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Archive – Q4 week 2 – 19-20

Week of 4/13 – 4/17

4/13 – Monday –  We will meet today at 10:00!
 
1. Review 2017 AP Chemistry Free Response part 2 section.
 
2. Tomorrow we begin taking Our First Complete AP Practice Exams.  These will count as grades if and when grades come back this quarter.  If grades do not come back this quarter then I would suspect that we will be on a Pass/Fail and to PASS this assignment everyone needs to at least attain an AP Grade of 3 on the the practice test that we complete moving forward. Now I will drop the lowest grade(s) from the total number that we take.  That is only fair.  You will improve if you use my resources and put the work in.  
 
– The purpose of these practice tests is for everyone of you to observe where you stand in terms of an AP grade.  I have given these secured exams for many years and I know with about 95% reliability that they give very accurate evaluations of student performance on the actual AP.  I know this years AP is different but MY GUESS is that they will construct a test that will align with their past test statistically. THEY HAVE TOO!!  They cannot make a test where everyone gets an AP grade of a 5 or and AP Grade of 1!  They have to construct a test that will provide similar results to past and future tests.  Since I do not have any practice tests of the version that you will see in May will will use the old tests that review the entire curriculum. Lets prepare for anything!
 
– Now do not get too worried if you are not reaching ‘Your number” in the first test(s) that you take.  Getting a bunch of questions incorrect is not a bad thing as it only identifies what you need you to work on.  The most effective review is one that is individual and where the student has access to the teacher for review FOR EVERY QUESTION THEY GET WRONG!  You have that with the review videos that will be posted.  Review every incorrect question AND YOU WILL IMPROVE! We could review every unit but that is not nearly effective as time will be spent on topics that YOU know and some will not and vice versa.  These practice tests will identify what each individual student has weaknesses in.  How do you really know what your weaknesses are? Practice Tests!  Besides by taking all these AP practice tests, you will become familiar with how the College Board writes their questions.
 
I have had students get an AP grade of 3 in early review tests and eventually earn 5’s! It is possible to move up 2 AP grades. For most, moving up 1 AP grade is possible.

Spectrophotometry


                                
4/13 – Tuesday – Homework
 
1.  Please complete the practice test 1 multiple choice test and review with the posted videos in the Review Page (4th quarter). This was assigned last Wednesday.
 
 
2. Please complete the older part 2 questions that will review spectrophotometry labs.  There is no need to time yourself here.  I would like you to think about these questions and how they relate to the 2 spectrophotometry labs that we completed.  Please read through my notes on how we completed 2 labs using the spectrophotometer.
 
In your reference tables:   A = abc
 
        A = absorbance (- log of Transmittance)  
                 Transmittance is the ratio of light reaching the detector to the light being emitted from the source.
                 The more that light is absorbed, the lower the light hitting the detector and thus the lower the          
                 Transmittance.  This number will be less than one so we perform a .-log on its value to make it positive                      and a larger that 1 value and when we do this it becomes Absorbance.
        a = absorptivity constant (proportionality constant like R for gas laws or k for rate law)
         b = path length (distance that the source light travels to the detector)
        c = Concentration of colored chemical (Molarity chromophore or crystal field)
 
So based on A = abc the Absorbance is dependent upon the concentration of the colored chemical and the distance that the light has to travel through the cuvette.
 
% mass of copper in brass: 
Brass shot (alloy of Cu & Zinc) was dissolved with nitric acid. The solution was blue due to the crystal field splitting of Cu+2 with water. The Zinc in the alloy (Brass) also dissolved but it has no color.  We performed a serial dilution of a known concentration of [ Cu+2 ] and we put theses known concentrations in cuvettes and determined the Absorbance of each known concentration (after we set the spectrophotometer to absorb a certain wavelength of the Cu+2  solution called the peak wavelength).We plotted a Beer’s Law graph (linear relationship of diluted Cu+2 ] with lowered Absorbance. We (logger pro) plotted the graph of measured absorbance with Known concentration (we used the keep button to add the concentrations for each measures absorbance of the known concentrations).
We made a line of best fit and we used the slope and y intercept data to help with the next part
 
We then took the dissolved Cu+2  from the brass shot and made a 100.0ml solution.  We put that in a cuvette and measured the absorbance. Using this absorbance, and the Beer’s Law graph (utilizing linear algebra, y = mx +b from the regression line of the graph) we determined the concentration of the dissolved Cu+2 ].  We used that to calculate moles and then percent by mass.
 
Love this lab!
Determining the order of  reaction (with respect to Crystal Violet) of reaction (CV) with OH_
In this lab used placed a known solution of [CV] with is a chemical indicator (or a chromophore!) with a known concentration of OH into a cuvette in a spectrophotometer that plotted the Absorbance decreases in real time for 30 seconds. We identified the order of the CV while keeping the [OH] constant.  (The concentration of the OH was so much larger than the dilute CV that we also assumed that its concentration did not change significantly.) From the absorbance data we collected, we assumed that the concentration of the CV was proportionate to the changes of the Absorbance. (A = abc and because a and b are fixed values for the experiment we used the concept that A is proportionate to c which is concentration) Remember that over time the cuvette changes from a purple color to clear. How much it turned clear was an indication of the RATE of the reaction!  Using the absorbance values collected for each time interval as the proportionate concentration we changed the absorbance values to ln [A] and 1/[A) respectively and then made a new graph of each.  The graph that was the most linear determined the rate order with respect for CV.
2004 Free Response question 2 spec.pdf
View Download
 
In the above question (e) the Arrhenius equation used to be part of the course and it was on the old reference tables:
when you look at this equation you get a linear function.
                                                                                                   y   =        m       x      +     b

We used this equation to understand the relationship of activation energy (Ea) and temperature with the rate law constant but the equation is not part of course anymore so question (e) no longer is applicable.

