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I am currently investigating the vitamin C content of fruit juices and vitamin C supplements. I have used a colorimeter and have carried out the investigation. I am just having some problems with the calculations of how to get from a reading the concentration of iodine off of the calibration curve, to how much ascorbic acid is present. Please could you give me some help?
191108
Igloo writes ...
If you already have a calibration curve, you should have plotted absorbance (or perhaps transmittance) against iodine concentration.
Presumably you carried out experiments reacting an excess of iodine with the sample of the fruit juice, and eventually finished with a brown/orange/yellow solution for which the absorbance was then measured. Using the calibration curve you read off the concentration of iodine from the absorbance reading. Next, knowing the original concentration of iodine, you can deduce the amount of iodine which has been destroyed by the vitamin C.
You need to have carried out another set of experiments using a solution of vitamin C of known concentration, so that a comparison can be made with the results from your fruit juices experiments.
I admit that the calculations are somewhat long-winded, but, taken individually, are conceptually fairly straightforward.
There are several FAQs on the React website (see link to 'Sorted FAQs on Investigations' at the bottom of the Re:act Homepage) which, taken together, will fill in some of the gaps in my answer above.
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updated: 19 November 2008
