Electrolysis

Two graphite rods, placed in a liquid and connected externally to a power supply can be used to test if a liquid conducts electricity. If a liquid conducts electricity and is decomposed by it, electrolysis is taking place.

"Electrolysis is the decomposition of a liquid electrolyte using a direct current of electricity."

The electrolyte is the liquid or solution which conducts electricity and is decomposed by it. The graphite rods are called electrodes. Graphite is used because it conducts electricity and is unreactive. More inert (unreactive) materials such as titanium or platinum are sometimes used

All electrolytes conduct electricity as they have free ions that can move and carry charge.

When these positive and negative electrons are free to move, the positive ions (cations) move to the negative electrode (cathode) and the negative ions (anions) move to the positive electrode (anode).

The positive cations at the negative electrode gain electrons to become atoms (which may combine to form diatomic molecules in the case of H2)

The negative anions at the positive electrode lose electrons to become atoms (which may combine to form diatomic molecules for all other diatomics).

Molten Ionic Compounds

• Lithium chloride (LiCl)
• Lead bromide (PbBr2)

Aqueous Ionic Compounds

• Copper (II) sulphate (CuSO4)
• Sodium chloride (NaCl)

Acids

• Dilute sulphuric acid (H2SO4)

Molt Lithium Chloride, Molten Lead Bromide & Aqueou Sodium Chloride

Molten LiCl
Anode: Yellow-green pungent gas evolved
             2Cl(-) = Cl2 + 2e
Cathode: Silvery-grey liquid formed
               Li(+) + e(-) = Li

Molten PbBr2
Anode: Red-brown pungent gas evolved
           2Br(-) = Br2 + 2e(-)
Cathode: Silvery-grey liquid formed which sinks to bottom
              Pb(2+) + 2e(-) = Pb

Aqueous NaCl
Anode: Yellow-green pungent gas evolved

Cathode: Colourless, odourless gas evolved
                2H(+) + 2e(-) = H2