## Writing Cell Diagrams

Chiao-Wei Cheng 3e
Posts: 16
Joined: Wed Sep 21, 2016 2:55 pm

### Writing Cell Diagrams

$MnO^{-}_{4}(aq) + 5Fe^{2+}(aq) + 8 H^{+} (aq)\rightarrow Mn^{2+}(aq)+ 5Fe^{3+}(aq)+ 4H_{2}O (l)$
and the cell diagram looks like:
$Pt(s)|Fe^{3+} (aq), Fe^{2+} (aq) ||H^{+}(aq), MnO^{-}_{4}(aq), Mn^{2+}(aq)|Pt(s)$

My question is why the cell diagram is written in this particular order? For example, why is $Fe^{3+}$
is in front of $Fe^{2+} (aq)$ and why $H^{+}$ is in front of$MnO^{-}_{4}$?

Brandon_Phan_3J
Posts: 21
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Writing Cell Diagrams

I could be wrong but I don't think the placement of the aqueous ions matter in terms of which one comes before or after matters. As long as you have the rest of the notation down: (solid being oxidized | aqueous ions in anode beaker || aqueous ions in cathode beaker | solid being reduced), the aqueous ions are interchangeable with respect to their solutions. Hope someone can confirm or clarify!

Da_Rhee_1O
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Writing Cell Diagrams

I am not too entirely positive, but I was also told that the general notation is what is more important than the order of the aqueous ions.

Da_Rhee_1O
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Writing Cell Diagrams

I took a look again and confirmed with someone that for the order, the element before it is reduced is placed first, then the reduced form of it comes afterwards. There is an example in the coursereader on page 48 where Fe3+(aq) is written before Fe2+(aq). And it also looks like this is the case for most cell diagrams.

samuelkharpatin2b
Posts: 55
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Writing Cell Diagrams

When writing cell diagrams, we usually write everything that's in a solid form towards the far left/right, while anything other than solid, such as gas, aqueous solution, etc., is placed towards the "inside" of the cell diagram. For example, (s)I(aq)II(aq)I(s) would be a correct way of writing it. Double vertical lines represent a salt bridge, while a single vertical line represents a porous disk.

Chiao-Wei Cheng 3e
Posts: 16
Joined: Wed Sep 21, 2016 2:55 pm

### Re: Writing Cell Diagrams

Da_Rhee_1O wrote:I took a look again and confirmed with someone that for the order, the element before it is reduced is placed first, then the reduced form of it comes afterwards. There is an example in the coursereader on page 48 where Fe3+(aq) is written before Fe2+(aq). And it also looks like this is the case for most cell diagrams.

I'm guessing this only applies to the cathode side? And that for the anode side the element before it is oxidized is placed first, then the oxidized form of it comes afterwards.