"Worst case, you might mix something like bleach and ammonia, and kill half the school."

Wow, alarmist much? Two seconds of googling suggests that it makes chloramine, which isn't exactly mustard gas ( http://chemistry.about.com/od/toxicchemicals/a/Mixing-Bleach... ).

As for not knowing what the mixture will do--well, there's a really obvious way to find out, right? We're all about TDD here.