Archive – week 2 – 19-20
Week of 9/9 – 9/13
9/9 – Monday – period 2
1. Review the Voltaic Spontaneity HW Form-
Skills: Solubility, Spontaneity, Equilibrium,
How concentration of soluble ions in a voltaic cell affect its voltage.
2. NO2 and N2O4 ampule demo with heat.
3. LeChateliers Principle/ with worksheet
4. Revist the Classroom Daniell cell and predict voltage
by manipulating concentration of free ions
– period 3/4
1. Review the Voltaic Spontaneity HW Form-
Skills: Solubility, Spontaneity, Equilibrium,
How concentration of soluble ions in a voltaic cell affect its voltage.
2. NO2 and N2O4 ampule demo with heat.
3. LeChateliers Principle/ with worksheet
4. Revist the Classroom Daniell cell and predict voltage – did not get to.
by manipulating concentration of free ions
9/9 – Monday – Homework:
1. Complete LeChateliers Principle worksheet (front side) given out in class
and review the key below:
2. Please complete Intro Voltaic Cells Worksheet 2
BUT PLEASE Complete QUESTION 2 ONLY!!
THIS IS THE SIDE THAT HAS NO TITLE. Sorry both sides are numbered 1!
3. Review question 2 with the key below.
4. And/or you can follow along with me going over Question 2 with lecture below.
Intro Voltaic Cells worksheet 2 – skills.pdf worksheet Lecture:
Click on START AT 23:12 to view the video below to start directly at question 2.
End of Monday!
* From this moment on All students are responsible for the timely completion of the online assignments. A form homework IS ALWAYS DUE by 4:00 am the following morning unless it is a weekend homework and then it is due Monday morning by 4:00 am. If there is an issue of any kind I NEED AN EMAIL with any concerns or problems. The email must occur before the 4:00 am deadline.
Without this email, YOUR zero will have to stand. Each assignment has a purpose and they build on each other. If you do them at your own pace then what I am doing in class will not make any sense.
9/10 – Tuesday – period 2 and 4 are the same.
1. Review LeChateliers Principle – using worksheet – Remember that U diagram!!
2. Revisit the Classroom Daniell cell and predict voltage
by diluting the Reduction half cell ( Cu/Cu+2 ) or Blue One with water!!!
By adding water Cu+2 ion solution (molarity) decreased and thus the
Voltage Decreased!!!! Explained in terms of LeChateliers Principle and Spontaneity!
Zn0 (s) + Cu+2 —–> Zn+2 + Cu0
Stress: decreases
Response: <—————– Shift
The reverse is now favored more than it was which LOWERS the forwards reactions
pathways or spontaneity, which results in lowering the voltage!
3. Precipitation reaction demo – Double replacement reactions or precipitation reactions-
Net ion reaction written to eliminate spectators!
A) Wrote the precipitation reaction between lead (II) nitrate and potassium nitrate.
We used the following worksheet:
B) Particular Diagrams
C) Identified the precipitate.
D) Performed the demonstration.
Classwork on worksheet:
Today’s demonstration:
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4. Revisit the Classroom Daniell cell and predict voltage by making the Zn+2 ions precipitate out with Na2CO3
being added to the Zn/Zn+2 half cell.
*By adding Na2CO3 I was really delivering CO3–2 ions to the oxidation half cell because Na2CO3 is soluble due to the group one ion (Na+) that has weak Coulombic attractions with the CO3–2 in the salt (ionic compound).
Na2CO3 (s) —-> 2 Na+ (aq) + CO3-2 (aq)
Then CO3-2 reacted with Zn+2 to form a precipitate, which takes Zn+2 out of the solution.
Zn+2 (aq) + CO3-2 (aq) ——> ZnCO3 (s) which is a precipitate = insoluble
Lowering the Zn+2 will cause the overall reaction in the Daniell cell to “shift” Right or be move spontaneous in the forward direction increasing the voltage.
Zn0 (s) + Cu+2 —–> Zn+2 + Cu0
Stress: decreases
Response: Shift —————–>
The forward reaction is now more favorable or spontaneous than the reverse thus
the voltage increases (becomes more positive)!
Video of the shifts on the Daniell cell:
Period 3:
5. Lab 1 – Rebuild Voltaic Cells – Complete Lab up to question 4 in the conclusion page.
9/10 – Tuesday Homework: completing the other side of the 2 worksheets that have been
assigned previously.
1. Please complete Intro Voltaic Cells Worksheet 1
BUT PLEASE Complete QUESTION 2 ONLY!!
THIS IS THE SIDE THAT HAS the TITLE. (OPPOSITE OF LAST NIGHT’s HW).
Sorry both sides are numbered 1!
