<p>We took a mock AP test today using the 2002 (or 1999…I forgot) AP exam and I got 100.55 points total which put me in the 5 range!!! :DDD</p>
<p>But my AP Chemistry teacher still is pouncing on me. That’s still not good enough for her…</p>
<p>Somebody posted a cram review packet in another thread.
Someone could find it if they need something to study for the last week.</p>
<p>Great job, whs2012! As long as you get a 5, she doesn’t have to know your raw score, right? Hahaa.</p>
<p>I posted a few questions a while back but it probably got lost with other posts, as they were at the bottom of the page:</p>
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<p>Any help would be much appreciated.</p>
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<p>Because sulfuric acid is a strong acid for its first dissociation. You need to write strong dissociators as ions.</p>
<p>H2SO4 is a diprotic acid; each proton leaves one at a time. In the predicting reactions, you’re only writing out the equation for the first reaction. For example, the complete dissolution of sulfuric acid goes as follows:</p>
<p>H2SO4 –> H+ + HSO4 (no equilibrium because sulfuric acid is a strong acid)
HSO4 <–> H+ + SO4 (equilibrium because it is not a strong acid, so there is not 100% dissociation)</p>
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<p>When something is heated or is decomposing, always write them in their individual elements. This is just a generic rule I suppose; I haven’t seen a case where it doesn’t work.</p>
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<p>Freezing point depression is when the amount of energy required to melt a substance is decreased (just think of why people salt the roads when there’s snow – to make it melt faster). This only makes sense when you think about it in Kelvin or Celsius. Suppose the regular freezing point is -50. Freezing point depression causes the freezing point to decrease to a higher temperature. I think of it as an absolute scale. Rereading this makes it seem more confusing than it actually is – if you agree I’ll try to come up with a better explanation.</p>
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<p>Yes the bond length of carbon trioxide is 4/3. CO2’s bond length is 2 though. You have two double bonds, so 4 total bonds divided by 2 bonding sites equals 2. That answer seems fine to me but it isn’t directly relatable because one doesn’t have any single bonds. You can’t directly compare. The bond length is more exact in the sense that it accounts for every variation.</p>
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<p>Kp is actually products^coeff divided by reactants^coeff, not the other way around. That should solve your dimensional analysis question.</p>
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<p>Monarchy, where is this review packet that you speak of? I tried creeping through your previous posts and didn’t find a link (yes, I’m a creeper…fear the wrath of my grumbling stomach). Could you please post a link to it on here? Thanks!</p>
<p>Thank you for the answers!</p>
<p>Freezing point - so if something normally had a -50 freezing point, lowering it would bring it to, let’s just say, -30? </p>
<p>I recall reading somewhere that CO3 had a larger relative bond length than CO2 though, am I just remembering incorrectly?</p>
<p>Yes, sorry about that - I meant to put products over reactants. I still don’t understand how that would change anything though?</p>
<p>I’m just looking over PR as a review, and getting in as much practice on the FRQs as I can. On the weekend I’m trying to get in some multiple choice practice. </p>
<p>I’m scared for the reactions part of the exam. I “kind of” know how to do them, but just the simple ones, like redox and precipitate, ■■■■■, and combustion. Acid Base…<em>iffy</em>. </p>
<p>Ughhh.</p>
<p>@Abrayo: No, I’m fairly sure it actually goes lower (for example, dropping 10 to -60 from -50). Then the putting salt on the roads example makes sense. If something has to be colder to be a solid than it did previously, and the outside temperature remained constant, then it would melt because the outside temperature would not be below the new freezing point.</p>
<p>@coffeeandtea;
All right, so lowering a freezing point is too make it more negative, correct?</p>
<p>Another question:
This is taken from the 2002 Free Response Form A:
Question 1.c)ii, here: <a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>I’m afraid I don’t understand what they’re saying, at all.</p>
<p>What I did was use the pH = pKa + log ([A]/[HA]) equation (I forget what this is called). I used the given Ka to calculate pKa. And then for [A] and [HA] I used the molarities given in the question. Is this wrong because of the expected volume change?</p>
<p>Edit: Okay so I understand why they said OBr- was the pH-determining species, because it’s the one being added, right?
I don’t understand the other two. What does Kb represent, and how does it answer the question? How was the pH of 10.79 calculated?</p>
<p>How accurate are PR’s practice exams?</p>
<p>^ I’ve heard they’re normally pretty accurate for just about everything?</p>
<p>Alright. Hopefully that holds true for AP Chem, because I’m going to try to take a practice exam within the next two days.</p>
<p>Also, I’ve come across a cram packet: <a href=“http://www.ocf.berkeley.edu/~daradib/chsntech/review/science/chem/notes.pdf[/url]”>http://www.ocf.berkeley.edu/~daradib/chsntech/review/science/chem/notes.pdf</a></p>
<p>Awesome!
I would definitely take a real practice exam if you haven’t yet, after the PR one - just for accuracy’s sake.</p>
<p>I never purchased a real one, but I suppose I can find one floating around online somewhere.</p>
<p>@Abrayo: Correct. It actually gets less. You are subtracting from the original freezing temperature. As for your other question, those are just other ways of solving it, so you don’t HAVE to worry about them. Finding the Kb shows that it will move at least a small amount forward (for example, it isn’t to the -22 power or anything insanely small like that) which will bring the pH up at least a little bit past 7. The pH was probably done using an ice box.</p>
<p>@Azyrk13:
You can go here for all the free-reponse questions in the past: [AP</a> Central - The AP Chemistry Exam](<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board)
and then here [AP</a> Central - AP Chemistry Course Home Page](<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>AP Chemistry Course – AP Central | College Board) under “Exam Information and Resources” there are two free multiple choice ones, so that’s good practice!</p>
<p>@coffeeandtea:
Ahh, I see, thank you very much!</p>
<p>Question about rounding:
On free response questions, do we wait to round until the final answer? Should I truncate or use the normal rounding method?
If I have the right answer, but too many significant figures, will my answer count (forgive the question about sig figs, but I was told that they don’t matter so I want to be really clear)?</p>
<p>@Imagodei</p>
<p>Do it either way, but I’d stick with waiting to round for the most accurate answers. If you have your work written and the scorer can follow it, I think one off might be okay (but try not to if you can). Sig Figs wise, you can go one digit over the proper # of sigfigs without losing any points.</p>
<p>^Thank you!</p>
<p>The significant figures make sense…that is why all of the AP Chem FRQ solutions have answers that have one extra significant figure.</p>