Rates of reaction - kinetics (A2)
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Hi, I am doing a practical investigation on the rate of reaction between iodine and propanone. I did the clock reaction - waiting for the colour to become clear, using iodine in water. Now I want to use titration and looking up I have found that potassium lodide us used.
I am not sure if I should continue using iodine in water or should I use potassium iodide? Is there going to be a difference in the result that I get? Can I compare the results if I have two different iodines?
Corrie writes ....
Remember, the reaction you are studying is between propanone and iodine, not iodide ions, in both cases.
Iodine is not very soluble in water, but it is, strangely, quite soluble in aqueous potassium iodide solution. So bottles marked I2(aq) in the laboratory actually contain KI as well.
For most purposes, including the reaction you are studying here, the presence of KI does not matter, and it is colourless in solution. So I am sure the 'iodine solution' you used for your first experiment would have contained KI as well.
You will need a similar solution (for example 0.02 M I2 in 0.2 M KI solution) for your titration experiment.
By the way, on the subject of colour of solutions, be careful in your use of the word 'clear' to describe a colourless solution. Examiners very much dislike phrases such as 'the colour became clear' in your question. You should say 'the solution/reaction mixture became colourless, or lost its colour.' A solution, such as iodine can be both clear (see-through) and yet have a colour (light brown).
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
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updated: 26 March 2007
