Electrolytic cell


by kristof
Tags: anode, cathode, electrochemistry, electrolysis, voltammetry
kristof
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#1
Nov16-12, 07:49 AM
P: 3
Hello

Please help me with this.

Cathode has negative charge, anode has positive charge. Electrons travel from anode to cathode.

Question 1: why is anode positive and attracts anions? How can the charge build up on this electrode if electrons are constantly flowing out of this electrode? If it has constant supply of electrons, then it also should be negative.. I would understand that anions would be attracted to it if the charge was fixed and positive. I understand that there would be a lack of electrons causing positive charge at anode and negative at cathode. But I don't understand what causes anode to be of positive charge.

If you can, please answer also the second question:
Question 2: During electrodeposition on the cathode, a potential is appied and metal cations become reduced to zero charge (in anodic stripping voltammetry). In case of using glassy carbon electrode, they are deposited on the electrode and stripped back into the solution which causes faradaic current to flow into the cathode and is indicative of the metal concentration in the solution. Is that correct understanding of this? If so, when the metal cations are becoming reduced at cathode, why they don't flow back into the solution? There are no forces holding them onto the glassy carbon electrode (no amalgamate is formed).
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Borek
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Nov16-12, 10:09 AM
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Quote Quote by kristof View Post
why is anode positive and attracts anions? How can the charge build up on this electrode if electrons are constantly flowing out of this electrode?
If you observe potential difference, you can be sure there is a charge difference - by the definition of potential. So apparently there is something wrong with the idea that flowing electrons mean no charge difference, as half of physics would be wrong if you were right.

Think about the situation we observe when there is a water flowing between two tanks located at different heights. When the water level difference is zero, water doesn't flow, but you need some time to reach that point, as the flow speed is not unlimited. Situation with the electrodes and charges is not identical, but in many ways analogous.
kristof
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#3
Nov16-12, 10:51 AM
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Thanks Borek, I didn't say I'm right , I said I just don't get it. Still don't get it. Even if there is charge difference due to potential difference, why is the anode positive if eletrons are flowing out of it constantly? If electrons are flowing through it and coming out of it , why is it not negative?

Borek
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Nov16-12, 10:59 AM
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Electrolytic cell


It is "positive" relative to cathode, doesn't mean it is really positive.

Besides, presence of electrons doesn't make something automatically negative, Fe2+ is positive even if it has 24 electrons.
kristof
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#5
Nov17-12, 01:30 PM
P: 3
of course! thanks Borek, why didn't I think about it already.


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