AP Chem – Q1 – week 3 – 21-22 | Mr. Grodski Chemistry

Week 3 – 9/13 – 9/17

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9/13 – Monday – A Day – 2/3a Lab, 4 single

Main focus –

a) To link the concepts of spontaneity to the voltaic cell.

b) To teach the concept of Le Chatelier’s Principle.

1. Review the Voltaic Spontaneity HW Form- with key

Skills: Solubility, Spontaneity, Equilibrium,

How concentration of soluble ions in a voltaic cell affect its voltage.

Voltaic Spontaneity Form – Key.pdf
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2. NO₂ and N₂O₄ ampule demo with heat, viewing the ampule as equilibrium.

Manipulating the spontaneity with heat, in phase changes, adding salt to ice

3. LeChateliers Principle/ with worksheet

LeChateliers principle worksheet p.pdf
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LeChateliers principle worksheet KEY 2012 p.pdf
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4. Re-vist the Classroom Daniell cell and predict voltage

by manipulating concentration of free ions

2/3a Lab –

LAB Activity 1 – Making of batteries (voltaic or galvanic cell) – last 15 minute. In this Lab each person will make a pair of voltaic cells that if successfully created will power a 3 volt transistor radio.

a) Made one voltaic cell and identifies anode, cathode and tested voltage.

Identified the spontaneous process with positive volts

wrote half reactions, identified ox and red agents.

LAB 1 – Voltaic Cell.pdf

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Notice that concentration of the NO₂is large initially and decreases as the reaction proceeds.

Notice the initial concentration of N₂O₄ is zero (it has not been made yet) and increases as the reaction proceeds.

Both NO₂and N₂O₄ eventually level out and at this point equilibrium has been reached!

If the rate of 2NO₂combining to make N₂O₄ (forward reaction) is as fast as rate of N₂O₄ decomposing into 2NO₂ (reverse reaction) then the concentration of both chemicals become CONSTANT at equilibrium.

At point C, there 100% NO₂ and 0% N₂O₄ thus there is no competing reaction because there is no NO₂to combine to make the N₂O₄. The reverse reaction is at it maximum spontaneity and the forward reaction is at its minimum. There is a Shift in the reaction to move in the reverse. Over time its spontaneity will steadily decrease until it reaches the point of equilibrium and the “death of the reaction”.

Notice that the equilibrium position is at the bottom!! This is where the death of the reaction or where there is ZERO Spontaneity or No more release of energy into the Universe.

ΔS_universe = 0

At point A we have 100% NO₂and 0% N₂O₄. At this point there is tremendous pathway to go forward! There is No competing backwards reaction!! The reverse reaction is impossible here. It so spontaneous in the forward that the reverse is impossible!

At point B, there is 60% NO₂ and 40% N₂O₄.
Here we have a competing reaction reverse reaction thus the forward reactions is not as spontaneous and the reaction is getting closer to its death. The reverse reaction is still not as spontaneous as the forward but it is closing in, thus the overall Net direction is still forward but this pathway is not nearly as great as point A.

Dissolving of a soluble salt : Water can compete with the Coulombic attractions of ions in a salt.

LeChatelier’s Principle Lesson : If you need to review this..

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9/13 – Monday Homework: –

1. Complete LeChateliers Principle worksheet (front side) given out in class

and review the key below:

LeChateliers principle worksheet p.pdf
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LeChateliers principle worksheet KEY 2012 p.pdf
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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!

Intro Voltaic Cells worksheet 2 – skills.pdf
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3. Review question 2 with the key below.

Intro Voltaic Cells worksheet 2 – skills Key p.pdf
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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.

4: AP Chemistry Voltaic Cell Concepts Review worksheet 2 Video:

Today’ lesson:

End of Monday

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9/14 – Tuesday – B Day – 2 single, 3b/a Lab

Main focus –

a) To identify the voltage change in a voltaic cell due to Le Chatelier’s Principle with changes in the concentrations of ions in half cells, specifically when a precipitate is made.

b) To identify the precipitate in a net ion equation using the solubility rules or concepts.

1. Quick Review of the LeChateliers principle worksheet p.pdf – Keep connecting to the U diagram

LeChateliers principle worksheet KEY 2012 p.pdf
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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 = voltage drop!}

^{(lowers spontaneity of forward reaction)} The reverse is now favored more than it was which LOWERS the forwards reactions

pathways or spontaneity, which results in lowering the voltage!

