What is electrolysis?

Electrolysis is the production of a chemical reaction by passing an electric current through an electrolyte. In electrolysis, positive ions transfer to the cathode and negative ions to the anode. The reactions occurring depend on electron transfer at the electrodes and are therefore redox reactions. At the anode, negative ions in solution may lose electrons to form neutral species. Alternatively, atoms of the electrode can lose electrons and go into solution as positive ions. In either case the reaction is an oxidation. At the cathode, positive ions in solution can gain electrons to form neutral species. Thus cathode reactions are reductions.

What is electrolyte?

Electrolyte is a liquid that conducts electricity as a result of the presence of positive or negative ions. Electrolytes are molten ionic compounds or solutions containing ions, i.e. solutions of ionic salts or of compounds that ionize in solution. Liquid metals, in which the conduction is by free electrons, are not usually regarded as electrolytes. Solid conductors of ions, as in the sodium–sulphur cell, are also known as electrolytes.

e.g. acids, alkali, salts dissolved in water, molten salts

Electrolysis of molten lead (II) bromide

During the electrolysis of molten lead(II) bromide, PbBr₂, bromine gas, Br₂ is released at the cathode while the lead metal is formed at the anode.  

Pb²⁺ and Br^- ions are present in the molten lead(II) bromide, PbBr₂.  At the anode, bromide ions, Br^- are discharged by donating electrons to form bromine molecules, Br₂. At the cathode, each lead(II) ion, Pb²⁺ is discharged by accepting two electrons to form a lead atom.

SPM Form 4: Electrochemistry (Checklist)

• Electrode: A conductor in the form of a wire, rod or plate which carry electric current in and out of an electrolyte during electrolysis.
• Electrolyte: A substances that can conduct electricity in molten state or aqueous solution and is decomposed by electric current.
• Non-electrolyte: A substances that cannot conduct electricity in molten state or aqueous solution.
• Anion: A negatively-charged ion.
• Cation: A positively-charged ion.
• Anode: An electrode which is connected to the positive terminal of the source of electricity during electrolysis. (donation of electrons)
• Cathode: An electrode which is connected to the negative terminal of the source of electricity during electrolysis. (acceptance of electrons)
• Electrolysis: The process whereby a compound is broken down into its constituent elements when electricity is passed through an electrolyte.
• Aqueous solution: A solution produced when a compound is dissolved in water.
• Electrochemical series: An arrangement of metals based on the tendency of each metal to donate electrons.
• The lower the position of an ion in the electrochemical series, the higher is the tendency of the ions to be discharged.
• Purification of metals: The process of obtaining a pure metal from an impure metal through electrolysis. E.g. Impure copper can be purified through electrolysis when the impure copper is used as the anode and a pure copper is used as the cathode.
• Electroplating of metals: The process of coating a layer of metal onto another metal using electrolysis.
• Simple voltaic acid: A cell that converts chemical energy to electrical energy. The chemical reactions in a simple voltaic cell produce electricity. No current flow will flow if both electrodes are made of the same metal.
• Electropositivity: A measurement of the ability of an atom to donate electrons to form a positive ion.
• Displacement reaction: A reaction where a more electropositive metal displace another metal from its salt solution. A metal which has a higher position in the electrochemical series is able to displace the metal below it in the series from their salt solutions.