Identifying Lewis Acids and Bases

[Ray Guo 4C]

Question 6.5 in 7th edition asks that, in the reaction between hydrogen peroxide H2O2 and sulfur trioxide SO3 to form H2SO5, which reactant is Lewis acid and which is base. Can anyone explain why SO2 is the acid and H2O2 the base?

[Tiffany_Cacy_3D]

I don't fully understand why SO3 is the base but when I draw the lewis structure you can see that there is resonance in its structure and in order to fill the octet rule the Sulfur in the center has to make one double bond. When you draw the lewis structure for H2O2 it is nicely balanced, it is non-polar and has no need for any extra electrons while SO3 on the other hand is ready to accept electrons. I am sure there are other contributing factors but that is what I observed from this problem.

[Rachel Dang 1H]

This is a good question, can someone answer it?

[Matthew Mar 1J]

Maybe It's because SO3 has the option to include either single or double bonds? If all three oxygens are double bonded to the sulfur, the molecule is stable, but if it acts as an acid, some of the double bonds can switch to single bonds to create room to accept electrons. H2O2 on the other hand is stuck with its arrangement since hydrogen can't double bond, so it always has lone pairs on the oxygens open to donate to other molecules.