How do you know which is the anode and which is the cathode?

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Jenna Smith 3F
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Joined: Wed Sep 21, 2016 2:55 pm

How do you know which is the anode and which is the cathode?

Postby Jenna Smith 3F » Sun Feb 12, 2017 9:19 pm

I know that left side is associated with the anode and oxidation, while the right is associated with the cathode and reduction, but how do you tell them apart when you are only given the elements involved? For example, Q8 on the Winter 2016 Midterm only mentions that a silver electrode is placed into a 1.0 M Ag+ solution and a cadmium electrode is placed into a 1.0 M Cd2+ solution. In cases like this, how do you know which is which?

Noor_Burney_1L
Posts: 13
Joined: Wed Sep 21, 2016 2:55 pm

Re: How do you know which is the anode and which is the cathode?

Postby Noor_Burney_1L » Sun Feb 12, 2017 9:37 pm

When you look up the standard reduction potential values, you identify which Enot value is the most positive, and which Enot value is the most negative.
The most positive Enot value tells you which is being reduced, and the the most negative Enot value tells you which is being oxidized. So for question 8 of the midterm, because the standard reduction potential for silver is +0.80 V, you know that silver is being reduced. And because the standard reduction potential for cadmium is -0.40 V, you know that cadmium is being oxidized.

Jenna Smith 3F
Posts: 10
Joined: Wed Sep 21, 2016 2:55 pm

Re: How do you know which is the anode and which is the cathode?

Postby Jenna Smith 3F » Mon Feb 13, 2017 3:30 pm

Thanks. In the case of Q8 the Winter 2014 Midterm, though, how come the one with the more positive value is the anode?

Patrick_Mac_3D
Posts: 12
Joined: Wed Sep 21, 2016 2:58 pm

Re: How do you know which is the anode and which is the cathode?

Postby Patrick_Mac_3D » Wed Feb 15, 2017 3:06 pm

You are being asked for the acid dissociation constant (Ka) for HF. Therefore, you need to end up with the form HF-->H^+ + F^-. Then, you would have to flip the top reaction to resemble oxidation. I hope this helps.


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