Science Buddies: "Ask an Expert"

Posted on behalf of family/student
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We got the Orange Juice Titration kit for my daughter’s science fair project and she was attempting to use it for testing of vitamin C in multi vitamins. The idea was to confirm the milligrams on the label to actuals since they’re not regulated by the FDA.

One test on a tablet worked with a color change, but two of the ones she used were capsules and neither one had a color change.

The ratios of milligrams to distilled water were 1:10. We are trying to determine if this was the right kit for this type of experiment or not, and if so, what some reason reasons for a lack of color change might be.


[Administrator note: The kit being used is the kit for the Orange Juice Titration project. Project: https://www.sciencebuddies.org/science- ... -vitamin-c Kit: https://www.homesciencetools.com/produc ... t/?aff=SB1 ]

Weds., 22 Jan 2025

Hi and thanks for the question.

I read the part of the experimental protocol about the measurement of ascorbic acid by iodine titration, and I think the problem is with the form of vitamin C in your capsules.

The reference states that:
"The method is suitable for use with vitamin C tablets,
fresh or packaged fruit juices and solid fruits and
vegetables."

I suspect that the vitamin C in the capsules is ascorbic acid that has been modified in some way, maybe as a buffered or time-release formulation that does not react with iodine. You know that the redox titration works because you were able to measure ascorbic acid in the tablets. Was the concentration that you found close to what it was supposed to be (e.g., 500 mg)?

Check the product information label of the capsules and let me know if it says anything about the vit C being in a modified form.

I hope this helps. Please let me know if you have further questions. We are here to make the experiments work for you if we can!

Sybee