Chemistry 3.22 - 3.24, 3.25(e), 3.26 - Molten electrolysis

Building an electrolysis cell

An ionic solid contains charged particles, but those ions are locked in a lattice. They cannot move through the solid, so the solid does not conduct electricity. Melting the ionic compound, or dissolving it in water, frees its ions to move.

Water acidified with sulfuric acid is one named setup in this lesson. The acid forms mobile ions in water and allows a useful current to flow; pure water contains too few ions to conduct well.

Electrolysis uses electrical energy from a direct current (DC) supply to decompose an electrolyte. Direct current matters because the two supply terminals keep the same polarity. Two conducting electrodes dip into the electrolyte:

• the cathode is connected to the negative terminal;
• the anode is connected to the positive terminal.

Graphite electrodes are often used. They are described as inert because they conduct electricity but are not intended to become reactants or products in the electrolysis.

Opposite charges attract, so the electrode connections determine the ion routes:

• positively charged cations migrate through the electrolyte to the negative cathode;
• negatively charged anions migrate through the electrolyte to the positive anode.

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Charge through the liquid is therefore carried by moving ions. The products form only when selected ions reach and are discharged at the electrode surfaces.