Rates of reaction - kinetics (A2)
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I am doing an experiment to determine the rate equation between iodine and propanone using a colorimeter. I wonder why a green filter is used in this experiment. Also I’ve been asked to compare the methods of using a titration method and colorimeter method to find the rate equation. What are the advantages and disadvantages of each method?
Igloo writes
A green filter is appropriate since an aqueous solution of iodine is coloured brown/orange/yellow, depending on the concentration, and green is the complementary colour of orange. For more details about all this you should refer to a recent FAQ written by Ulex on our web site. See:
How exactly does a colorimeter work, and how does light (or the EM spectrum) play a part in this? Also, what does transmission mean?
As for the second half of your question, it is not appropriate for me to give you a detailed reply since this is a task which you have obviously been set to do for yourself, and you must think out some answers for yourself.
However, in general you need to realise that the titration method involves sampling, followed by chemical analysis (titration), and that this leads to a difficulty deciding which time to use when plotting your concentration readings. Colorimetry, on the other hand involves reading off values of transmittance (a physical property) at regular and precise times, so is generally regarded as the better method.
I’ll leave you to think out some of the other advantages and disadvantages of each method. Consider what readings you will need to make with each method, and the accuracy with which values can be determined. For example, is your colorimeter digital or analogue, and, if analogue, what are the scale divisions on the instrument?
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updated: 04 April 2006
