[John404]

Hello!

For a lab in my class we're supposed to determine the molarity of an acid in a consumer product. One way of going about this is of course performing a titration, however, I was considering a different approach.

If I were to use carbonated water as my consumer product I could mass it, stir it to get the carbonic acid out, mass it again, and use the change in mass to determine the moles of CO₂ which is equal to moles of H₂CO₃ in the solution (CO₂(g) + H₂O(l)  H₂CO₃(aq)).

My question is, Is there enough carbonic acid in about 500 mL of carbonated water for this change in mass to be measurable? Triple beam balances are made available to us for massing.

Thanks!

[thetada]

I think it's an imaginative idea but my concern would be whether you could flush out all of the carbonic acid and how you could tell. There are various equilibria at work, between carbonic acid, hydrogen carbonate ions, aqueous carbon dioxide, gaseous carbon dioxide. It's the type of chemical situation where, for example, as molecules of carbon dioxide leave solution, others are simultaneously dissolved into it from the air. In fact, according to the below link, the proportion of carbonic acid is lower than the proportion of aqueous carbon dioxide...

http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic%20Acid.html

I think you should do it anyway BUT alongside a titration so that you can compare the accuracy of the methods.