Concentration in M. of H2CO3 at Equilibrium?

Question

If a sample of water has a pH of 5.2 due to dissolved carbon dioxide forming the weak acid, H2CO3, with a Ka1= 4.3 * 10^-7, what is the concentration in M. of H2CO3 at equilibrium?

Answer 1

pH = 5.2
[H+] = 10^-5.2 = 6.31 x 10^-6 M
The equilibrium is
CO2 + H2O <---> H+ + HCO3-
[H+] = [ HCO3-]
K = 4.3 x 10^-7 =( 6.31 x 10^-6)^2 / x
x = [HCO3-] = 9.26 x 10^-5 M

Answer 2

You mean Molarity ??????