2014 Released Free Response Comments & (draft) Answers

Below you will find my initial comments (there will likely be more after some reflection) and draft answers to the 2014 Free Response questions that were released by the College Board earlier today. As ever, these are in draft form and I would be happy to receive comments and corrections.

General comments

Based upon the released free-response questions alone, I don’t think that there is a single question that could not have been asked in previous years! There had BETTER have been a significant number of references to some combination of PES, semi-conductors, mass spec, bio applications, surface tension, chromatography, capillary action etc. on the multiple-choice, otherwise the College Board will have led us all on a merry dance – again.

I would HATE to be a reader this year! I would not want ANY part of grading multiple parts of this exam including 1(a)(ii), 1(c), 1g(ii), 2c(ii) or 5(d) amongst a number of others.

As ever, when you read my answers there will be many other ways of getting the points, and in some cases BETTER ways.

Question 1:

It’s too long. I suspect g(i) will require some reference to Ksp but to me (and I bet many students), this is not obvious. g(ii) is problematic since I THINK it assumes a tablet of similar mass as in the original data, and that is not obvious. Without specifically stating it, I do not like this question. Here’s what I wrote on the AP discussion group;

I think there is a potential problem with 1g(ii) as well.

The number of significant figures that can be recorded on a centigram balance depends on what is being weighed, does it not? The question may be assuming that all of the tablets and filter papers have very similar masses to that of those in the data, but this is NOT stated as far as I can tell, and the reference to access to only one KI tablet does not IMO, mean the SAME KI tablet as in the data. Isn’t it possible that a very large KI tablet could generate a mass of precipitate with three significant figures? Am I missing something here?

This may not be ‘in the spirit of the question’, but isn’t it a possible answer? I believe significant figures to be a math, and NOT a chemistry concept so feel no shame in asking such a question! I have always believed that there should be NO reference to them on the AP chemistry exam at ALL.

Question 2:

Not much comment here other than we start down the organic reference path which I DON’T like.

Question 3:

For me, (a) and (b) are the same problem. Why a diagram (rather than simply stating which way the ions travel) is necessary in part (c) is beyond me here; it’s just part of the College Board ‘particulate diagram’ obsession nonsense – another blog post coming about this thing, soon.

(d)(i) – I like the Nernst equation. In the real world I suspect that you would generally need to actually calculate the new voltage in most situations of this type! You could tackle this with a Q and K argument, too.

Question 4:

No comment here (yet).

An alternative way of stating that the carbonate has not completely decomposed is to do some math to prove that not all of the solid has decomposed by considering the stoichiometry.

Question 5:

(a) is pathetic. It’s arithmetic and middle school knowledge – it’s not worthy.

(d) is a mess. Imagine trying to grade this!?!? No thanks!

Question 6:

Even though (a) and (b) are not organic questions per se, I hate the use of these molecules, especially polymers, to illustrate this. Why not choose other things?

Question 7:

MORE organic molecules being used to represent non-organic theory? Why? Again?

EDIT (05/13/14)

Robert McDaniel writes;

“Just curious, Adrian, but it is certainly possible that many students might be thinking about the kinetic energy of molecular collisions (the normal explanation) to explain the temperature effect even though they just finished determining it is a first order reaction.  In this case vagueness may well be rewarded over those who impute improper behavior in the molecules.  Do you think collision energy will still get a point in this answer or must it be vibrational or some unidentified form of kinetic energy?”

My response;

It’s a great point and not one that even occurred to me at the time! I think it’s entirely feasible (as you suggest) that some kind of reference to vibrational energy of the molecule might be sought*, but I’m not sure what % of kids are going to even think about that. Maybe I fail to get that point!

*I think that they idea of introducing vibrational energies and the like, without any significant organic component to the course, would be another example of things being improperly aligned.

ANSWER PDF

38 Comments

  1. Dan Reid

    My first comment is this: WOW! This test was really long! I timed myself taking it and I carefully and thoughtfully did each problem at a nice easy pace (for me) and considering that I really screwed up on (1) (c) and had to re-do the whole thing b/c I was an idiot, I still finished the first 3 questions in 57 minutes with no errors. And this is the veteran AP teacher we’re talking about. I can only imagine how many stressed out kids feeling rushed really freaked out.

    Now with this said, when I gave my practice AP exam the week before, I told them that usually they will run out of brains on the MC and then they will run out of time on the FR, so I said to them, “make sure that you jump around and try to get as many points as you can on the FR”. Did they listen? Some did and some didn’t. The ones that I expect to get 5’s barely finished, but they finished none the less. They have no excuse for “not getting to #7”.

