Core practical 13a - Follow the rate of the iodine–propanone reaction using a titrimetric method

Similar experiments show that the reaction is first order with respect to both propanone and to hydrogen ions. Use this information to answer the following questions.

1. What is the effect on the rate if the concentration of the hydrogen ions is doubled?

2. What is the effect on the rate if the concentration of the propanone is doubled?

3. What is the effect on the rate if the concentration of the iodine is doubled?

4. Write the overall rate expression for this reaction.

5. Two students monitored the concentration of propanone as the reaction proceeded and plotted a concentration–time graph from their results. What shape would you expect the graph to be? How would you use this graph to prove that the reaction is first order with respect to propanone?

1. The rate doubles.

2. The rate doubles.

3. The rate remains the same.

4. Rate = k[H⁺][CH₃COCH₃]

5. The graph would be a curve. To prove that the reaction is first order, you can look at the half-life at various points; the half-life will be constant for a first-order reaction. Alternatively, plot a graph of rate against concentration; for a first-order reaction this will be a straight-line graph.

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d

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c

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b

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a