<p>I’m also sitting for the May 4 SATII (BioM,Chem,Physics) so I’m going a bit slow. Gonna be done with chapter 10 today (Princeton Review book). I’ll be solving both practice tests on May 4th and 5th after my SAT II’s…
SCARED!!! <em>fingers crossed</em></p>
<p>We haven’t done any labs this year cause they were all messed up. There seems to have been a lab question every year, so does anyone have suggestions for how to prepare? (Obviously I can’t do all the labs between now and the APs). Also, I’ll be taking the SAT II for Chemistry on May 4th. I’m really scared cause I got semifinalist for the Chemistry Olympiad, but I only got a 750 on the Barron’s practice!!! If I don’t get an 800, colleges might be suspicious. How accurate was the test, and do I have a good chance to get an 800 on the SAT II?</p>
<p>Can someone help me out? I have a PR book from 2004-2005 and a more recent (6th edition) Barron’s book… Which one should I use to hardcore cram for this exam? At this point I know it’s kind of far-fetched but I want to get a 5 if humanly possible considering how little I know.</p>
<p>I would read up as much as possible on some of the common labs. From what I’ve seen, these could include (this isn’t a comprehensive list):
-Titrations. Know how to set up the buret (rinse it with the titrant, not just distilled water, to prevent dilution and also remove the air bubbles from the neck and tip) and how to calculate the desired value (concentration, molar mass, etc.) based on the volume change. Be sure to also know how to read the volume in a buret, since it’s different from reading a graduated cylinder.
-Collecting a gas over water. Know how to use the ideal-gas law to relate the volume of gas produced in the tube over the water to the desired value. The purpose of lowering the tube such that the water inside matches the water level in the container is to allow the pressure in the tube to equal the atmospheric pressure. The vapor pressure of water must be considered when determining the pressure of the gas inside: P(gas) = P(atm) - P(H2O). Gases that are soluble in water, such as carbon dioxide and especially ammonia, aren’t good choices to be collected over water.
-Determining the mass percentage of an element/ion in a compound. Usually, you would first dissolve the sample and then use a salt solution to precipitate out whatever you want to analyze. (Ex: Adding AgNO3 to a sample containing chloride ions will precipitate AgCl). The precipitate is dried, and then weighed. You can determine the mass percentage of the ion in the precipitate because its formula is known, and use that to determine the mass of chloride ion. Then, you can use that and the mass of the original sample to determine the percent by mass of the ion in the sample.</p>
<p>A common lab question they ask is to describe the effect of lab errors on the results. (ex. whether the value would increase, decrease, or stay the same) For these, I would first set up the equation that is used to solve for whatever they’re interested in. After that, it’s much easier to isolate the effects since you have a place to organize your thoughts.</p>
<p>Thank you so much for this comprehensive list.</p>
<p>I have decided to take off Thursday and Friday to study for chem. Tomorrow I will try and learn these labs.</p>
<p>Again, the list was far from comprehensive. However, many lab problems they might ask can be reasoned out without significant experience in the lab.
It’s useful to also be familiar with calorimetry as well: how a calorimeter works, the purpose of using one, and how to use q=cm(deltaT) to determine the enthalpy of a reaction based on the temperature change and other quantities. A common source of error for a coffee-cup (constant-pressure) calorimeter is heat loss, since they are not perfectly insulated.</p>
<p>If anyone wants additional practice for a lab FRQ, here’s one that I wrote:
Assume you have 2 substances, A and B. The substances react to form substance C according to this reaction: A(aq) + B(aq) -> C(aq). One thing that can be observed in this reaction is a rapid, noticeable color change.
You are given some plastic disposable pipets, a stopwatch, some test tubes, and 0.10M solutions of both A and B.
(a) Explain how you could use the provided materials to determine the rate law for the reaction.
(b) Describe one potential source of error for the experiment and explain how they can affect your results.
(c) If the temperature is lowered, how will that affect the value of the rate constant? Explain.
(d) The reaction has an enthalpy change of +57 kJ/mol. How will lowering the temperature affect [C] at equilibrium?</p>
<p>@Dragon Which exam year(s) have you seen that experiment or an experiment like that?</p>
<p>(a) Rinse chemistry containers accordingly with distilled water… Place substance A in one test tube, and substance B in another test tube. Measure out equivalent amounts of substances A and B in equal amounts using pipets. Combine the two together, and record the time it takes for the color change to occur, as well as the concentration of C formed using stoichiometry and knowledge of volume.</p>
<p>Repeat the same procedure, except using a concentration of B twice as much as A.
Repeat the same procedure, except using a concentration of A twice as B.</p>
<p>Maybe I wasn’t specific enough, but I’m quite lazy rn to formulate an answer, haaa. But you would compare the data, once you collect it to compare the rates of formation to whichever ratio of concentrations when either A and B are held constant, find the power to which you raise it in order to equal the ratio of the rates of formation. That power is the order of the rate…</p>
<p>The rate law would be written so:</p>
<p>Rate = k[A]**
With A raised to whichever order it is determined to be . If it is zero order exclude from the reaction; most likely affected by a catalystt/intermediate!</p>
<p>(b) One source of error would be not stopping the timer in time. This would most definitely alter the data because the rate would be too big for a certain trial. Depending on which ratios are compared, this would cause the order to be a bit inaccurate, either too large or too big; again, too lazy to go into the specifics but hopefully i got the gist of it baaaah</p>
<p>(b) It will decrease the value of the rate constant. The temperature when increased always increases the rate constant, and when decreased, always decreases the rate constant. Temperature is the only thing that affects K.
