[TheObnoxiousOne]

I am doing a project in my lab to determine the effect of Metal ions ( Cu2+, Fe3+, Zn2+ ) on the degradation of Ascorbic Acid. Theoretically these ions accelerate the oxidation of AA. However I dont have a clue to what concentrations of metals I'll be using. These metals are available in the form of nitrate salts and my sample consists of lemon juice with 12 mg of Vitamin C. Here are two things that I suppose I could try. Suppose I intend to use
Cu(NO3)2.XH2O and do a trials with 1:5 of metal to ascrobic acid concentration.
No of moles of AA are:- 6.89e-5.
so obviously ill need 1.37 e-5 moles of Copper. Now heres what I dont get.
 Do I calculate the mass of Copper in the salt and use a mass of the salt which gives 1.37e-5 moles of copper or do I take a mass which gives 1.37e-5 moles of the salt?
Can you guys point me in the right direction please.

Thanks.

[AWK]

Write down an oxidation reaction and think!
http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA5/MAIN/1ORGANIC/ORG12/TRAM12/E/0400110/MOVIE.HTM

[TheObnoxiousOne]

So i went ahead with my experiment and changed the variable i was measuring from metals to temperature and used temperature of 60,70 and 80 deg. However the lemon juice was much more concentrated than I anticipated with a concentration of 30 mg/ 50 ml sample rather than 12 mg, due to which the stock KIO3 was too dilute and instead of the 25.00 ml titrant intended I ended up using 60 ml for 60 deg, 65 ml for 70 deg and 68 ml for 80 deg, which really is a puzzle and confuses me. As the temperature is increased vitamin C content in lemon juice should be lesser and I should require less of the titrant to reach the end point, but obviously this was not the case.
Is their any scientific explanation to this or only procedural errors, heres some of what i did:-
-) I did not maintain the temperature for any duration of time and as soon as the erlenmeyers hit the temperature i desired i took them off and allowed them to cool in a cold water bath.
-) Before titrating i added appx 5.0 ml HCL, 5.0 KI and 3.0 ml starch, however unlike as suggested in the protocol i did not dilute my sample with 100 ml of deionized water prior to titration.
Any help or ideas will be much appreciated.