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May16-11, 12:52 PM
Sci Advisor
P: 1,395
Quote Quote by Nemus View Post
I am not sure that I should put more fuel onto this fire but, since I have tried this in real life first in an accident ( I coose calium carbonate because it was in a sack next to me) and then playing with it later, I think I'll say it anyway. I think calcium carbonate is the better choice because it reacts less violently and therefore doesn't cause so much aerosol to form. Nitric acid aerosol is very bad for the person trying to save that day and also for everything in the room. The most common form of sodium carbonate contains some crystal water (10?) and I think that's why it reacts much more violently and boils like crazy when you pour it on concentrated nitric acid.
The crystal water may indeed have an effect, but I am pretty sure that it is the solubility that causes the major difference in the reactivity. Sodium carbonate is soluble in water (21.6 g/100g) , so it dissolves extremely quickly when it comes into contact with the aqueous nitric acid solution, so that *all* the carbonate ions are almost immediately available to react with the acid. On the other hand, calcium carbonate is about 20,000 times less soluble (~0.001g/100g), so only the surface of the calcium carbonate particles are undergoing reaction at any given time, and so the local volume around the particles quickly becomes saturated, and you have to wait for more reactant to diffuse to the surface, and the overall reaction proceeds more slowly.