Cathode/Anode & Electron Flow

[MedPR]

Advertisement - Members don't see this ad

VERY confused now. I thought I had this down, but after doing this passage I guess not.

Which way do electrons flow? From anode to cathode?

 

[SaintJude]

Yes, always from anode to cathode.

 

[davcro]

This got me too! Really confusing.

Electrons flow from anode to cathode. In a circuit, the direction of current is opposite electron flow. This is because by convention (i heard it's ben franklins fault) current is the direction of positive charge.

 

[MedPR]

Yes, always from anode to cathode.

This got me too! Really confusing.

Electrons flow from cathode to anode. In a circuit, the direction of current is opposite electron flow. This is because by convention (i heard it's ben franklins fault) current is the direction of positive charge.

You're saying opposite things!

 

[davcro]

I was wrong. Anode to Cathode. Sorry.

 

[MedPR]

Ok so..

Current (protons) flow is from cathode to anode, but electrons really go from anode to cathode..? I'm doing this AAMC problem that says "The net movement of charge through an element in a circuit - which occurs here when an electron moves from the cathode to the anode - is the definition of current" AAMC says electrons move from cathode to anode.. I thought protons "moved" from cathode to anode. I know there isn't really proton flow, but don't electrons flow from anode to cathode?

 

[SaintJude]

MCAT-Review recommends remembering "ABCs"--electrons always flow from Ancode to Cathode. And it actually makes sense when you think of the definitions of oxidation and reduction.

B/c at the anode the metal is actually "losing electrons" that have to leave it and then are accepted at the cathode, where reduction (gain of electrons) occurs.

 

[SaintJude]

Ok so..

Current (protons) flow is from cathode to anode, but electrons really go from anode to cathode..? I'm doing this AAMC problem that says "The net movement of charge through an element in a circuit - which occurs here when an electron moves from the cathode to the anode - is the definition of current" AAMC says electrons move from cathode to anode.. I thought protons "moved" from cathode to anode. I know there isn't really proton flow, but don't electrons flow from anode to cathode?

They're just saying what davcro said in their usual non-sensical MCAT tone. Physics convention unfortunately have the direction of current flowing in opposite direction to actual electron flow

 

[MedPR]

MCAT-Review recommends remembering "ABCs"--electrons always flow from Ancode to Cathode. And it actually makes sense when you think of the definitions of oxidation and reduction.

B/c at the anode the metal is actually "losing electrons" that have to leave it and then are accepted at the cathode, where reduction (gain of electrons) occurs.

Oh right, I just explained this kind of to you in that galvanic cell thread.. lol.

Electrons flow from anode to cathode and anions flow from cathode to anode.

So current actually flows from anode to cathode, but convention has it set to the opposite.. So how do we know when to use which rule?

 

[SaintJude]

haha true, you were.

The rule that the depicted current is in the opposite direction of electron flow? You're in luck my friend, that always applies.

 

[davcro]

Electrons flow from the anode of a discharging battery to the cathode plate of a capacitor. TBR Electrochemistry chapter has a great diagram that ties together all the conventions. Another tricky one is that cations in an electric field are attracted to the cathode. This always confuses me

http://imgur.com/L44pg

 

[MedPR]

haha true, you were.

The rule that the depicted current is in the opposite direction of electron flow? You're in luck my friend, that always applies.

So we say that electrons flow from anode to cathode. But current flow is from cathode to anode. That's what I thought before I did this problem. In white is an explanation to an AAMC question (from 4R) so if you don't want to read it, I understand. It is what is causing my confusion though.

The net movement of charge through an element in a circuit -- which occurs here when an electron moves from the cathode to the anode -- is the definition of current. I'm confused because it says electrons are going from cathode to anode, even though we know that electrons move from anode to cathode..


Also, another question says that the electric field points from anode to cathode.. which doesn't make sense either since electrons flow from anode to cathode, so protons would technically flow from cathode to anode and so the E field should point from cathode to anode.

I think I might just ignore this AAMC question.

 

[thais]

Wait, convention is set up the opposite but still can't say that electrons move from cathode to anode. As you said, it would be "flow" of protons, right?

 

[411309]

Think about it this way; why would electons move towards the negatively charged terminal? Wouldn't make sense. Electron flow is always opposite to the current.

 

[SpecterGT260]

The CONVENTION is flow = movement of positive charge. This is a misnomer due to ignorance of early scientists. Protons do not flow.

The REALITY is flow of electrons which move opposite to conventional flow. Remember "red cat" reduction happens at the cathode. Electrons are negatively charged so they REDUCE.

 

[thais]

The CONVENTION is flow = movement of positive charge. This is a misnomer due to ignorance of early scientists. Protons do not flow.

The REALITY is flow of electrons which move opposite to conventional flow. Remember "red cat" reduction happens at the cathode. Electrons are negatively charged so they REDUCE.

