[shrapnel2]

So, my (Gen Chem 2) lab is set up so that we are given a vague idea of research questions to contemplate, and then we write procedures and whatnot to test them. It isn't inherently a bad setup, and I understand that it is closer to what the Real World is going to be like, but there is just absolutely no input from the TA on our data, experiments, anything. So I'm here.

Our experiment was basically to examine the usefulness of a coffee cup calorimeter, versus a lab-provided purpose-made calorimeter. We were then supposed to evaluate enthalpies of reactions of various reactions (we chose acid-base neutralizations, using 3M HCl and 1M NaOH, and 3M H₂SO₄ and 1M NaOH).

Here's the problem- our data is deeply confusing. For the HCl-NaOH reactions, the results that we got averaged out a solid 27% (for the coffee cup) and 35% (for the lab calorimeter) above what the known enthalpies of neutralization are. Ok, something clearly went wrong, but for the H₂SO₄-NaOH reaction, our results were 34% (for the coffee cup) and 38% (for the lab calorimeter) below what the known enthalpies of neutralization are. I can post my calculations and whatnot if anyone needs to see them, but how is it possible that we're getting results that are so wildly off, in opposite directions? Can anyone think of some common or likely mistakes that would result in such divergent results?

We calculated the heat capacity of the calorimeters, and are factoring that into our results. The only thing I can think of is that we had to mix our own NaOH solutions, and dilute the H₂SO₄ down from 18M, and I didn't do that part personally, so I don't know how much I can trust that it got done correctly, maybe? Anyway, I'm terribly confused, and any help would be greatly appreciated.