Electrolysis Topic Notes

Electrolysis means splitting up using electricity. Using Electricity to break down a substance. An electrolyte is the substance that is broken down by electrolysis.

OIL RIG:

Gaining electrons is called Reduction and losing electrons is called Oxidation.

Oxidation Is Loss, Reduction Is Gain

The Electrolysis of Molten Lead Bromide:

Electricity is passed through molten lead bromide.
The positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced. Here molten lead is produced.
Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised. Bromine gas is produced.
Lead Bromide -> Lead + Bromine

Electrolysis of CuCl :

The negative (chloride) ions go to the Positive electrode, lose electrons and form Chlorine gas.
The positive (copper) ions go to the Negative electrode, gain electrons and form Copper.
Copper is formed at the negative electrode and Chlorine gas is formed at the positive electrode.
You can test for Chlorine gas because it will turn litmus paper red because it’s acidic.

Aluminium:

Aluminium is a reactive metal that has a low density but is strong. Aluminium ore is a bauxite

Aluminium Bauxite is mixed with Cryolite to lower the melting point from 2500 → 850℃ It has to be molten for the ions to move.

The high temperatures mean that a lot of energy is required so the plant will have its own power station.

Extraction of Aluminium:

Negative Electrode – Positive Al atoms are attracted to the negative electrode. They gain electrons and are reduced to form aluminium (atoms).

Positive Electrode – Negative O ions are attracted to the positive electrode. They lose electrons and are oxidised to form Oxygen. This reacts with the carbon electrode to form Carbon dioxide.

Electrolysis of Brine:

Molten NaCl produces Na + Cl ions

NaCl solution (brine) produces Na + Cl + H + OH

When we electrolyse brine, the products depend on their reactivity.

The more reactive ions stay in the solution. Na + OH →NaOH (alkaline turns universal indicator blue/ red litmus blue)
+ve electrode 2Cl -2e → Cl
–ve electrode 2H + 2e → H

Uses:

Chlorine = Disinfectant in swimming pool

Hydrogen = Rocket Fuel

Sodium Hydroxide = bleach

What happens in the electrolysis of Brine?

NaCl(aq) → Na + Cl + H + OH

Positive Electrode:

The negative chloride ions are attracted to the positive electrode (anode).
They lose electrons
It Oxidises to form Chlorine Gas (molecules)
2Cl (aq) – 2e → Cl (g)

Negative electrode:

The positive Sodium ions are attracted to the negative electrode (cathode).
They gain electrons
It reduces to form Sodium (atoms).
Na + e → Na(s)

An electrolyte is a substance that is broken down by electrolysis.

Test for Chlorine:

Red litmus paper → blue

Test for Hydrogen:

The pop test. Lit splint → pop

Electroplating:

At the negative electrode – Copper ions gain electrons (reduction) to form Copper metal. Cu + 2e → Cu
At the positive electrode – Copper strip loses electrons (oxidisation) to form Copper ions. The positive electrode dissolves Cu – 2e → Cu

Electroplating is useful because we can plate items to make them look nicer and its cheaper than using pure metal.

Copper plating:

Negative Electrode – Copper goes to the Negative electrode because they are positive ions. They gain 2 electrons and are reduced. This makes a layer of Copper on the nail. Cu + 2e → Cu

Positive Electrode – Sulphate stays in solution. (The solution is losing copper ions and it wants them back. This is because the positive electrode is being dissolved). The copper atoms at the copper electrode lose electrons, they are oxidised. This forms copper ions which go back into the solution. Cu – 2e → Cu

The concentration of the solution stays the same because the copper is lost at the same time it is gained. It is losing/ gaining electrons at a steady rate.