Archive – AP Chem – Q1 – week 4 – 21-22

Week 4 – 9/20 – 9/24

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9/20 – Monday – A Day – 2/3a Lab, 4 single

Main focus –

a) To review the voltaic cell quiz 1 – specifically the solubility rule that the last

question is based on..

b) Introduce the Electrolytic cell (in Homework).

1. Review the Voltaic cell quiz 1

Skills: Solubility rules in Table F, Spontaneity,

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

Voltaic Cell quiz 1 key.pdf
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2/3a Lab –

LAB Activity 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

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9/20 – Monday Homework: –

1. Please read the notes below and view the videos on the 12 volt car battery (lead acid) UNLESS

its an electric car (Lithium Ion).

2. Complete the form below on battery in your car (lead acid) UNLESS

its an electric car (Lithium Ion). You have a total of 3 submissions to this form.

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.

from: https://www.batterystuff.com/kb/articles/battery-articles/secret-workings-of-a-lead-acid-battery.html

Lead Acid Battery Animation :

Lead Acid Battery Tutorial :

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

Lead Acid Form: This form is based in the information above. You have 3 more submissions tonight.

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End of Monday!

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9/21 – Tuesday – B Day – 2, 3b/4 single

Main focus –

a) To Complete or begin Lab 2 – STEM Lab

– design of the highest voltage voltaic cell

Students gather their materials and design their battery. Design needs to be in the lab groups presentation before they begin. Lab 2 – This is a slide-up lab done per each lab group. Please follow instructions:

This Lab write-up is a group slide-up. There is only one presentation per lab group and the entire group will get the same grade. I have emailed everyone with their group a link to the shared presentation

You need to present on the slides in the Presentation the following:

1. Title page with all Lab partners listed.

2. Objectives.

3. Materials Page listed with all available components

4. Labeled Diagram Slide of proposed voltaic cell design – Draw a diagram with your phone

A) labeled anode and cathode and identity of metals

B) direction of the flow of electrons.

C) all available ions present

D) salt in salt bridge – and ion flow

E) Charge on the electrodes

F) Half reactions for each half cell

G) Overall net ion equation

H) E^o cell

5. Labeled Diagram Slide of actual voltaic cell design – Use a picture you took with your phone Label as you did in #4

6. Diagram of manipulations of Spontaneity – U diagram, LeChateliers principle chart

7. Best Measured voltage (need a picture or video with the battery).

8. Discussion section of why your design or choice of materials lead you to your results. Chemical reactions are needed (overall reaction) as well as any side reactions that were competing, Why was you final choices better than your original and what factors came into play? Why was your design a compromise of ideas or concepts?

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9/21 – Tuesday Homework: –

1. Please work on your Lab 2 write-up with your lab partners.

Period 2 Class: You get more time but you should have slides 1 – 4 completed and you should have a plan for tomorrow based on what you accomplished today. You should get a start on slide 7 and 8 as you learned what did not work in your initial design.

Period 3/4 Class: There is no more class time for data collection and battery building. You should have all slides completed by tonight. I will show you my voltaic cell and review the limitations of the lab. This will help with your slide 8 discussion and you will probably improve on that slide once I review the lab with you.

2. Please review Voltaic cell quiz 2 with Key. I will email out the graded quiz for period 2 and provide a link to the key. Period 3/4 was given back the quiz with the key in class. I will review this quickly in class.

Anyone who wants another try at this quiz can take a third one after school on a day of your choosing. I am after everyday. I will take the best out of 3 in this case.

End Of Tuesday!

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9/22 – Wednesday – A Day – 2/3a , 4

Main focus –

a) To Complete the Lab 2 – STEM Lab – design of the highest voltage voltaic cell – — (period 2/3 today)

b) To discuss the limitations of the designs by modeling my own voltaic cell choices – this will help in your conclusion of the lab write-up c) To complete our discussion of the voltaic cell with an apple battery.

2/3a Lab –

LAB Activity 2 – design a voltaic cell with greatest voltage– modest breakfast up for grabs -Last period of data collection

1. Mr. Grodski’s Voltaic cell and explanation of choices and limitations:

Mr. Grodski’s voltaic cell design :

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9/22 – Wednesday Homework: –

1. Please complete your Lab 2 write-up with your lab partners. Lab requirements are posted under Tuesday. Grading the Conclusion very tough!

