Question

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

Answer 1

Probably not. It means that the sulfur oxides are the acid anhydrides of common acids.

Explanation:

So what is an acid anhydride? It is the acid LESS the elements of water, `H_2O`. The acid anhydride of sulfuric acid `H_2SO_4` is `SO_3(g)`, the acid anhydride of sulfurous acid, `H_2SO_3` is `SO_2(g)`. 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.