[sparkly]

 I am not sure which direction i should go withthis. I can determine the concentration of H+ fromthe pH, but then what?

Atmospheric CO2 level seem to have risen by approximately 20% over the past 40 years from 315 ppm to 375 ppm.

(a) Given that the average pH of clean, unpolluted rain today is 5.4, determine the pH of unpolluted rain 40 years ago. You may assume that carbonic acid (H2CO3) formed by the reaction of CO2 and water is the only factor affecting pH by the reaction:

CO2(g) + H2O(l) <===> H2CO3(aq);

(b) What volume of CO2 at 25oC and 1 atm is dissolved in a 20.0-L bucket of today’s water?

[Borek]

What do you know about pH of a weak acid?

[sparkly]

I know that the pH of a weak acid is between 3 and 7, so this is a weak acid. Can you give me another nudge in the right direction?