 
2004 free response scoring guidelines ques 2 spec.pdf
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2006 Free response question 5 – spec.pdf
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2006 Free response scoring guidlelines ques 5 spec.pdf
View Download
Notes on Spectrophotometry:

Spectrophotometry

End of Monday..

4/14 – Tuesday   – We will meet today at 9:25, MC test will begin at 9:30 sharp!
 
Practice Test 2  – Begins  – Multiple Choice today                                
 
Please have a blank sheet numbered 1 – 50 on it and your reference table ready!
The link to todays test will be opened at 9:30 and closed at 10:45!
          1. Practice test AP Exam 2 – 4th quarter Exam Grade – completing a full test for AP Grade of 1 – 5 .
 
                Pacing = 1.5 minutes per question
 
        75 minutes completed (50 /1.5 min )  =  50 questions will be completed.
                           
Enter you MC questions into the form posted in the Review page before you leave the meeting today!
 
4/14 – Tuesday  – Homework – due Thursday
 
1. Please view Review video for the MC section of the test in the AP Chem review page.  YOU need to review every wrong answer WITH me using this video!!
 
Look at the statistics of the class.  I will have this up by 12:00 or so.
Did you get questions that most of the class got wrong or did you get questions that most of the class got right?  
 
To access the Practice test 2 review video you need to have the correct gmail account selected IN YOUTUBE!
 
End Tuesday…

4/15 – Wednesday – We will meet today at 9:55. Free response test begins at 10:00 sharp.
 
We will take questions 1 and 2 in the free response section (part 2) today, which will be like your actual test.
Taking the first 2 questions (each a 10 point question) will require 45 minutes.  This is about what I gave you for our free response tests in Thermo, Ksp, Rate Law and Acid/Base.  Below is the reasoning.
1. Practice test AP Exam 2 – Free Response section begins (50% of past tests): 105 minutes total
 
Based on the pacing of the “past tests” the part 2 or the free response section had the following breakdown:
 
Question 1:    10 points
Question 2:   10 points
Question 3:   10 points
Question 4:     4 points
Question 5:     4 points
Question 6:     4 points
Question 7:     4 points
                        46 total points awarded in the Free Response section in 105 minutes.
 
105 minutes / 46 total points = 2.30 minutes per point
 
Question 1 and 2 =  20 points   x    2.30 minutes   =  45 minutes (for two 10 point questions).
                                                                 1 point
46 minutes (out of 105 minutes) will be completed today.
                                                          
4/15 – Wednesday – Homework:
 
1.  Complete your MC review of the practice test 2 with video posted in Review Page.
     Use the statistics to see how you did with the rest of the class.
End of Wednesday…

4/16 – Thursday – We will meet today at 9:25! 9:30 Start time to complete the test.
 
1: Practice Test 2 – Part 2 continues (45 min Wed, 60 min left of part 2) – 
    Completed questions 1 and 2 yesterday.
                                                   
Question 3:   10 points
Question 4:     4 points
Question 5:     4 points
Question 6:     4 points
Question 7:     4 points
                        26 points remaining
 
                        26 points  x  2.30 minutes  =   60 minutes to complete the Free Response Section
                                                      1 point   
 
I will do all I can to grade these completed tests and give them back to you by Friday.
 

Have we reviewed your Part 1 – MC section?
 – 
as of Thursday 4/16 @ 3:00 am
 

     Average raw score in part 1 : 27 correct

      50 questions – 27 = 23 incorrect (average)

23 x 28 students = 644 incorrect answers

  858 minutes viewed /644 = 1.3

   1.3 minutes viewed per incorrect question!


                                                 
4/16 – Thursday- Homework:
 
1. The Practice test 2 video for the part 2 will be open for you to start reviewing the part 2 free response questions you just completed today.  It is posted in the AP Review Page directly under the MC review video.
 
I will have emailed you an invitation to the College Board Key to Practice Test 2. Please use this key and grading rubric to review the Free Response part of this weeks test.  Some of you may want to wait until I grade and return your graded Free Response test before you review. That is perfectly fine as long as you review every incorrect or skipped response.  You need to complete your review of the test by Monday, 10:00 am when we will meet to go over the Test and class statistics.
 
2. Make sure you have Reviewed all of the MC questions you got wrong or guessed incorrectly with the 
    Practice Test 2 MC (part 1 video) that is posted in the AP Review Page.  This should of been completed already!
 
 
Here is how we will finish out the Review:
 

4/17 – Friday – We will NOT MEET TODAY!  
 
I am busy grading your Free Response sections and combining it with your Multiple Choice Grade for a complete AP score.  YOU WILL GET YOUR GRADED FREE RESPONSE TODAY with your complete AP score from Practice Test 2 in your email.
                                   
4/17 – Friday – weekend homework – 
1.  Complete the review of MC questions (part 1 ) with posted video in the AP review page.
 
2.  Complete the review of the Part 2 (free response) with the posted video in the AP review page.
 
 
3.  Complete selected questions from the 2016 Free Response sections and upload your work into  
      the shared doc that I will send you.
 
      You only need to complete questions:   1, 2 (skip 2f), 3, 5, 6      
2016 Free Response Questions.pdf
View Download
 
Review your work with the keys below.
2016 free response chemistry College Board Key.pdf
View Download
 
AP Chemistry Free Response 2016 – Grodski Solutions p.pdf
View Download
Have we reviewed your Part 1 – MC section?  as of Thursday 4/16 @ 3:00 am
 

     Average raw score in part 1 : 27 correct

      50 questions – 27 = 23 incorrect (average)

23 x 28 students = 644 incorrect answers

  858 minutes viewed /644 = 1.3

   1.3 minutes viewed per incorrect question!


  

End of week 2!