Vitamin C titration

[qrangotang]

I am doing a science fair project, and I have not gotten into detail with chemistry in school. For this project I am calculating the vitamin C content in bananas, but I do not know/understand the chemistry equations which are found on a pfd from the university of Canterbury.

I have been using this guide, which I understand because it uses cross multiplying to find the answer:
http://chemistry.about.com/od/demonstra ... tion_2.htm

however, if I wanted to carry out this experiment, I would have no way to measure milligrams, as buying a scale that can measure those increments is out of my budget.

Is the iodine solution used by the about.com article (0.005 mol L-1)? Because if it is, then would I be able to substitute the Canterbury recipe for the (0.005 mol L-1) iodine solution for the about.com articles recipe for the iodine solution?
This would mean that I wouldn't have to measure in milligrams, and I wouldn't have to work with sulfuric acid.

This is the iodine solution for about.com
ABy Anne Marie Helmenstine, Ph.D., About.com Guide
Vitamin C Determination by Iodine Titration

Iodine Solution

Dissolve 5.00 g potassium iodide (KI) and 0.268 g potassium iodate (KIO3) in 200 ml of distilled water.
Add 30 ml of 3 M sulfuric acid.
Pour this solution into a 500 ml graduted cylinder and dilute it to a final volume of 500 ml with distilled water.
Mix the solution.
Transfer the solution to a 600 ml beaker. Label the beaker as your iodine solution.

And the university of canterburys':
Iodine solution: (0.005 mol L-1). Weigh 2 g of potassium iodide into a 100 mL beaker. Weigh 1.3 g of iodine and add it into the same beaker. Add a few mL of distilled water and swirl for a few minutes until iodine is dissolved. Transfer iodine solution to a 1 L volumetric flask, making sure to rinse all traces of solution into the volumetric flask using distilled water. Make the solution up to the 1 L mark with distilled water.

If i cannot do the above, can i modify the canterbury experiment to use cross multiplication?
http://www.outreach.canterbury.ac.nz/ch ... iodine.pdf

So i would basically follow the canterbury guide to the titration part, using their recipes, and then use a .250g vitamin c powder control test, and then do my tests and cross multiply like in the about.com guide?
http://chemistry.about.com/od/demonstra ... tion_4.htm

I know i was probably really confusing, so thanks if you do read this.

edit: if theres a way to measure milligrams affordably without buying 3000 dollar scales it would make my life a lot easier

[deleted-71417]

Hi,

Have you examined this Science Buddies experiment writeup for the determination of Vitamin C in orange juice? It gives a method for calibration of your iodine solution that does not require a balance having a sensitivity of more than 0.1 gram:

https://www.sciencebuddies.org/science- ... p044.shtml

This procedure also does not use sulfuric acid.

I hope this helps. Good luck with the project1

Best regards,


Barrett L. Tomlinson