Anion/cation movement vs. electron/proton movement

[md_in_md]

I'm confused about two statements made in the Kaplan books:

"Anions always move towards the anode,
and cations always move toward the cathode."

"Electrons always flow through the wire from the anode to the cathode
and current (protons) flows from cathode to anode."

But isn't an electron an anion?
And isn't a proton a cation? :/

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[aldol16]

An electron isn't an anion because an ion is an atom or molecule with a net charge and an electron is neither an atom or molecule. It's a subatomic particle. Protons, however, are cations with the strictest definition of the term and so I guess you could call protons cations. But they're very specific cations that have very specific properties because they're small and move about freely in solution.

 

[md_in_md]

An electron isn't an anion because an ion is an atom or molecule with a net charge and an electron is neither an atom or molecule. It's a subatomic particle. Protons, however, are cations with the strictest definition of the term and so I guess you could call protons cations. But they're very specific cations that have very specific properties because they're small and move about freely in solution.

Thanks so much! I actually realized my confusion is in that the electron/proton movement is across the wire, while the anion/cation movement is in reference to the salt bridge.

 

[JustinM88]

Yeah this makes sense b/c the cations(+) travel through the salt bridge in order to balance out all that negative electron(-) charge

 

[JustinM88]

Could someone speak to the “movement of protons in a wire”? I was under the impression that protons are locked in the nuclei of the (solid) metal wire atoms and do not move (even when the electrons move down the wire)...?

 

[BerkReviewTeach]

You are correct, protons do not move at all through a wire. Replace the word "proton" above with "imaginary positive charge" and you have the concept of current as defined in physics. I think it would be best to make the "proton" part an afterthought. Also, for what it's worth, in an ideal electrochemical cell there is no net cation flow through a salt bridge. For electrochemical cells, anions migrate from the cathode to the anode through the salt bridge to offset the electrons that flow from anode to cathode through the wire connecting the two half cells.

Cations in the cathode half-cell migrate through the solution to the surface of the electrode to get reduced, but they do not travel through the salt bridge into solution. They start as part of the solution.