PLZ HELP! Caculating pH of a Polyprotic acid!?

Question

If the pH of a 1.00-.in rainfall over 1600 miles^(2) is 3.50, how many kilograms of sulfuric acid,H2SO4 , are present, assuming that it is the only acid contributing to the pH?

For sulfuric acid,Ka1 is very large and ka2 is 0.012.

Answer 1

find volume:

1600mi2 @  2.590 e6 square meter/ mi2 = 4.144e9m2

1 inch @ 1 metre / 39.37 inches = 0.02540 metres

(0.02540 metres)(4.144e9m2) = 1.0526e8 m3

1.0526e8 m3 = 1.053 e11 litres

--------------------------------------...

find molarity:

@ pH = 3.50 ,... H+ = 3.162 e-4 Molar H+ ion

3.162 e-4 Molar H+ ion = 1.58 e-4 molar H2SO4

-------------------------

moles of sullfuric acid:

1.053 e11 litres @ 1.58 e-4 mol / litre = 1.66e7 moles H2SO4

grams of H2SO4:

1.66e7 moles H2SO4 @ 98 grams/mol = 1.63e9 grams

your answer is: 1.6e6 kilograms of H2SO4

(the pH had only 2 sigfigs)