Homework Help: chemistry

Posted by Gweedo8 on Friday, July 3, 2009 at 3:10pm.

I have this long online lab that I am working on and I am stuck on converting Molarity then ultimately finding the % of phosphoric acid in the cola? There is all of different steps I went through with information but I am going to try to give only the info needed to help me out. (hopefully I do not miss any)

Coca-cola contains acids including carbonic acid which is formed from the dissolution of the carbon dioxide in the water, and phosphoric acid, which is used to give it a little “kick” when you are drinking it.

The chemical reactions for the titrations of the acids are given below.

H2CO3(aq) + 2NaOH(aq) → Na2CO3(aq) + 2H2O(l)
H3PO4(aq) + 3NaOH(aq) → Na3PO4(aq) + 3H2O(l)

My unanswered questions:

Give the molarity of phosphoric acid in the original cola?
What is the density of the cola?
What is the % phosphoric acid in the cola?

Some helpful data:

Pipet 2.0mLs of the decarbonated cola into a 100mL volumetric flask. Add 10mLs of the ammonium molybdate/vandate solution and fill to the mark with distilled water. This will be your unknown.

Using McVc=MdVc, calculate the molarity of phosphate in the original cola. The answer was .0063 using
Mc=?
Vc=2.0mLs
Md=.00126
Vd=100

If this is not enough info can you please let me know what I am missing and I will re post with more info.

Thank you

chemistry - DrBob222, Friday, July 3, 2009 at 4:36pm
There isn't enough information, for me at least, to determine % phosphate. Did you titrate the phosphoric acid (note that by using decarbonated cola that you are getting rid of the CO2/H2CO3 and the solution now contains only the phosphoric acid.) You describe the solution made up in the 100 mL volumetric flask as the unknown, what did you do with that? You may have used a colorimetric procedure. And where did the 0.0063 come from?

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