Chemblog!

AP Solubility Titration exam was generally a good test for almost all. That bodes well for your AP exam score. The most common errors were the ones that I warned about (BECAUSE these errors are common...that means that you should take special care in the first MINUTE of EVERY test to write down the warnings and FOLLOW THEM): 1. not using the coefficient from the balanced equation in calculating the Ksp value 2. not starting from scratch for each SRFC table...S means "at the very START"
Some are getting into the habit of contradicting themselves right in the middle of their explanations. You could not possibly be reviewing these explanations because the contradictions are blatant (akin to increase means decrease). ALWAYS review your answers before handing in your test.
Overall, a good class average so far on the second-toughest test of the year, though.
Answers to previous AP exam hw through March 17 are posted. Do not bother to hand in hw after I have posted answers or handed the corrected hw back. Some of you are neglecting to hand in hw and your average is going to take a significant hit due to this foolhardiness. Don't ask to make it up now. You cannot. Meanwhile, others reliably hand in hw that is neatly and methodically done, which is excellent rehearsal for AP day since these questions are directly from past exams.
In the fourth quarter, each night's hw is worth about 40 points! An entire part II section EVERY night for about two weeks and change. If you are remiss then, you will fail the last quarter badly no matter what else you do- this HAS happened, sadly. If you do those practice exams honestly and make corrections, a score of 5 is nearly impossible to avoid.

AP Class: The thermo notes can be found on Edline.
Here are the links:
https://www.edline.net/files/1502bfd495f476f33745a49013852ec4/040105apn.pdf

https://www.edline.net/files/2b82de2d658a16143745a49013852ec4/040105apn.ppt

https://www.edline.net/files/c8329cf889edf6533745a49013852ec4/032306Thermodynamicsppt.pdf

Kudos to all 7 students who came in for extra help for Friday's exam. Extra help Thursday will be before (usual day 6) and after school. Make sure that your gas law explanations are thorough, down to the particle (molecular) level (formally called "collision theory" -FYI). If your answer doesn't EXPLICITLY relate molecular collision frequency and (kinetic) energy of molecular collisions to the variables P,T,V, and n of a given law, then you have not begun to EXPLAIN the gas laws. If you took good notes, you will already have the explanations written down and ILLUSTRATED from our class discussion. If you do not have the thorough explanations, make sure you write and DRAW the explanations and check them with me (if you are not sure of your answer) at extra help. Also, know how to apply the four tenets of K-M Theory.

Our next test will be given on Friday (more study time for you all). The test will cover objectives not tested on the last test
( K-M theory explanations of gas laws, real vs. ideal gases etc.) as well as heating cooling curves, specific heat capacity determination and finally just the intro material to this new unit: reaction rate measurements/units and reaction mechanism recognition (very brief, nothing complex).
Study carefully by pre-writing your answers STARTING WITH AN ILLUSTRATION and the DIRECTLY AND REPEATEDLY REFERRING to your illustration in your explanation. You are long past the point at which you don't employ this crucial test-taking skill regularly and naturally. Furthermore, clearly due to a lack of focusing on/underlining/circling/highlighting keywords in the questions, countless points were lost on the last test. If you are not answering what is being asked for, you will not receive credit (especially on the Regents exam). Again, this simple test-taking skill MUST be automatic and EARNESTLY applied on each test (even in other subjects- identifying what is specifically asked for can't possibly hurt you and it will definitely help you). It is sad to see people who do correct work for a question that isn't even there.

Considering all of the exams this year, the next two exams are the most challenging. You must know ALL of the material from the last acid base exam and subsequent material up to and including common-ion calculations for sparingly soluble salts (from today). There is no AP exam hw question tonight; just CONTINUE to study for the test by doing as many practice problems of every kind that you can find among the worksheets/notes/ text.
One of the keys to success on this test (as you noticed on the last test) is RECOGNIZING the problem type! Is it a buffer problem? a titration? a salt of a conjugate acid or base problem? The only way to know what you are doing is to get experience with each problem type and recognize the differences among them.

Buffer/Acid Strength/Titration tutorials:
http://www.wwnorton.com/chemistry/overview/ch16.htm

http://highered.mcgraw-hill.com/sites/0073656011/student_view0/chapter16/elearning_session.html

Here are a couple of links showing titration techniques and questions:
http://dvaction.northwestern.edu/mediaplayback.php?id=76#

http://www.uwplatt.edu/chemep/chem/chemscape/LABDOCS/catofp/measurea/concentr/titrate/titraon.htm

Gas Law etc. test tomorrow- Wednesday. In addition to the posted objectives, make sure that you know the tenets of kinetic-molecular theory and how they relate to ideal vs. real gases as well as how k-m theory relates to the gas laws (i.e. frequency and force of collisions are the two MAIN FACTORS that determine how P, V, n and T are related). Especially study your notes and all the examples that we did in class.
Good luck on the test.