I get all that but I'm confused how can AAMC state this, as MedPr quoted:
"The net movement of charge through an element in a circuit - which occurs here when an electron moves from the cathode to the anode - is the definition of current"

Shouldn't they still say that an electron move from the anode to the cathode? Even though the convention is the opposite, it does not say that electrons move from a positive (cathode) to a negative (Anode) terminal. Current is how a positive charge would flow, IF it did flow (I know positive charges don't flow.

(Sorry for coming back to the subject. I just want to make sure I get it down.)

 

[SpecterGT260]

http://www.av8n.com/physics/anode-cathode.htm

 

[gettheleadout]

http://www.av8n.com/physics/anode-cathode.htm

"As always, electrons flowing in is the same as positive current flowing out, and vice versa."

Their diagram shows positive current flowing out of the cathode, as it does. This all makes sense, but I have the same question as thais: the AAMC quote specifically says electrons flow from cathode to anode, and in reality they flow in the other direction.

 

[SpecterGT260]

Let's see... Reduction is the addition of an electron to a species so let me clarify. Anode to cathode for electrons applies to the wire connecting the electrodes. No free electron movement happens between solutions (usually a salt bridge is used which allows k+ or sodium to move. i.e. electrolytes)

So take a solution containing electro active solutes w electrodes , and connect the electrodes w a wire. Positive ions (not protons) will migrate to the cathode. At the same time negative ions will migrate to the anode. When a negative ion reaches the anode it is OXIDIZED - it gives up an electron. This electron travels through the wire and REDUCES the positive ion at the cathode - the electron joins that ion.

"positive" and "negative" ions are used relatively here. a negative ion can sometimes be further reduced depending on what electrode materials and counter ions are used. So dont think that positive and negative ion flow within the cell is always intuitive. Half rxn potentials will tell u who goes where

 

[SpecterGT260]

"As always, electrons flowing in is the same as positive current flowing out, and vice versa."

Their diagram shows positive current flowing out of the cathode, as it does. This all makes sense, but I have the same question as thais: the AAMC quote specifically says electrons flow from cathode to anode, and in reality they flow in the other direction.

Then they got it wrong. Free electron flow does not happen within the cell. Ions carry electrons inside. So technically a POSITIVE ion will carry electrons toward the anode, but this is not the same as electron flow.

If we are loose w definitions, electron flow toward anode within cell, toward cathode outside of cell (in conducting wire)

 

[gettheleadout]

Let's see... Reduction is the addition of an electron to a species so let me clarify. Anode to cathode for electrons applies to the wire connecting the electrodes. No free electron movement happens between solutions (usually a salt bridge is used which allows k+ or sodium to move. i.e. electrolytes)

So take a solution containing electro active solutes w electrodes , and connect the electrodes w a wire. Positive ions (not protons) will migrate to the cathode. At the same time negative ions will migrate to the anode. When a negative ion reaches the anode it is OXIDIZED - it gives up an electron. This electron travels through the wire and REDUCES the positive ion at the cathode - the electron joins that ion.

"positive" and "negative" ions are used relatively here. a negative ion can sometimes be further reduced depending on what electrode materials and counter ions are used. So dont think that positive and negative ion flow within the cell is always intuitive. Half rxn potentials will tell u who goes where

Meaning the electron travels from the anode to the cathode, right?

Ok so..

Current (protons) flow is from cathode to anode, but electrons really go from anode to cathode..? I'm doing this AAMC problem that says "The net movement of charge through an element in a circuit - which occurs here when an electron moves from the cathode to the anode - is the definition of current" AAMC says electrons move from cathode to anode.. I thought protons "moved" from cathode to anode. I know there isn't really proton flow, but don't electrons flow from anode to cathode?

This does not happen.

 

[gettheleadout]

Then they got it wrong. Free electron flow does not happen within the cell. Ions carry electrons inside. So technically a POSITIVE ion will carry electrons toward the anode, but this is not the same as electron flow.

If we are loose w definitions, electron flow toward anode within cell, toward cathode outside of cell (in conducting wire)

Okay, just making sure. Thanks. 🙂

 

[SpecterGT260]

Is there a link to the specific AAMC problem and explanation? They say "here" as if there is a diagram

 

[gettheleadout]

Is there a link to the specific AAMC problem and explanation? They say "here" as if there is a diagram

You have one, MedPR?

 

[davcro]

Can you post the aamc question? This thread is still bothering me.

 

[pfaction]

Can you post the aamc question? This thread is still bothering me.

RED
CAT
GETS
FAT
ANOX

Reduction occurs at the cathode, which means electrons are flowing from the anode to the cathode in both galvanic and electrolysis. The cathode gets "fat" as well, ie, larger in size. Anions are attracted to the positively charged anode, cations to the cathode.

 

[MedPR]

I'm just going to make a new thread so nobody is forced to see it if they don't want to. Here's the link:


LINK TO AAMC QUESTION that this thread pertains to..

http://forums.studentdoctor.net/showthread.php?p=12285795#post12285795