Electrolysis Question

I don't really get what ions have to do with electrolysis.. Why do they only work in molten state. I know that ions can't move towards their opposite electrodes when they're in solid state but that still doesn't explain why a current can only flow when they're in molten state. Please help thanks!

How do they carry charges..

Why do they form lattice?

Oh yeah, I forgot this rule thing. Is it like you can only get a metal if it is lower than hydrogen in the reactivity series and a halogen? What's that? I forgot all about that.. please remind me about it. Thanks.

Reply 1

Excalibur

15

Catchetat

I don't really get what ions have to do with electrolysis.. Why do they only work in molten state. I know that ions can't move towards their opposite electrodes when they're in solid state but that still doesn't explain why a current can only flow when they're in molten state. Please help thanks!

How do they carry charges..

Why do they form lattice?

Oh yeah, I forgot this rule thing. Is it like you can only get a metal if it is lower than hydrogen in the reactivity series and a halogen? What's that? I forgot all about that.. please remind me about it. Thanks.

Electrolysis is when you separate a compound using electricity. Electricity flows due to the flow of charge - and this charge is carried by the ions (the fact that they are ions, by definition, means that they are charged. Ions are charged atoms). As electricity is passed through from the source at the top, there is a flow of electrons, causing an electric current. Because the electrolyte is a molten ionic compound, the ions can carry the charge around so there is a complete circuit. As you say, the electrolyte must be molten so as the ions are free to move.

As for the rule.... at the anode, if halide ions are present (Cl-, Br-, F-, I-) then they always form. If there are no halide ions present then it's usually OH- that's attracted, forming oxygen.

At the cathode, if you have both metal and hydrogen ions there (say Na+ and H+) - if the metal is more reactive than hydrogen, it wants to stay as an ion and stay in solution. Thus H+ is attracted to the cathode and hydrogen forms. If a less reactive metal is there, like Cu2+, then that would form at the cathode instead of hydrogen.

This site helped me when I was stuck on electrolysis: http://www.s-cool.co.uk/topic_quicklearn.asp?loc=ql&topic_id=7&quicklearn_id=3&subject_id=21&ebt=222&ebn=&ebs=&ebl=&elc=4

Hope that helps.

They do not form a lattice as far as I am aware :confused:

Reply 2

Catchetat

OP

15

Yeah but the ions themselves are charged. What charge are they talking about?! The ions themselves or the electrons.

And thanks for the explanation on the electrolyte stuff.

The actual charges on the ions are what attracts them to the electrodes (that are charged electrically) the positive ions migrate to the negative elctrode and vice versa.

When a negative ion arrives at the positive electrode it has its extra electron stripped off by the electrode. This electron continues on its journey to the the battery just like normal electricity (all electrons are, of course, indistinguishable)

When a positive ion arrives at the negative electrode it finds billions of electrons just waiting to fill up its positive 'hole'. One of these extra electrons jums onto the positive ion cancelling it out.

The overall effect of these two processes, or electrode reactions, is that one electron has left the catrhode and one electron has arrived at the anode. From the point of view of the battery and external circuit one electron has left the negative side and has arrived at the positive side. i.e. a current has flowed around the circuit.

Nothing actually flows across the electrolysis cell, the electrons are absorbed by one electrode and produced at the other by two different reactions. For these reactions to be able to occur the ions in the cell must be able to move, i.e. in solution or molten.

Electrolysis Question

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