AP: tomorrow, we have the second in our trilogy of acid-base equilibria exam: this exam encompasses the skills from the first exam (of course) and then expands to the following subtopics: explanation of relative acid strengths based on bond polarity and bond strength- make sure that you can DRAW the Lewis structure for any acid molecule and relate that structure specifically to source(s) of bond polarity and bond strength and how each affects acidity ; acidic/basic/neutral salts based on hydrolysis of water (be able to write equations thereof);bronsted acid-base and Lewis acid-base theory: meaning and applications; the meaning, application and relationships of Ka and Kb expressions and values; acid-base equilibria calculations using acids, bases, or salts; calculations involving buffers of a specific pH- the Henderson-Hasselbalch equations; calculations involving the addition of strong acid or base to a buffer solution or to a weak acid or base solution.
I was very impressed with the class performance on the last exam; I sense that you can make it two in a row; study hard!

Since we have a big acid-base equilibrium test on Friday, Day 4, we won't have any more daily AP Chem exam questions until this weekend. Good times.
I want you to focus on the hw/notes/tutorials from this unit/chapters 16 and 17.
After school tomorrow, we'll continue our AP exam review book sessions. Feel free to ask about anything that you didn't easily recall from our recent AP exam problem homework questions.

Tonight's AP Chem Exam question (due Tuesday) is posted on Edline; I'll post it on the class website later, too.
Here is the Edline link:
https://www.edline.net/pages/St_Anthonys_High_School/Classes/6068/03_06_06_AP_Chem_Exam_HW_quest

I keep having to correct a solubility curve error on the last exam so TAKE HEED!
In a question, when you are given an ACTUAL amount of solute dissolved in a given amount of solvent, DO NOT EVER SCALE the solute or solvent quantities UP or DOWN or CHANGE THOSE NUMBERS IN ANY WAY!!! If you do, YOU NO LONGER HAVE THE ACTUAL QUANTITIES THAT ARE RIGHT IN THE QUESTION. In every example that we did in class and in EVERY ONE of the DOZENS of worksheet examples, WITHOUT EXCEPTION, the ACTUAL amount of solute dissolved in THE ACTUAL AMOUNT of SOLVENT was NEVER ALTERED or SCALED in ANY WAY.

For example, if 10. g of sodium chloride are dissolved in 50. g of water at 80 degrees Celsius, then the solution is unsaturated. According to the solubility curve Table D, 40 g of NaCl would saturate 100 g of water so, proportionally, 20 g of NaCl would saturate 50. g of water. NOTICE THAT I DID NOT ADJUST THE ACTUAL AMOUNT OF NaCl or water !!! I simply scaled down the solubility curve to concur with the ACTUAL amount of SOLVENT-water = 50 g. So, since 10 g of NaCl are ACTUALLY dissolved and 20 g of NaCl would make a saturated solution, then the solution in UNSATURATED AND adding 10 more grams of NaCl would make the solution saturated.

The ONLY quantities that MAY be scaled are those on the experimentally determined SOLUBILITY CURVES. Those curves tell you the MAXIMUM amount of a given solute that can be dissolved in 100. grams of water ONLY!!! The curves do not reflect the TOTAL ACTUAL AMOUNT OF SOLUTE FOR ANY OTHER AMOUNT OF WATER; most questions do NOT give you a quantity of solute in exactly 100 grams of water (as I promised)!!!

Half of the students in each class are scaling the ACTUAL amount DOWN or UP to the amount of solute that COULD be dissolved in 100. gram of solvent. Furthermore, they DO NOT BOTHER TO SCALE THE AMOUNT BACK UP TO WHAT IS ACTUALLY IN THE QUESTION.
On the other hand, there are quite a few perfect or near perfect (write your UNITS!) scores so obviously some were well-versed and practiced on all of the given objectives.

A little worksheet practice BEFORE the test would have brought this scaling error to light. Obviously, some of you are just looking at the worksheet answers (or not) without doing the problems first. Unless you have the WRITTEN experience and reinforcement/repetition of the class material, you are NOT studying and your grades will be lower than they could be. This is the Math of Chemistry quarter and the math is below the 8th grade level; by regularly applying the math to these problem types, most students increase their averages significantly. Count on seeing this question type again on this week's test.

Because we lost another 2400 seconds of AP Chem instruction today (we have so little time left that every second counts; you have NO idea), there will be another two AP exam questions posted for hw. Today, we would have finished explaining the relative strength of any acid and then moved on to the "hardest" (tied for first, actually) question type on the AP exam: BUFFER solutions/Titrations. So make sure that you peruse (that does NOT mean skim; it means scrutinize/carefully read) text section 16.5 and do exercise 16.4 within that section- the answers are in the back of the text. Then, preview text section 17.5 .
Honors: E Period will have part 1 of the exam tomorrow and do part 2 sometime next week ( I'll let you know when) . B and D Periods will continue the exam with part 2 (20 minutes) after we have a half-period lesson tomorrow.

Enjoy your snow (half) day.

I received a link to a national essay contest on DNA. You can make a cool $350 (that's three-FITTY!) if you win. Use your well-versed writing skills to write about this most important molecule of life. The essay question choices are:

1.Why is it important for everyone to know about DNA and genetics?
In your essay, include what you think everyone should know about genetics. Consider how genetics plays a role in our daily lives. Why is genetics important now? How will it play a role in the future?

2.If you were a genetics researcher, what would you like to study (and why)?
Here is the link:
http://www.ashg.org/genetics/ashg/mentor/essay-contest.shtml