Using the Iodine Clock Method to Find the Order of a Reaction
Using the Iodine clock method to find the order of a reaction
Introduction
When peroxodisulfate (VI) ions and iodide ions react together in solution they form sulfate (VI) ions and iodide. This reaction is shown below:
S2O82-aq+ 2I-aq SO42-aq+ I2(aq)
The reactants and the sulfate (VI) ions are colourless however the Iodine is a yellow/brown colour. This allows you to measure the progress of the reaction through the colour change when the iodine is produced. In order to determine the order of the reaction we need to measure the initial rate of the reaction by timing how long the reaction takes to produce a small, fixed amount of iodine. This can be measured clearly and effectively by using the iodine clock method.
When you add thiosulfate (VI) ions to the starting reaction mixture the thiosulfate (VI) ions turn iodine back into iodide ions. The equation for this reaction is shown below:
2S2O32-aq+ I2aq S4O62-aq+ 2I-(aq)
The products of this reaction are both colourless so no Iodine colour will appear until all the thiosulfate (VI) ions have been used up. The appearance of the iodine can be made much clearer by adding some starch to the reaction mixture as iodine forms an intense black/blue colour in its presence. This means that the mixture will suddenly experience a colour change from colourless to intense blue/black. By measuring the time taken for this colour change to occur you know how long it took to use up all the thiosulfate (VI) ions and so how long it took to produce the iodine that reacted with it. This is known as the iodine clock method and can be used to find the order of a reaction and determine the effect of Iodide ion concentration on rate of reaction.
The procedure
First of all I measured out 5 different volumes of 1.00 mol dm⁻³aqueous potassium iodide solution and put these into 5 different boiling tubes. This was the only reactant that differed in concentration throughout the investigation. All other reactant concentrations
Introduction
When peroxodisulfate (VI) ions and iodide ions react together in solution they form sulfate (VI) ions and iodide. This reaction is shown below:
S2O82-aq+ 2I-aq SO42-aq+ I2(aq)
The reactants and the sulfate (VI) ions are colourless however the Iodine is a yellow/brown colour. This allows you to measure the progress of the reaction through the colour change when the iodine is produced. In order to determine the order of the reaction we need to measure the initial rate of the reaction by timing how long the reaction takes to produce a small, fixed amount of iodine. This can be measured clearly and effectively by using the iodine clock method.
When you add thiosulfate (VI) ions to the starting reaction mixture the thiosulfate (VI) ions turn iodine back into iodide ions. The equation for this reaction is shown below:
2S2O32-aq+ I2aq S4O62-aq+ 2I-(aq)
The products of this reaction are both colourless so no Iodine colour will appear until all the thiosulfate (VI) ions have been used up. The appearance of the iodine can be made much clearer by adding some starch to the reaction mixture as iodine forms an intense black/blue colour in its presence. This means that the mixture will suddenly experience a colour change from colourless to intense blue/black. By measuring the time taken for this colour change to occur you know how long it took to use up all the thiosulfate (VI) ions and so how long it took to produce the iodine that reacted with it. This is known as the iodine clock method and can be used to find the order of a reaction and determine the effect of Iodide ion concentration on rate of reaction.
The procedure
First of all I measured out 5 different volumes of 1.00 mol dm⁻³aqueous potassium iodide solution and put these into 5 different boiling tubes. This was the only reactant that differed in concentration throughout the investigation. All other reactant concentrations