Carbonic acid forms when carbon dioxide dissolves in water. A typical can of soda contains a 0.120 M solution of CO2. Assuming that all dissolved CO2 is present as carbonic acid, and that no other substances dissolved in solution affect the pH, what is the pH of this solution?

Question

H2CO3: Ka1 = 4.68 x 10-7, Ka2 = 5.6*10-11
I'm not sure how to get from the concentration of CO2 to the Concentration of the H2CO3 reaction to get the pH

Answer 1

I think the secret is "assuming that all dissolved CO2 is present as H2CO3".
.......H2CO3 ==> H^+ + HCO3^-
I.......0.12......0.....0
C.......-x........x.....x
E......0.12-x.....x.....x

Set up the E line into k1 and solve for H^+ and convert to pH.