CET Karnataka Medical CET - Karnataka Medical Solved Paper-2014

  • question_answer
    \[50c{{m}^{3}}\]of \[0.04M\text{ }{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]in acidic medium oxidizes a sample of \[{{H}_{2}}S\] gas to sulphur. Volume of \[0.03M\text{ }KMn{{O}_{4}}\]required to oxidize the same amount of \[{{H}_{2}}S\] gas to sulphur, in acidic medium is

    A)  \[60c{{m}^{3}}\]    

    B)  \[80c{{m}^{3}}\]        

    C)  \[90c{{m}^{3}}\]        

    D)  \[120c{{m}^{3}}\]

    Correct Answer: B

    Solution :

    : \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]and \[KMn{{O}_{4}}\] both are good oxidizing agents in acidic medium. The reaction is as follows: \[CrO_{7}^{2-}+14{{H}^{+}}+6{{e}^{-}}\to 2C{{r}^{3+}}+7{{H}_{2}}O\] \[MnO_{4}^{2-}+8{{H}^{+}}+5{{e}^{-}}\to M{{n}^{2+}}+4{{H}_{2}}O\] Normality of \[C{{r}_{2}}O_{7}^{2-}=Molarity\times no.\,of\]                              \[electrons\text{ }involved\] \[=0.04\times 6=0.24N\] Normality of \[MnO_{4}^{-}\] = Molarity \[\times \] no. of                                           electrons involved    \[=0.03\times 5=0.15N\] \[\underset{({{K}_{2}}C{{r}_{2}}{{O}_{7}})}{\mathop{{{N}_{1}}{{V}_{1}}}}\,=\underset{(KMn{{O}_{4}})}{\mathop{{{N}_{2}}{{V}_{2}}}}\,\] \[\Rightarrow \] \[0.24\times 50=0.15\times {{V}_{2}}\] \[{{V}_{2}}=\frac{0.24\times 50}{0.15}=80c{{m}^{3}}\]


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