<p>My daughter took it today and since it was the last day the test coordinator let the students take home parts I and II of the test (the lab portion was turned in with their test). My daughter said she didn’t think the MC questions were necessarily harder than last year, but they took more time to answer and she didn’t finish. :(</p>
<p>Do any of you remember how you answered the free response question about why the decomposition rate of A and B at 25 degrees Celsius was the same but the decomposition rate of B at 15 degrees Celsius was higher than the decomposition rate of A at the same temperature?</p>
<p>Also, if the cutoff for top 150 is lowered, does that mean the cutoff for top 20 is also lowered?</p>
<p>the answer was because the activation energy of A is greater than the activation energy of B</p>
<p>Oh, good. That’s what I put. Did any of you know how to do the concentration cell problem? (The part that asked which is the anode). How were you supposed to tell?</p>
<p>The concentration cell one has voltage go to zero after alot of time has passed… so the anode = oxidation, so the one where the concentration of Cu2+ is lower than the other cell? So oxidation makes cu2+ go up? moves cell towards equilibrium? idk. thats what i put.</p>
<p>^ I second this explanation.</p>
<p>Yeah the cell proceeds until Cu2+ concentration are same on both sides, at which time voltage becomes 0. So, the lower concentration solution is the anode because that is where Cu2+ is oxidized from Cu while the higher conc. is the cathode because Cu2+ is reduced to achieve equilibrium. </p>
<p>How did people do on this test, and what do you think the various cutoffs will be? I personally think I got around 57 on MC and probably some random points off on FR on the explanations, assuming no stupid calculation mistakes.</p>
<p>which solid does not react with a small amount of 3 M HNO3?</p>
<p>potassium sulfite or silver chloride?</p>
<p>compounds of uranium 235 and 238 can be separated from one another by?</p>
<p>i put effusion</p>
<p>more questions later</p>
<p>I think the one about the 3M HNO3 was AgCl due to extreme insolubility of AgCl?</p>
<p>Test seemed pretty hard… i already know I missed 4-5 on the MC and those are only the ones i can remember…</p>
<p>The answer was AgCl, because it is not soluble in HNO3. The answer to the Uranium question was effusion.</p>
<p>On question number one for the free response, what structure did you guys give? A carboxylic acid w/ a ketone group or a dicarboxylic acid? Also what is the method to separate the product?</p>
<p>for question 1 … i gave a carboxylic acid with two carbons , so like H3CCOO-? and i’m not positive but i suppose fractional distillation is a good way to separate most stuff…</p>
<p>I think I had a dicarboxylic acid, and I think I remember in that part c(?) where they gave you the titration and asked you to find the molar mass again, I got that it was diprotic, which i thought supported the dicarboxylic acid structure I had. Oh and for separating the original structure from the newly created one, I said dissolving it in water since a dicarboxylic acid would be able to Hydrogen bond with water, but the ester that was created when it reacted with the alcohol wouldn’t.</p>
<p>Also, @BigNub, what do you mean by the dash in H3CCOO-? wouldn’t you need something replacing that - like H or something in order to make it a complete structure?</p>
<p>the molecule was definitely a dicarboxylic acid. when they asked for the two apparent molecular masses, the only way the second calculation matches the first one was if it were diprotic, hence a dicarboxlyic acid. </p>
<p>how do we distinguish between the fractional distillation and effusion?</p>
<p>fractional distillation separates based on differences in boiling point while effusion does so based on differences in molecular mass</p>
<p>Oh… well maybe i’m wrong,</p>
<p>but i’m under the impression that carboxylic acids dimerize in aqueous solution. Thus, the freezing point depression experiment should give a value for the molar mass that is twice as high as it should be (or to correct for it the van’t hoff factor = 1/2)? I’m not completely sure though… maybe i misinterpreted the results of the 2nd experiment because i don’t remember exactly what stuff was… </p>
<p>IDK about the structure being CH3COO-
by the dash, i just mean a minus sign.</p>
<p>if what i said above has any validity putting in that structure was the only way i could get it to work.</p>
<p>When they asked you to find the apparent molar mass twice, one with titration and the other with freezing point depression, were you supposed to get two answers that were almost the same?</p>
<p>it was the same molecule, so the molar mass was supposed to be the same, that’s my reasoning. the first time i did the calculations, the second molar mass was half of the first, but taking into account dicarboxlyic acid, the two should be about the same.</p>
<p>pretty sure you enrich uranium with gaseous diffusion.
come to think of it, I’m not sure if I put that. come to think of it, I’m not sure that was a choice.</p>
<p>the only choices that made sense for that question were effusion and distlilation</p>
<p>no, distillation does not make sense at all.
and was diffusion definitely not a choice?</p>