Electrolysis is the chemical deposition of a compound into its constituent elements brought about by a flow of electric current.
- Direct current is passed through the compound (the compound can be in molten or aqueous state).
- Electrical energy (From the direct current) is changed into chemical energy (the decomposition of the compound).
- One common example is the electrolysis of water, where water decomposes to hydrogen and oxygen.
Video of electrolysis of water:
An electrolytic cell
Main components of an electrolytic cell: Battery, Electrolytes, Electrodes
The positive terminal of the battery is connected to the positive electrode (anode) while the negative terminal of the battery is connected to the negative electrode (cathode).
Electrolytes are usually made up of an ionic compound in solution or molten state OR aqueous solutions of acids or alkalis.
- Electrolytes conduct electricity with decomposition at the electrodes as it does so.
- Electrolytes can be classified into three categories: Non-electrolytes, weak electrolytes and strong electrolytes.
- Strong electrolytes = lots of ions to carry the charges from one electrode to the other. Examples of strong electrolytes: Strong acids or alkalis (sulphuric acid, aqueous sodium hydroxide), salt solutions (aqueous sodium chloride)
- Weak electrolytes = few ions to carry the charges from one electrode to the other. Examples of weak electrolytes: Weak acids or bases (Ethanoic acid, aqueous ammonia)
- Non-electrolytes = no ions available to carry the charges from one electrode to the other. Examples of non-electrolytes: Pure water, organic liquids or solvents
Electrodes are conductors through which electrons enter and leave the electrolyte.
- Anode is the POSITIVE (+) electrode from which electrons leave the electrolyte (or the electric current enters the electrolyte)
- Cathode is the NEGATIVE (-) electrode from which electrons enter the electrolyte (or the electric current leaves the electrolyte)
- Electrodes are typically made up of inert materials (which do not participate in any redox reactions), such as carbon, platinum, titanium, or stainless steel. (NOTE: There are some cases where the electrodes undergoes redox reactions during electrolysis.)
What happens during electrolysis?
- Negative ions (Anions) are attracted to the anode while the positive ions (cations) are attracted to the cathode.
- When the ions reaches their respective electrodes, they will be discharged. (They lose or gain electrons and form neutral atoms)
- Hence, at anode, anions are discharged through loss of electrons; while at the cathode, cations are discharged through gain of electrons.