Chemblog!

Thanks to the dedicated AP Chem class for coming in this weekend to take a real, timed, proctored, full-length AP exam. I think that the test experience mutually benefited us: You and I both have a good idea of how you rate on this test but, much more importantly, you can now analyze your errors and improve your performance over the next ten days.

Error analysis requires two initial steps: 1. Identify the problems that you got wrong and discover what caused your error (misread/careless error/lack of knowledge) and 2. identify problems that you GUESSED CORRECTLY; that is, you didn't know the answer directly but you guessed right anyway; then, review the subtopic involved in that question so that you do not have to guess next time.

I expect you to ask me about any question that gave you trouble/on which you made an error. Once we clear up these mistakes, you can go into your May 10 exam a much stronger and well-prepared candidate.
Though you may have done well, you want to know that you can COMFORTABLY get a 5 on this test. Scoring a borderline 5 (107 - 115) on the 2002 exam may or may not get you a definite 5 on the 2006 exam. You DO have time to pump up your performance into the higher-echelon 5 region.

In addition to our classwork, use your "5-Steps" review book and , over the next ten days, make sure that you have answered EVERY part I question in that book (including practice exams at the end). All of the answers are explained and the questions do not require the use of a calculator.

I AM AVAILABLE TO ANSWER YOUR QUESTIONS PRACTICALLY 24/7 (including email) UNTIL THE EXAM- TAKE ADVANTAGE OF THAT AND DON'T WORRY ABOUT BEING "WRONG"- JUST CLEAR UP ANYTHING ABOUT WHICH YOU ARE NOT CERTAIN. I AM YOUR ADVOCATE.

You are in striking distance of getting a guaranteed 5 on this exam. Persevere over the next ten days and you will achieve what less than ONE percent of all high school students have achieved!

Here are some of the errors that I have encountered on the organic NAMING/DRAWING test:
The NUMBER ONE error among those who did not do well involves the NUMBER ONE rule and FIRST STEP in naming a compound (SEE NOTES!!!)- find the longest continuous carbon chain THAT CONTAINS/INCLUDES the main functional group (e.g. acid,ketone,aldehyde,alcohol,amine,halide, if any) and NUMBER THE CARBONS on THAT CHAIN!!!!
Those who failed did not NUMBER their carbon structures and tried to do all of the figuring in their heads (which leads to careless errors!). This is a VERY POOR test-taking practice. HOW MANY times have I told you to write/draw things out?
STOP SHOOTING YOURSELF IN THE FOOT and start taking my test-taking advice seriously or you will continue to cause yourself to fail.

The co-NUMBER ONE error is that many of you do not know the meaning of the term ISOMER! I spent two days giving examples of isomers! "Iso" means SAME!!! An isomer of a compound has the SAME EXACT IDENTICAL MATCHING chemical FORMULA but a DIFFERENT bonding arrangement. NEVER FORGET THAT AGAIN.

You had twelve days to prepare for this basic memorization exam (no higher-level thinking required at all) plus two full class periods for review and (poorly attended!) extra help sessions AND I put some problems from the worksheets VERBATIM on this test. Do not EVER blow off another assignment or put it off until its to late to learn it.

On a positive note, about half of the class did quite well and it is obvious that they studied by adequately PRACTICING/APPLYING the notes and other information (which is the ONLY way to study).

I'll post the rest of the acid/base files (review book assignment and answers) as well as our NEW unit (REDOX) notes this weekend. You all did great on the kinetics/equilibrium test before vacation- get back to work and pick up your averages.

12 days to go...
Rightfully, most of you are getting your hw in and are showing an effort (which is beyond crucial at this final stage of the class). You will not be reminded or warned if you do not hand in your hw ON TIME. As I have repeatedly warned, you may see an F for the 4th quarter if you continue to not hand in your hw. Doing the hw and not handing it in is masochistic. Good day.

Major errors on the part I exam:
Q75: I knew that this question was coming so I did it TWICE IN CLASS LAST WEEK! Most of you did not think/draw/show work/read your direct example in the notes otherwise you would have known the correct answer.

To purify an ore of a precious metal (like Cu), in an electrolytic cell, make the impure ore the ANODE and put a pure bar of the precious metal at the cathode; then electrolyze the sample and the precious metal will oxidize into its cations which will then be reduced onto the pure metal at the cathode. The contaminating metal will either react with the water of the solution or will not be as easily reduced at the cathode (by choosing an appropriate applied voltage to the cell) so it usually ends up as "mud" at the bottom of the cell. DON'T FORGET THIS AGAIN.

AP: make sure that you check this blog daily as I will use the "power of the blog" to live blog the common errors that I see among your homeworks. This way, you can alll learn from each other's errors and BE AWARE of these errors as you take the real AP exam in 13 days.

