AP Chemistry: Thoughts from an Experienced Teacher
Dale Jensen
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9/4/2011
I had hoped to get this, the first installment of my thoughts, out before now. After 33 years of teaching in Oregon, I retired in 2010. Being 55 years old, I quickly found I was not ready for retirement. Two weeks ago I accepted a Chemistry/Physics position at Syracuse High School, which is located just outside Salt Lake City. I am essentially starting over – and loving it.
Being at the AP Chemistry Reading for 10+ years as a Reader and as a Table Leader, I have seen where our students are the strongest and where they are the weakest. As an AP Chemistry Consultant who has presented at one day workshops and at week long institutes, I have heard the concerns of new and experienced teachers.
High School Chemistry for A.P. Achievement has revolutionized the way in which we can teach Chemistry. The traditional textbook approach should be reconsidered. Now students will have a personal tutor that can go home with them. This tutor will have the patients of a saint, can be rewound and played over and over, and will adjust to the student’s performance. Teachers who receive the DVD need a source to ask questions relating to how to best to use it.
What I would like to do throughout this school year is offer suggestions of how to optimize the use of the DVD, suggest labs, suggest activities, and suggest a schedule of topics.
I encourage your comments and questions. I would also like to include with my response in future installments. Please email me at This email address is being protected from spambots. You need JavaScript enabled to view it.. I will try to respond as soon as I can.
Chapter I: Traditional Schedule or Modified Schedule?
Step 1: Between the start of your school year and the AP Chemistry Exam (Monday, May 7th at 8:00 am) you must develop a plan to cover a full year of college level Chemistry – including the AP recommended labs. It starts with pulling out your 2011-2012 school calendar. What I like to do is block out all Sundays, holidays, no class days (block scheduling), and … notice I do not block out Saturdays. These may be used for review and labs. What you should be left with are the ‘teaching’ days that you have between the start of school and the exam.
Step 2: Next decide the sequence that you want to teach. Traditionally, you follow the textbook that you have. Begin with Chapter 1 and plan to go thru the chapters that the author has laid out. This approach has been successful for many teachers and their students.
Alternatively, a new approach has been growing in popularity. After beginning with the Gas Laws, do the second half of your book first.
Let me give you the sequence of each:
Traditional | Alternative |
---|---|
Review Nomenclature and Stoichiometry | Review Nomenclature and Stoichiometry |
Reaction Products | Gas Laws |
Thermochemistry | Kinetic |
Atomic Structure | Equilibrium |
Periodic Table | Acid-Base Equilibria |
Chemical Bonding | Solubility Equilibria |
Molecular Geometry and Hybridization | Thermodynamics (include Thermochemistry) |
Intermolecular Forces | Electrochemistry |
Solution Properties | Atomic Structure |
Gas Laws | Periodic Table |
Kinetic | Chemical Bonding |
Equilibrium | Molecular Geometry and Hybridization |
Acid-Base Equilibria | Intermolecular Forces |
Solubility Equilibria | Solution Properties |
Thermodynamics | Reaction Products |
Electrochemistry | Review |
Review | Exam – May 7th |
Exam – May 7th |
Let me first start by stating that AP CHEMISTRY SHOULD BE A SECOND YEAR COURSE. This comes directly from the latest College Board publications. I am aware that there are many ‘interesting’ schedules that have been devised by schools to have AP Chemistry be the first course, but for the moist part, Chemistry is such an abstract topic that most students need the time to fully grasp the concepts.
The topic can be broken into two categories – Memorization and Mathematical:
Mathematical | Memorization |
---|---|
Review Nomenclature and Stoichiometry | Review Nomenclature and Stoichiometry |
Gas Laws | Atomic Structure |
Kinetic | Periodic Table |
Equilibrium | Chemical Bonding |
Acid-Base Equilibria | Molecular Geometry and Hybridization |
Solubility Equilibria | Intermolecular Forces |
Thermodynamics (include Thermochemistry) | Solution Properties |
Electrochemistry | Reaction Products |
The traditional sequence may be easier for the new teacher and for many students to follow, but starting with the Mathematical topics allows for more review throughout the year and places the Memorization topics where they belong. The Memorization topics are basically a review of the first year course.
