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KVPY Sample Paper KVPY Stream-SX Model Paper-18

  • question_answer
    The reaction, Sucrose \[\xrightarrow{{{H}^{+}}}\] Glucose + Frustose, takes place at certain temperature while the volume of solution is maintained at 1 litre. At time zero the initial rotation of the mixture is \[34{}^\circ .\]After 30 minutes the total rotation of solution is \[19{}^\circ \] and after a very long time, the total rotation is \[-\,11{}^\circ .\] Find the time when solution was optically inactive, (log 3 = 0.477, log 11 = 1.1)

    A) 135 min

    B) 103.7 min

    C) 38.7 min

    D) 45 min

    Correct Answer: B

    Solution :

    \[k=\frac{2.303}{t}\log \left( \frac{{{r}_{\infty }}-{{r}_{0}}}{{{r}_{\infty }}-{{r}_{t}}} \right)\]\[=\frac{2.303}{k}\log \,\,\left( \frac{-\,11-\,34}{-\,11-\,19} \right)\]\[=1.35\times {{10}^{-2}}{{\min }^{-1}}\]
    If solution is optically inactive \[{{r}_{t}}=0\]
    \[t=\frac{2.303}{k}\log \left( \frac{-\,45}{-\,11} \right)=103.7\,\,\min \]


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