2. Sample Papers
  3. NEET

NEET Sample Paper NEET Sample Test Paper-87

  • question_answer
    The bromination of acetone that occurs in acid solution is represented by this equation. \[C{{H}_{3}}COC{{H}_{3}}(aq)+B{{r}_{2}}(aq)\to \] \[C{{H}_{3}}COC{{H}_{2}}Br(aq)+{{H}^{+}}(aq)+B{{r}^{-}}(aq)\] These kinetic data were obtained for given reaction concentrations.
    Initial Concentrations, M Initial rate of disappearance of \[B{{r}_{2}},\]\[M{{s}^{-1}}\]
    \[[C{{H}_{3}}COC{{H}_{3}}]\] \[[B{{r}_{2}}]\] \[[{{H}^{+}}]\]
    0.30 0.05  0.05 \[5.7\times {{10}^{-5}}\]
    0.30 0.10  0.05 \[5.7\times {{10}^{-5}}\]
    0.30 0.10  0.10 \[1.2\times {{10}^{-4}}\]
    0.40 0.05  0.20 \[31\times {{10}^{-4}}\]
    Based on given data, the rate equations is:

    A) Rate \[=k[C{{H}_{3}}COC{{H}_{3}}][{{H}^{+}}]\]

    B) Rate\[=k[C{{H}_{3}}COC{{H}_{3}}][B{{r}_{2}}]\]

    C) Rate\[=k[C{{H}_{3}}COC{{H}_{3}}][B{{r}_{2}}]{{[{{H}^{+}}]}^{2}}\]

    D) Rate\[=k[C{{H}_{3}}COC{{H}_{3}}][B{{r}_{2}}][{{H}^{+}}]\]

    Correct Answer: A

    Solution :

    [a] Rewriting the given data for the reaction \[C{{H}_{3}}COC{{H}_{3}}(aq)+B{{r}_{2}}(aq)\xrightarrow{{{H}^{+}}}\] \[C{{H}_{3}}COC{{H}_{2}}Br(aq)+{{H}^{+}}(aq)+B{{r}^{-}}(aq)\]
    S. No Initial concentration of\[C{{H}_{3}}COC{{H}_{3}}\]in M Initial concentration of\[B{{r}_{2}}\]in M Initial concentration of \[{{H}^{+}}\]in M Rate of disappearance of\[B{{r}_{2}}\]in \[M{{s}^{-1}}\]i.e\[-\frac{d}{dt}[B{{r}_{2}}]\]or \[\frac{dx}{dt}\]
    1 0.30 0.05 0.05 \[5.7\times {{10}^{-5}}\]
    2 0.30 0.10 0.05 \[5.7\times {{10}^{-5}}\]
    3 0.30 0.10 0.10 \[1.2\times {{10}^{-4}}\]
    4 0.40 0.05 0.20 \[3.1\times {{10}^{-4}}\]
    Actually this reaction is autocatalyzed and involves complex calculation for concentration terms. We can look at the above results in a simple way to find the dependence of reaction rate (i.e., rate of disappearance of \[B{{r}_{2}}\]). From data (1) and (2) in which concentration of \[C{{H}_{3}}COC{{H}_{3}}\] and \[{{H}^{+}}\] remain unchanged and only the concentration of \[B{{r}_{2}}\] is doubled, there is no change in rate of reaction. It means the rate of reaction is independent of concentration of \[B{{r}_{2}}.\] Again from (2) and (3) in which \[(C{{H}_{3}}COC{{H}_{3}})\] and \[(B{{r}_{2}})\] remain constant but \[{{H}^{+}}\] increases from 0.05 M to 0.10 i.e. doubled, the rate of reaction changes from \[5.7\times {{10}^{-5}}\] to \[1.2\times {{10}^{-4}}\]\[(or\,12\times {{10}^{-5}}),\]thus it also becomes almost doubled. It shows that rate of reaction is directly proportional to \[[{{H}^{+}}].\] From (3) and (4), the rate should have doubled due to increase in conc of \[[{{H}^{+}}]\] from 0.10 M to 0.20 M but the rate has changed from \[1.2\times {{10}^{-4}}\]to \[3.1\times {{10}^{-4}}.\] This is due to change in concentration of \[C{{H}_{3}}COC{{H}_{3}}\] from 0.30 M to 0.40 M. Thus the rate is directly proportional to \[[C{{H}_{3}}COC{{H}_{3}}].\] We now get rate \[=k{{[C{{H}_{3}}COC{{H}_{3}}]}^{1}}{{[B{{r}_{2}}]}^{0}}{{[{{H}^{+}}]}^{1}}\] \[=k[C{{H}_{3}}COC{{H}_{3}}][{{H}^{+}}].\]


You need to login to perform this action.
You will be redirected in 3 sec spinner