JEE Main & Advanced Sample Paper JEE Main Sample Paper-2

  • question_answer
    The ionisation constant of \[HCOOH\] is\[1.8\times {{10}^{-4}}\]. What is the percent ionisation of a 0.001 M solution?

    A)  66%                                      

    B)  42%

    C)  34%                                      

    D)  58%

    Correct Answer: C

    Solution :

    \[\underset{0.001-x}{\mathop{HCOOH}}\,\,{{\underset{x}{\mathop{HCOO}}\,}^{-}}+{{\underset{x}{\mathop{H}}\,}^{+}}\] As \[\alpha =\sqrt{\frac{{{K}_{a}}}{C}}=\sqrt{\frac{1.8\times {{10}^{-4}}}{0.001}}=0.42\] As \[\alpha >0.1\] so can?t be neglected, \[1.8\times {{10}^{-4}}=\frac{{{x}^{2}}}{0.001-x}\] and \[x=3.4\times {{10}^{-4}}\] Now, % ionization \[=\frac{\text{Ionised}\,\text{HCOOH}}{\text{Total}\,\text{HCOOH}}=\frac{3.4\times {{10}^{-4}}}{0.001}\times 100=34%\]


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