One should also look at what happens at the end of the school year, just before the test. State testing, students visiting colleges, spring sports, and other courses take your students out of your class.
If you feel comfortable with ALL of the AP Chemistry topics, I recommend looking at the Alternative sequence.
When planning out the 2011-2012 school year, I suggest that if you are following the Traditional sequence, be ready to start Kinetics after the Christmas (Winter) break. If you are following the Alternative sequence, be ready to start Atomic Structure.
Two topics are not found in either sequence – Nuclear and Organic Chemistry. These are great topics for the Christmas (Winter) Break and Spring Break.
Finally, I like to put Reaction Products at the end. With the new format of Question 4, this becomes a great review of the course. Students are now asked to write must balance their net ionic reactions and answer a question that finds its roots in acid-base, redox, thermodynamics, or …
One final thought. Leave time for lab. In the recent years, the AP Chemistry test is requiring more lab knowledge and skill. Do not short change your students. Give them a rich lab experience. The two lab manuals that I use are AP Lab Experiments by Sally Vonderbrink (Flinn Publishing) and AP Lab Experiments by David Hostage and Martin Fossett (Peoples Publishing).
For this first unit, I recommend the following labs:
Sally Vonderbrink: Finding the Ratio of Moles of Reactants in a Chemical Reaction
Hostage/Fossen: Job’s Method of Continuous Variation
How to Utilize High School Chemistry for A.P. Achievement
If at all possible, each student should be given or be required to purchase a copy of the DVD. Within the first 2 weeks of class, Inorganic Nomenclature and Stoichiometry should be reviewed and tested. This is true if you use the Traditional or the Alternative sequence. This should be a time of review. It is important that your students have a solid background going into the upcoming AP Chemistry topics. The recommendations are the minimum that your students should do for each of these topics. I think you will find that your students will do more after they see the interactivity of the DVD.
Inorganic Nomenclature -
Chapter 1: Atoms, Molecules and Ions
Begin with 1.17 Concept of Ion (Part 1)
Students should work thru section 1.47 Periodic Table (Molecular Compounds with Polyatomic ions and Hydrogen)
Stoichiometry –
Chapter 3: Mass Relations in Formulas and Chemical Reactions
Be sure students go thru 3.11 Percent Composition, 3.13 Empirical Formula, and 3.17 Molecular Formula
Chapter 4: Amounts, Stoichiometry and Reactions in Aqueous Solutions
I recommend the students review the entire chapter.
As the instructor, during class you should review Inorganic Nomenclature and Stoichiometry topics. Teacher generated worksheets and an exam should be included in your overall lessons.
Good luck and enjoy the upcoming AP Chemistry year.
Dale Jensen
AP Chemistry
Thoughts from an Experienced Teacher
Dale Jensen
This email address is being protected from spambots. You need JavaScript enabled to view it.
10/4/2011
From my email …
I have received some emails and I want to thank you for your comments. I had more than one person asking me about ‘my’ DVD. High School Chemistry for A.P. Achievement was written by Dr. Ketan Trivedi and edited for the AP Chemistry world by John Hnatow. These two gentlemen (whom I consider my good friends) are the ‘brains’ behind this revolutionary product. I use the DVD in my classroom and I recommend it to teachers that I meet. I have never received any money or other forms of reimbursement for what I do. As a teacher and as a Reader, I want all AP Chemistry students to do well on the exam.
I hope each of you that read my first installment have had time to plan out your school year. If you are new to this site, I highly recommend that you quickly look over the topics that I addressed last month.
