<p>when molecules are rearranged are IMF’s broken, or do only intramolecular bonds break?</p>
<p>@skateme: About your van’t Hoff factor question, if anything, volatile would mean non-polar. Dipole-dipole IMFs are relatively strong and as you said the IMFs should be rather weak, so they wouldn’t be polar and therefore would not dissociate.</p>
<p>@CORVIDS:
- You have to balance the number of moles of reactant with the stochiometric coefficients of the CO2 on the other side. Ignore the smallest molecules because they will have more moles, but the one with the greatest molar mass (choice E) will produce five times the number of moles of CO2 as the number of moles of that compound to begin with. Without doing any calculations B looks correct because the moles are in a 1:1 ratio, but I haven’t checked that out and I may not be correct, but hopefully you now know how it should be approached.
- You know it is 1x10^-2.5. I think you can just look and see which exponent value is closer (3 is closer to 2.5 than 1 is). Again I’m not 100% sure that this will always work, but if you think about it, it seems to make some sense.
- You can eliminate A because it has a van’t Hoff factor of 1 and the lowest concentration. You can also eliminate E because it has a van’t Hoff factor of 1 as well. I think for a best estimate you can multiply the molarities by the respective van’t Hoff factors (I know it is actually molality) to see which one will be biggest and it should be that one. You can compare them because they will all be done with molarity and even if done with molalities the largest one would still be the largest one. It should be B because it is 3<em>.25=.75 vs 2</em>.30=.60 for the other choices.
- Yeah, I think it’s Rb as well.
- Find moles Mg produced*2 (Mg2+ + 2e- –> Mg) –> moles electrons
You need 3 electrons for each Al3+ ion to get reduced so divide the moles of electrons by 3 to get the moles of Al and then convert to grams. I think it would be D, but there’s a chance I messed up the math (I did it without a calculator to practice for the test).</p>
<p>Let me know if you have the answers to these because I’d love to know if I got them correct!</p>
<p>So did we agree that the acid strength question is II and III? xD</p>
<p>Also:
What are some stupid recall questions that might appear?
This is directed towards Sparknotes’ SAT Chemistry Practice Test, but the SAT threads are always dead.
The questions that screwed me up were “_____ and copper mix to form bronze.” And “_____ and copper mix to form _<strong><em>.” “Petroleum does not make </em></strong> (answer was Rubber).” And some stupid stuff. . . </p>
<p>Anyone know any of these stupid trivia questions?
Does the AP test on these? Would I be better off asking in the SAT forum?</p>
<p>@coffee: Um, yeah… you’re getting a 5 haha. You got everything right. (:</p>
<p>You’re also really good at explaining. Thank you! By the way I think you might have read the first choice wrong for #3. CaCl2 (calcium chloride) has an van’t Hoff factor of 3, right? You still got the right answer though.</p>
<p>@Abrayo: I’ve seen a couple of those types of questions, but never any that were that arcane. Usually it’s easier questions like “____ is a component of natural gas,” and the choices are so different (like A. CH4, B. NaCl, etc.) that you can use logic and common sense to figure it out.</p>
<p>@CORVIDS: Right, I got confused on my solubility rules, I forgot that it was AP/H for Cl, I, and Br. I’m happy to explain anything else (it helps me a lot!) if you need it.</p>
<p>So for MC, focus points should be…</p>
<p>Atom Structure and Periodic Table
Bonding
Stoichiometry and Chemical Equations
Gases
Solutions
Equilibrium
Acid and Bases
Oxidation-Reduction Electrochemistry</p>
<p>For FRQ…
Equilibrium
Acid and Bases
Kinetics
Thermochemistry
Oxidation-Reduction and Electrochemistry</p>
<p>Right?</p>
<p>Can someone explain to me how to figure out the overall dipole movement of a molecule?</p>
<p>Are we tested with specific scientists and what they did and how they did it?
