# Is H2CO3 (carbonic acid) soluble or insoluble in water?

I am asking this because I know that acids are normally aqueous but according to the solubility rules, all carbonates are insoluble.

• Have you looked at general references, such as the Wikipedia page for carbonic acid, before asking here? – F'x Oct 21 '13 at 9:08
• Also, all carbonates are not insoluble - the alkali metal carbonates, like [sodium carbonate](sodium carbonate) are soluble. – Ben Norris Oct 21 '13 at 11:09
• Please note that Arrhenius' definition of acidity is not the only one. – Klaus-Dieter Warzecha Jan 22 '14 at 6:44

Yes, it is soluble.

For example, the oceans are constantly getting $\ce{CO2}$ from the atmosphere that gets converted into carbonic acid and thus decreasing pH on a global scale. Or the soft drinks we drink contain carbonic acid in them in dissolved form only due to mixing of $\ce{CO2}$ gas.

Also, not all carbonates are insoluble as Ben Norris has commented.

Hard and fast 'rules' in chemistry tend to be rare. Consider them guidelines.

• The oceans are only "constantly getting CO2" when we've filled the atmosphere with gaseous CO2 to disrupt the equilibrium. Prior to the last century, the oceans were mostly in a nice dynamic equilibrium with atmospheric CO2 (save a few nasty turns here and there) – ericksonla Feb 22 '16 at 14:27

Yes, it is soluble.

The fizzy part of your soda does not form a layer at the bottom of the bottle. (Personally, I find the empirical solutions best for chemistry)

The carbonate rule only applies to alkali metal carbonates.

Also, as a general rule, anything with the word "acid" is probably soluble in water. Seeing as acids are sometimes defined as yielding $\ce{H+}$ ions when dissolved.