As I explained last time, I use a non-traditional sequence that puts the more mathematical topics first. As I am writing this, my class is just finishing the Gas Laws. For most students, and teachers, this is usually one of the easiest chapters. There are a few fine points that need to be emphasized, but for the most part the labs that can be done are relatively easy and the students normally get good results.
Since this is my first AP topic, I would also like to start introducing some of my ideas on teaching. But please … what works for one teacher in one type of school may not work for everyone. Schedules, administrative requirements, and the type of school all contribute to what you can and cannot do in your course.
I remember what my mentor teacher told me when I was going thru the student teaching program some 35 years ago …
‘Teaching is an evolutionary process. When you walk into your first classroom, you will have had numerous college courses and you will have one or more degrees, but you will not know your subject. To really understand, you must be able to teach it to someone else. The first 2 or 3 years will be learning what works and what doesn’t work. You will be a good teacher when you can make the complex simple and have your students leaving your class wanting more.’ Mr. McDonnell
Photo-Labs …
Before I address the Gas Laws, I want to introduce you to my photo-labs. I have been using these descriptors for labs in my summer workshops and I have found a very positive response. Essentially, I have taken a series of photos and have put them into a PowerPoint to show the steps that I use in labs. These Photo-Labs may be used to introduce the lab, review the lab, and (perhaps the best use) show students who were absent what they missed. Photo-Labs are also going to help make each of my teaching guide installments much shorter. Please feel free to use, modify and share them.
If you find this format interesting and develop your own photo-labs, please send them to me and I will share them in following installments. Sharing is one of the best ways to help our students.
The Gas Laws …
I like to teach from the student’s lab experiences. I find that the students doing the labs before we have any formal presentation, allows them to form questions and it makes them eager to know the ‘real story’ behind their activity.
I also believe that different people learn in different ways. You have the mathematical learners that simply need an equation; the hands on learner who really benefits from touching the equipment and seeing how everything works; and the auditory learner who needs the teacher to explain the concept. These learning styles are at the center of my personal teaching method.
DAY 1 … I start the Gas Laws with a review of units as well as the mathematical and graphical relationships of P, V and T. This is a first year topic and I treat it as a review and spend only part of a day 1. I also use the first part of day 1 going over the previous exam.
How to Utilize High School Chemistry for A.P. Achievement 5.1 Pressure Measurements in Gases |
DAY 2 … I begin the period with a lab. I have modified the lab found in Sally Vonderbrink’s lab manual, The Molecular weight of a Volatile Liquid. Her lab is a variation of numerous labs that attempt to produce a gas and then collect data to determine its Molecular Weight. I found that her lab, as well as others that I tried, had built in problems. Many use either aluminum foil or a rubber stopper to trap the gas as it is being produced when the volatile liquid is heated. This causes condensation of the vapor. After experimenting and getting help from my students, I came up with a different approach. View the attached lab with its use of Parafilm. It is a simple procedure and the entire lab may be done in 30 minutes. The following will link you to my PowerPoint.
Molecular Weight of a Volatile Liquid … Photo-Lab
The following are suggestions and comments …
- The lab that I describe uses very small amounts of a liquid. I prefer ethyl alcohol.
- The I2(s) is a great tip. It allows you to see the liquid at the bottom of the test tube.
- I would suggest that each student prepare their own test tube. Many tubes will fail.
- Why Parafilm? Parafilm creates a great seal and has the ability to stretch when the pressure in the test tube increases.
- Condensation of the vaporized liquid can be reduced by keeping the test tube as low into the hot water bath as possible. My students have come up with numerous, very clever setups (look at the PowerPoint).
- The values that my students determine are very close to the theoretical 46 g/mol
- Finally, what do you do if you do not have a .001g or .0001g balance? The mass of the gas that is normally calculated is approximately .01 grams. Instruct your students that the mass is .01 +/- .005 grams. Have them calculate the molecular weight with a mass of .015 and .005 grams. Most students who have taken the time and watched their test tubes will see that their calculated molar mass will be within this range. I find this whole process is very good for students to visualize how important the precision of the instrumentation is and how important it is for students to record all of the digits presented.