    I did the rest of the test in the allotted time (barely), but again, I took my time and wrote out really clear responses in complete sentences and they were pretty easy, IMO. Even with the organic stuff, I was OK with it being used as the molecule example, although I agree with you that it was totally unnecessary, so why do it? I was glad to see that the “lab question” (#1…gravimetric analysis) was one that I did in the early spring. I hadn’t done the lab in years past, but I altered the version from the lab manual this year, so I got lucky (or I prepared myself well) and I hope this helped my students feel more comfortable on it.

    As for the other questions, I agree with you that they are no more difficult than other tests in the past. And like Paul C. said, I’m glad that I didn’t change the way I taught stuff this year. Yes, I taught them PES and what a mass spec. graph is used for, and I de-emphasized phase diagrams and did NO colligative properties which still hurts my chemistry soul, but I spent one day on the very basics of PES and mass spec. Thank God I didn’t waste a week on it.

    More importantly, the lack of any AP level complicated calculation is sad. A smart 1st year student can handle the rigor of the calculations. I had my kids do WAY more math for each individual chapter test, but I can understand (somewhat) that the AP Exam is trying to cover many things at once which limits them to “the basics”. But still, having success on this math-wimpy exam isn’t preparing them for the reality of college-level calculations that will be expected. Also, I really am disappointed that the CB used a t-shape. I thought that sp3d hybrid orbital shapes would NOT be on the exam. I taught ALL the shapes (sp3d2 included), but I mistakenly told my students that only 4 domains would be on the exam. Oh well. It’s not like they had to come up with the name “t-shape”.

    Last but not least, in previous years, I could somewhat accurately predict how a certain % in my class would translate into a 5, 4, 3, etc, on the AP exam. With the number of kids that took the test for me this year AND with the huge range in their grades (from 100% A+ down to a kid getting a 57% F) I will hopefully get a nice “revised” guideline for future predictions in AP scores. Thanks for all of your posts this year!

    Reply
    • Adrian

      Thanks for taking the time to comment, Dan.

      Regarding T-shape – I think it’s fair game, since just because the hybridization *explanation* is in flux, it doesn’t make any difference to the number of electron domains and the shape consideration. Obvious they can’t ask about hybridization of such things, but the shapes beyond 4 centers seem fairly in play to me.

      Reply
  2. Bruce Outland

    Hi Adrian,

    Regarding 4(b): The prompt says, “Based on the data in the experiment…”. I wonder if just saying that there must be CaCO3 remaining because it’s a reversible reaction is enough to get credit. I answered it by converting the grams of CaCO3 to moles (0.50mol), and comparing to the moles of CO2 calculated in (a) to justify that not all of the CaCO3 had decomposed (due to the 1:1 reaction ratio).

    Reply
    • Adrian

      Hi Bruce – Great point and you may well be right. I’d argue that the equation is ‘part of the data’, but your point is well made, and you are probably on safer ground than I am!

      Reply
    • James Hays

      Just a thought on 4(b). Two experiments were done 50 g and 100 g. If the reactions went to completion( all the CaCO3 decomposed) then the second experiment would have provided twice the pressure of CO2. Since the pressure was the same in each, an equilibrium is the mostly likely explanation. Most people will look at the graph and think…equilibrium when that graph tells you nothing about that. A reaction to completion would look the same. If you did some stoichiometric calculations, then you could tell that solid CaCO3 was left and that an equilibrium existed. Also with the dropping of reaction memorization, most students would not know that the reaction is an equilibrium.

      Reply
      • Adrian

        James – Agreed on the stoichiometric treatment. See the comments by both Bruce and I, above and my comments in the post.

        However, I’m not sure that the lack of need for reaction knowledge (which I agree has come to pass) has any bearing on knowledge of whether this is an equilibrium or not. I’ve NEVER mentioned equilibrium when I taught this very reaction as a the decomposition of a carbonate to yield the metal and non-metal oxide. To me, those are two entirely UNrelated things!

        Reply
  3. Derek

    Hi Adrian

    Thanks for all your posts and your quick work on the 2014 exam. My students here in the UK had exactly the same exam so I am thinking that there is no longer a form B or an international version?? I agree that all of this paper could have been taken quite easily by any of my previous AP classes so like you I’m assuming that any of the new content like PES must have been(!?) covered on the multiple choice questions. Most of my students had a similar reaction to Dan. It was a long exam.

