Electrolysis uses electricity to break down an ionic compound. The compound must be molten or dissolved in water, so that its ions are free to move. This liquid is called the electrolyte. Two electrodes are dipped into it and connected to a power supply. Inert electrodes, such as graphite or platinum, do not react, so they only carry the current.
Ions with a positive charge are called cations. Ions with a negative charge are called anions. Opposite charges attract. The negative electrode is the cathode, so cations move to the cathode. The positive electrode is the anode, so anions move to the anode.
This gives a simple rule for the products. Metals, or hydrogen, form at the cathode, because they come from positive ions. Non-metals form at the anode, because they come from negative ions.