Many students will finish the lab and will be ready to begin the calculations. I have them work on their lab notebooks (more about this in a later installment) and make sure they have all of the data. We will go over the calculations next time.
Day 3 … A review of the previous day’s lab is important. Go over the lab’s procedure and what data was obtained. PV = nRT is then introduced. Most students will have seen this in their first year course. When I deal with the units for each of the variables, I like to use 4 simple letters – K.I.S.S. This of course stands for Keep It Simple Students. I instruct my students to use atmospheres for pressure, liters for volume, and Kelvin for temperature. When moles are used for ‘n’, R is .0821 (liters)(atm)/(mol)(Kelvin). Students have one value for R and simply make sure that P, V and T are in the correct units.
The power of the Ideal Gas Law is then explored as it shows that the density, and molecular weight may be determined. Student data is then used to determine the molecular weight of the volatile liquid
How to Utilize High School Chemistry for A.P. Achievement 5.11 The Ideal gas Law |
Day 4 … Deviation of the Idea Gas Law and the Kinetic Theory are discussed. The Van der Waals Equation should be discussed as an attempt to make corrections for the volume and interaction of gas particles. The actual math that can be done, should be minimized. Emphasis should be placed on how this equation correlates with the Kinetic Theory of Gases. I leave the last 15-20 minutes of the period to do my Graham’s Law Lab. The following will link you to my PowerPoint.
I like to do the lab and send the students home to finish the calculations. Students will get very different result from the predicted 35 g/mol for the molecular weight of NH4OH. This is because the gas that is produced is NH3. Many students will come to class the next day very disappointed in the lab. When the ‘trick’ of the lab is explained, they may be upset, but they will remember that NH3 is the gas that is produced from a NH4OH solution.
The following are suggestions and comments …
- Practice is very important. Because of the short length of the straw, the Q-tips must be inserted at the same time.
- The straw must be new. Re-using the straws is very difficult
- Why does the ring move? If you assume that objects only move if an unbalanced force is applied, you must conclude that the force from the NH4OH Q-tip is greater than from the HCl Q-tip. If FORCE divided by AREA is PRESSURE, one can conclude that the vapor pressure of the NH4OH must be larger than the HCl.
- Clean up is easy. Push the Q-tips into the straw and throw the straw in the trash.
How to Utilize High School Chemistry for A.P. Achievement 5.19 Partial Pressures in Gas Mixtures Video |
Take Home Exam … These have become a large part of my teaching. Before I give the traditional end of topic exam, I like to give my Take Home exam. Students are given the exam near the end of the topic and are given at least 48 hours (great for block schedules). They may use their book, the internet, and the other members of their class. The exam is designed to take the average student 2 hours. I highly suggest that the students form small (3-5 members) work groups. I have had groups go to pizza parlors, a member’s home, or the local library. The exams are usually a mix of multiple choice and free-response questions from released exams.
I will now stand on the soap box … Please do not place any College Board released exam questions on the internet. I do not care how secure you think the questions may be, students will find them. I should also note that the College Board owns the rights to the questions and you may receive a nice reminder to remove their questions from your site.
It sounds like a lot to grade, but here is a little trick. Have each student write down the other members of their study group. I then group the exams that were done in each group and the papers will look very similar. The second benefit of this is that you can now see who is not doing their own work. A student that does poorly on In Class test, but did well on the Take Home needs to have a sit down moment. An explanation of doing ones owns work is very useful.
Of course, the Take Home exam is simply a review. Because of the points attached, students take it very seriously, and I have seen an increase in their In Class exam scores.