2. Please view the 2 lectures below on the Electrolytic Cell. 3. Please complete the worksheet and review with the key below:

Intro Electrolytic Cells worksheet 1 .pdf
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Intro Electrolytic Cells worksheet 1 Key.pdf
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4. Please complete the form below.

1: Electrolytic Cell intro lecture :

2: Electrolytic Cell Lecture :

4: Electrolytic Cell Intro form : This form is based in the information above. You have 3 submissions

tonight.

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End of Wednesday!

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9/23 – Thursday – B Day – 2, 3b/4

Main focus –

a) To Review the concepts of the electrolytic cell with an electroplating demo and electrolysis demo.

b) To take Notes on the 2 types of Electrolytic Cells.

1) Electrolytic Cell- Electrolytic cell Demo of electrolysis of KI (aq)

Electroplating demo

– Took notes on worksheet for the 2 demos.

Intro Electrolytic Cells Demo worksheet.pdf
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Last nights Homework: Intro Electrolytic Cells worksheet 1 Key.pdf

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3b/4 Lab –

LAB Activity 2 – design a voltaic cell with greatest voltage– modest breakfast up for grabs -Last period of data collection

1. A discussion of complex ions an their acidity and it effect on Aluminum Hydroxide

Electroplating Demo : For Today’s Notes

Today’s Lesson:

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9/23 – Thursday Homework: –

1: Complete Stiochiometry 8 redox electrolytic – 1999.pdf worksheet SIDE 1 One ONLY with

the lecture below that reviews question below!

Please complete side 1 of this worksheet the following ways:

a) You need to be able to draw and label the electrolytic cell that the question describes just like

you did from the diagram of the demo’s today. 3 hints below will help!

* Please remember that you are heating the AlCl₃ (s) until the ions are free. Based on the chemical formula you

should be able to figure out what ions are present. Also this goal of the electrolytic cell is make the elemental

form of each ion. We are looking to make pure Al and Chlorine gas (Cl₂).

*Remember that you will include a battery (batt) in your diagram and depending where you draw the

anode/cathode of the Battery (voltaic cell) and how you connect it to the electrodes (that do not react) in

the electrolytic cell will determine which electrode is the anode/cathode in the electrolytic cell. There are many correct ways to diagram this.

*But the ions will move only to the correct electrode based on their charges!

b) The second part, determining how many grams was deposited on the cathode is tonight’s

stretch. Please read the Notes on Electrolytic Cell below.

c) Try making the calculation using the notes, the key, or the lecture. I suggest that you try it

after reading the notes and then view my lecture below to see how I did the question.

You could use the key below or just let me walk you through the problem.

Do not worry about the calculation in the second part if it gives you trouble. I will go over and reteach that in class tomorrow.

Stiochiometry 8 redox electrolytic – 1999.pdf

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Stiochiometry 8 redox electrolytic KEY – 1999.pdf
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NOTES on the Electrolytic cells:

These electrolytic problems are centered around a couple of concepts:

1. Coulomb = SI unit of charge

2. Faraday’s Constant

If the current in a circuit is 1 Ampere then 1 coulomb of charge passes a point in the circuit every second.

1.0 A = 1 C/sec (1 Amp = 1 Coulomb per second)

Abbreviation: C as in Amperes above

Equation symbol: q or Q (as in Coulombs Law)

q = -1.60 x 10^-19C in a single electron (the charge in a single electron = -1.60 x 10^-19C )

There are also 1.60 x 10¹⁸electrons in 1 Coulomb

We use the concept of Coulomb to connect Amperes which measures current (or measure amount of the flow of electrons) that is being pushed through the conductor (or wire) by a voltage (Energy). A measures amperage over a measures amount of time will give us the AMOUNT OF CHARGE that passes over a point in the wire IN THAT TIME INTERVAL.

So Amperage (A = C/sec ) describes TOTAL CHARGE IN A TIME INTERVAL! So the key is the TIME and measured Amperage will give us total charge.

Now once we have TOTAL CHARGE we can relate Faraday’s Constant which came from Faraday’s laws of electrolysis that *basically states:

1: The mass of the deposited metal is directly proportional to the quantity of electrical charge that passes through the electrolyte.

2: For the same quantity of electricity or charge passes through different electrolytes, the mass of the deposited chemical is directly proportional to its chemical equivalent and inversely proportional to its valency.

