## Cell Diagram and Ecell [ENDORSED]

Tarika Gujral 1K
Posts: 62
Joined: Fri Sep 28, 2018 12:27 am

### Cell Diagram and Ecell

1) With gaseous and nonconducting solid compounds, is the order
Inert|Gas/solid|Chg || Chg|Gas/solid|Inert?
Or does it follow the order of reactants to products?
Inert|Ox Reactant|Ox Product || Red Reactant|Red Product|Inert

2) With a positive Ecell, reduction is always on the right. Is this order reversed when Ecell < 0?

Jesse Kuehn 1B
Posts: 40
Joined: Wed Nov 14, 2018 12:23 am

### Re: Cell Diagram and Ecell

I believe the solid is always on the outside (or just inside the inert part) so the second form should always be right, and yes everything is reversed when the E is less than zero.

Chem_Mod
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Joined: Thu Aug 04, 2011 1:53 pm
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### Re: Cell Diagram and Ecell  [ENDORSED]

Using what I discussed in class, and the example I did in class:

ANODE (LEFT) || CATHODE (RIGHT)

Cu(s) | Cu2+(aq) || Fe3+(aq), Fe2+(aq) | Pt(s)

Put the conducting solids (electrodes) on the outside and aqueous next to the salt bridge.

Always include phase in the equation and cell diagram.

In a homework problem, there is a cell diagram answer key written as: Pt(s) | I- (aq) | I2(s) || .......

This is a saturated I-(aq) solution with undissolved I2(s) in the same solution. Both the salt bridge and the platinum electrode are in contact with the same saturated I-(aq) solution.
As one can see this simple notation does give the information needed to build or visualize the cell (battery).

Another homework problem used KOH (aq) instead of OH- (aq), but you do not need to include K if there is no information about potassium in the question. You can just put OH-(aq) to indicate alkaline conditions.

In cell diagrams: Anode (oxidation half-reaction) is always on the left; and the cathode (reduction half-reaction) is always on the right.

Some homework problems intentionally ask what is wrong with a given cell diagram, and an incorrect notation is given (which one can figure out because the voltage is negative).
By switching the left and right half-reactions one gets the correct cell diagram with a positive voltage.
To be correct the cell (battery) must have a positive voltage (as I repeated and joked about in class :-).

jane_ni_2d
Posts: 67
Joined: Fri Sep 28, 2018 12:23 am

### Re: Cell Diagram and Ecell

how can you tell which is the anode and which is the cathode?

davidryan3f
Posts: 63
Joined: Fri Sep 28, 2018 12:23 am

### Re: Cell Diagram and Ecell

jane_ni_2d wrote:how can you tell which is the anode and which is the cathode?

the anode is always on the right of the cell diagram and the cathode is on the right.

riddhiduggal
Posts: 30
Joined: Fri Sep 28, 2018 12:21 am

### Re: Cell Diagram and Ecell

In which cases do you flip the sign for the E, when calculating Ecell?

lukezhang2C
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

### Re: Cell Diagram and Ecell

For a Galvanic Cell it should be Anode || Cathode, where there are single lines (|) separating different states of matter, and commas separating different agents with the same state of matter. i.e (aq), (aq), || (aq)| (s)

AnayaArnold_3L
Posts: 56
Joined: Wed Sep 18, 2019 12:19 am

### Re: Cell Diagram and Ecell

Thanks for clarifying!!

lukezhang2C wrote:For a Galvanic Cell it should be Anode || Cathode, where there are single lines (|) separating different states of matter, and commas separating different agents with the same state of matter. i.e (aq), (aq), || (aq)| (s)

bloodorangefield
Posts: 24
Joined: Wed Sep 18, 2019 12:19 am

### Re: Cell Diagram and Ecell

How do you tell the difference between when it is an anode vs when it is cathode?