Cell Notation - Video Tutorials & Practice Problems
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1
concept
The Cell Notation
Video duration:
6m
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Now you're going to say that our cell notation, also called our cell diagram, is a quicker method to describe the overall redox reaction in an electrochemical cell. Now, here we're gonna have 2 types of boundaries involved. We have our phase boundaries and then we have our physical boundaries. Our phase boundaries represents a sudden line going up. Here we're gonna say this is the condition where 2 phases of the same substance can coexist at equilibrium. Our physical boundary is shown as 2 solid lines going up. This is the physical space that separates the anode and the cathode of your electrochemical cell. So when we're talking about a cell notation or cell diagram, we're referring to this portion here. Now, within this cell diagram or cell notation, we can plug in different elements, different types of ions, different types of compounds. So how exactly do we do that? Well, here let's take a look at our electrochemical cell. In this electrochemical cell, we have the anode on the left and we have the cathode on the right. Here, we're going to assume that we're dealing with a spontaneous electrochemical cell, otherwise known as the galvanic or voltaic cell. That means that our anode will be negatively charged and our cathode positive. Remember, the anode is the site of oxidation, and the cathode is a site of reduction. Remember, oxidation we're losing electrons, so electrons will be leaving here we have a chromium electrode, it'd be leaving and heading towards the cathode. The voltmeter would just register the amount of electricity being generated by the transferring of electrons from the anode to the cathode. Here we know that the copper electrode is gaining these electrons. Now if we think about this reaction in terms of half reactions, we're gonna say here canceling out the intermediates gives the overall reaction. Now in the cathode compartment, what's going on? We know reduction is occurring. If reduction is recurring, the electron is reacted. So if we look at the cathode compartment we have cu 2 plus ions and the copper neutral form. So here we have c u 2 plus, it will gain 2 electrons and that will create our c u neutral form. The outer compartment where oxidation is occurring. With oxidation, remember, electrons are products. We have the chromium electrode and the c r two plus ions within the solution. So here, we'd have our c r solid. This is solid here and this is aqueous here. So we have CR solid being oxidized to give us CR 2+iaquias, and here are all the 2 electrons we're producing over here. Our intermediates. Your electrons must always be intermediates, and they have to be the same number. 2 electrons, 2 electrons. They cancel out. What's left at the end is our overall redox reaction. So that give us Cu 2+aqueouspluschromium solid, gives us Cu solid plus c r 2 plus aqueous. We have our half reactions, we cancel out the intermediates, then we have our overall reaction. Now we go to the cell notation portion. Remember, the cell notation portion is a quicker way of drawing or describing what's happening here in the electrochemical cell. You don't have time to draw this for another chemist, so you quickly write it down in cell notation form. Now, memory tool here. Cell notation is as easy as a b c. That's because we have a phase boundary here which is a, we have our physical boundary, which is B, and here we have our next phase boundary, which is C. A is for anode, so this portion here represents the anode compartment. B is the physical break, so the physical space between my 2 half cell containers, and then c, you probably guessed it, is the cathode. So this portion represents the cathode. Now when it comes to this cell notation, we'd say that the lower oxidation states or lower oxidation numbers will be found on the ends on both sides, and then the higher oxidation numbers will be found inside. With this information, we can write our cell notation here based on what's going on in this electrochemical cell. So on the anode compartment, we have chromium neutral and chromium 2+. Chromium neutral has an oxidation number of 0. Chromium 2+ has an oxidation number of 2+. So the lower oxidation number is on the end, so c r solid, Higher oxidation number in the in the center, c r two plus. Calthal compartment, over here. What are the 2 species interacting with each other that are the same substance? We have copper 2+ion and and just copper neutral. Their higher oxidation state is copper 2+, which would be in the interior, and then copper is solid here on the end. So basically, this cell notation or cell diagram is equivalent to me drawing this entire electrochemical cell, at least in its basic design. Well, we're not talking about the ions in the salt bridge, we're just talking about, okay, we have an anode compartment, these are the species involved, we have our cathode compartment, and then these are the species involved and how they interact with each other. So just from this information, we don't need to draw an entire electrochemical cell. So that's the beauty of our cell notation or cell diagram.
2
example
Cell Notation Example
Video duration:
1m
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Here it says consider an electrochemical cell where the following reaction takes place. From this overall redox reaction, it asks, what is the sub notation for this cell? Or remember, sub notation, we're gonna have a phase boundary, a physical boundary, and another phase boundary. Subnotation is as easy as a, b, c, where a represents our anode, b is our physical break between both half cell compartments or containers, and c is our cathode. Remember that our lower oxidation numbers are on the ends, and then our higher oxidation states or numbers are in the interior or inside. So here, if we take a look at our overall reaction we have 10 2 going to 10 neutral. Its oxidation number goes from plus 2 to 0. Its oxidation number was reduced, therefore, it represents the cathode. So here it'd be in the cathode compartment which is this portion here. Remember the higher oxidation state is on the interior, so that'd be s n 2+ aqueous, and then the lower one is on the end, so that'd be s n solid. Aluminum goes from 0 to plus 3. Its oxidation number went up, so it's been oxidized and therefore represents the anode. Again, the higher oxidation states on the interior, so a l 3 +auseaqueous, and the lower oxidation state is on the end, a l side. So this here would represent our cell notation or cell diagram for the following electrochemical cell.
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Problem
Problem
Write the half reactions as well as the overall net ionic equation for the following line notation:
Fe (s) | Fe2+ (aq) || Mg2+ (aq) | Mg (s)
A
Anode: Fe (s) → Fe2+ (aq) + 2e-
Cathode: Mg2+ (aq) + 2e- → Mg (s)
Overall: Fe (s) + Mg2+ (aq) → Fe2+ (aq) + Mg (s)
B
Anode: Fe (s) → Fe2+ (aq) + 2e-
Cathode: Mg2+ (aq) + 2e- → Mg (s)
Overall: Fe2+ (aq) + Mg (s) → Fe (s) + Mg2+ (aq)
C
Anode: Fe (s) → Fe2+ (aq) + 2e-
Cathode: Mg (s) → Mg2+ (aq) + 2e-
Overall: Fe (s) + Mg2+ (aq) → Fe2+ (aq) + Mg (s)
D
Anode: Fe2+ (aq) + 2e- → Fe (s)
Cathode: Mg2+ (aq) + 2e- → Mg (s)
Overall: Fe (s) + Mg2+ (aq) → Fe2+ (aq) + Mg (s)
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Problem
Problem
The cell notation for a redox reaction is given as the following at (T= 298 K). Calculate the cell potential for the reaction at 25ºC.
Zn (s) | Zn2+ (aq, 0.37 M) || Ni2+ (aq, 0.059 M) | Ni (s)
Standard Reduction Potentials
Zn2+ (aq) + 2 e– →. Zn (s) E°red = - 0.7621
Ni2+ (aq) + 2 e– → Ni (s) E°red = - 0.2300
A
0.3130 V
B
0.4033 V
C
0.5085 V
D
0.1199 V
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Problem
Problem
What is the [Cu2+] for the following cell notation diagram if the cell potential is 0.4404 V?