HSO4- + H2O. What arises?

Question

Denote acids and their conjugate bases.

Answer 1

HSO_4- can be an acid by donating H⁺ to become SO₄^2- or it can be a base by accepting H⁺ to become H₂SO₄. H₂O can do the same. It can donate H⁺ to become OH^-, or accept H⁺ to become H₃O⁺. These are known as amphoteric compounds (can act as either acids or bases). So which is which in the current case.

We look at the Ka for HSO₄^- and compare it to the Ka for H₂O. The Ka for HSO₄- is 1.2x10^-2 compared to that for water which is 1x10^-14. So clearly, HSO₄^- is a stronger acid. So, here is the reaction...

HSO₄^- + H₂O ==> SO₄^2- + H₃O⁺

acid.......base....conj.base......conj.acid