    It wasn’t any harder than previous years from what I can see but the amount of reading and comprehension required seems to have increased considerably. Also I know that next year I will be putting even more emphasis on clarity of writing in answers. The math content has (as we suspected it would) dwindled whilst the amount of answers requiring explanation or discussion seems to have increased.

    Question 2 is our old favorite equilibrium question. simpler in fact than most but with more words than normal. Question 3. Even though I like the dual ion movement in the salt bridge question, I have to admit I have not emphasized this in my course. I suspect that like most I have simply stated that ions move in the salt bridge to keep the charge balanced without going into much greater detail. I’ll know for next time!

    Question 3d is very easy to answers using the Nernst equation BUT using a Le Chat discussion for this particular case is actually quite difficult conceptually. I think many will struggle with this.

    On Q4b I suspect that they are hoping students will do some math but I agree that your answer that its an equilibrium so there must be some solid present has to be an acceptable one.

    And of course, I agree that 5d will be a nightmare for the examiners to grade. I’m glad its not going to be me!

    Well done Adrian. Keep up the good work

    Reply
    • Adrian

      Derek, great to hear from you and thanks for taking the time to comment!

      Reply
  4. Donna B

    Thanks, Adrian – really appreciate your work. I was amazed at the amount of “words” in 4 & 5 – for students to do that in 7 minutes is crazy! My best student finished the m/c with 1/2 hr to spare (after going over it a few times), yet barely had enough time to finish the free response. By the way, there must have been 2 versions

    Reply
    • Adrian

      There are SEVERAL versions, not just two!

      Reply
  5. Scott

    On the practice exam, they required the use of x in the Ka calculation in 2 since x is given and the difference in K vs. x is not tremendous. I’m expecting to see the same on this, where ignoring x removes a point.

    Reply
  6. Karen Evans

    I did this test and it took me a long time. OMG, my kiddos must have been pressed for time. All I know is that some said it was really hard and others said it was not. Which brings about the multiple versions – if one is harder than the other how is that fair to the students? I did not necessarily think this was hard, just time consuming to read and write an answer (brief as it may have been). If some of my kids see this one and tell me their questions were harder, I don’t think that gives a fair chance to some. Just food for thought CB.

    Reply
  7. Paul Hessler

    Hi Adrian,

    I feel like this exam and the practice exam both suffered from the same problems:
    Trying to ask the same question as in past exams, but contorting language to get the same idea across, reducing agent removal is a perfect example. My students were all groaning when we got to that question on the practice exam. Also the “removal” of the Nernst equation and the inclusion of the concept in another convoluted manner.
    A lack of precision in the way some of the questions were posed, 1g(ii) is a good example of this, as you point out.
    I feel like the new curriculum and the new exam were rushed and the products (practice exam and actual exam) suffered b/c of it.
    While I think lab work is an essential part of chemistry, it definitely seems that a student can still pass the exam without ever having done a lab. So much for the new emphasis on lab, not to mention the ridiculous inquiry emphasis, which I actually went out of my way to address and follow.

    Question 1: This was the longest FRQ I remember seeing. Starting the FRQs with this long problem set a tone for my students that all of these questions were going to be a slog. Even my best students felt taxed by the overall length. I agree with your assessment that a mention of Ksp was going to be required. and was not really obvious in the phrasing. I did assume that Ksp would be required when I wrote my answer, and did warn my students that if something was mentioned in the question they would have to address it in the answer, BUT in the moment of testing I am sure some of them did not remember what I said.

    Question 2: I don’t mind this problem at all. I think one of the places where organic molecules work well is for weak acids and bases. That being said, it is the beginning of the overuse of organic molecules in these FRQs.

    Question 3: When I answered this question, I did it the way I taught my students to answer it and included the answer for (b) in (a). I hope the kids could sort it out in the end. I am disappointed with the obvious overlap here and am worried about how (a) and (b) will be graded.

    Question 4: I do not have any complaints with this question. I actually thought is was fairly straight-forward.

    Question 5: We spend lots of time on this topic, and (a) and (b) are obvious gifts. I like (c) and (d). I think they get at VSEPR theory and bonding in a good way. However, the mention of periodicity is a bit odd, since the only thing to mention is number of valence electrons which i think would be included in any covalent bonding explanation anyway.

    Question 6: I feel like we see the organic reference in questions like this because these molecules exhibit trends that can buck traditional behaviors, like LDFs trumping dipole-dipole interactions, however they did not use that for this problem, so they could have used any two molecules here. I do not like that the problem seemed to hinge on knowledge of polymers for many students and it may have confused them for the rest of the problem.

