Chemistry CC11 - Electrolysis

Electrolysis

The breakdown of ionic substances using an electrical current

Anode

positive graphite electrode that attracts anions

Cathode

negative graphite electrode that attracts cations

Electrolyte

a solution of ions which can move

What happens if multiple cations reach a cathode?

When electrolysis occurs, the least reactive cation will be made at the cathode.

If you have dissolved your substance (aq), then the water will also form H+ ions

They will both be attracted to the cathode.

The electrons will move to the least reactive cation

Hydrogen is less reactive than sodium, so the hydrogen will gain one electron

If the substance is molten (l) there is only one option of cation

Simple Anions

These are from group 7

They have all gained 1 electron

They all have a -1 charge

1 electron gives them a full outer shell

Examples are: Cl-, Br-, I-

Complex Anions

Negatively charged compound

Examples are: OH-, NO3-, SO4-, CO3 2-

What happens at the anode during electrolysis? (

- The negative ions will be attracted to it

- The simplest anion will lose electrons

- Simple anions are usually the halogens -> Cl, Br, I

- When they lose electrons they are oxidised and form atoms; these atoms are unstable by themselves so they form diatomic molecules - Cl2, Br2, I2:

2CL -> Cl2 + 2e-

2Br -> Br2 + 2e-

2I -> I2 + 2e-

- If you have a complex ion, you will always produce oxygen gas (O2) at the anode

Purifying Copper

1. Cu2+ in solution attract to cathode

2. Cu in the anode lose 2e- & form Cu2+ (Cu -> Cu2+ + 2e-)

3. Cu2+ attract to cathode

4. Cu2+ at the cathode gain 2e- & turn into Cu (Cu2+ + 2e- -> Cu)

5. Cathode gets bigger

6. Anode gets smaller and remaining elements drop to the bottom as anode sludge

What is at Cathode? (Cheat Sheet)

If molten (l) you make the metal

If acid/water you make H2

If solution (aq) you make lest reactive thing (reactivity series)

What is at Anode? (Cheat Sheet)

If simple anion it makes diatomic molecules

If complex it makes O2