#1 AP HW errors:

1- many of you misread the question on which solution would have the highest H2O vapor pressure; you should have reasoned that the colligative property of "vapor pressure depression" is solely dependent on the number of dissolved particles per unit volume of solution. Since ethanol does not ionize in water, its solution has the lowest concentration of dissolved particles (compared to the other salts or weak acid) and therefore had the LEAST vapor pressure lowering effect i.e. the highest Pvap of H2O. Many of you answered in terms of which substance had the weakest intermolecular attractions (ignoring the fact that these were SOLUTIONS, NOT pure substances) and thus reasoned that ethanol had the weakest intermolecular attractions and the highest vapor pressure at a given temp, WHICH IS TRUE BUT IRRELEVANT. THE MOST IMPORTANT RULE OF ALL ON THE AP EXAM IS TO ANSWER EXACTLY AND ONLY WHAT IS ASKED FOR!

2- many of you STILL do not know the logic of molecular geometry EVEN THOUGH ALL of the molecular geometry GRAPHICS have been on the class webpage since DECEMBER. Look at them; draw them out; KNOW THEM.
SeF4 has 34 valence electrons of which 32 are used on the F octets so the Se has ONE lone pair. That is the classic AX4E general formula which is NOT trigonal bipyramidal (AX5 ONLY!!!) but rather a SEE-SAW or SAW- HORSE shape. Trig Bipyramidal is the ELECTRON GEOMETRY of that molecule.
DO NOT CONFUSE ELECTRON GEOMETRY WITH MOLECULAR GEOMETRY- THEY WILL BE DIFFERENT WHENEVER THERE IS/ARE LONE PAIR(s).

3. One important note on semantics: I worry that even AP readers may incorrectly interpret the phrase " delta G increases". Some of them may think that you mean that delta G becomes more negative from that statement (and THEY would be wrong, mathematically).
Instead, to take no chances, always write either delta G BECOMES MORE NEGATIVE or delta G BECOMES MORE POSITIVE depending on your calculation.
Also, avoid using the phrases "more spontaneous" or "less spontaneous" because a given reaction either is spontaneous or non-spontaneous; instead, use "more product favored" or "more reactant favored".


4. Remember, the rate of a reaction depends on the fraction of reactant particles that meets or exceeds the activation energy barrier. Activation energy of a given reaction HAS NOTHING AT ALL to do with delta H, delta S, or delta G of that reaction. Therefore even the most spontaneous reaction in the universe (large negative delta G) may occur ridiculously SLOWLY (very large energy of activation) at , say, room temperature.

5. When a photon is emitted or absorbed by an atom, state the LAW OF CONSERVATION OF ENERGY FIRST - AP readers LOVE that law: "energy cannot be created or destroyed"; that is why the energy of the photon emitted must equal the difference in energy between the energy levels of the electron transition.

Thanks to Paul, the only member of our class to point out that AP Exam Part II A question 3 did not have the relevant and necessary chemical reaction in the question.
I have updated that question with the equation: 2 A + B --> C
which is required in order to answer part c of that question.
Recall the very first objective in kinetics, which relates the rate of (dis)appearance of one substance to the rate of (dis)appearance of another substance. (If you don't recall that important yet very simple relation, there are examples in the notes and text). A balanced equation is a must to answer such a related rate question.

Curious how there are just two days left to complete the assignment and this is the FIRST that I am hearing about that misprint. If you have questions about the assignment, get them in BEFORE Sunday or you most likely will not receive a response.
I know that many (maybe most) people cram but MAKE SURE that such a "concentrated" effort does NOT detract from your understanding of the material. The course is almost over; there is no time to procrastinate.

Our supermegaextended vacation is winding down...I know: it hurts, it HURRRTS!
Anyway, get a hold of yourself and ease back into Chem this weekend.
AP: under 20 total days left till "the show". I put up an entire course "quick" review sheet in the general files section (at the top of the files section). Check it.
Also, the Nuclear notes and supplements are up for our Day of Nuke on Monday.
I also posted some Organic supplements. To wrap up the course, Nuclear/Orgo/Transition Metals/Electro will be on our next day 4 exam.
To get right into review this week, we will complete one part I and two or three part II exams between class time and hw; get that accurately done hw in daily- that will strongly influence your quarter grade. These exams (along with all of your painstaking work on KARMA and the other three AP exams) will PRIME you for next Saturday's (04/29) REAL practice AP exam. Your grade on that exam will definitely show you where you are and what you need to do with your remaining 11 days.

Honors: Those helpful Organic-Naming mnemonics are now posted! Your orgo test this week will test your ability to name and draw the structures of organic compounds. This will be a 100 point written test so make sure that you are an organic expert by Wednesday.
You CANNOT learn organic only by reading about it. You must HEAVILY practice drawing the compounds based on their IUPAC names and vice-versa. Merely looking at correct answers will not give you any useful experience, ability or confidence. Remember, WRITING/DRAWING is studying. Reading is pre-studying.
After our (I hope) successful orgo test, we will complete our acid/base/salt unit by the weekend. Check out the Bronsted conjugate acid-base worksheets.

Now back to our regularly scheduled vacation...zzzzzz

Before (or during) your AP break assignment, you should consult your "5 Steps to a 5" Review book: at the end of each unit is a section called "common errors to avoid". For example, the most conspicuous error listed (which was a common error on our exams) is the (lack of) use of the BALANCED stoichiometric equation in solving a given problem (especially in thermo).
The lists of errors, which were compiled by experienced AP exam readers, is the most valuable part of that review book. Be wary of these errors as you do the problems.

