AP Chemistry Review Thread

<p>I already took the AP exam last year, but I've signed up to take it again this year, hoping for a higher score.</p>

<p>My biggest problem is that I have done maybe 1/6 of the total labs that we were supposed to do. Last year, we ran out of time so we didn't do any lab past the 2nd six-week (out of 6 grading periods).</p>

<p>Does anybody know any websites with good lab overviews? The lab question was what got me last year, and I think that's what will get me again this year, too. If anybody can help, I would be very grateful!</p>

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Ok, question. I am doing the 2003 Free response. Q3 is kinetics. There is a table of concentrations and initial rates, but there are 3 reactants. Do both of the other 2 reactants need to be constant when you find the order of the third, or does only 1 need to be held constant? I can't figure out how to do it.

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<p>You find the first one Br- which has one that's different and the other two that's constant. Then when you know that order you can use differing concentrations of Br- AND BrO3- to find BrO3-'s exponent because you already know the exponent to plug in.</p>

<p>So for BrO3- when you've found Br-'s order to be first, use exp 2 and 3 which will then be (5 x 10^-4) / (3.75 x 10^-4) = (.005)^x (.002) / (.0075)^x (.001)</p>

<p>and solve for x.</p>

<p>edit: note - the (.002) and (.001) isn't part of the exponent on the numerator or denominator as they are concentrations themselves.</p>

<p>"mentioning LDF won't hurt you though. I.E., H20 has LDF as well as H-bonds, while CO2 only has a dipole and LDF."</p>

<p>H2O has LDF and Hbonding. CO2 has only LDF (no dipole - its linear.) Explaining their properties should mention all of the above. Mentioning LDF's will hurt you if you are talking about network covalent, ionic, or metallic substances. LDF's are intermolecular forces. NC, ionics, and metallics aren't molecules.</p>

<p>Sorry if I seem obstinate, I'm just trying to help.</p>

<p>fhq - There should be a set of 2 experiments where 2 reactants are kept constant. Solve for the order of the third reactant. Once you have that order, you don't have to hold the third reactant constant anymore to get things to cancel - you can plug in actual numbers.</p>

<p>I'm confused about how to figure out the n number of electrons transferred in a reaction?</p>

<p>Can someone give me a (preferably) simple example?</p>

<p>Thanks!</p>

<p>fhq - use exp 1 and 2 to find order of Br-. Then use exp 1 and 3 to find order of BrO3. Then use exp 3 and 4 to find order of H+. (The bromides will cancel because they're held constant, but you need to plug the already determined order of bromate in to the equations.</p>

<p>Hey, thanks for the explanation of the rate laws on 2003 #3. Makes sense now.</p>

<p>Fe(Cl)2 is yellow and Fe(Cl)3 is orange. Right?</p>

<p>And remember the product of Ka and Kb must equal 1 x 10^-14
the sum of pH and pOH must equal 14</p>

<p>Just remember 14.</p>

<p>Does anyone have any cool ways of remembering all the compounds' shapes (e.g: bent, tetrahedral, octahedral)... that alone could be the death of me tomorrow.</p>

<p>hey, I have a question for you guys. I'm studying from the Barron's review book for chem right now and it appears that the only titration problems they talk about and actually calculate are strong acid-strong base ones. But my teacher made a big deal also about strong acid-weak base and vice versa titration problems. So why would the review book not cover this topic, or is my teacher just overly preparing us? Should I still take time to study it? Thanks!</p>

<p>To find number of electrons, balance the individual half reactions. The two half reactions must have the same number of electrons, find common denominator as needed.</p>

<p>Ex: (A --> B + 2e) x 3
(3e + C --> D) x 2
Yields a six electron transfer</p>

<p>I'm not sure I've ever seen a strong-strong titration on the FR. Generally they are strong-weak.</p>

<p>Hey, specify, did you get that Br- is first order, Bro3- is first order, but i can't figure out what H+ is...</p>

<p>Thanks gfaith!!!</p>

<p>STrong acid-strong base titrations are much simpler and easier than when one is weak, because you don't have to deal with all that Ka/Kb stuff.</p>

<p>@Austin solution or solid?</p>

<p>Can someone clarfiy: do we no longer have any choice of what problems to do in FR?</p>

<p>its likely that a strong acid weak base of vice versa will be 1 on the FRQ this year (that or Ksp, or Keq/Kp)</p>

<p>learn it, just react leftover weak base or weak acid with water and solve for pH using the Ka or Kb.</p>

<p>Austin - no clue on the colors off the top of my head, but I gotta say, they don't really get that picky. For example - Cu1+ tends toward the green, Cu2+ tends toward the blue, but generally you could say bluish green for either and they would take it. :-) For Fe, it's probably sufficient to know its ions are in the orange-reddish brown range (think rust!). That and FeSCN2+ is a distinctive blood red.</p>