Complete Table 1.1 so that the order of the reaction is described.\n\n• order of the reaction with respect to $[\text{CH}_3\text{COCH}_3]$\n• order of the reaction with respect to $[\text{I}_2]$\n• order of the reaction with respect to $[\text{H}^+]$\n• overall order of the reaction
The experiment is carried out with a large excess of $\text{CH}_3\text{COCH}_3$ and a large excess of $\text{H}^+(aq)$. The starting concentration of $\text{I}_2$ is $1.00 \times 10^{-5}\,\text{mol dm}^{-3}$. The initial rate of decrease in the $\text{I}_2$ concentration is $2.27 \times 10^{-7}\,\text{mol dm}^{-3}\,\text{s}^{-1}$.
On the axes, sketch a graph of $[\text{I}_2]$ against time for the first $10$ seconds of the reaction.
State whether a numerical value for the rate constant, $k$, can be found from your graph. Justify your answer.
The reaction is carried out again at a different temperature. The initial concentrations of $\text{H}^+$ ions, $\text{I}_2$, and $\text{CH}_3\text{COCH}_3$ are each $0.200\,\text{mol dm}^{-3}$. At this temperature, the value of $k$ is $2.31 \times 10^{-5}\,\text{mol}^{-1}\,\text{dm}^3\,\text{s}^{-1}$. Calculate the initial rate of this reaction.\n\n$\text{rate} = \ldots\ldots\ldots\ldots\ldots\,\text{mol dm}^{-3}\,\text{s}^{-1}$
The experiment is carried out again using an excess of $\text{H}^+(aq)$. The revised rate equation is shown.\n\n$\text{rate} = k_1[\text{CH}_3\text{COCH}_3]$
The value of $k_1$ is $1.1 \times 10^{-3}\,\text{s}^{-1}$. Calculate the half-life, $t_{\frac{1}{2}}$.\n\n$t_{\frac{1}{2}} = \ldots\ldots\ldots\ldots\ldots\,\text{s}$
Using your answer to (i), draw a graph of $[\text{CH}_3\text{COCH}_3]$ against time for this reaction. The initial value of $[\text{CH}_3\text{COCH}_3]$ on your graph should be $0.200\,\text{mol dm}^{-3}$. The final value of $[\text{CH}_3\text{COCH}_3]$ on your graph should be $0.0250\,\text{mol dm}^{-3}$.
A four-step mechanism has been proposed for the overall reaction.\n\n$\text{CH}_3\text{COCH}_3 + \text{I}_2 \rightarrow \text{CH}_3\text{COCH}_2\text{I} + \text{H}^+ + \text{I}^-$ \hspace{1em} $\text{rate} = k[\text{CH}_3\text{COCH}_3][\text{H}^+]$\n\nA section of this mechanism is shown.\n\nstep 1: $\text{CH}_3\text{COCH}_3 + \text{H}^+ \rightarrow \text{CH}_3\text{C}^+(\text{OH})\text{CH}_3$\n\nstep 2: $\text{CH}_3\text{C}^+(\text{OH})\text{CH}_3 \rightarrow \text{CH}_3\text{C(OH)}{=}\text{CH}_2 + \text{H}^+$\n\nstep 3: $\rightarrow$\n\nstep 4: $\text{CH}_3\text{C}^+(\text{OH})\text{CH}_2\text{I} \rightarrow \text{CH}_3\text{COCH}_2\text{I} + \text{H}^+$
Give an equation for step 3.
Suggest the slowest step in the mechanism. Explain your answer.
Identify one conjugate acid-conjugate base pair in the mechanism.\n\nconjugate acid ...................................... conjugate base ......................................