Explaining electrolysis

Here we investigate electrolysis and try to explain our findings with a few diagrams and animations. In this diagram we are showing how heating causes the ions to become mobile, and then the electric field causes the ions to separate.

This allows us to separate elements in a molten ionic compound.

Electrolysing molten compounds:

electrolysing molten lead bromide

In this example, molten lead bromide is electrolysed.

At the cathode, lead ions gain electrons and become atoms, therefore they are being reduced.

At the anode, bromide ions lose electrons and become pairs of atoms (diatomic molecules), therefore they are being oxidised.

Making aluminium

Answer the questions below when you have watched the animation:

What are the electrodes made out of?

The anode and cathode are both made out of carbon.

What is the electrolyte made out of?

The electrolyte is made out of cryolite and aluminum oxide at 900C.

(A mixture is used because it decreases the melting point.)

What chemical process happens at the cathode?

Aluminium ions gain electrons

Aluminum ions are reduced.

What chemical process happens at the anode?

Oxide ions lose electrons

Oxide ions are oxidised to oxygen molecules.

(This causes the carbon anodes to be eroded)

Aqueous electrolysis

we used this simulation to investigate electrolysis in aqueous solutions

Adding water complicates electrolysis because introducing water introduces hydrogen (H+ aqueous) and hydroxide ions (OH- aqueous) to the solution.

The effect of this can be seen in the results table below.

the results table after investigating aqueous electrolysis

When the metal is of low reactivity...

the metal gets deposited at the cathode

When the metal is of high reactivity...

hydrogen gas is produced at the cathode

When the anion (- ion) is a halide...

The corresponding halogen is produced at the anode

When the anion (- ion) is not a halide...

oxygen gas is produced

in this experiment we find the approximate charge of an electron.