Writing half reactions from a cell diagram

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Glenda Marshall DIS 3M
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Joined: Sat Sep 27, 2014 3:00 am

Writing half reactions from a cell diagram

Postby Glenda Marshall DIS 3M » Wed Feb 04, 2015 10:20 pm

I was wondering if someone can help me understand the process of writing half-reactions from cell diagrams. My main question is if there is particular order that the species are written in. I know that the anode will be to the left of the salt bridge (the double line) and the cathode will be to the right, but how do you know what order to put the ions in? For example, in 3.11 part (e), the cell diagram is as follows:

Pt l Sn4+, Sn 2+ ll Cl- l Hg2Cl2 l Hg

How would I know that Cl- and Hg are on the same side of the half-reaction for the anode? And are they just randomly arranged in the cell diagram or are they in that order for a reason? For example, why is Cl- before Hg2Cl2?

Thank you for your help!

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Re: Writing half reactions from a cell diagram

Postby Chem_Mod » Sat Feb 07, 2015 12:34 am

When writing out a cell diagram, the electrodes are written on the outside (far left or far right). The order of all ions do not matter as long as you put them on the correct side, either oxidation or reduction. In other words, there is no particular order in which ions of the same state need to be written.

Justin Le 2I
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Joined: Fri Sep 26, 2014 2:02 pm

Re: Writing half reactions from a cell diagram

Postby Justin Le 2I » Wed Feb 11, 2015 12:06 pm

Usually any substances that are aqueous are closest to the double line. If you want to know what goes on what side, just look at the table of standard reduction potentials and use the one that has the elements that you have.

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