A little backstory to confuse you:
One of my characters is in Chemistry class (not university level). Someone dares her to sniff a gas byproduct of a chemical reaction during one of the labs. And she does it. Because she's sixteen and stupid. (Not calling all sixteen-year-olds stupid, but this one -- rather is.)
I'm not sure what chemical reaction would be best there because a) I'm not trying to kill her off (because she might turn out to be cool by the end; I'm not sure, though), and b) I need to know what chemical reactions produce a gas that would only knock someone out for a spell.
I thought of magnesium strips and hydrochloric acid, but that produces a hydrogen gas that is -- really a respiratory irritant.
Any suggestions on experiments that could yield this? Or maybe proof that hydrogen gas can knock someone out from a whiff? ('Cause I sure haven't seen it.)
Thanks in advance.