    Question 7: I agree that the over-emphasis on the organic molecules is completely unnecessary here and there are plenty of other ways this could have been discussed. It makes me wonder if we need to use (many?) more organic molecules as examples for periodic trends, IMFs, bonding, …

    Thanks for your comments and contributions. They are always appreciated.

    Reply
  8. Blake

    I disagree with your answer for 4(c). Am I just thinking about this wrong? Here’s what I got:

    The final pressure would be greater than 1.04 atm, but less than 1.5 atm. According to Le Chatlier, if the pressure of a product increases, the system will try to balance by shifting to the left, which means gas is being lost. However, the reaction will reach equilibrium before the pressure returns to the initial pressure of 1.04 atm.

    Reply
    • Adrian

      My take is this. If the temperature has not changed then Kp will be the same. Give Kp ONLY depends on the partial pressure of CO2 (as it does), then the only way that Kp can still equal the same number is if the partial pressure of CO2 is still the same. Of course, this does rely upon there being sufficient CaO present to allow the CO2 to react and for the reaction to go bakcwards.

      Reply
  9. Alesa Rehmann

    Question #2 part c, i. This should be true because the reaction between the strong base and weak acid goes to completion with the strong base being able to take off all H+ from the propanoic acid. As it does this the acid needs to maintain equilibrium and will dissociate further until a ph of 7.00 is reached.

    Please correct my thinking if this is incorrect.

    Reply
    • Adrian

      You are correct that the reaction goes to completion, BUT the pH will be greater than 7 because the salt that is produced (by the complete reaction) will hydrolyze in water and create free hydroxide ions. Did you see my answers at the bottom of this post?

      Reply
      • Alesa Rehmann

        Oh, yes, missed that part–you are so right–thanks!

        Reply
  10. Rich Homie

    Hey Adrian,

    Thanks for taking the time to post your answers! How many points do you think that you have to get out of 120 to make a 5, 4, and 3?

    Thanks!

    Reply
    • Adrian

      Rich – It depends upon a couple of things. Firstly what the national statistics look like, and secondly if they decide to rearrange the grade distribution as they did in AP Biology last year – that was DEVASTATING!

      Having said that, my GUESSES are these; A 5 could get cut-off anywhere between approx. 81 (very best case) and 93 (very worse case). I CANNOT envisage ANY situation where a score of 93 or more does NOT score a 5. Then I would go with points ranges of approx. 12, for each AP grade down from there. However, these are really ‘shot in the dark’, guesses!

      Reply
      • Rich Homie

        Adrian — Thanks!

        In the 5 Steps to A 5 AP Chemistry 2014-2015 book, it said a

        Total Raw Score

        68–120 (would be a 5)
        52–67 (would be a 4)
        40–51 (3)
        24–39 (2)
        0–23 (1)

        How accurate do you think this is?

        Reply
        • Adrian

          I think that is WAY, WAY, WAY too low, UNLESS it turns out that huge numbers of kids failed to get to the final problems because of time pressure. If so, the raw scores will come down and with them so will the boundaries but even so, 68 seems a HORRIBLY low threshold, and apart from the time issue this was a fairly straightforward exam. We’ll see but I’ll be amazed if it were that low.

          Reply
          • julie mullane

            if they scale the fr, do you think they will weight the first three more than the last four?

          • Adrian

            Well, the first three are worth more points as a whole but as for weighting within that, no idea.

        • carol lund

          I thought the total raw score would be 106 max so I am unclear how these numbers apply to this years exam.

          Reply
          • Adrian

            Well, I am basing the calculation on;

            + knowing that the MCQ and FRQ are 50% each
            + knowing that there were 60 MCQ’s
            + assuming that the FRQ will be scaled to be out of 60 (regardless of the original raw points) to make the raw score out of 120

            Having said that, these are ALL ‘ballpark’ guesses.

  11. Todd

    Thank you for all your work (on these solutions and for so much else you do and share). GREAT solutions! I just wondered, on 4a shouldn’t the 1100K limit the sig figs to 2, or 0.011mol? My intuition matched yours, but as for the values placed on the exam, 1100K has two sig figs. J. Hnato and I had many conversations about “100” deg C having 1 vs. 3 sig figs. If the CB is going to be nit-picky about things, do you understand why the flub so much on this one? (He kept saying it was 3, i.e. the exception that proves the rule…). Thanks for your thoughts…

    Reply
    • Adrian

      Todd – Who knows?? Sig. fig’s are largely a mystery to me, I don’t consider them to be appropriate for the AP (or any) chemistry course, and the fact that the College Board doesn’t have an official policy on this doesn’t help.

