Propanone, CH3COCH3, reacts with iodine, I2, in the presence of an acid catalyst. CH3COCH3 + I2 → CH3COCH2I + H+ + I® The rate equation for this reaction is shown. rate = k[CH3COCH3][H+]

1. (a)Complete Table 1.1 to describe the order of the reaction. Table 1.1 order of the reaction with respect to [CH3COCH3] order of the reaction with respect to [I2] order of the reaction with respect to [H+] overall order of the reaction[2]
2. (b)(i)An experiment is performed using a large excess of CH3COCH3 and a large excess of H+(aq). The initial concentration of I₂ is 1.00 × 10-5 moldm-3. The initial rate of decrease in the I2 concentration is 2.27 x 10-7 moldm-3 s-1. Use the axes to draw a graph of [I2] against time for the first 10 seconds of the reaction. 1.00 x 10-5 0.90 x 10-5 0.80 x 10-5 0.70 x 10-5 0.60 x 10-5 [I2]/mol dm-3 0.50 × 10–5. 0.40 x 10-5 0.30 x 10-5 0.20 x 10-5 0.10 x 10-5 0 0 1 2 3 4 5 6 7 8 9 10 time/s[1]
3. (b)(ii)State whether it is possible to calculate the numerical value of the rate constant, k, for this reaction from your graph. Explain your answer.[1]
4. (c)The experiment is repeated at a different temperature. The initial concentrations of H+ ions, I2 and CH3COCH3 are all 0.200 moldm-3. The value of k at this temperature is 2.31 × 10–5mol−1 dm³ s−1. Calculate the initial rate of this reaction. rate = ............................ moldm-³s-1[1]
5. (d)(i)The experiment is repeated using an excess of H+(aq). The new rate equation is shown. rate = k₁[CH3COCH3] The value of k₁ is 1.1 × 10–3s-1. Calculate the value of the half-life, t1. t½ = ............................ s[1]
6. (d)(ii)Use your answer to (i) to draw a graph of [CH3COCH3] against time for this reaction. The initial value of [CH3COCH3] on your graph should be 0.200 moldm¯³. The final value of [CH3COCH3] on your graph should be 0.0250 moldm-3. [Figure for graph axes][1]
7. (e)(i)A four-step mechanism is suggested for the overall reaction. CH3COCH3 + I2 → CH3COCH2I + H+ + I¯ rate = k[CH3COCH3][H+] Part of this mechanism is shown. step 1: CH3COCH3 + H+ → CH3C+(OH)CH3 step 2: CH3C+(OH)CH3 → CH3C(OH)=CH2 + H+ step 3: ............................................ step 4: CH3C+(OH)CH2I → CH3COCH₂I + H+ Write an equation for step 3.[1]
8. (e)(ii)Suggest the slowest step of the mechanism. Explain your answer.[1]
9. (e)(iii)Identify one conjugate acid-conjugate base pair in the mechanism. conjugate acid ............................................ conjugate base ..............................................[1]

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