Yesterday I added water to the Zinc half cell and the voltage increased because I was

decreasing the molarity of the concentration of the Zn⁺² ions.

Zn⁰ (s) + Cu⁺² —–> Zn⁺² + Cu⁰

^{Stress: decreases}

^Response:^{Shift ———————> = Voltage increase!}

^{(increases spontaneity of forward reaction)}

We can decrease the concentration of dissolves ions (aq) another way besides adding water.

3. Precipitation reaction demo – Double replacement reactions or precipitation reactions-

Net ion reaction written to eliminate spectators!

Net Ion Reaction Intro – Precipitation 1920.pdf
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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.

Today’s demonstration:

Todays Notes: (period 2 class needs to read this and watch demo video below!):

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^–²in the salt (ionic compound).

Na₂CO_3 (s) —-> 2 Na⁺(aq) + CO₃^-2(aq)

Then CO₃^-2reacted with Zn⁺²to form a precipitate, which takes Zn⁺²out 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 that were described today in the notes above.}

– At 0:35 I add water to dilute the Cu⁺² :

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 = voltage drop!}

^{(lowers spontaneity of forward reaction)} The reverse is now favored more than it was which LOWERS the forwards reactions

pathways or spontaneity, which results in lowering the voltage!

– At 1:33 of the video I add Na₂CO_{3 (s):}

Today’ lesson:

3b/4 Lab –

LAB Activity 1 – Making of batteries (voltaic or galvanic cell) – In this Lab each person will make a pair of voltaic cells that if successfully created will power a 3 volt transistor radio.

LAB 1 – Voltaic Cell.pdf

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a) Made one voltaic cell and identifies anode, cathode and tested voltage.

Identified the spontaneous process with positive volts

wrote half reactions, identified ox and red agents.

b) Completed the diagram, conclusion questions, and reviewed errors for the writing of the

conclusion

&nbsp

. 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 for the conclusion:

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).

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9/14 – Tuesday Homework: –

For Period 2 Class today please Read todays notes above and connect them with Daniel cell – Le Chateliers Demo video and follow below:

1. Please complete Intro Voltaic Cells Worksheet 1

BUT PLEASE Complete QUESTION 1.

THIS IS THE SIDE THAT HAS the TITLE. (OPPOSITE OF LAST NIGHT’s HW).

Sorry both sides are numbered 1!

Intro Voltaic Cells worksheet 2 – skills.pdf
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2. Review question 2 with the key below.

Intro Voltaic Cells worksheet 2 – skills Key p.pdf
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3. And/or you can follow along with me going over Question 2 with lecture below.

Intro Voltaic Cells worksheet 2 – skills.pdf worksheet Lecture:

4. Complete Question 1 and 2 (AP Question 2002 and 2003)

Intro Voltaic Cells worksheet 1.pdf worksheet –

( They are Past AP problems ) –

Intro Voltaic Cells worksheet 1.pdf
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Intro Voltaic Cells Worksheet 1 key pp.pdf
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5. Review with key posted above or the video posted below.

3: AP Chemistry Voltaic Cell Concepts Review worksheet 2 Video:

Start from the beginning in the video.

5: Intro Voltaic cell worksheet 1 video:

End of Tuesday!

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9/15 – Wednesday – A Day – 2/3a Lab, 4 single

Main focus –

a) To identify the voltage change in a voltaic cell due to Le Chatelier’s Principle with changes in the concentrations of ions in half cells, specifically when a precipitate is made or a common ion is added.

1. Review of the Daniell cell with 2 stresses in video posted yesterday.

Intro Voltaic Cells worksheet 2 – skills Key p.pdf
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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.– question 1: Intro Voltaic Cells

worksheet 2 – skills

C) Adding a salt that provides a common ion. – question 2: Intro Voltaic Cells

worksheet 2 – skills

* B) and C) 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

(∆S) increasing= energy dispersed = obtain Free Energy (∆G) to do work (power our phones!)

^{Video of the shifts on the Daniell cell that were described today}

– At 0:35 I add water to dilute the Cu⁺² :

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 = voltage drop!}

^{(lowers spontaneity of forward reaction)} The reverse is now favored more than it was which LOWERS the forwards reactions

pathways or spontaneity, which results in lowering the voltage!

