Anode/Cathode, which one is positive and negative? (3 Viewers)

[vds700]

I've started ideas to implementation and the text says that the cathode is negative and the anode is positive.

When we did galvanic cells in chem, it was the cathode that was positive and the anode negative.

Could someone please explain??? Thanks!

 

[Studentleader]

Varies with situations.

Copy&Paste from wikipedia:

When the electrodes are connected externally (as in the figure, with wire and a lightbulb), the electrons tend to flow from the more negative electrode (Zn) to the more positive electrode (Cu). Because the electrons have negative charge, this produces an electric current that is opposite the electron flow. At the same time, an equal ionic current flows through the electrolyte. For every two electrons that flow from the Zn electrode through the external connection to the Cu electrode, on the electrolyte side a Zn atom must go into solution as a Zn2+ ion, at the same time replacing the two electrons that have left the Zn electrode by the external connection. By definition, the anode is the electrode where oxidation (removal of electrons) takes place, so in this galvanic cell the Zn electrode is the anode. Because the Cu has gained two electrons from the external connection, it must release two electrons at the electrolyte side, where a Cu2+ ion plates onto the Cu electrode. By definition, the cathode is the electrode where reduction (gain of electrons) takes place, so the Cu electrode is the cathode.

Anode is negative :l

Oxidation is loss of electrons but the electrons don't go into the other electrode. Instead they combine with the solution to form crystals on the opposing electrode. The anode is oxidised so it must be more negative to form equalibrium between the two electrodes.

 

[vds700]

Varies with situations.

Copy&Paste from wikipedia:

When the electrodes are connected externally (as in the figure, with wire and a lightbulb), the electrons tend to flow from the more negative electrode (Zn) to the more positive electrode (Cu). Because the electrons have negative charge, this produces an electric current that is opposite the electron flow. At the same time, an equal ionic current flows through the electrolyte. For every two electrons that flow from the Zn electrode through the external connection to the Cu electrode, on the electrolyte side a Zn atom must go into solution as a Zn2+ ion, at the same time replacing the two electrons that have left the Zn electrode by the external connection. By definition, the anode is the electrode where oxidation (removal of electrons) takes place, so in this galvanic cell the Zn electrode is the anode. Because the Cu has gained two electrons from the external connection, it must release two electrons at the electrolyte side, where a Cu2+ ion plates onto the Cu electrode. By definition, the cathode is the electrode where reduction (gain of electrons) takes place, so the Cu electrode is the cathode.

Anode is negative :l

Oxidation is loss of electrons but the electrons don't go into the other electrode. Instead they combine with the solution to form crystals on the opposing electrode. The anode is oxidised so it must be more negative to form equalibrium between the two electrodes.

yeah this explains the chemistry side of things, but why is it opposite in physics?

 

[Studentleader]

yeah this explains the chemistry side of things, but why is it opposite in physics?

Electron current is opposite to conventional current.
Physics uses conventional alot

Electron current is negative to postive (electron flow)
Convention current is positive to negative

 

[vds700]

Electron current is opposite to conventional current.
Physics uses conventional alot

Electron current is negative to postive (electron flow)
Convention current is positive to negative

yeah i know that.

In a galvanbic cell, oxidation occurs at the anode, so electrons flow to the cathode, which reduces. So conventional current flows from cathode to anode. So for a galvanic cell, the cathode is positive.

Why is it in a cathode ray tube that the anode is positive and the cathode negative?

 

[vds700]

Can someone please explain this. I'm really confused as to why its opposite in physics and chemistry. Thanks

 

[vds700]

Thanks. Yeah in chem the anode is negatuve and cathode positive.

Whereas in a cathode ray tube, the textbook says the anode is positive and cathode is negative. Is this right? Can someone please explain? Thanks!

 

[lacklustre]

Yeah i am a bit confused about this too.

 

[lyounamu]

when we did chem last year we remembered that anion -> onions -> tears -> -ve

That is the hardest way to remember.

How is tear related to -ve

EDIT: What about cation?

