<p>Thanks, Abrayo.</p>
<p>Also, what are some important equations to memorize for the multiple choice? We’re given the rest on the FRQs, correct?
I’m sure we don’t need to know them all since we don’t have calculators (for example, the Henderson-Hasselbalch Equation is probably not needed?)</p>
<p>Can someone explain why HOBr determines the pH for Abrayo’s question on titrations.</p>
<p>At the equivalence point and ONLY then, the acid and base used in the rxn both cancel out (the OH anions in Ba(OH)2 and H cations in HOBr are canceled out), leaving the solution’s pH to be determined by the conjugate base of the weak acid. Ba(OH)2 is a strong base, so the conjugate acid (Ba2+) would be very weak and insignificant in the calculation for the pH. OBr- may be a weak base, but since its the conjugate base of a weak acid, it is still relatively strong in this solution and determines the pH of the solution (instead of water). Had this rxn been a strong A/B, the pH would have been determined by H2O at the equivalence point.</p>
<p>Though that explanation made sense to me, please feel free to ask questions/correct me if something is not comprehendable.</p>
<p>@chewydog:
Oh, I thought it was determined by OBr- because that’s what you’re adding, and you can add as much/as little as you want, and the pH would be according to the amount.
Could you provide an example when it would be the other substance that determines the pH, that you don’t add to your solution? (that is, something else is added to it, yet it still determines the pH.)</p>
<p>@Azyrk13:
Unsure. Everything except for the log equations, maybe?</p>
<p>Hey chewy, that was an excellent explanation. It makes so much sense, thanks.</p>
<p>IMO the Princeton Review SAT Subject Test Chemistry book is much more descriptive than the Princeton Review AP Chemistry book. I guess it makes sense because if one were to take AP Chem then he/she should already know everything from their textbook. </p>
<p>But if anyone doesn’t understand something go on wikipedia or look through PR SAT Chem. </p>
<p>:)</p>
<p>I’ll probably be cramming with AMSCO for APUSH facts and Wikipedia for topic trends.</p>
<p>My class is so behind. We’re doing an Acid-base chapter test this friday. gah. I’m so screwed.</p>
<p>Can anyone explain this question?</p>
<p>Which of these changes will cause the value of the potential for this halfreaction to be less negative? (E* = -0.28V for the reaction)
[the * is for standard potential]</p>
<p>Co2+ (aq) + 2e- –> Co (s)</p>
<p>A. increasing the amount of solid Co
B. Decreasing the amount of solid Co
C. increasing the concentration of Co2+
D. decreasing the concentration of Co2+</p>
<hr>
<h2>Also, why is the anode positive in electrolysis and negative in voltaic cell?</h2>
<p>Does anyone know where to get past MCs and answers??</p>
<h2>I’m using a review book by peterson’s and its pretty old (2005). I also don’t know if its accurate.</h2>
<p>Sorry for the bombardment of questions ;D</p>
<p>Happy revision :)</p>
<p>I believe the answer is C (increasing the concentration of Co2+) because of Le Chatelier’s Principle. Shifting the reaction right would cause the potential to become more positive/less negative.</p>
<p>The anode is negative in a voltaic/galvanic cell because electrons flow away from it towards the positive cathode. The anode is positive in an electrolytic cell because the cathode is negative, so energy is required to “push” the electrons towards the negative cathode. Just remember how negatives repel and negative (electrons) are attracted to positive.</p>
<p>Thanks kimberlyy. </p>
<p>But, I don’t understand why shifting the equillibrium to the right make the potential less negative?</p>
<p>If you add a little bit of Co2+ it will react with the electrons to shift a little bit to the right.</p>
<p>Co2+ reacts with some e- to produce Co. This increases Co, while decreasing the electrons.</p>
<p>Less electrons means less negative, because electrons have a negative charge.</p>
<p>Wouldn’t the answer be D decreasing [Co2+]? Here it’s not really a question of what makes or positive. It’s more what decreases the magnitude of the negative potential. If you have less reactant, you’ll make less product and the neg potential can be thought of as one of the products.
I could be missing something here but that’s how I would answer it.</p>
<p>Does anyone else have a PR book that lablse Osmotic Pressure as lambda and not pi? Or does it not matter? I always thought lambda was wavelength. </p>
<p>Also, one of the solubility rules states that salts containing chlorides are soluble except those containing Ag+
But, the PR Book just showed me the common ion effect between AgCl and NaCl…So if it is not soluble, then how did that example make sense?