As my cousin enthusiastically says when good news ensues: are... YOU... KIDDING ME??!!!
All 3 Honors classes put in a powerful and excellent performance on the Kinetics/Equilibrium/deltaG unit exam.
All 3 Honors classes tied with a 96 test average per class.
It is very difficult to achieve a perfect score on a Le Chatelier exam but there were many 100's. Thanks for demonstrating great test-taking skills on your test papers, also!
An awesome start to your 4th quarter. Keep this up and you may have the highest chem averages ever!
Enjoy your break. Happy Easter to you and your families!
Mr.C.

AP: One of the objectives that was not tested on the last test but that we went over in class last week was the effect of pH on the solubility on certain insoluble salts. On tommorow's exam, there will be a question regarding that concept and why it occurs.

Honors: regarding the Kinetics and Eq. Worksheets/Practice Test worksheet from 04/05/06, on questions 27,30, and 43, just go to either Table E, which will tell you the relative solubilities of those salts (the more soluble, the greater the Ksp value) or go to Table M (I'll refer to that tomorrow in class) which gives you the Ksp values of certain insoluble salts.
I'll post the worked out solutions to the Ksp worksheet (also 04/05/06) this afternoon and then you can see how they are solved (same as the examples in the notes).

Theeaaanks.

We have a lengthy 12-day vacation commencing on Wednesday. I wish that I could change the extreme paucity of time that we have to learn so much material but that is not within my control. Here's the straight story for what that means for our classes:

AP: The AP class will have literally 12 school-days to complete the course before exam day, May 10. (Do not miss ANY of those days for any reason.) On Saturday , April 29 at 10 AM in the Board Room, we will have a REAL released AP Chemistry exam from 2002 (do NOT do this exam beforehand or you will ruin your chance of knowing what you are going to get on the 2006 AP exam). We will then immediately score the exam. Do NOT miss that test; it will be conducted in the exact same manner as your real exam- same timing, same proctoring instructions, same everything (except two hour later start time - no biggie). You will have the golden opportunity to make test-taking errors that you will have time to address/correct in the 11 days to the exam. I can even schedule one more mock exam for the next weekend but it may have to be on that Friday afternoon or Sunday. Bottom line, nothing will be a more realistic assessment of your AP Chem ability than the test on April 29. Don't miss it.
There is much to accomplish and perfect over the vacation. The vacation assignment consists of three complete part II AP exams (questions that you should be well-accustomed to by now via the hw) and some lab-based questions and project KARMA. I will post a list of this year's exams in case you need a reprint of one or more of them. The KARMA assignment will especially long for those who made many errors this year without taking the time to come in to extra help to make the corrections and learn from those errors; but look at the assignment in a positive manner given that, if you do the corrections carefully and thoroughly so that you will not repeat those errors, you stand a MUCH better chance of achieving a 5 on the AP exam. This will vindicate your class average from earlier quarters and you will objectively achieve in this course. Naturally, if you need help in figuring out what you did wrong, you can email me over the break; however, review your notes and read the relevant text sections first.
Warning: do not come back to class without that correctly completed project. Start early and work steadily on that assignment throughout the vacation. It CANNOT be completed in a weekend. Keep in mind that , in 35 days, the pressure will be COMPLETELY and suddenly off. Do not give up before then; keep the pressure full on. I have had students who quit from sometime during the second semester and, the day after the test, they had nothing but depressing regrets and self-blame. They couldn't even grasp why they had been so negligent (they didn't even bother to come in for a last-minute refresher the day of the test!); the sad fact is that they can never get a second chance.

Honors: We must make up for the lost time and future lost time (fire drills and who knows what else) by completing the memorization part of the Organic Chemistry unit. I will post tutorials, worksheets and a practice test with answers. As soon as you come back from vacation, you will be tested on the assignment (written test) before we continue with acids and bases. The assignment will require NO EXPLANATIONS. The Organic Chem assigned will just involve memorization of names, rules, and reactions.
Work through the assignment gradually over the 12 days. Email me if you need some clarification.

When we come back, perhaps I will be able to teach without a hoarse voice.

I can't get to the server right now to update the webpage...
here's the AP HW for tonight...time to refresh yourself on balancing redox reactions via the half-reaction method.
Read Text Ch. 20.1-20.4; do questions 20.32, 34, 38, 40, 44, 48

Kudos to E Period for putting so much effort into the difficult and very important
Le Chatelier + Kinetics test!
Your thorough answers and question-labeling demonstrate the time put into this topic and test; your work during extra help (two or more days for some) really paid off. Most of the class got a 94 or higher! Such high numbers are not typical for the Le Chat test which usually causes quite a few failures.
This topic will continue to be a dominant theme for the rest of the Chemistry course. I can't overemphasize the importance of the Le Chatelier/Equilibrium topic.
I'll continue to grade the other classes and I hope to report results that are just as good.