Solution

The Na⁺ ions and K⁺ ions have no acid-base properties and function purely as spectator ions. Therefore any reaction which occurs must be between the hydrogen sulfate ion, HSO₄^– and the hydrogen carbonate ion, HCO₃^–. Both HSO₄^– and HCO₃^– are amphiprotic, and either could act as an acid or as a base. The reaction between them is thus either

`HCO_3^- + HSO_4^- -> CO_3^(2-) + H_2SO_4`

or

`HSO_4^- + HCO_3^- -> SO_4^(2-) + H_2CO_3`

Table 1 tells us immediately that the second reaction is the correct one. A line drawn from HSO₄^– as an acid to HCO₃^– as a base is downhill. The first reaction cannot possibly occur to any extent since HCO₃^– is a very weak acid and HSO₄^– is a base whose strength is negligible.