In Class Exam … Designed to take the entire period/block, I like to use previous AP Chemistry exam questions. I would like to offer a couple of thoughts:
- Grade and score the free-response as a Reader. Use the College Board rubric or use the rubric that you create. Remember, the average score on a free-response question is about 50%. It is very important that your students realize that they will not be getting 90+% on each exam.
- Throw in a question from a previous topic. If you are testing Acid-Base Equilibrium, throw in a Kinetics question. Please, make sure you tell your students to expect prior topics on the exam.
- Allow the students to use only the College Board Released Equation sheets, Periodic Table and Reduction Series Table. Familiarization with these pages will help your students when they take the exam in May.
I hope these thoughts have been useful. I am available to answer your questions and I appreciate your comments.
Good luck and enjoy the upcoming AP Chemistry year. May 7th is not that far away.
Dale Jensen
AP Chemistry
Thoughts from an Experienced Teacher
Dale Jensen
This email address is being protected from spambots. You need JavaScript enabled to view it.
10/7/2011
Welcome to installment 3. In the past two installments I gave my thoughts on teaching an AP Chemistry course, picking an approach that works best for you, and the Gas Laws.
This time I will address Kinetics. I must admit that this is my favorite topic to teach. Students like the labs and the beauty of the mathematics behind the Integrated and Differential approaches. My problem is that I sometimes find myself spending too many class periods doing extra labs and problems.
As mentioned in installment 2, I would like to address the AP Chemistry Lab notebook before looking at Kinetics.
As a consultant for the College Board, I received the 2011-2012 Handbook for AP Chemistry. On page 5, there is new wording under the Topic Outline section.
“Because chemistry professors at some institutions ask to see a record of the laboratory work done by an AP student before making a decision about granting credit, placement or both, in the chemistry program students should keep a laboratory notebook that includes reports of their laboratory work in such a fashion that the reports can be readily reviewed.”
This is the first time that the College Board has addressed the notebook and I believe it is very clear. If your students want to receive credit for the lab work they did in your course, require a very structured report for each lab. Students may then present their notebook to the Chemistry Department for evaluation.
The following will link you to my required format:
When I first started to use lab notebooks, I questioned my decision. It saw this huge stack of books coming in and I was intimidated. Actually, the notebooks have some great benefits:
- The quadruled composition book that I suggest may be used for my first year and my AP course. It is close, but for most students, the composition book has enough pages for both years.
- Students can see my past comments to learn their past mistakes.
- You can show the student’s growth (or lack of) to parents and counselors.
- The quadruled paper allows for easy construction of tables and graphs.
- The day labs are due, you will not have to go to the gym to do your upper body workout.
Kinetics …
DAY 1 …
After I finish reviewing the In Class exam for the Gas Laws, I begin Kinetics with a lab.
You will need about 30 minutes to introduce and perform the lab. I like to time the lab so that the students will collect the data and when they go home, they have 3 graphs to construct.
I am attaching a copy of my Integrated Rate Law lab. It may look similar to a radioactive decay lab that many do in first year chemistry, but it has a twist that makes it appropriate for Kinetics.
Students work in pairs and before they may begin they must roll a die. This is used to determine the time when the students need to stop and count their sample. This time becomes their half-life. After the students collect their data, they go home and construct their 3 graphs. I do not tell them what they are looking for or what the graphs mean. The next day I discuss the graphs and the calculations
One last note: The lab requires the students to ‘properly’ dispose of the chemical waste. If the lab is done at the beginning of the period, students will use valuable class time to draw graphs that they can do at home and (most importantly) candy will make some students become hyperactive. If done at the end of the class, the students will go to their next class with a little extra energy.
How to Utilize High School Chemistry for A.P. Achievement The recommendations are the minimum that your students should do for each of these topics. Of course I highly recommend that students use the interactive component of the DVD to test what they have learned. 13.1 Intoduction to Chemical Kinetics and Reaction Rates 13.3 Instantaneous Rate 13.5 Reaction Rate and Concentration Video |
DAY 2 …
I start class by grading the 3 required graphs that the students constructed. I give them credit for 3 graphs drawn correctly. This is a quick look by me. This helps keep the students on task.
