posted by luis .
what is the strongest acid here?
For oxyacids, the acidity increases with increasing number of oxygen atoms; therefore, H2SO3 and H2SeO3 will be weaker than either H2SO4 or H2SeO4. We have a problem determining which is the stronger of H2SO4 or H2SeO4. Atoms that are larger tend to have larger acid strengths and those with increasing electronegativity of the central atom tend to be less acidic. Se is slightly larger but both have about the same electronegativity. Does your text and/or your notes list ionization constants. If so, look them up. Both acids are strong acids; therefore, their first ionization is 100% so k1 will not be listed. But k2 is a weak acid (not ionized 100%) but is still relatively large as K2s go. I looked up k2 for H2SO4 and H2SeO4 and both are listed at 1.2E-2.