] \[0.9=1-0.2\left( 1-\frac{1}{n} \right)\] On solving, \[\left( 1-\frac{1}{n} \right)=\frac{1}{2}\] \[\frac{1}{n}=1-\frac{1}{2}=\frac{1}{2}\] \[\therefore \] \[n=2\]


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