[FouRRaW]

Hi, my question is..

How do i ko nw which compound is the stronger acid in aqueious solution?

H₂SO₃ or H₂SO₄ 

attempt: the only thing i can think of is to set up an example and use the molar mass to eventually figure out moles of H₃O⁺

Like use moles = mass(made up)/molar mass     

and maybe i'd use a made up volume as well??

Is there not a simpler way?
Thanks in Advance

[mike]

If you knew their pK_a maybe this would help.

The molar mass or number of moles won't tell you which one gives up it's proton more easily. I think in general a strong acid will easily give up its proton/s and will also have a conjugate base that is happy to be deprotonated.

Also remember there is a difference between a strong acid and a concentrated acid...

[Borek]

There are simple rules for comparing such acids strengths - number of oxygen atoms in the central ion, number of protons, electronegativity of the element...

Of course as these rules are simplified, they not always work, but they will work perfectly in this case.

[Will]

There are simple rules for comparing such acids strengths - number of oxygen atoms in the central ion, number of protons, electronegativity of the element...

Yup!
FouRRaW: Think about the bonding in H₂SO₄ and H₂SO₃- the oxygens surround the sulfur- and the two protons are on two different oxygens. Now you know oxygen is a very electronegative element- so think about what this does to the O-H bonds if the S=O is withdrawing electron density. Also think about how stable the anion is once the proton has been donated- how many atoms in the anion can stabilise that negative charge?