2. Review question 1 with the key below.
3. And/or you can follow along with me going over Question 1 with lecture below.
4. Complete ONLY Question 2 (AP Question 2003 side)
Intro Voltaic Cells worksheet 1.pdf worksheet – This was given out last week and we are doing the
opposite side of the weekends homework.
( It is a Past AP problem worksheet) –
5. Review with key or the video posted below. (Just question 2!)
End of Tuesday..
9/11 – Wednesday – period 2/period 3
Quiz Thursday (tomorrow) on everything that we have done! The Intro Voltaic Cells worksheet 1.pdf and The Intro Voltaic Cells worksheet 2.pdf worksheet are KEY! Dig into the lectures that go with them!
1. Review of the Daniell cell with 2 stresses in video posted yesterday.
A) Dilution of an ion: Adding water that will lower the molarity = ratio of amount of ions to volume of water
B) Adding a salt that causes a precipitate that lowers the molarity of an ion.
NEW C) Adding a salt that provides a common ion.
* A) and B) only have an effect on changing voltage or spontaneity of the forward direction of the redox reaction if the ion that is effected is in the overall reaction! For the Daniell cell is must be:
Zn0 (s) + Cu+2 —–> Zn+2 + Cu0
So only the Cu+2 or Zn+2 are the ions and their concentration changes that can create a stress that will cause the reaction to shift (become more favorable). If the ion is NOT COMMON to the overall reaction of the redox reaction (in the voltaic cell) then there will no effect on spontaneity or voltage.
Positive volts = Favorable Pathway = Spontaneous = entropy of universe (∆S) increasing = energy dispersed = obtain Free Energy (∆G) to do work (power our phones!)
Daniell Cell Demo 2 – Time Lapse – Helpful for Lab:
period 4 Lab
1. Lab 1 – Complete the diagram of the voltaic cell on page 2 and all conclusion questions.
Use your picture on your phones to help with the diagram.
– Reviewed the charges ion the anode (-) and cathode (-)
2. Completed Questions 1 – 4 in the conclusion page.
3. Started answering questions 5, 6, 7, 8
question 6: I should NOT have written that the Cu ions cannot pass through the dialysis tubing
question 7: what ions flowing can pass through the Dialysis Tubing (cellulose).
question 8: What is fizzing – I will get to this the next lab period.
-Error Analysis
Conclusion: DO NOT START YOUR CONCLUSION.
9/11 – Wednesday – Homework:
1: Please Study for a 15 minute – 1 page Quiz the voltaic Cell Thursday 9/13.
A very good review would be to review and redo the following worksheets And/Or Re-vist the videos that went over this weeks topics:
Topics:
A) Labeling a complete voltaic cell:
1. Identify Anode and Cathode.
2. Determine the flow of electrons.
3. Label all ions in half cells (oxidation and reduction areas) AND in Salt Bridge.
4. Movement of ions in salt bridge.
B) Write the Half reactions.
C) Determine the overall Balanced Net ion reaction.
D) Calculate the Net Potential (E0 cell) of the voltaic cell.
E) Predict how the voltaic cell’s voltage will change in response to stress.
Underlying Principles:
Coulombs Law, Le Chatelier’s Principle, Voltage vs Amperage, Spontaneity and Equilibrium,
Solubility and Precipitates, Reduction potentials
9/12 – Thursday – period 2 (we will do lab first instead of period 3)
1. Started answering questions 5, 6, 7, 8 from Lab
question 6: I should NOT have written that the Cu ions cannot pass through the dialysis tubing….
question 7: What ions flowing can pass through the Dialysis Tubing (cellulose).
question 8: What is fizzing – I will get to this the next lab period.
-Error Analysis
START YOUR CONCLUSION.
| Conclusion Writing:
1. What did find or measure Quantitatively? What are the important values of your data? This is normally posted in your results section of a formal writeup. How accurate are you (how close are you to a known standard, E0 cell )?
2. Make the leap! = connect your quantitative value and comparison with the known standard in terms of atom/ions or particle to explain a possibly reason for the outcome.
3. Error discussion.
Every laboratory is limited in errors in measurement and human errors. Do not write about these!! Please describe in detail every major limitation of this laboratory and why you believe it may have lead to your outcome.
IN this Lab the error discussion will result from things that are NOT FROM YOUR LEAP! Do nor just list errors. I want an explaination how these errors could of resulted in YOUR OUTCOME.
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period 3 (lab period for period 2 class)/4:
1: New Voltaic Cell Demo with the same metal electrodes and ion with the same concentrations
2: Voltaic Cell quiz
Today’s demonstration: Concentration Cell
9/13 Thursday Homework:
1. Lab write up – conclusion writing for Lab 1 – Lab is due Monday 9/16
Please write the Objectives to the Lab on the first page.
1: To Construct a voltaic Cell
2: To measure the voltaic’s cell voltage.
3: To determine the Accuracy of your results.
