Here is some information on buffering, or neutralising, vitamin C with Calcium Carbonate, or CaCO3

Vitamin C, or 'ascorbic acid', will often irritate the stomach lining when taken orally in quantities larger than the recommended maximum daily dose of 500 mg. Some people take in daily doses of orally up to 10 g, so to prevent problems it seems advisable to neutralise the acid before ingesting such amounts. It is well known that the carbonate group CO32- as dissolved in water can effectively accomplish this in the following reaction:

2H3O+ + CO32- → 3H2O + CO2

So here we will try to establish how much calcium carbonate is needed to neutralise a certain amount of vitamin C until it is neutral (pH = 7).
The chemical formula of ascorbic acid (vitamin C) is C6H8O6 from which we can find the molecular weight of ascorbic acid:
• carbon (atomic weight=12.011, say: 12): 6 atoms
• oxygen (atomic weight=15.9994, say: 16): 6 atoms
• hydrogen (atomic weight=1.00794, say: 1): 8 atoms

Giving us a total molecular weight of ascorbic acid:
6 x 12 + 6 x 16 + 8 x 1 = 72 + 96 + 8 = 176

The atomic weight of Ca is 40.078, say: 40, so the molecular weight of CaCO3 is:
40 + 12 + 3 x 16 = 40 + 36 + 48 = 124.

Now, because with every 1 molecule of CaCO3 we can neutralise 2 molecules of ascorbic acid, we need half the amount of molecules of CaCO3 to neutralise a certain amount of molecules of ascorbic acid. And because the molecular weights of CaCO3 and ascorbic acid have a ratio of 124:176, we need 124 / ( 2 x 176) = 0.35227 g of CaCO3 to neutralise 1 g of ascorbic acid.

In other words, if we use tablets of 500 mg CaCO3 to neutralise tablets of 500 mg ascorbic acid, the amount of CaCO3 tablets we need is 1/3 the amount of tablets ascorbic acid.

Last update: 2011-02-23
Editor: NEdit