Now at the time of Michael Faraday there was very little support for the idea of atoms , atomic or moles. Just chemical properties. One property that was well know was the valency of elements. Copper has a valency 2 because they knew 2 Cl ions would bind with Cu. This valency of course is valence electrons and is related to the

ELECTRONS IN THE HALF REACTION!!!!

Cu⁺² + 2e^– —-> Cu (s)

There was no understanding of mole concept yet so Faraday could not relate these observations in an electrolytic cell to moles. Once the mole equivalent was determined in the turn of the Century (1905) could a constant be described that relates charge of electrons with a mole of electrons. Faraday set the stage and the mole concept closed the door. Faraday would dance aggressively happy is he saw what we can predict with this constant given in his name:

F (Fancy) = 96,500 C / 1 mole of electrons

SO we can Now link the Total charge we get from measures Amperes and Time to the Quantity of electrons that are being forced through conductor. Since these electrons are being used at each electrode to “Force” an non-spontaneous reaction we can use the ratio of electrons that are responsible for the Coulombs to determine the number of atoms that are being produced at either electrode.

In the case of Copper above there are 2e^– per 1 Cu⁺²in the half reaction above so

if there will be twice as many electrons needed as Cu atoms deposited.

Faraday’s constant the total charge (we get from Amperage and time) to total number of electrons in half reactions occurring at the electrodes. Using the ration of electrons to atoms produced in the half reaction we can determine the amount of atoms.

Example: How many grams of Cu are deposited on the cathode in an electrolytic cell if the cell runs for 90 minutes at an amperage of 3.0 A?

Tonights lecture for the Stoichiometry 8 redox worksheet : For Homework!

End of Thursday!

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9/24 – Friday – A Day – 2/3a , 4

Main focus –

a) To discuss the last implication of the Fe+3 and OH- in the reduction cell in Lab 2.

b) To connect Faraday’s early work with our new stoichiometric calculation that determines the amount of metal plated at the cathode. c) To discuss the use of units in dimensional analysis.

1. Last discussion on how Fe+3 and OH- helped in the oxidation cell.

2. Reviewed Dimensional analysis

3. Discussed Faraday’s work and what was discovered in his electrolysis experiments

4. Reviewed Page 1 of the homework and continued to the second page as classwork.

Stiochiometry 8 redox electrolytic – 1999.pdf

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Stiochiometry 8 redox electrolytic KEY – 1999.pdf
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2/3a Lab –

LAB 3 – Determine the grams of copper collected at the cathode of an electrolytic cell of an unknown concentration of copper (II) chloride–

Setup an electrolytic cell complete the lab diagram collect and filter your copper place in the oven over the weekend

Lab 3 – Electrolysis of CuCl2.pdf

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9/24 – Friday Homework: –

1. Please complete your Lab 2 write-up with your lab partners. This Lab is due Monday! Lab requirements are posted under Tuesday. I am Grading the Conclusion very tough!

2. Please view the lecture below and follow along with me to complete the Lecture on Electrolytic cell – Molarity calculations worksheet: These are the calculations that I used to setup today’s lab.

Electrolytic cell – Molarity calculations .pdf
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Electrolytic cell – Molarity calculations Key p .pdf
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3. Please Complete Intro Electrolytic Cells worksheet 2.pdf worksheet and review with key below:

This worksheet is an example of a Past AP problem* that is asking for the students to solve for the Molarity or the concentration of a initial concentration in an electrolytic cell. IT is based on the Lecture above.

It is a great example of how you have to understand the material.

This question is using a voltaic cell with Amperage type questions that usually are seen with electrolytic cells.

*The key to this worksheet is identifying that the electrochemical cell chemical reactions are for a voltaic cell and that its setup is a little different then we have seen, except in Lab 2. The solutions will not always contain the ions of the metal electrode AND sometimes as in this case in this problem the oxidation occurs from the solution and not the Anode. They did not provide a diagram, but if you could envision 2 platinum electrodes in the 2 solutions in separate cells with some sort of a salt bridge then you are Gucci.

*Also when they state, ” at which point the C₂H₅OH (aq) has been totally consumed” just means when all of the C₂H₅OH (aq) has oxidized and the reaction stops. How much Amperage (flow of electrons) was needed to run the oxidation half cell empty?