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NEET AIPMT SOLVED PAPER SCREENING 2008

  • question_answer
    The bromination of acetone that occurs in acid solution is represented by this equation. \[C{{H}_{3}}COC{{H}_{3}}(aq)+B{{r}_{2}}(aq)\xrightarrow[{}]{{}}\] \[C{{H}_{3}}COC{{H}_{2}}Br(aq)+{{H}^{+}}(aq)+B{{r}^{-}}(aq)\] These kinetic data were obtained for given reaction concentrations. Initial concentrations, M \[[C{{H}_{3}}COC{{H}_{3}}]\]      \[[B{{r}_{2}}]\]                  \[[{{H}^{+}}]\] 0.30                        0.05       0.05 0.30                        0.10       0.05 0.30                        0.10       0.10 0.40                        0.05       0.20 Initial rate, disappearance of \[B{{r}_{2}},M{{s}^{-1}}\] \[5.7\times {{10}^{-5}}\] \[5.7\times {{10}^{-5}}\] \[1.2\times {{10}^{-4}}\] \[3.1\times {{10}^{-4}}\] Based on these data, the rate equation is

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

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

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

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

    Correct Answer: A

    Solution :

    Key Idea: By comparing the rate and concentration, the order of the reaction can be calculated. Let the rate of the reaction wrt \[[C{{H}_{3}}COC{{H}_{3}}],\]\[[B{{r}_{2}}]\] and \[[{{H}^{+}}]\] are x, y and z respectively. Thus, Rate \[\propto {{[C{{H}_{3}}COC{{H}_{3}}]}^{x}}{{[B{{r}_{2}}]}^{y}}{{[{{H}^{+}}]}^{z}}\] \[5.7\times {{10}^{-5}}={{[0.30]}^{x}}{{[0.05]}^{y}}{{[0.05]}^{z}}\]             ?(i) \[5.7\times {{10}^{-5}}={{[0.30]}^{x}}{{(0.10)}^{y}}{{(0.05)}^{z}}\]             ?(ii) \[1.2\times {{10}^{-4}}={{[0.30]}^{x}}{{(0.10)}^{y}}{{(0.10)}^{z}}\]             ?(iii) \[3.1\times {{10}^{-4}}={{[0.40]}^{x}}{{(0.05)}^{y}}{{(0.20)}^{z}}\]             ?(iv) From Eqs (i) and (ii) y = 0 From Eqs (ii) and (iii) x = 1        From, Eqs (i) and (iv) x = 1 Thus, rate law \[\propto [C{{H}_{3}}COC{{H}_{3}}][{{H}^{+}}]\] \[=k[C{{H}_{3}}COC{{H}_{3}}][{{H}^{+}}]\]


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