How to remember the charge of electrodes?

Abdul Quadeer

How do I remember that anode is positive in electrolysis but negative in electrochemical cells?
I always forget it :|

NobodySpecial

ACID = Anode Current Into Device

Although you have to remember this is conventional current flow

Abdul Quadeer

I did not understand that. How do we remember positive or negative from it?

alxm

One's where an oxidation occurs and the other is where a reduction occurs.

I think. I have to admit I never can remember that either. I just look it up again whenever i need to know. Even got confused about it when defending my Master's Thesis a number of years ago.. :) The only ones I know who seem to get it right consistently are actual electrochemists.

I can do tensor calculus, but plus and minus still manages to baffle me...

DrDu

alxm is right. Kathode is always where reduction occurs. Best you figure it out when you need it from some easy reaction. E.g. in electrolysis of a copper sulfate solution positive copper 2+ ions get reduced to metallic copper by taking up two electrons which have to be delivered by the negative electrode.
In the case a copper rod acts as an electrode in a battery, the copper will get oxidized and will deliver two electrons whence the electrode is negative again but this time it is the anode (due to oxidation).

pzona

I always remembered that the cathode is where reduction occurs because both start with consonants; oxidation corresponds to the anode and both begin with vowels. Weird little mnemonic devices like that are what got me through general chem...

Borek

Cathode is where the cations go.

DrDu

Not in a battery.

mack_10

in valves (showing my age here) the cathode was where the electrons came from and the anode is where they go to

Abdul Quadeer

Haha...good to see I have got a company here

Abdul Quadeer

valves ?

Abdul Quadeer

How do you decide the charge of electrodes from this?

Borek

Positive charge is attracted by the negative charge. It works nicely for electrolysis.

NobodySpecial

Tubes if you're American

wajagawa

"Red cat, Anny Ox" (Reduction at the cathode, oxidation at the anode. )and "LEO says GER" (Lose electron oxidation/ gain electron reduction).

Knowing these two phrases (?) you will know how electrons flow and can tell which is positive and negative with ease.

Abdul Quadeer

No we cannot tell which one is positive/negative from that. In both electrolytic and electrochemical cells, electrons flow from anode to cathode outside the cell but still they have different signs in 2 cases.

Abdul Quadeer

I found out one easy word to remember.
In electrolytic cells, remember the word PANIC.
Positive=Anode & Negative Is Cathode.
So whenever you forget about the signs in electrolytic cells, don't panic

If you remember this, the charges of electrodes in electrochemical cells is opposite to it.