Spreadsheets are my favorite tool for writing and correcting lab reports. If I thought my wife would say yes, I would like to name our next dog EXCEL. When my Integrated Rate Law lab is opened, you will see three tabs at the bottom. The Student’s version of the lab, the Instructor’s version with the calculations, and the 3 required graphs.
I have my students use the Instructor’s spreadsheet AFTER they have completed their calculations based on their data. If they agree with the spreadsheet, they print a copy of the Instructor’s spreadsheet and place it loosely in their lab notebook. I now do not need to check the calculations and I can focus my attention at other parts of the lab report. This has been a great time saver.
The 3 graphs that the students should have constructed should look like the following examples:
The underlying premise of the discussion that is to follow is that AP Chemistry students should have seen in their math courses and be familiar with the application of the equation of a straight line.
y = mx + b
I begin with looking at the graphs that the students generated. Unless they read ahead, they come in with 3 graphs, but are unsure of they mean.
Questioning Strategy:
Question: ‘Is the graph of [A] vs. time a straight line?’
Answer: ‘No.’
Question: ‘If it was a linear relationship, could we write an equation that represents the relationship between [A] and time?
Answer: Usually, it takes very little prompting to get ‘y = mx + b.’
The students and I then generate the specific equation
[A] = -kt + [A_{o}]
The ZERO Order relationship.
Question: ‘Is the graph of ln[A] vs. time a straight line?’
Answer: ‘Yes.’
Question: ‘Can we write an equation that represents the relationship between ln[A] and time?
Answer: ‘y = mx + b.’
Repeating the same questioning reinforces the student’s understanding.
The students and I then generate the specific equation
ln[A] = -kt + ln[A_{o}]
The FIRST Order relationship.
Question: ‘Is the graph of 1/[A] vs. time a straight line?’
Answer: ‘No.’
Question: ‘If it was a linear relationship, could we write an equation that represents the relationship between 1/[A] and time?
Answer: ‘y = mx + b’
The students and I then generate the specific equation
1/[A] = kt + 1/[A_{o}]
The SECOND Order relationship.
Question: ‘For a first order reaction, can we write the Integrated Rate Law:’
ln[A] = -kt + ln[A_{o}]
‘What would this equation look like when half of the original reactant is used up?’
Answer: The students and I then generate the specific equation
ln[1] = -kt + ln[2]
-ln[2] = -kt
.693 = kt
t1/2 = .693/k
Students can calculate the half-life of their lab. They should see the relationship of their half-life and the initial roll of the die.
I finish the lab discussion with a series of Integrated Rate Law questions selected from the textbook to be done as homework.
Final thought before students leave – if temperature is held constant, k is a constant.
How to Utilize High School Chemistry for A.P. Achievement 13.6 Rate Law and Rate Constant |
I have been asked by participants of my summer workshops if I have a zero order and a second order. I have 2 labs that are almost ready to be revealed. They are formatted similar to the MM lab and use very common lab materials. When they are ready, I will post them in a future installment.
DAY 3 …
I begin the class by going over the assigned homework.
The first differential rate law lab that we do takes about 40 minutes to complete. The lab is my version of the Sulfur Clock Reaction.
Sulfur Clock Reaction: Photo-Lab
Sulfur Clock Reaction: Student Copy
Sulfur Clock Reaction: Instructor’s Spreadsheet
This lab is easy for the students to start and finish in half of a period (40 min). The key is drawing a light X and stopping when the X is no longer visible. It is a good lab and the students will get good results.
IT IS VERY IMPORTANT THAT YOU TELL YOUR STUDENTS TO WASH OUT THE WELL PLATE AS SOON AS POSSIBLE AFTER THE REACTION IS COMPLETE. FAILURE TO DO SO WILL RESULT IN A WELL PLATE THAT IS PERMANENTLY PITTED.
