Chemistry Project


This experiment involves an Iodine clock reaction, using Peroxidisulfate(VI) ions and Iodide ions in solution to form Sulfate(VI) ions and iodine: \[S_2O_8^{2-}(\textup{aq}) + 2I^-(\textup{aq})\rightarrow SO_4^{2-}(\textup{aq})+I_2(\textup{aq})\] As both of the reactants are colourless, the progress of the reaction is shown by the blue colour of the Iodine. If starch is added, this becomes clear.

To measure the rate of the reaction, the time for a set amount of Iodine to be produced can be measured. To do this, Thiosulfate(VI) ions were added to the reaction mixture. These turn Iodine back into Iodide ions, so no Iodine will be evident until all the Thiosulfate is used up. \[2S_2O_3^{2-}(\textup{aq})+I_2(\textup{aq})\rightarrow S_4O_6^{2-}(\textup{aq})+2I^-(\textup{aq})\] This will result in a sudden blue colour. The time for this colour to appear will be quantified as the rate of the reaction.


This experiment had several aims. These were:

  • Find the orders of the reactants in reaction 1.

  • Find the value of k, the constant in the rate equation

  • Find how the reaction rate is affected by temperature using a water bath

  • Use the Arrhenius equation to find the activation energy and collision factor of the reaction

Experimental Procedure



A table to show the equipment used, and to justify its usage
Equipment Justification
Thermometer (0-100\(^{\circ}\)C) The reactants must be at the correct temperatures for the experiments involving a temperature change, and a digital probe is unnecessary