Edexcel International A Level Chemistry

Revision Notes

4.1.9 Acid-Catalysed Iodination of Propanone

Acid-Catalysed Iodination of Propanone

  • The iodination of propanone is carried out using a catalyst of dilute sulfuric acid
  • The reaction between iodine in an acidic solution and propanone is

CH3COCH(aq) + I2 (aq) → CH3COCH2I (aq) + H+ (aq) + I(aq) 

  • We can follow the rate of this reaction by using a continuous monitoring method and therefore we will be able to deduce the order of reaction with respect to a substance using a concentration line graph 
  • We can calculate the order of reaction with respect to iodine as the propanone and acid are in a large excess so their concentration do not change during the reaction 
  • Once a portion of the reaction mixture has been removed, we stop the reaction by adding sodium hydrogencarbonate
  • Performing a titration again sodium thiosulfate(VI) solution and using starch as an indicator is used to determine the concentration of iodine

2S2O32- (aq) + I2 (aq) → 2I- (aq) + S4O62- (aq) 

Results

Sample Data from the Reaction

4-1-9-sample-data-from-the-reaction-table

  • This graph is a straight line graph
    • As the gradient is constant, the rate of reaction is constant, and therefore independent of the concentration of the iodine solution
    • This means the reaction is zero order with respect to the iodine
    • The rate equation for the reaction is
      • Rate = k[CH3COCH(aq)] [H(aq)]

Reaction Kinetics - Zero Order Concentration, downloadable AS & A Level Chemistry revision notes

Concentration-time graphs of a zero-order reaction

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