In addition, can someone give me a run-down of the common ion effect? I think I have it, but I’m not 100%.</p>
<p>@Monarchy
lol, you’re welcome. I’m glad it made sense :D</p>
<p>@Abrayo
HOBr was originally in the solution and the titrant was barium hydroxide, meaning that Ba(OH)2 is ADDED to HOBr. I checked today with my chemistry teacher and he said my explanation was correct. pH is related to the amount present, so you’re right there, but it depends upon the concentration of OBr- present in the solution. </p>
<p>
The concentration of hydrogen from HOBr would determine the pH up until the equivalence point because all hydroxides from Ba(OH)2 would be used up until past the EQPT. Then, after the EQPT, the solution’s pH would be determined by the amount of excess hydroxide present from Ba(OH)2 because at and past the EQPT, the hydrogens are all used up by the hydroxides to make water.</p>
<p>@orangefoot
There’s a link from skateme in this thread…I think he/she posted it a week ago or so.</p>
<p>@Azyrk13
My PR book represents osmotic pressure with the pi symbol. Which edition is yours?</p>
<p>Guys, what are my chances of getting a 5 on the AP Chemistry exam based on MC?</p>
<p>On the 2008 I got a 54 raw on MC.</p>
<p>On 2002 I got 52 raw on MC.</p>
<p>On 1999 I got 46 raw on MC.</p>
<p>I really want a 5, but the free response is killing me. It’s not necessarily hard…I know the information. When I see the answer key I feel soo stupid because I make the questions more complicated than they are, but is there anything that I can do to improve it? With my raw scores on MC, what would I need to score (out of 100%) on the free-response…roughly…to get a 5? What about a 4?</p>
<p>Thanks! </p>
<p>Also if anyone wants the links to the 2002 AP Exam and answers:</p>
<p>Exam: </p>
<p><a href=“http://griffithchem.com/AP/AP%20Tests/AP%202002%20Multiple%20Choice%20Exam.pdf[/url]”>http://griffithchem.com/AP/AP%20Tests/AP%202002%20Multiple%20Choice%20Exam.pdf</a></p>
<p>Answers: </p>
<p><a href=“http://web.me.com/dbyrum/Ris/APChem/page24/files/AP2002_MC_ANS.pdf[/url]”>http://web.me.com/dbyrum/Ris/APChem/page24/files/AP2002_MC_ANS.pdf</a></p>
<p>New Scoring Guideline:</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>Haha I’m a dude. To improve your free response score you should simply do more free response questions. Do all of them for the last 10 years and you’ll be fine. You’ll know what they expect in your answers that way.</p>
<p>Do we need to know osmotic pressure? My teacher said we don’t need to know it so she didn’t go over in class.</p>
<p>Btw, are we allowed to see the formula sheet for the multiple choice? (sry if this has already been answered already a few pages back)</p>
<p>I guess osmotic pressure could be on it, but it’s really not that hard. Although in my class we took three practice tests (official previous tests from college board) and it wasn’t on any of them, so maybe not.</p>
<p>And no, we have no formula sheets for the multiple choice, which is really a pain!!</p>
<p>Hello guys. Please help me out on a AP Chem FRQ: 2010B #4(b)(i) (<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>
<p>“Excess concentrated aqueous ammonia is added to a solution of nickel(II) nitrate, leading to the formation
of a complex ion.
(i) Balanced equation:
Ni2+ + 6 NH3 → [ Ni(NH3)6]2+”</p>
<p>…Where the heck did they get [Ni(NH3)6]2+ from? Are you supposed to memorize complex ions now? Please help.</p>
<p>I have the 2009 PR book.</p>
<p>Okay, can someone explain this to me:
A 50.0 mL sample of distilled water is added to the solution described in part (b), which is in a beaker with some solid AgBr at the bottom. The solution is stirred and equilibrium is reestablished. Some solid AgBr remains in the beaker. Is the value of [Ag+] greater than, less than, or equal to the value you calculated in part (b) ? Justify your answer.</p>
<p>CB Answer: The value of [Ag+] after addition of distilled water is equal to the value in part (b). The concentration of ions in solution in equilibrium with a solid does not depend on the volume of the solution.</p>
<p>Why does it not depend on volume? I thought if you added water, the concentration went down?
I really need to work on solutions and Ksp…I’m bad at those for some reason.</p>
<p>If this was answered before, I’m sorry! Does anyone have an approximate breakdown of the typical AP Chemistry Curve? Not using percentages but using approximate scores.</p>
<p>Ex: 80 - 140 5 etc.</p>