system
Given the following post, respond as if you're commenting on Reddit:
human
Why is 90% sulfuric acid more corrosive than 99% sulfuric acid?

I tried doing some research on this but the only reason I can find that explains this is that 90% acid has a higher water content. However, that is not too clear to me why the extra water content affects corrosion.
gpt
The applicable definitions of acids refer to their ability to produce H+ in solution or to donate H+. They can only do that when they are in solution, i.e. dissolved in water.

The water allows for dissociation of the proton, H+, yielding H+ and HSO4-. It's the H+ that does the work of corroding metals and reacting as an acid.