I do not show the students the slide that goes over the calculations of order. This is saved for the next class.
Homework: Determine the initial concentrations of the Na2S2O3 and HCl in each of the 6 trials. This is relatively easy for students to do and therefore other problems should be assigned.
How to Utilize High School Chemistry for A.P. Achievement 13.7 Rate Law Expressions and Rate Constant Calculations Involving a Single Reactant |
DAY 4 …
I begin the class by going over the assigned homework.
Discussion of the Sulfur Clock Reaction will take some time. For many students, this will be their first exposure to math that incorporates logarithms.
Before the period ends, I make every effort to show a differential rate law problem that may be seen on the AP Chemistry exam. The following is very important to remember …
The AP Chemistry Exam is not a test of the student’s math skills, but rather a test of the student’s knowledge of Chemistry.
The problems on the test use simple numbers that me answered mathematical or verbally. (i.e.; doubling the concentration of the reactant doubles the reaction rate. The order of the reactant is first-order.)
Assign differential problems from the text.
DAY 5 …
I begin the class by going over the assigned homework.
It is important to spend time on determining the rate constant and its units. Students will be asked to do this on the exam.
The last half of the period is used to prepare for Sally Vonderbrink’s Lab #12 - Study of the Kinetics of a Reaction
This is one of the more complicated labs that we do. Preparation is critical. The students have the following tasks:
- Clean a 96 well plate
- Label pipettes (one for each reactant)
- Label test tubes (one for each reactant)
- The student that will administer the drops must practice. (see lab)
- Secure all equipment until the next class period.
Homework: Students should do the initial concentration calculations for each of the 8 experiments.
Sally Vonderbrink’s Lab #12 - Study of the Kinetics of a Reaction: Photo-Lab
DAY 6 …
Sally Vonderbrink’s Lab #12 - Study of the Kinetics of a Reaction
This will take most of the period. I have not had good success with changing the temperature or adding a catalyst. Therefore, I skip these parts.
DAY 7 …
The postlab calculations will take time. Be prepared to explain the fundamentals of a clock reaction.
DAY 8...
The Arrhenius Equation and the Mechanisms are the last 2 topics.
From past AP Chemistry questions, the Arrhenius Equation and the determination of Ea are always associated with a graph. Students may be asked to …
- label the x- and y- axes of a graph used to determine the Ea.
- Sketch a line that represents the
- Given a graph , explain what the slope of the graph represents
Mechanisms …
For many years, the free response portion of the AP Chemistry test did not address mechanisms. But in 2008 and 2009 two great questions were on the AP Chemistry exam. I cannot post these questions in this format, but they may be found on AP Central.
For me, the most important statement that I make to my students is …
A mechanism may be possible if it meets the requirements of the stoichiometry and the rate law expression. Then only experimentation can determine if what is proposed is the true mechanism.
How to Utilize High School Chemistry for A.P. Achievement 13.20 The Arrhenius Equation |
FINAL NOTE:
As I mentioned earlier, I like teaching Kinetics. One of my new favorite labs is Kinetics: Differential and the Integrated Rate Laws, found in the Hostage-Fossett lab manual.
This lab, as all of the labs found in this publication, is extremely well written. Actually, it is a compilation of 4 labs.
Differential Rate Law: Catalyzed Decomposition of H2O2
Method 1: Heterogeneous Catalyst
Method 2: Homogeneous Catalyst
Integrated Rate Law: Kinetics of Radioactive Decay
Unfortunately time is the AP Chemistry teacher’s worst enemy. I find myself picking each year from all of the labs that I have discussed. I wish we had the time to do them all. There is always after the exam.
I hope these thoughts have been useful. I am now preparing my class for Equilibrium. This will also be the subject of my next installment.
Dale Jensen