<p>what did everyone get for the calcium phosphate question? It seems the intended answer was phosphate, but calcium could be technically right.</p>
<p>I think all answers are posted on the ACS website early this week.</p>
<p>@COMBO. The lowest vapor pressure would be a soln of sodium sulfate (definitely not acetic acid, that readily evaporates so it has high vapor pressure). Sodium sulfate is Na2SO4, it has more ions than NaCl so it would have lower vapor pressure.</p>
<p>I think the arrangement, from lowest ionization energy to highest would be:
Br-, Cl-, Ar, K+… not completely sure.
Br- is larger than Cl- so bromide’s electrons should be easier to take. K+ should definitely have a very high ionization energy because it’s already positively charged, to get K+2 would be extremely difficult. </p>
<p>@YouTwo, don’t remember the question, what was it asking for?</p>
<p>My chem teacher contacted the local chem O. coordinator. You need to get like a 55 (that’s the average) to get in top 20 (study camp). And also, 88% on the free response. The free response is worth the most (50%). Lab is only 12.5% and multiple choice is 37.5%. The multiple choice is used as a cut-off (if you don’t make the cut-off, they don’t bother grading your free response or lab).</p>
<p>I think you can barely make study camp with a 53+ multiple choice, 86%+ free response, and an average or excellent score on the lab.</p>
<p>Doing amazing on the free response will go a long way.</p>
<p>@COMBO–hmm we definitely had different tests then. I don’t remember the ionization energy problem you mentioned either.</p>
<p>@YouTwo–I answered calcium, and I’m pretty sure it’s right. I might be misunderstanding the problem, but how could phosphate be right?</p>
<p>@Sophia7X–thanks for elucidating the cutoffs. Everything seemed kind of hazy to me before.</p>
<p>Does anyone remember the buffer question? With CH3COOH and NaCH3COO. It asked which of the following will change the pH. Was the correct answer A (add 15 ml of 0.1 M HCl)?</p>
<p>Probably. All I remember about that question is that diluting won’t change the pH (ratio of concentrations of protonated acid to conjugate base does not change).</p>
<p>@sunshine02–Yep, I do remember that one. They listed three options–adding HCl, adding CH3COO- (or was it the acid?), and adding water. Either way, I think both of the non-diluting options changed the pH.</p>
<p>It’s a buffer so adding 0.0015 moles of HCl would barely disturb it. Maybe adding CH3COO- would be better. (did it indicate how much CH3COO- added?)</p>
<p>The question makes no distinction to how much the pH has to change. As dobbyoshi said, the answer is both HCl and CH3CO2- (I believe the answer choice was “I and II”).</p>
<p>calcium phosphate question was something like this:
100 mL 0.30M sodium phosphate is added 150 mL 0.20M calcium nitrate. When reaction is complete, which ion is present in lowest concentration? </p>
<p>All calcium ion is used up (if a technical calculation is made, then ~10^-30 calcium ion remains but probably supposed to ignore this), so is the answer phosphate or calcium?</p>
<p>I’m sorry but I have to disagree, YouTwoThirtyFive.</p>
<p>With significant figures I found the difference in pH to differ by 0.004 (where the pH given was up to hundredths only) or something similar, making it negligible. Also, the Henderson-Hasselbach equation states: pH = pKa + log([A-]/[HA]), taking no note of adding small amounts of acid My answer was simply II.</p>
<p>As for the calcium question, I found that it was calcium because the concentrations of the two ions are the same. However, the compound formed is Ca3(PO4)2, meaning that the calcium ions are the “limiting reagant” (in a sense) and are therefore there in the least concentration.</p>
<p>XGeneration, I do not believe the pH was given on the problem, but thanks for giving this new insight. I can see it going both ways and we’ll know soon.</p>
<p>Also, the reasoning based on the Henderson-Hasselbach is incorrect, because adding strong acid converts some A- to HA.</p>
<p>:( I was afraid of missing this question on the technicality that “no calcium ions in solution” counts as a concentration.</p>
<p>XGeneration–I see your point, and I find it valid. However I heard from my coordinator that I got 60/60, and I chose “Both I and II,” so I think that’s the right answer. I agree with YouTwo that it’s really almost a matter of interpretation. </p>
<p>I also reached the same “limiting reactant” conclusion for the calcium ion.</p>
<p>Got something in the mid 20s, but I had to compete against the AP Chemistry students at my school (I’m in honors chem), so I really didn’t try that hard. Teacher said that the highest a first year chemistry student that he had taught had gotten a 30. There’s always next year when I take AP Chem…</p>
<p>What about the last question, the one about the functional groups of aspirin? Is it D (ester, ether, alcohol, and acid)?</p>
<p>[Aspirin</a> - Wikipedia, the free encyclopedia](<a href=“http://en.wikipedia.org/wiki/Aspirin]Aspirin”>Aspirin - Wikipedia)
has two functional groups: an acid and an ester</p>
<p>Are there anybody else still waiting for their results. We still haven’t heard anything from our local coordinator in Princeton NJ.</p>
<p>I have a couple questions. I got a 56 on the test ,which means I qualify for nationals.</p>
<ol>
<li><p>I looked at the free response questions on the acs website. It seemed like for most of them, you only had to write a sentence and not a paragraph. Is that accurate?</p>
<ol>
<li>Does anyone know the cutoffs for high honors? ( top 150)</li>
</ol></li>
</ol>
<p>By the way guys, answers are up: <a href=“American Chemical Society”>American Chemical Society;
<p>ahh… now I know the other question I missed.</p>
<p>ARG the sulfite question was sooo mean… >.< didn’t notice they added that extra lone pair on the double bonded O atom in choice (B) (which would otherwise be the correct and most stable structure). (D) was right even though it’s not the predominant resonance structure</p>
<p>very very tricky hehe</p>
<p>@Gardenstatesouth
Last year, I didn’t hear from the Princeton NJ coordinators until a week before the national finals, so you should expect to hear from them this Saturday.</p>
<p>Guys, assuming I didn’t misbubble anywhere, I got a 60/60 :D</p>