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Redox Reactions
In a redox reaction, one substance gains electrons, and another substance loses them. The substance that gains electrons is reduced, and the substance that loses electrons is oxidized. The words "reduction" and "oxidation" combine to form the synthetic word "redox," a word that chemists invented to describe such reactions.
Oxidizing Agent
Potassium permanganate causes other substances to lose electrons, so it is called an oxidizing agent. In aqueous redox reactions, the permanganate ion readily loses some or all of its oxygen and becomes either manganese dioxide or a positively-charged manganese ion. The liberated oxygen oxidizes other reactants that happen to be present. For example, the permanganate ion oxidizes oxalic acid (H2C2O4) to carbon dioxide (CO2).
Reaction Rate
In some reactions, hot permanganate reacts considerably faster than cold permanganate. For example, the permanganate ion oxidizes the oxalate ion while the oxalate ion reduces the permanganate. The reaction takes place in a highly acidic aqueous solution. However, the reaction proceeds so slowly at normal room temperature that it has limited value as a laboratory experiment. However, after heating the solution, the substances react at a satisfactory rate, according to Los Angeles Harbor College.
Hypergolic Reactions
Potassium permanganate often serves as an oxidizing agent in hypergolic reactions. A hypergolic reaction is a vigorous reaction that usually occurs spontaneously when a suitable substance comes into contact with an oxidizing agent. A mixture of ethylene glycol, propylene glycol and glycerin is suitable for a hypergolic reaction. If a small amount of these substances mingles with solid potassium permanganate, the mixture ignites if the temperature is reasonably warm. However, the reaction might not take place at cold temperatures, according to alternative fuels research engineer Sam Barros.
Excessive Oxidation
In some permanganate experiments, cold temperatures are necessary. For example, ethylene has the formula C2H4. A double bond connects the two carbon atoms. When mixed with potassium permanganate in a cold solution of diluted sulfuric acid, the permanganate oxidizes ethylene, which becomes ethylene glycol. However, at high temperatures, the reaction goes too far. The permanganate does not just change ethylene into ethylene glycol. It breaks the double bond and further oxidizes the reactant, resulting in carbon dioxide as a final product, according to Jim Clark, author of "Calculations in AS/A Level Chemistry."