The generic equation for a reaction between an acid and water is
[tex]HX_{(aq)} + H_{2}O_{(aq)} --> X_{(aq)}^{-} + H_{3}O_{(aq)}^+ [/tex]
When an acid "reacts" with water, water acts as the base that accepts the proton (H+) from the acid. The remaining ion that is formed after the acid has donated its proton is called the conjugate base ([tex]X^-[/tex]), and the conjugate acid-base pair is [tex]HX[/tex] - [tex]X^-[/tex].
Hydrogen sulfate ([tex]HSO_{4}^-[/tex]) is an ion from sulfuric acid. It is still an acid in itself and can "react" with water (([tex]H_{2}O[/tex]) to form the sulfate ([tex]SO_{4}^2-[/tex]) and hydronium ([tex]H_{3}O^+[/tex])ions.
[tex]HSO_{4(aq)}^{-} + H_{2}O_{(aq)} --> SO_{4(aq)}^{2-} + H_{3}O_{(aq)}^+ [/tex]
Based on the previous discussion, [tex]SO_{4(aq)}^2-[/tex] is identified to be the conjugate of the acid [tex]HSO_{4(aq)}^-[/tex]. Thus, the conjugate acid-base pair is [tex]HSO_{4(aq)}^{-} - SO_{4(aq)}^{2-}[/tex].
