Chapter 5 Quiz

Tomorrow is a quiz over Chapter 5, Thermochemistry. If you experienced success with the WebAssign set and you understood the pre-lab exercise for the Hess's Law lab , you should be fine with the material on the quiz. Below is a solution to the problem that I had for #8 on WebAssign. I was given three reactions to add together to get a target reaction. I did not use the third equation because two of the substances, water and hydrogen sulfate, are not part of the target equation and could not be factored out. The second equation is reversed and multiplied by two to achieve the correct factoring out. Remember, if a reaction is reversed, the enthalpy sign must be changed. Also, if a reaction is multiplied by some variable, the enthalpy must also be multiplied by that variable. Come and see me tomorrow if you have any questions.

Hess's Law Lab

Below are some of high points that I want to discuss about the Hess's Law lab.

• The water of the solutions is what captured the heat of the reaction. This remained constant at 100.0 mL (50.0 mL of one solution added to 50.0 mL of the other solution) for each trial of the lab. For calculation #1 of the analysis, mass is needed for q = s x m x delta T. Since the solutions are not pure water, the mass is determined by multiplying the total volume of solutions (after adding them together) with the density of the combined mixture. Since the mixture was mostly water, we did use the specific heat of water.


• The intent of the lab was not to prove the conservation of energy. There was a systematic error of heat being lost to the surroundings. This was true for all trials, so this factors itself out for the purpose of the lab. The only intent of the lab is to prove that achieving a heat of a reaction can be achieved through one step or multiple steps, given that the net of the multi-step approach is the same as the direct approach in terms of the same reactants and products.


• As indicated by the pre-lab, hypothetically, the sum of the heats of reaction for reactions #2 and #3 are supposed to equal the heat of reaction for reaction #1. Systematically across the board, this did not turn out to be true. The reaction #3 (hydrogen ions with ammonia) went way off the chart. I have a theory as to why. The ammonia solution used to make the 2.0 M solution for the lab was very old. Because water has evaporated from the solution over time, traces of some precipitate can be seen floating in the solution. It is my theory that as the reaction occured, the precipitate from the ammonia solution dissolved. As you will find out later this semester, some processes of dissolving are quite exothermic. This is my proposition for the undesirable results.


• I will be performing the experiment myself with new solutions. I will be giving you a write-up to place with this lab in your portfolio describing the inadequacies of the lab. This way, any criticism of your results can be placed upon the situation, not your abilities.


• IT IS NOT YOUR RIGHT TO FUDGE THE RESULTS TO MAKE IT FIT THE THEORY. IT IS YOUR RESPONSIBILITY TO PRESENT THE RESULTS "AS IS" AND EXPLAIN ANY DISCREPENCIES IN HOW THE THEORY AND DATA DO NOT COINCIDE. THE RESULTS ARE WHAT THEY ARE. SCIENCE HAS NEVER PROGRESSED BY MANIPULATING RESULTS TO GET THE DESIRED AFFECT. YOU WILL GET PAID MONEY IN THE FUTURE TO FIGURE OUT THE PROBLEM AND FIX IT, SO GET USED TO IT!! And now Mr. Brueckner is stepping off his soap box. :)

Key for Mole Ratio Lab Practice Quiz

Go to the AP Chemistry Calendar page and under today's date is a pdf file of the key for the mole ratio lab practice quiz. Remember, tomorrow you will be taking a quiz for real.

Chapter 4 Test Review

Below are images of a solutions guide to the optional practice exam. Remember, the pdf file for the Chapter 4 test review can be found on the AP Chemistry calendar. I changed the review since I made the key, so problem #15 is different. The bottom image is the solution to number 15.
You will be given all equations needed for the test. You will be able to use your periodic table. You will not be supplied with the solubility rules. If you remember the basic solubility rules, an assumption can be made that anything that does not fit a basic solubility rule is not soluble, thus a solid. The test is 20 multiple choice questions. Do not think that you do not have to do the work to solve a problem. Just looking at the answers will not suffice.

Chapter 4 Practice Exam

I have posted a practice exam for the chapter 4 test. The file for the test is on the AP Chemistry calendar under the date, Monday, September 12th, 2011. The test will be this Thursday, September 15th, 2011. The answers are on the very last page of the practice test.

Hydrogen Peroxide Titration Pre-Lab Questions

I have placed a Podcast on the AP Chemistry calendar under the date Friday, September 9th, 2011. The Podcast gives another example on how to balance a complex redox reaction in a basic solution. Feel free to view it as you complete the problems from WebAssign.