Please start writing your conclusion. You can write on the lab but you can also use the computer by printing and attaching to your lab.
Lab 1 Conclusion review:
1. Please tell me what you measured (voltage) and calculated (percent error). Do not mince words. Get to the point. This is like our results section last year in our formal labs.
2/3: Explain your errors (why your percent error was so low or negative). You will combine the leap with the error analysis here. The leap last year was always about an organism and the leap this year is always about atoms or ions. So what did the atoms or ions do that may have contributed to the large negative error? There is one error that is the largest and I like to think of it as a love triangle between Mg, Cu+2 , and H2O. I think this was the inspiration to Ed Sheeran’s song, Happier.
I saw you in another’s arms
Only a month we’ve been apart You look happier Saw you walk inside a bar
He said something to make you laugh I saw that both your smiles were twice as wide as ours Yeah, you look happier, you do Ain’t nobody hurt you like I hurt you
But ain’t nobody love you like I do Promise that I will not take it personal, baby If you’re moving on with someone new ‘Cause baby you look happier, you do
My friends told me one day I’ll feel it too And until then I’ll smile to hide the truth But I know I was happier with you Sat on the corner of the room
Everything’s reminding me of you Nursing an empty bottle and telling myself you’re happier Aren’t you? Ain’t nobody hurt you like I hurt you
But ain’t… |
 This cell was left over night. Notice the Mg electrode is smaller and the cloudy mixture. Were there precipitates?
How did this contribute to the error? Or was this a competing error? Notice some of the precipitates seem to be bluish green, which is an indication that Copper precipitates were also made.
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Chemical reactions that may have contributed:
Mg + HOH (water) —–> Mg+2 + 2OH– + H2 (g)
Would these ions (Mg+2 + 2OH–) form a precipitate with ions already present? The color of the entire battery was bluish? What does that say about movement of Cu+2 ions?
What factors were competing? Based on the experimental voltage which factor dominated?
My video below illustrates the reaction occurring above (the fizzing or production of hydrogen gas).
End of Thursday..
9/12 – Friday – period 2 class/ period 3 class –
1: Voltaic cell Quiz review-
2: Classwork: Previous AP questions and related concepts
Its important to see how AP Central thinks and view how these concepts are tested
– period 4 Lab (2nd period for period 3) –
1: Voltaic cell Quiz review-
2: Lab 1 completion/conclusion writing
2: Lab 2 – Group Slide aUp – discussion/begin
*Update – The second Voltaic cell quiz will be given in extra help and not in class. Remember I will give you the better of the 2 grades. I have it ready when ever you come in. Please do so by next week.
9/13 – Friday (weekend HW): Watch for Black cats!
1: Lab 1 due Monday 9/16 in the purple crate.
2. Complete the form below on battery in your car (lead acid) UNLESS
its an electric car (Lithium Ion).
Battery Form:
Lead acid Battery (Car Battery):
How It Works
Let me give you the big picture first for those who aren’t very detail oriented. Basically, when a battery is being discharged, the sulfuric acid in the electrolyte is being depleted so that the electrolyte more closely resembles water. At the same time, sulfate from the acid is coating the plates and reducing the surface area over which the chemical reaction can take place. Charging reverses the process, driving the sulfate back into the acid. That’s it in a nutshell, but read on for a better understanding. If you’ve already run from the room screaming and pulling your hair, don’t worry.
The electrolyte (sulfuric acid and water) contains charged ions of sulfate and hydrogen. The sulfate ions are negatively charged, and the hydrogen ions have a positive charge. Here’s what happens when you turn on a load (headlight, starter, etc). The sulfate ions move to the negative plates and give up their negative charge. The remaining sulfate combines with the active material on the plates to form lead sulfate. This reduces the strength of the electrolyte, and the sulfate on the plates acts as an electrical insulator. The excess electrons flow out the negative side of the battery, through the electrical device, and back to the positive side of the battery. At the positive battery terminal, the electrons rush back in and are accepted by the positive plates. The oxygen in the active material (lead dioxide) reacts with the hydrogen ions to form water, and the lead reacts with the sulfuric acid to form lead sulfate.
The ions moving around in the electrolyte are what create the current flow, but as the cell becomes discharged, the number of ions in the electrolyte decreases and the area of active material available to accept them also decreases because it’s becoming coated with sulfate. Remember, the chemical reaction takes place in the pores on the active material that’s bonded to the plates.
Lead Acid battery 1 video:
Lead Acid battery animation:
PbO2(s) + HSO–4 (aq) + 3H+ (aq) + 2e– —> PbSO4 (s) + 2H2O (l) E0 = + 1.69 V
PbSO4(s) + H+ (aq) + 2e– —-> HSO4– (aq) + Pb (s) E0 = – .35 V
Pb+2 + 2e– —-> Pb0 E0 = – .13 V
End of week 2!