Need help preparing for the General Chemistry section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Disproportionation Reactions of Electrochemistry. Watch this video to get all the MCAT study tips you need to do well on this section of the exam!
Disproportionation reactions are a special case of redox reactions, where an atom is simultaneously oxidized and reduced. Previously, when we looked at redox reactions, one atom was oxidized and one atom was reduced, but in this case the same atom undergoes both processes.
Example
Consider the breakdown of hydrogen peroxide, forming water and oxygen. Initially, both hydrogens have an oxidation state of +1. At the end of the reaction, hydrogen also has an oxidation state of +1. Therefore, hydrogen is essentially a spectator ion that doesn’t participate in the redox reaction. However, the oxidation state of each oxygen in hydrogen peroxide is -1, but the oxidation state of oxygen on the products side is not -1. Instead, the oxygen of water has an oxidation state of -2, and the oxidation state of free oxygen is zero. Therefore, some of the oxygen was reduced from -1 to -2, and some of the oxygen was oxidized from -1 to 0. Oxygen functioned as both a reductant and an oxidant, so this must be a disproportionation reaction.
2H2O2(aq) → 2H2O2(aq) + O2(g)
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