<p>@huehuehue</p>
<p>I think it may be Fe3+.</p>
<p>Fe(H2O)63+ is colorless in some solutions, but can become amber yellow upon hydrolysis. I don’t know if anyone else did this but when I identified the necessary vials to make the yellow solution, I dumped the entire vial into the other one and the color was a dark amber, almost orange. In the spotplate it may have looked light yellow. </p>
<p>Also, Fe3+ is capable of making a Prussian blue precipitate and that blue was definitely a precipitate because I recall gel-like specks slowly disappearing as I gradually add drops of the fourth unknown. Hmm, I did not see bubbles at all. I also smelled everything and no odors (lol literally had my nose in the spot plate and when I looked up, the proctor was staring at me, I think she thought I was snorting chemicals).</p>
<p>I also considered vanadium since +4 is blue and +5 is yellow but no oxidation state is colorless and also, that blue was a precipitate!</p>
<p>@gertrude
Changing temperature will also affect pressure and since you are graphing T and V, changing T will also affect P and this could negatively impact results</p>
<p>I’m at 52-54 (depending on the debates?) on the MC and 86% on FR, with okay on lab. Is this enough for camp (harder year…)</p>
<p>Meh, I did horrible. I didn’t get my test back but I probably got around 35.</p>
<p>@Sophia</p>
<p>Why would it change pressure? I’m pretty sure that v/t=v/t holds…Charles law?</p>
<p>Also the lab was a iodine clock reaction basically. The substance was iodide ion, and the other one was probably the peroxide since it made bubbles. The third was starch, which complexes with the triodide and the last was a reducer, probably the thiosulfate.</p>
<p>@FlyingWombat Same, but please realize that you are competing against hundreds of other amazing chemistry students across the nation and that it is perfectly fine if you didn’t do so well. :)</p>
<p>@Sophia, I2 is aqueous iodide solution is amber orange. When you dumped the two vials together, some iodide oxidized to I2 and the excess I- causes the orange color (due to I3- complex formation). Aqueous I2 absent excess I- is yellow, which is what most people observed when mixing in the reaction wells.</p>
<p>what would a ~42 on MC and ~50% on FRQ get me?</p>
<p>12 has to be D. Normalizing the pressure would do literally nothing to the graph since there is no reason that the experimenter would allow the syringe not to reach equilibrium at surrounding pressure. Also, if the volume was adjusted for pressure, then the focus of this experiment would not be finding the value of absolute zero with a volume-temperature graph, but basically using a pressure-temperature graph (because of the assumption that volume doesn’t adjust to equilibrium pressure) to then make a volume-temperature graph.</p>
<p>As for 12, Helium is a gas at all temperatures above 4K, so it would fill up the entire volume of the 10-mL syringe at all temperatures in the experiment. This entirely defeats the purpose of “measuring the volume” of the gas (i.e. the problem statement implies V is held constant). So I have no idea what they are looking for.</p>
<p>With that said, the answer is probably D because deviations from ideality at low temperatures need to be taken into account so extrapolating only from 0-100C temperatures would not give an accurate value for a real gas.</p>
<p>For lab two, the substance was DEFINITELY iodine, and it was a redox reaction. I almost put vanadium too put the blue from vanadium cations is significantly brighter. There’s a video of the second part of the lab in one of the wikipedia links below. I- ions form a colorless solution, then are oxidized to I3- which forms a yellow to red-brown solution depending on concentration, which then reacts with starch to turn a deep dark blue.</p>
<p>[Iodine</a> test - Wikipedia, the free encyclopedia](<a href=“http://en.wikipedia.org/wiki/Iodine_test]Iodine”>Iodine–starch test - Wikipedia)
[Iodine</a> clock reaction - Wikipedia, the free encyclopedia](<a href=“http://en.wikipedia.org/wiki/Iodine_clock_reaction]Iodine”>Iodine clock reaction - Wikipedia)</p>
<p>I’m pretty sure I bombed the first lab though, very possibly 1000% percent error -_-</p>
<p>For #45, wouldn’t the answer just be A? Core electrons stay constant across a period, and my impression was that valence electrons can’t shield each other…</p>
<p>valence electron shielding varies though with additional e- repulsing each other</p>
<p>this @0:40 seems to support that pressure is constant regardless of normalizing.
[Charles</a> Law and Absolute Zero - YouTube](<a href=“Charles Law and Absolute Zero - YouTube”>Charles Law and Absolute Zero - YouTube)</p>
<p>Yes I don’t understand why pressure changing will be an issue. It’s the whole reason why we use gibbs free energy and enthalpy rather than helmoltz free energy and internal energy for chemistry; it’s enough to assume that pressure is constant in most of the processes.</p>
<p>The chemical in the solution lab was indeed iodine. Our coordinator told us the contents of every solution right after we completed the lab portion - two of them were water haha.</p>
<p>Anyways, I’ll try to make a list of the mistakes I know I made on the free response later, and check my multiple choice.</p>
<p>EDIT: By the way, I don’t get number 8. Both sodium peroxide and potassium superoxide are used in self contained breathing equipment for that purpose.
Na2O2 + H2O → NaOH + 1/2 O2
Na2O2 + CO2 → Na2CO3 + 1/2 O2
2 KO2 + H2O → 2KOH + 3/2 O2
2 KO2 + CO2 → K2CO3 + 3/2 O2</p>
<p>Reaction of sodium peroxide with water gives hydrogen peroxide, not oxygen.</p>
<p>@U235
When I search “sodium peroxide self-contained breathing apparatus” on google I keep seeing problems that have to do with how sodium peroxide is often used in self contained breathing apparati.</p>
<p>Guys can someone help me out for these MC questions:
30. Given the formula ln (k1/k2) = Ea/R (1/T-1/T), isnt the answer choice B?
32. Can someone show me how to solve this problem?
45. Is the answer choice just I and II or all three?
49. I tried the VSEPR theory for p4 and I got a tetrahedral, with three single bonds and one lone electron pair. Isn’t that 3 sigma bonds?</p>
<p>Also does anyone think the cutoff might be lower than the 43 for 2010? I really hope this MC was more difficult than the 2010 one…</p>
<p>@Ramboacid
Shielding does not actually mean electrons are physically blocking each other, but rather, electrons canceling out a bit of the nuclear charge. Thus, electrons with the same n quantum number are able to shield each other.</p>
<p>thanks for clearing up lab 2. Hmm should have put the chemicals on my skin and tested to see whether or not my skin would turn orange 
… Only kidding. Maybe. last year I spilled iodide solution all over my wrist and I had an orange stain the shape of a wrist watch for 3 weeks.</p>
<p>@justin
I personally think this is slightly harder than 2010. So maybe 42 or even as low as 41.</p>