Archive – week 3 – 19-20
Week of 9/16 – 9/20
9/16 – Monday – period 2/3
1. 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
– period 4
1. Lab 2 – design a voltaic cell with greatest voltage–modest breakfast up for grabs
9/16 – Monday – Homework
1: Please make one more submission to the Lead Acid Battery Form.
2: Please review the electrolytic cell lecture below: (Due by Wednesday morning)
*Make new lecture on this worksheet directly.
3: Please complete the worksheet and review with key.
9/17 Tuesday – period 2 –
Lab 2 completion – you should have a working design that you need to just improve on
period 3/4 –
Lab 2 completion – you should have a working design that you need to just improve on
9/17 – Tuesday – Homework – Due Wednesday
1. Complete 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.
You need to present on the slides the following:
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Title page with all Lab partners listed.
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Objectives.
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Materials Page listed with all available components
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Labeled Diagram Slide of best voltaic cell design – Use a picture you took 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) Eo cell
5. Diagram of manipulations of Spontaneity – U diagram, LeChateliers principle chart
6. Best Measured voltage (need a picture with the battery).
7. 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?
End of Tuesday..
9/18 Wednesday – period 2/3
1) Review the Lead Acid Battery Form
2: Review Lab 2 – /specifically the reactivity of Al /water like lab 1.
How precipitates help and hurt
3: Apple Battery
4) Monday’s Homework –
5) Electrolytic Cell- Electrolytic cell Demo of electrolysis of KI (aq)
Electroplating demo
period 4
*we will review Lab 2, Lead acid form, apple battery tomorrow..
1) Electrolytic Cell- Electrolytic cell Demo of electrolysis of KI (aq)
Electroplating demo
Today’s Demos:
Electrolysis of fused salt demo:
Electroplating Demo:
9/18 – Wednesday – 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 give you trouble. I will go over and reteach that in class tomorrow.
Stiochiometry 8 redox electrolytic – 1999.pdf
Lecture for question 1 on side 1(Stiochiometry 8 redox electrolytic):
End of Wednesday..
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 10-19 C in a single electron (the charge in a single electron = -1.60 x 10-19 C )
There are also 1.60 x 1018 electrons 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+2 in 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?
9/19 – Thursday – period 2
1. Review of Stiochiometry 8 redox electrolytic – 1999.pdf worksheet – (side one and into side 2).
Concepts: Mole concept, Faraday’s Constant, dimensional analysis (using your units to cancel)
2) Modeled Stiochiometry 8 redox electrolytic – 1999.pdf worksheet – side 2
Stiochiometry 8 redox electrolytic – 1999.pdf
period 3/4
1: Review Lab 2 – /specifically the reactivity of Al /water like lab 1.
How precipitates help and hurt
2: Apple battery
3. Review of Stiochiometry 8 redox electrolytic – 1999.pdf worksheet – (side one and into side 2).
Concepts: Mole concept, Faraday’s Constant, dimensional analysis (using your units to cancel)
4) Modeled Stiochiometry 8 redox electrolytic – 1999.pdf worksheet – side 2
Mr. Grodski’s Lab 2 battery video:
9/19 – Thursday Homework:
1. Complete the Stiochiometry 8 redox electrolytic – 1999.pdf worksheet (side 2) and review with key below and make sure you SKIP question 2d.
Stiochiometry 8 redox electrolytic – 1999.pdf
2. Complete the Electrolytic Cell Form below:
9/20 – Friday – period 2/3
1. Classwork – Complete / Review the back side of Stiochiometry 8 redox electrolytic – 1999.pdf worksheet.
period 4 –
1. Classwork – Complete / Review the back side of Stiochiometry 8 redox electrolytic – 1999.pdf worksheet.
9/20 – Friday – (Weekend Homework)HW:
Please read carefully!
1. Please make one more submission to Thursday night’s form. I had a problem with my key on question 6. I graded everyone’s form incorrectly for question 6 and thus I regraded it and sent it out to you Friday at about 11:30 am. Please review that graded email and then make a new second submission. Please note that I am not changing the form at all and I will not grade the last row in question 1 as i did in the first graded submission.
The second submission is due Monday morning at 4:00 am.
2. View the lecture below and follow along with me to complete the
3: 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?
There is no form this weekend!
End of week 3!