Question

The bromination of acetone that occurs in acid solution is represented by this equation $CH_3 COCH_3 (aq) + Br_2 (aq) \longrightarrow $
$ CH_3 COCH_2 Br(aq) + H^+ (aq) + Br^- (aq)$
These kinetic data were obtained for given reaction concentrations.
Initial rate, disappearance of $Br_2, Ms^{-1}$
$5.7 \times 10^{-5}$
$5.7 \times 10^{-5}$
$1.2 \times 10^{-4}$
$3.1 \times 10^{-4}$
Based on these data, the rate equation is

Initial concentrations, $M$
$[CH_3COCH_3]$	$[Br_2]$	$[H^{+}]$
0.30	0.05	0.05
0.30	0.10	0.05
0.30	0.10	0.10
0.40	0.05	0.20

• A. rate=k$[CH_3 COCH_3][H^+]$
• B. rate=k$[CH_2=COCH_3][Br_2]$
• C. rate=k$[CH_3 COCH_3][Br_2][H^+]^2$
• D. rate=k$[CH_3 COCH_3][Br_2][H^+]$

Answer 1

Answer: (A)

Let the order of reaction wrt $CH_3 COCH_3, Br_2$ and $H^+$ are $x, y$ and $z$ respectively. Thus,
Rate $(r) =[CH_3 C0CH_3]^x [Br_2]^y [H^+]^z$
$5.7 \times 10^{-5}=(0.30)^x (0.05)^y (0.05)^z ...(i)$
$5.7 \times 10^{-5}=(0.30)^x (0.10)^y (0.05)^z ...(ii)$
$1.2 \times 10^{-4}=(0.30)^x (0.10)^y (0.10)^z ...(iii)$
$3.1 \times 10^{-4}=(0.40)^x (0.05)^y (0.20)^z ...(iv)$
From Eqs. (i) and (ii)
$y=0$
From Eqs. (ii) and (iii)
$z=1$
From Eqs. (i) and (iv)
$x=1$
Thus, rate law $ [CH_3 COCH_3]^1 [Br_2]^0 [H^+]^1$
$k=[CH_3 COCH_3][H^+]$