My DRAFT 2015 AP Chemistry Free Response Answers and Comments appear on this page.
Question 1 – Honestly, I hate this question – not for its content, but for its context. It’s another classic example of forcing a real world application into a question for the sake of it. It’s SO obvious that it’s painful. It reminds me of those questions where people’s names in questions used to be referred to as ‘John’ and ‘Mary’, and then there came this bizarre political correctness of inserting names that were deliberately lifted from certain, ethnic traditions, as if that somehow made a difference. Let’s just have a electrolysis cell without all the histrionics – political correctness for chemistry!
Outside of that, the question is painfully easy. The College Board is obligated (IMO) to honor answers in part (c)(ii) that refer to Q and/or Le Chatelier’s principle, since there is a VERY strong precedent for doing so. Isn’t it INSANE that after the removal of Nernst that they ask about non-standard conditions in cells two years in a row? How did THAT happen?
Question 2 – I find it crushingly ironic that question 1 should go out of its way to force new technology on to us and then question 2 looks like a question (and equipment/experiment) from the 1950’s!
The water in the displacement collection tube is not labeled in the diagram, which it should be.
In the old days, (a)(i) and (ii) would never have been separated from (b). It’s another example of step-by-step hand-holding that has plagued recent exams when compared to older ones.
As another example of that, wouldn’t have been better to NOT give the kids a heads up on the need to calculate ∆G in part (c), and leave it open-ended to give two reasons (high Eact and positive ∆G)? That would have been a stronger question IMO.
Question 3 – The context of the potassium compound is not needed IMO (see my comments on Q1). I think that a LOT of kids will be VERY confused by part (e), and the only way that they might get this question right is to actually calculate pH values at points between 0 and 30 mL added. It think that the question should have flagged this, and my bet is that (part) question will be a disaster (depending on the tolerance at the grading)!
Question 4 – Ksp and common ion problems used to be more difficult. I hope that they allow more (or less) than 4 water molecules around the ion. I fully understand that reading (and answering) the question as asked is important, but under exam pressure the AP exam should not be relegated to a reading comprehension.
Question 5 – I STRONGLY hope that it will not necessary to state whether the wavelength should be longer or shorter in part (c), since that would be pure recall that I thought we had moved away from. It had better be sufficient to say ‘different’, otherwise I think we have a flawed rubric.
Question 6 – Not much to report here, although I like the fact that it is explicit, that in order to predict the pH of a salt, it is seen as necessary to write a hydrolysis reaction.
Part (a) IS interesting to me though, and for this reason. Is one is obligated to use the data? This is another example where a ‘correct’ answer (regarding covalent character) could be derived by thinking about the differences in electronegativity. Of course, that would be knowledge that is NOT referenced in the question, and one would not be answering the question as asked as such, and one would not be falling into line with the CB’s obsession over ‘using data’, but should we be penalizing chemistry knowledge?
Question 7 – More, ‘forced’ real world applications! I object to excess verbs and nouns being used around a couple of chemical calculations. Isn’t this a little too easy?