Is there a general list of these people?</p>
<p>I.e. JJ Thomson -> cathode ray tube -> discovered electrons. etc…</p>
<p>which prep book would you recommend for ap chem?</p>
<p>you have 1 day, just go to PR…</p>
<p>^^^^^question above</p>
<p>Some of the PR questions have me going “lol wut”</p>
<p>Can someone list out the molecules that can have incomplete, expanded, and odd octets? I know that…</p>
<p>Incomplete octets:
BF3
BeH2
Aluminum???</p>
<p>Expanded octets:
PCl5
SF4
SF6</p>
<p>Odd octets:
NO
NO2</p>
<p>What about NH3 and NO3? These always confuse me. And, an element such as Boron does not always have to have an incomplete octet right?</p>
<p>And I remember a periodic table exception where Cr and Mn have different subshells. Can someone explain that.</p>
<p>
</p>
<p>First you draw the lewis dot diagram. The atoms are connected by either polar or nonpolar covalent bonds. You look at the electronegativities of each atom. Compare 2 atoms at a time. The atom with the higher electronegativity (to the right on periodic table) pulls the shared electron closer to itself. Draw an arrow toward toward the stronger atom. Do that for each atom until you get arrows for each bond. Now you can see where the OVERALL dipole movement is.</p>
<p>IBr: dipole movement towards Br
BF3: no dipole movement because all arrows point out in a “triangle”
CH2Cl2: this has a tetrahedral shape. Dipole movement towards Cl</p>
<p>Sometimes molecules can have resonance structures so the dipole movement can vary.</p>
<p>@aStyle: Anything from the 3rd level down can have an expanded octet. NH3 has 3 single bonds and a lone pair, and NO3- has 2 single bonds and 1 double, so they both have complete octets.</p>
<p>Here’s an explanation of the Cr thing (found here <a href=“http://library.thinkquest.org/C004970/atoms/orbital.htm[/url]”>http://library.thinkquest.org/C004970/atoms/orbital.htm</a>)</p>
<p>Cr Expected: [Ar] 3d [+ ][+ ][+ ][+ ][ ] 4s [±]</p>
<p>Cr Actual: [Ar] 3d [+ ][+ ][+ ][+ ][+ ] 4s [+ ]</p>
<p>Several atoms, including chromium, copper (which fills the 3d subshell by taking an electron from the 4s subshell), and silver, violate the usual filling order to increase stability in filled or half-filled subshells. </p>
<p>There are so many questions I don’t know the answer to. It’s freaking me out a bit haha.</p>
<p>Are we tested with specific scientists and what they did and how they did it?
Is there a general list of these people?</p>
<p>I.e. JJ Thomson -> cathode ray tube -> discovered electrons. etc…</p>
<p>isk82live,</p>
<p>According to Princeton Review, if it’s in their book then you need to know it. </p>
<p>Here’s their list: (page 23.)
Dalton’s elements
Development of periodic table
Thomson’s experiment
Millikan’s experiment
Rutherford’s experiment
Quantum theory
Bohr Model
Hesienberg uncertainty principle
Broglie hypothesis</p>
<p>Isk8: I have never seen that stuff even in review books. Doesn’t seem like AP level question.</p>
<p>For the AP 2009 B, Question 1 C</p>
<p><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>It seems sort of wrong. There us no way to know which is in a higher concentration unless you know the equilibrium value.</p>
<p>Yes, we know we have a weak base, so it doesn’t react completely to form the conjugate weak acid. but unless the equilibrium value could be 1 x 10^-7 or 1.0 x 10^-11 we don’t know how much dissociates.</p>
<p>How do we really know for sure?</p>
<p>Uh, since it doesn’t give a K value, doesn’t it mean that they’re the same? Since, from the balanced equation, it’s a 1:1 ratio?
Or is the answer actually one of them?</p>
<p>This is a weak acid reacting with a weak base. I’d assume that more reactant is present so [C2H5NH2] is higher, but let me check to make sure.</p>
<p>My statement was correct (justification missing but was too lazy to do full blown explanation). Here is collegeboard’s words:
</p>
<p>Does anyone know if the 2008 MC was really easy or something?</p>
<p>I just took in and finished in like 50min (out of 90min given) and only missed 2 out of 75. But everyone has told me MC was the harder part…</p>