(c) Since a positive enthalpy value indicates an endothermic reaction, lowering the temperature will cause equilibrium to shift to the left (more reactants favored), thus lowering the concentration of [C]</p>
<p>Anyone have some comprehensive cram packets? I think something that would be awesome would be to find every type of problem that could be on the test. There has to be over 100, but if you could get them down, you would be set (obviously knowledge of Chemistry needed to solve the problems would have to be known, but most of us have that stuff down). </p>
<p>I am going over a few tests and just writing down how to solve the problems, then I will be reviewing them later (like I said before, making sure that I know how to do almost every type of problem). I’m taking 5 exams and the SAT this Saturday, so I’m extremely overwhelmed right now.</p>
<p>I don’t have any cram packets, but I do have a link to this awesome website that has review packets and practice tests and other generally helpful stuff!
<a href=“http://apchemistrynmsi.wikispaces.com/[/url]”>http://apchemistrynmsi.wikispaces.com/</a></p>
<p><a href=“http://talk.collegeconfidential.com/ap-tests-preparation/921322-ap-cram-packets-list-yours-here-17.html#post15889427[/url]”>http://talk.collegeconfidential.com/ap-tests-preparation/921322-ap-cram-packets-list-yours-here-17.html#post15889427</a></p>
<p>@Niquii
No year in particular. I just modeled it after a lab that we did in class.
@Cindy
(a) Pretty much that. I don’t think you’ll need to determine [C] though.
(b) I was thinking something more along the lines of that the materials given are imprecise at measuring volume/concentrations, though what you have looks fine. Ex: You add 5 drops of A and 5 drops of B and measure the time. Then you add 5 drops of A and 10 drops of B (~ doubling **) and measure the time again. However, in doing so ** isn’t necessarily double what it was before, and [A] may be less due to the additional volume from B.
(c) You could further elaborate on your explanation. The rate constant would decrease because a decrease in temperature will lower the average kinetic energy of the reactant molecules. This results in 2 effects that will decrease k: the molecules have a slower average speed (due to lower KE), decreasing collision frequency and thus reaction rate; and a smaller proportion of the reactants will have enough energy to overcome the activation-energy barrier for the reaction, also decreasing the rate.
(d) Pretty much. Energy can be considered a ‘reactant’ in an endothermic reaction, so if temperature (therefore thermal energy) is lowered, the reaction will favor reactants.</p>
<p>@Dragon Ok. I read the lab you posted and I couldn’t think of any test in which CollegeBoard tested that topic in lab format.</p>
<p>guys, i don’t get complex ions D: anybody have a good run down on how to predict products & the charge on the ion?</p>
<p>Simple rundown, no knowledge needed explanation? I can do that! Memorize your ligands. Ligand are the “anion” of the ion. Your “cation” is your highly charged metal. [Al(OH)6]3- is a common way to write the complex ion. Basically you add the charge of your ligand which in the above case is -6 (OH has a charge of 1-), your aluminum has a charge of plus three. Add them together you get 3- so that is your charge of the complex ion. If you don’t know how many ligands you should have 2, 4, and 6 are “safe” numbers. </p>
<p>Say you’re a question four that goes like this:
Solution of copper (II) sulfate is mixed with NH3</p>
<p>You would write:
Cu2+ + 4NH3 ----> [Cu(NH3)4]2+</p>
<p>I highly suggest looking at about.com. They have a nice breakdown of complex ions full of resources as well.</p>
<p>It’s Monday. I’m terrified.</p>
<p>@Niquii77. For the complex ions, would it have to mention the terms concentrated or excess? Like in your example, it would be excess ammonia.</p>
<p>Also can you clarify a few things for me:</p>
<p>Is HClO3 a strong or weak acid. Some books have different answers.</p>
<p>And can you explain formal charge to me.</p>
<p>HClO3 is weak am i right? Perchloric is the strong one!</p>
<p>Thank for the complex ion explanation! 
</p>
<p>Are you guys going over FRQs? How far back should we look at them do you think?</p>
<p>Part 1
[AP</a> Chemistry Exam Review - Part 1 - YouTube](<a href=“AP Chemistry Exam Review - Part 1 - YouTube”>AP Chemistry Exam Review - Part 1 - YouTube)
Part 2
[AP</a> Chemistry Exam Review - Part 2 - YouTube](<a href=“AP Chemistry Exam Review - Part 2 - YouTube”>AP Chemistry Exam Review - Part 2 - YouTube)
Part 3
[AP</a> Chemistry Exam Review - Part 3 - YouTube](<a href=“AP Chemistry Exam Review - Part 3 - YouTube”>AP Chemistry Exam Review - Part 3 - YouTube)</p>
<p>READ THIS: I’ve seen this info on past FRQs, it’s not a big time committment and could earn you a point or two.
[Factoids</a> 2012 ? Nuggets of information that may help on the AP and SAT Chemistry Exams](<a href=“http://www.adriandingleschemistrypages.com/ap/factoids-2012-nuggets-of-information-that-may-help-on-the-ap-and-sat-chemistry-exams/]Factoids”>Factoids 2012 - Nuggets of information that may help on the AP and SAT Chemistry Exams - Adrian Dingle's Chemistry Pages)</p>
<p>Would boost your FRQ #5*** Good last min cram for the exam!
<a href=“http://www.adriandingleschemistrypages.com/apfactoidcolors.pdf[/url]”>http://www.adriandingleschemistrypages.com/apfactoidcolors.pdf</a></p>
<p>Nice summary of labs so we can BS our lab portion, cause who really remembers how to do some of these…All 22 that is fair game according to the College Board 
<a href=“http://www.adriandingleschemistrypages.com/aplabsummary.pdf[/url]”>http://www.adriandingleschemistrypages.com/aplabsummary.pdf</a></p>