– At 1:33 of the video I add Na₂CO_{3 (s):}

Na₂CO_3 (s) —-> 2 Na⁺(aq) + CO₃^-2(aq)

Then CO₃^-2reacted with Zn⁺²to form a precipitate, which takes Zn⁺²out 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)!}

What if I create voltaic cell with the same electrodes (Cu) and the same concentration of Copper ions?

Left Half Cell = Cu/ 0.1 M Cu(NO3)2

Right Half Cell = Cu /0.1 M Cu(NO3)2

Salt Bridge : 0.1M Cu(NO3)2

Stress 1: Add CuCl2 (s) to left beaker

Stress 2: Add H2O to right beaker

Do these 2 stresses counteract each other?

Watch me review this demo: https://youtu.be/yzdk9bcTJ8U

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2/3a Lab –

LAB 1 – Voltaic Cell.pdf

View Download

a) Made one voltaic cell and identifies anode, cathode and tested voltage.

Identified the spontaneous process with positive volts

wrote half reactions, identified ox and red agents.

b) Completed the diagram, conclusion questions, and reviewed errors for the writing of the

conclusion

&nbsp

. 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 for the conclusion:

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).

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9/15 – Wednesday Homework: –

1: Please Study for a 15 minute – 1 page Quiz the voltaic Cell for Friday 9/17.

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 and their charges.

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.

2: Complete Lab 1, including Conclusion . It is due Friday, 9/16

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 explanation how these errors could of resulted in YOUR OUTCOME.

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.

..Walking down 29th and Park

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…Blah Blah

End of Wednesday!

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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9/16 – Thursday – Yom Kippur – Off

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9/17 – Friday – B Day – 2 single, 3b/4

Main focus –

a) To identify the voltage change in a voltaic cell due to Le Chatelier’s Principle with changes in the concentrations of ions in half cells, specifically in a concentration cell

1. Review of the concentration cell using my video of the demonstration below:

Cu⁰ (s) + Cu⁺² —–> Cu⁺² + Cu⁰

So only the Cu⁺² ions and their concentration changes that can create a stress that will cause the reaction to shift (become more favorable). If there is no change in the concentrations in either the oxidation cell or the reduction cell then there is no spontaneity or no voltage. This voltaic cell can be manipulated by LeChatelier’s Principle by adding a

A) COMMON ion (ex. CuCl2)

B) an ion that will precipitate out Cu⁺²

C) water to one side that will dilute the molarity the concentration of Cu⁺²

Positive volts = Favorable Pathway = Spontaneous = entropy of universe (∆S) increasing

(∆S) increasing= energy dispersed = obtain Free Energy (∆G) to do work (power our phones!) 2. Take the voltaic/galvanic cell quiz.

My video below illustrates the a voltaic cell made from different concentrations: Concentration cell

Today’s lesson on the concentration cell:.

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3b/4 Lab –

LAB 1 – Voltaic Cell.pdf

View Download

a) Made one voltaic cell and identifies anode, cathode and tested voltage.

Identified the spontaneous process with positive volts

wrote half reactions, identified ox and red agents.

b) Completed the diagram, conclusion questions, and reviewed errors for the writing of the

conclusion

&nbsp

1. Completion of the conclusion of Lab 1. 2. Discussion of Lab 2 – voltaic cell Race! Start designing

Lab 2 – design a voltaic cell with greatest voltage– modest breakfast up for grabs

Given the following electrodes: Sn, Cu, Zn, Fe, Al

and solutions:

potassium hydroxide, copper (II) sulphate, tin (II) chloride,

iron (III) chloride, aluminum nitrate, zinc nitrate

Review of the Lab 1 that might help with conclusion:

Lab 1 fun:

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9/17 – Friday’s Homework: –

1. Please review the graded quiz that will be emailed back to you sometime Saturday. A blank copy and the key will be posted below as well as a complete review video. You have another quiz Monday which will be the best out of 2!

Voltaic Cell quiz 1.pdf
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Voltaic Cell quiz 1 key.pdf
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2. Complete both sides of the worksheet below and review with the key. Skip question 6 iii in question 6.

Recent Voltaic Cell AP Test Questions .pdf

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Recent Voltaic Cell AP Test Questions key p.pdf
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Review of the Voltaic cell quiz given Friday: I will open this video after both classes finish the quiz today.

End of week 3!