[bwarh]

Seems very simple, just can't seem to wrap my head around it.

Calculate the total CO2 in a solution of pH 6.5, in equilibrium with atmospheric CO2 at
390 ppm. How does this change if the atmospheric CO2 rises to 500 ppm (assuming, for
simplicity, that the pH is still 6.5)? (Note: "atmospheric CO2 at 390 ppm" means PCO2 =
390 x 10-6 atm)

I was thinking of using Henry's Law but why would it give the pH then....