Science Buddies: "Ask an Expert"

Hello,
This is fairly urgent; my project results are due January 20th, 2014 and I just performed my dry-run...with issues. The titration took more than 50 mL of diluted iodine solution to oxidize the Vitamin C in my standard solution. I had to modify the procedure online, so I used a 500 mg Vitamin C tablet, but dissolved it in 500 mL of water. It should have still been 1mg/1mL, but when I tried to dissolve it, the tablet stayed in tiny particles floating in the water. Obviously however, I continued to the titration; I did not think it would be a problem. It may be something else, but this was the most obvious diverging aspect in my experiment from the Science Buddies guide. If this helps, the tablet I used was 500 mg and was chewable, if that is the problem. It also contained a flavoring, according to the bottle. Thank you so much for helping. Please reply, thanks!

Hi there,

I am not sure how to help. If the vitamin C tablet was not pure vitamin C, then that could certainly alter the results. Also, if it was not completely in solution it would also alter the outcome, though as this would lower the concentration of Vit C in solution it should have reduce the amount of iodine required. The other ingredients in the tablet could possibly have affected the titration, particularly if there was starch in the tablet. Was the concentration of your iodine solution correct?

Now, that said, you can still maybe compare the standard to the oranges, you just don't know the exact concentration of Vitamin C in the standard. How much iodine did you need to use in the end for the standard? How much did you need to use for the various oranges? Were the oranges different from each other? Your interpretation will have to take into account the problems with the standard, and you may not be able to calculate the amount of vitamin C with any meaningful accuracy, but you still may be able to compare the fresh juice to the old juice. Discussing problems with the experiment and resulting limitations of the data is a big part of doing science. Just be honest, try to explain why your deviations from procedure might have caused the results to be the way they were, and decide what (if anything) you can conclude from the data. This is actually a very good exercise, and happens to just about everyone who does research at one time or another.

Cheers,
Colin