Science Buddies: "Ask an Expert"

Hi everyone
I'm doing a chemistry investigation on how peas are prepared (frozen,fresh,canned,dried)affect how much vitamin c are in the peas.I'm doing the iodine back titration that involves sodium thiosulfate as the standard solution the concentration of the sodium thiosulfate solution is (0.100molL).I don't know how many peas i should use to titrate with the sodium thiosulfate solution and how much water i should add with the peas.Can someone please help me?

A vitamin C titration usually uses the juices of the material you are testing. Try to talk with a local chemistry teacher at a high school where you live. They should have lots of information on exactly what to do and how to do it.

My high school teacher says he doesnt know and I was suppose to find the information out myself.if i blended 100g of peas with 200ml of water would some vitamin c react with the iodine?

In the research that I did, it appears that the amount of juice used doesn't really matter. I came across one protocol which said the following:

Fruit juice
For juices or fresh fruits, titrate 50 mL of juice.
If you are squeezing fresh juice or using a pulpy juice, strain out most of the pulp. Place two squares
of cheesecloth over a 150-mL beaker. While holding the cheesecloth in one hand, pour the juice ontothe cheesecloth (use a mortar and pestle if necessary to get all the juice out of the fruit). After most
of the liquid has passed through the cloth, bring the edges of the cloth up to make a sack of the
watery pulp. Gently press out the remaining liquid into the beaker. Measure the amount of liquid
collected in a graduated cylinder (you will calculate the mass of ascorbic acid per mL of juice).
Transfer the juice to a 250-mL Erlenmeyer flask. Add the KI, HCl and starch as before, and titrate
with the KIO3.
With the juices, it sometimes takes a little longer for the blue color to fade. In this case, the endpoint
is where the color is permanent.

The full description can be found at:
test-2.media.berkeley.edu/ ~chem1b/spring05/Lab/pdf/lab5.pdf

Hi raven!

Try this:


http://chemmovies.unl.edu/chemistry/bec ... BD047.html

Or

http://www.vitaminresourcelist.com/10/v ... ation.html


good luck!



julie