Topic 18- Electrolysis Flashcards
What is electrolysis?
The breaking down of a substance using electricity
What is actually happening in electrolysis?
An electric current is passed through an electrolyte (a molten or dissolved ionic compound), causing it to decompose
Why does electrolysis cause REDOX reactions?
The cations ions in the electrolyte move towards the cathode (negative electrode), and are reduced (gain electrons)
The anions in the electrolyte move towards the anode (positive electrode) and are oxidised (gain electrons)
As ions gain or lose electrons, they from uncharged (neutral) substances, and are discharged from the electrolyte.
What are electrodes?
Inert material that do not take part in the reaction
Describe the electrolysis of molten ionic compounds
• the substance is separated into its elements, both of which are attracted to separate electrodes
How do you set up an electrochemical cell?
1) get two inert electrodes (e.g. graphite or platinum)
2) clean the surfaces of the electrodes using some emery paper (or sandpaper)
3) from this point on, be careful not to touch the surfaces of the electrodes with your hands- you could transfer grease back into the strips
4) place both electrodes into a beaker filled with your electrolyte
5) connect the electrodes to a power supply using crocodile clips and wires. When you turn the power supply on, a current will flow through the cell
What is an electrochemical cell?
A circuit, made up of the anode, cathode, electrolyte, a power source and the wires which connect the two electrodes
What is the anode cheat rule for aqueous electrolysis?
• if a halogen is present, a halide is produced
• if not, hydroxide reacts:
4OH- —> 2H2O + O2 + 4e-
What is the cathode cheat rule for aqueous electrolysis?
You always make whichever element is less reactive
What are the products of aqueous electrolysis?
2 products given off + 2 leftover substances
Describe aqueous electrolysis
1) in aqueous solutions, as well as the ions from the ionic compound, there will be hydrogen ions (H+) and hydroxide ions (OH-) from the dissociated water.
2) at the cathode, if H+ ions and metal ions are present, hydrogen has will be produced if the metal is more reactive than hydrogen. If the metal is less reactive than hydrogen, a solid layer of pure metal is produced instead.
3) at the anode, if OH- and halide ions are present, molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, then oxygen will be formed