      Of course, it may not matter since this may not be the question that they pick on for examining sig figs. (assuming that unwritten policy is still in place on the new exam)!

      Reply
  12. Soomin Park

    Hello, I’m actually a student who took AP Chemistry 2014 exam on May 5th…

    As a student, I thought this exam was quite more stressing than the ones I practiced before, mainly because of too long FR questions that perplexed my brain a bit. I felt the time was way too tight (actually I always write more than needed…like I always answer in complete sentences with full explanation…because I don’t want to miss any single possible point!)…Actually I couldn’t get to #7 at all. But my other answer’s accuracy is quite fine thankfully 🙂

    About difficulty, maybe just because I was too nervous on M.C. (it was my first ever AP exam), right after the exam, I felt M.C. questions were a little bit hard but most of my classmates said they felt it was actually easier than the practice. Also thinking it after some time, I could see that they may have been just a little bit more tricky and longer but actually quite simple :)….(If I didn’t make any mistake in reading and understanding the wordings…!)

    I used to get quite high scores in every practice(solid 5 level) and my teacher always said I would easily get 5 in actual exam,too, but right now, I’m not that certain how my score will be….

    I heard that in the College Board practice exam released, if I scored higher than 85/120 (when both M.C. and FR are based on 60), I have high potential to get 5 and if higher than 90/120, it will almost surely 5…
    Do you still think that guideline will work???

    Can you please tell me if there will be somewhat large difference in your opinion??

    Thank you!!

    Reply
    • Adrian

      Soomin – Take a look at my comments earlier in this thread about my best guesses for grade boundaries.

      Reply
  13. Mary

    Hi Adrian,

    I was wondering if other schools had students who had 2 different forms, as our school did, and if they released the other free response questions. Our kids report having forms O and C, form C being much easier (more like the old exams) and O being more difficult, according to their reports.

    Do you have any feedback on this, and if this was done to compare the new testing version to the old? It seems unfair to me that kids were given multiple forms that varied in question type.

    I suspect that the form that was released was the C form.

    Reply
    • Adrian

      We had two forms. They will NOT release the other questions. Obviously (I think!), the different forms have to have grade boundaries set at different points, to allow for the relative difficulty of each form. I cannot imagine any other feasible circumstances.

      Reply
  14. Tom

    For 6a;

    Wouldn’t the fact that PVC is polar, due to the C-Cl bond, allow it to sink to the bottom? Since water is polar, the PVC would be miscible unlike the other non polar compound that sits on top of the water with the -CH3 group.

    Reply
    • Adrian

      Given the wording of the question, I really think this is a density, not a polarity issue.

      Reply
  15. Melanie

    Concerning question 1g(ii): I read this question very simply and feel like perhaps you are reading too much into it. When I teach sig figs I teach the old adage that your results can not be more precise than the instrument you use to collect your data. I really feel like that is all they are looking for in this question, if I am right that would mean they are testing basic sig fig concepts and this question was way too easy for an AP exam! Let me know your thoughts, maybe I am the one missing something here.

    Reply
    • Adrian

      Melanie – I agree that my comments are almost certainly NOT what the question is getting at but I offer them to highlight what I *think* is a flaw in the question. My main point is that in determining significant figures in this case, I think that one has to consider both the instrument AND the stuff that is being massed.

      As for what is (and is not) appropriate for an AP Chemistry exam, I vote for the COMPLETE removal of sig. figs!

      Reply
      • Melanie

        Ahh, I see, so I was the one missing something! I agree with you on sig figs. They cause so much uncertainty on the test. I never know what to tell my students. There seem to be a few “unwritten” rules concerning them on the tests. I have heard they can be given credit if over or under by one, I have heard they only score a random problem they pick on sig figs. So it is frustrating. I grade all their problems in chem I and AP chem based on work, ans, units, and yes…one point for sig figs. I usually give them the off by one lie-way. If I knew they didn’t need the on the test I would just tell them to round to two, would make grading so much easier! I would say if they are going to keep them, then they need to announce some formal guideline on it.

        Reply
        • Adrian

          There used to be an ‘unwritten rule’, that appeared to be largely consistently applied, that +/- 1 sig fig was acceptable. So, an answer that should have 5 was graded correct with 4, 5 or 6. THEN, completely out of blue, several years ago, they suddenly decided to pick on a particular question where the the sig. figs had to be exactly correct. Either way, neither of these things were ever ‘official’, but talking to readers and interrogating the scoring standards made them what I would call, ‘effectively official’.

          In short, I am of the opinion that none of this is chemistry, and it should not attract any credit or debit.

          Reply

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