From Academic Kids

Which is right? is anode negative? or positive? does the anode attract anions or cations? i thought that the negative electrode was ALWAYS the cathode, and I have textbooks that say so, but there's enough confusion here to twiddle anyone up. What's the right answer?

Quote:As it stands now, on the one page:

  • <i>"In an electrolytic cell the anode is positively charged",
  • <i>"In an electrolytic cell the cathode is positively charged";
  • <i>"in a galvanic cell the anode is negatively charged",
  • <i>"in a galvanic cell the cathode is negatively charged".

<i>That didn't really help much, yet. -- JohnOwens 09:59 Mar 26, 2003 (UTC)

Someone's mixed up their definitions a bit. Here's the candy: A galvanic cell is one where chemical energy is converted to electrical energy. The anode is negatively charged, as the metal forming it attracts the positive ions. An electrolytic cell is one where electrical energy is converted to chemical energy - It's the other way round. The anode is still in the same place, but as the metal is now converting atoms to positive ions, it is positively charged.

""In a galvanic cell, the cathode is positive while the anode is negative, while in an electrolytic cell, the cathode is negative while the anode is positive.""

I hope this helps clear the confusion!

Pete, Jan 21, 2005

I'm getting really confused by this article, it really needs to be cleared up. a lot. -- lommer 23:32 May 12, 2003 (UTC)

Wikipedia is correct. The words anode and cathode cannot be assigned fixed polarities. Some textbooks make such assignments, but they are talking about a specific type of electrochemical cell, and are not correct in the general sense. -- Heron
Ok, thanks for the info. However, in an electrochemical (primary) cell, my textbook (Green + Danje Chemistry, 2nd Ed.), it lists the Cathode as (-) and the anode as (+), in contradiction to what is written here. As well, this would make sense since cations (+, agreed on by wikipedia) are attracted to the cathode AND reduction (which happens at the cathode) is the gain of electrons (which should happen at the negative electrode). This should apply equally well when an electrolytic cell is discharging, but be reversed when it it being charged. Given this, it seems that wikipedia has the signs mixed up all the way through the article!!! Should Someone change this? I won't b/c i'm not 100% sure, but I do *think* that I am right and wikipedia is wrong on this... -- lommer 23:28 15 May 2003 (UTC)

This web page, a battery primer from Analog Devices, agrees with Wikipedia: Other web sites I have found from battery manufacturers also agree. Or how about this web page from NASA: ? (Not that NASA is infallible, of course!) -- Heron

I think I see the error in your explanation, Lommer. As you say, reduction happens at the cathode. The cathode material gains electrons, which it sucks from the external circuit, making that electrode positive, not negative as you say. The anode material is oxidized, meaning that it loses electrons, emitting them into the external circuit, making that electrode negative, not positive as you say. Perhaps an example will illustrate this. In a Leclanché cell:

<math>anode: Zn(s) -> Zn^{2+} (aq) + 2e^-<math>
<math>cathode: NH4^+ (aq) + MnO_2(s) + e^- -> NH_3 (aq) + MnO(OH)(s)<math>

At the anode the zinc is oxidized, releasing electrons which travel into the external circuit, making this the negative terminal. At the cathode the reaction consumes electrons, making this the positive terminal. -- Heron

Ahhhh! There is my confusion - I thought that the reduction/oxidation bit referred to the ions in solution, not the electrode. I'm gonna spend some time puzzling over all of this and see if I can eventually get everything straight, cuz I'm still a bit muddled on other things - but I've been effectively convinced that wikipedia is right! -- lommer 01:52 17 May 2003 (UTC) :-)

one DOES NOT say FROM WHENCE!!!! One says, quite simply, WHENCE, not FROM WHENCE, for that is absurd in english grammar!!!!!

Actually, this is Wikipedia, which means that instead of saying, quite simply, "whence", one just goes and sticks it in the article. -- John Owens

Anode and Cathode seem to me to be overly-specialized articles, I think all of this stuff should be merged into Electrode as subheaders. Any objections before I proceed? Bryan Derksen

I'm not sure, but the cathode article has a short notice about the ray tubes, so maybe there's more to tell (though it could be at cathode ray tube, of course). So I'd say these articles are not harming anybody, but: do what you think best. jheijmans

I may have moved too fast -- I saw Anode on the most wanted stubs list and proceeded in spinning it off the electrode article. The blurb on the cathode ray tube didn't seem appropriate for the unbiased electrode. -- Prefect

This page and cathode both describe themselves as fulfilling the same row in both kinds (electrolytic and galvanic) of cells, which is obviously wrong. On the other hand, I'm not sure which is which between the cells, so, anyone else know which should be which? -- JohnOwens 09:42 Mar 26, 2003 (UTC)

*cough* As it stands now, on the one page:

  • "In an electrolytic cell the anode is positively charged",
  • "In an electrolytic cell the cathode is positively charged";
  • "in a galvanic cell the anode is negatively charged",
  • "in a galvanic cell the cathode is negatively charged".

That didn't really help much, yet. -- JohnOwens 09:59 Mar 26, 2003 (UTC)

Well, at least we have the self-contradiction all in one place, so we can fix it once and for all. The Anome 10:02 Mar 26, 2003 (UTC)
OK, when does this "we" you speak of show up? ;) -- JohnOwens
We just did. Now we need to sort out the anion/cation business: the whole "attracted to" tratment in that article clearly needs changing. Over to you. The Anome 10:17 Mar 26, 2003 (UTC)
Thanks, we... err, I mean, Heron! :) -- JohnOwens
The modern definition, based on oxidation and reduction, has superseded Faraday's original definition, based on the attraction of anions and cations. Faraday's def. applied only to electrolytic cells and not to generalized reversible cells. I think the coexistence of old and new defs was causing the confusion in the article. To avoid this problem, I just scrapped the old definition, but perhaps it could be mentioned in an historical footnote, and not in the main text where it might cause more confusion. -- Heron

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