[brasarehot]

"The solubility of CO2 in H2O under standard conditions is 1.45g/L(partial CO2 pressure 1atm). Assuming that air contains 0.039% CO2, calculate the pH of H2O exposed to the air at standard conditions". ANSWER = 5.66

OK here's my math but I'm getting pH=5.12, could someone help me?
(0.039/100) x (1.45g/L) x (1mol/44g CO2) = 0.000128523M CO2
Ka H2CO3 = (4.47x10^-7) = [H]^2/0.000128523M
[H] = 7.58 x 10^-6
-log[H] = pH = 5.12