determining cathode from anode

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Abigail Urbina 1K
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Joined: Thu Jul 27, 2017 2:01 am

determining cathode from anode

Postby Abigail Urbina 1K » Fri Mar 16, 2018 8:12 pm

If we are given two half reactions with their standard cell potentials, how exactly are we supposed to know which is the cathode and which is the anode, and thus which reaction we would need to reverse?

For example on question 3C of the 2014 Final:
Fe3+ + e- --> Fe2+
Zn2+ + 2e- --> Zn(s)

It says that the second reaction is the anode and the first reaction is the cathode. How are we sure of this?

Michaela Capps 1l
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Joined: Thu Jul 27, 2017 2:00 am

Re: determining cathode from anode

Postby Michaela Capps 1l » Fri Mar 16, 2018 8:17 pm

You would look at the standard cell potentials. The most positive is the cathode. Also, cathode-(anode) should be positive.

Curtis Wong 2D
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Joined: Sat Jul 22, 2017 2:00 am

Re: determining cathode from anode

Postby Curtis Wong 2D » Fri Mar 16, 2018 8:21 pm

I am pretty sure that the only way to determine the cathode from the anode is based on their standard cell potential. Cathodes are the ones that are reduced and the the Anodes are the ones that are being oxidized. And we know our Galvanic cell needs to be a positive number so whichever combination of the two leads to the greatest positive cell potential determines the anode and cathode.

Michael Downs 1L
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Re: determining cathode from anode

Postby Michael Downs 1L » Fri Mar 16, 2018 9:09 pm

It is similar to the reducing and oxidizing agents

Rishi Khettry 1L
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Joined: Fri Sep 29, 2017 6:05 am

Re: determining cathode from anode

Postby Rishi Khettry 1L » Sat Mar 17, 2018 12:58 am

Calculate cathode - anode substituting both numbers and the combination that gives the most positive output is the correct one

snehabhargava
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Joined: Thu Jul 13, 2017 2:00 am

Re: determining cathode from anode

Postby snehabhargava » Sat Mar 17, 2018 7:48 pm

Check the standard cell potentials.

Gwen Peng 1L
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Joined: Sat Jul 22, 2017 2:01 am

Re: determining cathode from anode

Postby Gwen Peng 1L » Sat Mar 17, 2018 9:55 pm

The final most likely had a sheet with all of the standard cell potentials which then allows you to determine your anode and cathode. The anode is always the half reaction that has a more positive standard cell potential (higher voltage) because it will be flipped and the sign will become negative, therefore once it is plugged into the equation E standard (cell)= E standard (cathode) - E standard (anode) the double negative will turn into addition.

Caroline LaPlaca
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Joined: Sat Jul 22, 2017 2:01 am

Re: determining cathode from anode

Postby Caroline LaPlaca » Sat Mar 17, 2018 10:48 pm

RED CAT= reduced cathode

Troy Tavangar 1I
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Joined: Fri Sep 29, 2017 6:04 am

Re: determining cathode from anode

Postby Troy Tavangar 1I » Sat Mar 17, 2018 11:55 pm

The one with the greater cell potential is the cathode.


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