when carbon dioxide \"dissolves\" in water, essentially all of it reacts to form

Question

when carbon dioxide "dissolves" in water, essentially all of it reacts to form carbonic acid, H2CO3:

Co2(g)+H2O (l) <-------> H2CO3 (aq).

the carbonic acid can then dissociate into H+ and bicarbonate ions,

H2CO3 (aq) <-----------> H+ (aq) + HCO3- (aq).

Consider a body of otherwise pure water (or perhaps a raindrop) that is in equilibrium with the atmosphere near sea level, where the partial pressure of carbon dioxide is 3.4*10^-4 bar (or 340 parts per million). Calculate the molality of carbonic acid of bicarbonate ions in the water, and determine the pH of the solution. Note that even "natural" precipitation is somewhat acidic.

Explanation / Answer

CARBONIC ACID & ACIDIC
Carbon dioxide dissolves slightly in water to form a weak acid called carbonic acid, H2CO3: CO2 + H2O H2CO3
Carbonic acid reacts slightly and reversibly in water to form a hydronium cation, H3O+, and the bicarbonate ion, HCO3-: H2CO3 + H2O HCO3- + H3O+ This chemical behavior explains why water, which normally has a neutral pH of 7 has an acidic pH of approximately 5.5 when it has been exposed to air. It also explains the burning/stinging sensation in your nose and eyes when you inhale too quickly from a freshly-opened container of soda pop; the gas quickly reacts with the water in your eyes and nose to form a small amount of carbonic acid. http://www.ilpi.com/msds/ref/carbondioxi...

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