Question

The approximate pH of a 3.0 x 10-3 M solution of the strong acid H2SO4 is

a) 3.5
b) 3.0
c) 2.5
d) 2.2
e) -3.0

how do you do this?

Answer 1

With some difficulty.
What level chemistry are you studying.
This may be more than you ever wanted to know about H2SO4 but here are the facts (the correct answer is not given).
If you consider H2SO4 a monoprotic acid the pH = -log(0.003) = 2.5
If you consider H2SO4 a diprotic acid, and you consider both H atoms ionize 100% (which isn't true) then the H^+ = 2x0.003 = 0.006 and pH = 2.2
In reality, the second H on H2SO4 is a weak acid with a k of 0.012. If you factor that in the H^+ = 0.005 for which the pH is 2.3.
If you are in beginning chemistry, you probably are to consider this a diportic acid ionizing at 100% and a pH of 2.2.