A species is simultaneously oxidized and reduced, such as H2O2 forming water and oxygen.
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Disproportionation is a redox reaction in which the same element is simultaneously oxidized and reduced, forming two different products. It typically occurs when an element is present in an intermediate oxidation state that can both gain and lose electrons. Hydrogen peroxide decomposes into water and oxygen in this way, and chlorine reacts with cold dilute base to form chloride and hypochlorite. The tendency to disproportionate is governed by the relative standard potentials of the species involved. It is important in many industrial and biological processes.
Key ideas: A single species is both oxidized and reduced. Examples: Cl2 + 2OH- giving Cl- + ClO- + H2O, 2H2O2 giving 2H2O + O2, and 2Cu+ giving Cu2+ + Cu. It tends to occur when an element in an intermediate oxidation state sits above the line joining its neighbors on a Frost diagram.
Common mistakes and connections: Mistake: calling a decomposition a disproportionation without checking that the same element goes both up and down. The reverse, comproportionation, makes one intermediate state from two (Mn2+ + MnO4- giving MnO2). Predict using standard potentials: if E(right) exceeds E(left), the species disproportionates.
In disproportionation chlorine at oxidation number 0 is both reduced to Cl- and oxidized to ClO- in equal amounts. The interactive lesson shows this as a live animation or chart.
Chlorine in cold dilute base disproportionates: Cl2 + 2OH- -> Cl- + ClO- + H2O.
A species is simultaneously oxidized and reduced, such as H2O2 forming water and oxygen.
Disproportionation is a intermediate topic in Acids, Bases & Electrochemistry. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Acids, Bases & Electrochemistry first: Redox Reactions, Oxidizing Agent, Reducing Agent.
The next topics in Acids, Bases & Electrochemistry are Balancing Redox: Half-Reaction Method and Balancing in Acidic and Basic Medium.
Yes. The interactive lesson includes a self-check question on Disproportionation, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Disproportionation is topic 41 of 105 in Acids, Bases & Electrochemistry.