Is the reaction of hydronium and thisulfate an acid-base reaction? Is this reaction 
$$\ce{2H3O^{+}(aq) + S_{2}O_{3}^{2−}{(aq)} -&gt; 3H_{2}O(l) + SO_{2}(g)  + 1/8S8(s)}
$$
an acid-base reaction?
It starts with the protonation of the anion, so that part is acid-base, but then it continues as a redox reaction.