Anode and Cathode confusion?

Electron flow is normally (forget zeners) from cathode to anode and conventional current flow is opposite.

Diodes used as rectifiers used to have the cathode marked with a + symbol to denote the positive end of the load circuit.

To turn on a diode (forget zeners) make the anode positive with respect to the cathode.

Several hours of searching revieled a good explanation which furthers what the Green book

says. A chemistry nomenclature

States.

cathode

Cathode is a negative electrode of an electrolytic cell to which positively charged ions (cations) migrate when a current is passed as in electroplating baths.

In a primary or secondary cell (battery or accumulator) the cathode is the electrode that spontaneously becomes negative during discharge, and form which therefore electrons emerge.

In vacuum electronic devices electrons are emitted by the cathode and flow to the anode.

WayneL

Merriam-Webster online has this definition for cathode:

1 : the electrode of an electrochemical cell at which reduction occurs: a : the negative terminal of an electrolytic cell b : the positive terminal of a galvanic cell 2 : the electron-emitting electrode of an electron tube; broadly : the negative electrode of a diode

The definition for anode is the mirror image of this. Galvanic cells are batteries, and electrolytic cells are loads. Electrical diodes are loads and the terminals are named like those of electrolytic cells.

-- John

In chemistry class (back when there were only 4 elements) the mnemonic that worked for me was that an "anion" was "A Negative ION."

Hope this helps!

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

___

In electrolysis situations, I usually remember polarities by:

RED CAT REDuction is the process occurring at the CAThode. Therefore, oxidation must be the process occurring at the anode.

LEO GER Substances Losing Electrons are Oxidized. Substances Gaining Electrons are Reduced.

By knowing the two mnemonics, RED CAT and LEO GER you've got it all.

If you took two carbon rods and stuck them into a copper chloride solution, you could predict which one would produce the chlorine gas and which one would have copper plated on it:

Cu+2 + 2e- ---> 2Cu copper has GAINed electrons. GER. REDuction has occurred. This must be the CAThode. Copper will be plated here when electrons are supplied from a battery's electron supply side or (-) pole.

2Cl- ---> Cl2 + 2e- chlorine has Lost Electrons. LEO. Oxidation has occurred. This must be the Anode. Chlorine gas will be generated here when connected to the battery's electron deficient side or (+) pole.

The mnemonic we learned for that is "LEO the lion roars, GER"

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

The following is taken from the "Electrochemistry Dictionary"

rechargeable battery A battery in which the chemical reaction system providing the electrical current is easily "chemically" reversible. After discharging, it can be recharged by applying an electrical current to its terminals. Some batteries can be recharged hundreds to thousands times. See, e.g. the lead-acid battery. Also called "secondary" battery, and "accumulator." Contrast with non-rechargeable battery.

It operates as a galvanic cell during discharge and as an electrolytic cell during charge. As a consequence, the anode is the negative electrode during discharge, while it is the positive electrode during charge; at the same time, the cathode is the positive electrode during discharge, while it is the negative electrode during charge. This can create a confusing situation, and it is preferable to refer to the electrodes of a rechargeable battery as "positive" and "negative," because this designation is independent of the operational mode. Unfortunately, this nomenclature is not always followed. Often the "negative" electrode is designated as anode and the "positive" electrode is designated as cathode. This naming convention is a carry-over from the convention of the non-rechargeable battery.

Good luck: ZN

WAYNEL wrote:

I find OIL RIG more connvenient: Oxidation Is Loss, Reduction Is Gain.

Bye. Jasen