I suppose that I'm the one to blame for all of this.
On Worldbuilding, I asked How can I liquefy my enemies?, which was one of our pseudo-open-ended weapon-design questions. I was looking for some sort of process that would take a human being a reduce him or her to a liquid-y state within sixty seconds, give or take. There, Aify answered first, suggesting the use of fluoroantimonic acid. The rationale for it was explained, and its candidacy seemed to be an a firm base. The only thing in question was whether or not it could meet the sixty-second requirement. Therefore, Aify asked How long would it take to dissolve someone using fluoroantimonic acid? on Chemistry. Later on, DoubleDouble mentioned that s/he had brought up a more general question, Is there any chemical/mixture which could liquidize a person in a couple minutes or less?.
The reason that these questions were asked on Chemistry was to provide a solid scientific basis for all acid-based attacks on humans, to be used in answers to the question on Worldbuilding. Nobody that paid much attention to the acid proposals knew how to do any relevant approximate calculations or find relevant data (which most likely doesn't exist) - at least, nobody who stepped forward. Therefore, it made some sense, I suppose, for somebody (two somebodies) to ask on Chemistry, where there was a good shot at the questions being answered. Some of us made a stab or two at it - comments mentioning possible ways to figure it out can be found in a chat room - but there were no successful attempts.
I find the questions somewhat interesting, but - and I apologize if I come down hard on them - I don't think they should have been asked on Chemistry. They ask for a calculation, and that fits the pattern of a homework question, however weird it may be. Yes, some homework questions are allowed on Chemistry, but there are many that violate the homework policy, and so are closed. These are questions asking for computations, not a particular concept. Boiling it down, I think they are off topic. Perhaps that's an extreme interpretation, but I stand by it.
In the future
On Worldbuilding, there has been a push over time to have more questions be backed up by pure, solid scientific principles - we use the phrase and tag hard-science to describe it. I have been on of the most vocal and active - if not the most vocal and active - proponents of this philosophy. A recent question that exemplifies this is Creating a realistic world(s) map - Solar systems (disclaimer: I answered it). Even though the hard-science tag was not on my question - nor even science-based, an older version of the concept that became way too overused - I think there was some pressure to come up with answers that were as realistic as possible, which is our overall policy, unless otherwise specified.
So, in the future, should there be this kind of cross-site asking - or, to better describe it, the asking of supplementary science questions to support a Worldbuilding question or answer? I say no. There is, at the moment, an unfortunate divide between questions on Worldbuilding and questions on pure science sites (though a divide that I'm working to whittle down). Worldbuilding questions are asked differently - not necessarily in a jocular fashion, but not necessarily 100% focused on the process of the science, so much as the result in the situation at hand. Mixing via migration has happened, which far too often does not go well.
So this last section really applies more to Worldbuilding users. Perhaps we should reconsider our relationship with other sites. Let's not pretend that the question models are the same - they aren't. We need to realize that question tone differs across Stack Exchange, and we need to change the manner of asking supplementary questions likewise. I do disagree at Todd Minehardt's characterization of them as "childish" - naïve, perhaps, but not childish (said the child) - but I think that there is a difference in tone.
Apologies (especially to inɒzɘmɒЯ.A.M!) if I succumbed to the meta effect, but I needed to give some context here. Fortunately, posts are editable, and links are removable!