chemistry help! please!?

T

tanya

New member
Water in contact with air is acidic, rather than neutral, due to dissolved carbon dioxide. Water in equilibrium with the air contains 4.4 x 10^-5% CO2. The resulting carbonic acid, H2CO3, gives the solution a hydrogen ion concentration of 2.0 x 10^-6M, about 20 times larger than that of pure water. Calculate the pH of the solution.
 
Here's some additional info. That acidic water you spoke of doesn't contain any molecules of H2CO3. H2CO3 molecules cannot exist in aqueous solution. What we call "carbonic acid" is actually a solution of carbon dioxide dissolved in water. A small amount of the CO2 reacts with H2O to make H+ and HCO3-, and that is why the solution is acidic.

CO2(aq) + H2O <==> H+ + HCO3- .... Ka is small

As for your pH, we can still calculate that since we know the H+ concentration.

pH = -log[H+]
pH = -log(2.0x10^-6) = 5.69897
pH = 5.70 ... to two significant digits

(Only the digits to the right of the decimal are significant digits in a pH.)
 
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