# Does this mean that SO2 grabs an Oxygen out of every second OH(-) group present in the solution?

So what is an acid anhydride? It is the acid LESS the elements of water, ${H}_{2} O$. The acid anhydride of sulfuric acid ${H}_{2} S {O}_{4}$ is $S {O}_{3} \left(g\right)$, the acid anhydride of sulfurous acid, ${H}_{2} S {O}_{3}$ is $S {O}_{2} \left(g\right)$. Of course, these are formalisms, but they do help us to rationalize reactivity as an acid-base phenomenon when the sulfur oxides are dissolved in water.