NS FL1 Bio Q35

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vgp1993
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Joined: Wed Dec 20, 2017 12:14 pm

NS FL1 Bio Q35

Post by vgp1993 » Mon Apr 02, 2018 1:40 pm

I was hoping for some clarification on the electrodes in this particular electrophoresis setup and in general.

I thought that electrophoresis takes place with an electrolytic cell, so anions move towards the anode, which is marked (-) but positively charged, and cations or compounds will move towards the cathode which is negatively charges. This doesn't seem to be the way the figure is explained in this questions explanation.

Could I also just get a breakdown on the hard and fast rules of the electrode setups in galvanic vs electrolytic cells?


Thanks!
NS_Tutor_Andrew
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Re: NS FL1 Bio Q35

Post by NS_Tutor_Andrew » Mon Apr 02, 2018 5:20 pm

Hi vgp1993,

The hard and fast rules for cathodes is that oxidation always happens at the anode, while reduction always happens at the cathode. This is a pure matter of definition, w/ no room for ambiguity.

In a galvanic cell, the anode is considered to have a negative charge because it is the source of electrons, while the cathode is considered to have a positive charge because it is where electrons are taken out of solution via a reduction reaction. A key point here is to realize that this linked to the fact that galvanic cells are spontaneous.

The charge convention is flipped in electrolytic cells, so that the anode is positive and the cathode is negative. To some extent, you can just remember this. In terms of the underlying principles, here's an effective way to think about it. Remember that in electrolytic cells, we have to provide an external current to "push" an energetically unfavorable reaction forward. Since reduction means gaining electrons (as in the mnemonic OIL RIG), that means that we have to supply electrons to the cathode to push that reduction reaction forward. This means hooking up the cathode to the negative-current side of the battery, and that means that the anode has to be positive.

I hope this helps clarify the question! As far as I can tell, this is consistent with the figure and explanation in FL1 B/B Q35. You mention there being a convention to always label the anode with (-), regardless of its charge, but I don't think such a convention is always used, and if so, it would be very confusing!
Andrew D.
Content Manager, Next Step Test Prep.
vgp1993
Posts: 18
Joined: Wed Dec 20, 2017 12:14 pm

Re: NS FL1 Bio Q35

Post by vgp1993 » Sat Apr 14, 2018 3:23 pm

Okay, thanks!

Can it also be said that, in both cases, anions are always attracted to the anode because that is the site of oxidation and cations to the cathode?
NS_Tutor_Andrew
Site Admin
Posts: 520
Joined: Mon May 23, 2016 1:47 pm

Re: NS FL1 Bio Q35

Post by NS_Tutor_Andrew » Sat Apr 14, 2018 8:32 pm

Yes, that's correct. I don't generally like to point to Reddit as an authoritative source, but this thread isn't bad if you want a more detailed discussion including a few different points of view.
Andrew D.
Content Manager, Next Step Test Prep.
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