The initial rate of reaction for propanone and iodine in acid solution is measured in a series of experiments at a constant temperature. H⁺ catalyst CH₃COCH₃ + I₂ ⟶ CH₃COCH₂I + HI The rate equation was determined experimentally to be as shown. rate = k[CH₃COCH₃][H⁺]

1. (a)State the order of reaction with respect to • CH₃COCH₃ • I₂ • H⁺ and state the overall order of this reaction.[2]
2. (b)(i)The rate of this reaction is 5.40 × 10⁻³ mol dm⁻³ s⁻¹ when • the concentration of CH₃COCH₃ is 1.50 × 10⁻² mol dm⁻³ • the concentration of I₂ is 1.25 × 10⁻² mol dm⁻³ • the concentration of H⁺ is 7.75 × 10⁻¹ mol dm⁻³. Calculate the rate constant, k, for this reaction. State the units of k. k = units =[2]
3. (b)(ii)Complete the table by placing one tick (✓) in each row to describe the effect of decreasing the temperature on the rate constant and on the rate of reaction. [Table with rows for rate constant and rate of reaction, columns for decreases, no change, increases][1]
4. (c)From the results, a graph is produced which shows how the concentration of I₂ changes during the reaction. [Figure X.X] Describe how this graph could be used to determine the initial rate of the reaction.[2]
5. (d)On the axes below, sketch a graph to show how the initial rate changes with different initial concentrations of CH₃COCH₃ in this reaction. [Figure X.X][1]
6. (e)(i)The rate of a reaction between metal ions was studied. The following three-step mechanism has been suggested for this reaction. Step 1 is the rate-determining step. step 1 Ce⁴⁺ + Mn²⁺ → Ce³⁺ + Mn³⁺ step 2 Ce⁴⁺ + Mn³⁺ → Ce³⁺ + Mn⁴⁺ step 3 Mn⁴⁺ + Tl⁺ → Tl³⁺ + Mn²⁺ Explain the meaning of the term rate-determining step.[1]
7. (e)(ii)Use this mechanism to • determine the overall equation for this reaction • suggest the role of Mn²⁺ ions in this mechanism. Explain your answer.[2]

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