- Aqueous Solutions (dissolved in water)
- Molten Solutions (melted)
So electrodes are the things you stick into the substance and power.
By running electricity through them, you end up with one that is positively charged (connected to positive terminal) and you call that the Anode.
The one that is negatively charged is called the Cathode. You stick these 'electrodes' into the substance which is melted or aqueous as the ions in these solutions can move around freely, allowing current to flow.
Cathodes are negatively charged so attract positive ions in the solution - we call these ions cations
Anodes are positively charged so attract negative ions in the solution - we call these ions anions
This can be pretty confusing at first but you will eventually get your head around it.
In molten solutions, there's not much to mention. When the power is turned on, cations attract to the cathode and anions attract to the anode. Therefore the positively charged ions form a metal on the negatively charged electrode. As you probably guessed, negatively charged ions form a gas on the positively charged electrode.
In aqueous solutions it's pretty much the same but with 2 other rules:
- At the cathode/negatively charged electrode, if the metal that would normally form there is more reactive than hydrogen, hydrogen will form
- At the anode/positively charged electrode, if a halide ion is present (group 7 on periodic table) then that will always be formed. Otherwise, the oxygen molecule from the water will form there.
I think that's about it, you may need to know the ionic equations at the electrodes if you are doing triple sciences.