 

[foram]

yea. long winded way to remember something. Its like potassium sounds like possum. If you flatten a possum out with a steam roller, it's legs will be in a K position. Tahts how you remember the symbol of potassium is K. It's was pretty funny when my teacher said it, but it seems a bit long winded.

 

[Studentleader]

Can someone please explain this. I'm really confused as to why its opposite in physics and chemistry. Thanks

Seriously ask teacher because your not going to get any help here.

 

[vds700]

Seriously ask teacher because your not going to get any help here.

ok i will, I couldnt exactly ask him when i was on holidays could I?

i just thought that someone here might be able to explain it

 

[vds700]

i think i might have figured it out.

I think hundreds of years ago, they didn't know that electric current was a flow of electrons from negative to positive. They thought it ran from positive to negative. The rays in a cathode ray tube went from cathode to anode, so they thought the cathode was positive. But conventional current went from anode to cathode, so actually, anode is positive and cathode is negative in the case of a CRT.

hmm. this conventional and non-conventional current thing is really confusing.

 

[Pwnage101]

actually, staright from physics contexts 2 p.229 "the plate connected to the negative pole of the batter was called the cathode and the plate connected to the positive pole of the battery was called teh anode"

so basically some stoopid guy named it in such a way that the electrons go from the negative terminal to the Cathode to the anode to the positive terminal, thus, since electrons flow from (-) to (+), they flow from negative terminal on battery to cathode (relatively speaking, the cathode here can be seen as (+), but in the CRT, relatively, the electrons go from cathode to anode, so teh cathode is said to be (+) relative to teh CRT , while the anode is (-), etc

so basically, all u need to get out of this is The cathode is negative because it is conected to the negative terminal, however , we know (-)----> (+) therefore it is the CATHODE, as the negative terminal of the battery must be connected to a 'positive' terminal (hence cathode)

dunno if that helped, that's my understanding of it, and i knwo its not very well explained, but better than nothin i spose

 

[vds700]

actually, staright from physics contexts 2 p.229 "the plate connected to the negative pole of the batter was called the cathode and the plate connected to the positive pole of the battery was called teh anode"

so basically some stoopid guy named it in such a way that the electrons go from the negative terminal to the Cathode to the anode to the positive terminal, thus, since electrons flow from (-) to (+), they flow from negative terminal on battery to cathode (relatively speaking, the cathode here can be seen as (+), but in the CRT, relatively, the electrons go from cathode to anode, so teh cathode is said to be (+) relative to teh CRT , while the anode is (-), etc

so basically, all u need to get out of this is The cathode is negative because it is conected to the negative terminal, however , we know (-)----> (+) therefore it is the CATHODE, as the negative terminal of the battery must be connected to a 'positive' terminal (hence cathode)

dunno if that helped, that's my understanding of it, and i knwo its not very well explained, but better than nothin i spose

ah ok thanks. It kinda makes sense now

 

[clonestar]

Very easy answer.

In CHemistry you have an electrochemical cell and an electrolytic cell. One has current forced into it(electrochemical/galvanic) and one actually generates current(electrolytic).

Here is where the deinfitions are not the same thing. In electrochemical anode=oxidising and cathode = reduction.

In electrolytic = cathode = oxidising and anode=reduction

Basically the cathode generates electrons and forces them out to which the CAThode ray tube in Physics is the same principle. i.e. you connect an induction coil which pumps out electrons then you are using an electrolytic cell.

It is along those lines...

Hope it helps.

 

[Aerath]

Well, for an electrolytic cell and a galvanic cell, the two electrodes are switched too, right?

 

[justmeme]

depends on whether your talking chemistry or physics i think :S

 

[vds700]

Well, for an electrolytic cell and a galvanic cell, the two electrodes are switched too, right?

yeah. The way to remember is that oxidation always occurs at the anode and reduction at the cathode.

ANOX and REDCAT

electrolytic is basically opposite to galvanic

 

[Aerath]

OK, thanks. That sucks, trying to remember which is which. :\