Question

Carbon dioxide dissolves in water to form carbonic acid, which is primarily dissolved CO2. Dissolved CO2 satisfies the equilibrium equation.
CO2(g) <----> CO2(aq) The acid dissociation constants listed in most standard reference texts for carbonic acid actually apply to dissolved CO2. K=0.032 M/atm
For a CO2 partial pressure of 4.4×10-4 atm in the atmosphere, what is the pH of water in equilibrium with the atmosphere?
Note: Since carbonic acid is primarily dissolved CO2, the concentration of H2CO3 can be taken as equal to that of dissolved CO2.
My online homework is due tonight and I am hopelessly lost on how to solve this problem. :(

Answer 1

C = pK 
C = 4.4E-4*0.032 = about 1.41E-5 

H2CO3 ==> H^+ + HCO3^- 

k1 = (H^+)(HCO3^-)/(H2CO3) 
(H^+)= (HCO3^-) = x 
(H2CO3) = 1.41E-5 
Solve for x = (H^+) and convert to pH.