What would be the pH of a soda water made by saturating pure water with pure CO2 at 1 atm pressure?

Answer 1

If we call the (H2CO3) = 0.034M, then

...........H2CO3 ==> H^+ + HCO3^-
I..........0.034......0......0
C..........-x.........x......x
E..........0.034-x.....x.....x

Substitute the E line into k1 for H2CO3 (look that up in your text tables) and solve for x = (H^+) then convert to pH.