Below are the slides from the Power Point presentation of the pre-lab questions the the Analysis / Titration of Hydrogen Peroxide. On Monday, September 12th, you will be completing the lab. To complete the analysis, you will need to complete calculations like those shown below. Below this blog entry is the question that is to be completed for Tuesday, September 13th, 2011.

Take Home Quiz - Empirical and Molecular Formulas

Please answer all parts of the question below. Have the solutions to the problem ready for class on Tuesday, September13th, 2011. This type of question is a true AP Chemistry test question. What makes it so is that there are multiple parts of the test that require very different skills. Good luck.

Take Home Quiz

Below is the problem that needs to be solved for Thursday, September 8th, 2011.

Ecological / Responsible Chemistry with Dr. John Warner

For a chance to earn 10 points extra credit in your homework category, I would like to you watch two short videos and answer five questions. The two videos are from a talk given by an organic / industrial chemist by the name of Dr. John Warner. I had the pleasure of seeing Dr. Warner give his presentation in person at the American Chemistry Society conference in Denver last Sunday. He is the founder of a company that emphasizes creating chemicals that are chemically benign, which means they are ecologically neutral to the environment. Yet, the chemicals still do what they are designed for just as effectively as hazardous chemicals. He has a great message on how chemists / society can tackle the problem of environmentally aggresive chemicals by eliminating the toxicity in the design phase of a chemical. Dr. Warner and colleagues have come up with 12 principles of what makes chemistry "green". Those principles are in the images shown above.

Dr. Warner's talk is in two parts: Video 1 and Video 2

After you watch the videos, I would like you to answer the questions below and e-mail me the answers at cbrueckner@lps.k12.co.us .

1. What was Dr. Warner's orginal major as an undergraduate student at the University of Massachusetts in Boston?



2. Dr. Warner's picture appeared on the cover of a local Boston magazine with what other celebrity?



3. What event in Dr. Warner's life made him think about the possible toxicity of the chemicals that he had designed?



4. In Dr. Warner's opinion, what is a missing component of chemistry training programs (Master's and PhD)?



5. When is the best time to address the toxicity of a chemical?
   
   

Last but not least, below is the solution to problem #8 from the worksheet on solubility and ion concentration that was worked on in class on Friday. On Tuesday, September 6th, 2011, you must have the worksheet completed and the Ion Lab analysis completed. Of course, you can always work on WebAssign also.

Flipped Classroom

You are part of an experiment today. We are going to try a new, budding trend that I have learned of in science education known as the "Flipped Classroom". Instead of you coming into class on Friday, September 2nd and listening to me yap about some problem and showing you how to do said problem, you are going to learn how to do this type of problem online via a short instructional movie. The problem is the image below this text. Please read the problem and if you have any inclination on how to solve the problem, try it. If you have no idea, that is fine. Whether you try the problem or not, you then need to view the instructional video. The Quicktime Movie file can be found on the AP Chemistry calendar (<-- LINK) under the date Thursday, September 1st, 2011. There is no audio for the movie, but every step of the process is mapped out for you. Make corrections to your original attempt of the problem or write down the solution and take notes on the problem, just like you would do if I was lecturing to you in class. I will be checking for proof of viewing the movie (any means of recording the work that you have done) during class the next day. If you show up to class without doing any preparation work for class the next day, you will be sent down to the library to view the movie. This has consequences because you will not be allotted time to complete the homework associated with the material in class. If I may phrase it in another way, you will create more homework for yourself and not have the luxury of working with your peers (or me for that matter). I WILL NOT CONSIDER YOU HAVING THE VIDEO DOWNLOADED TO YOUR I-PHONE (or like device) AS SUFFICIENT PROOF OF PREPARING FOR CLASS. PENCIL OR PEN MUST GO TO PAPER. After doing this, you have completed what you are responsible for outside of class.

On Friday, September 2nd, 2011, you will do your homework on this material in class. I will be placing you in groups of four (the groups will be my choosing, thank you) and you will complete the homework assignment for this topic. The members of the group will help one another complete the homework. I will be walking around the room to help you, but to also ask questions to determine you level of comprehension, both as a group and as individuals. You must finish the assignment in class to receive full credit. If you do not complete the assignment because your are not prepared, that is nobody's fault but your own.

The write up for the Ions / Precipitate lab can also be completed after you finish your work presented in the movie. If you are efficient and thorough in your work, you will have no homework for AP Chemistry over the three day weekend. Please email me if you have any questions. I will respond if they are not sent too late.