Are you an EPFL student looking for a semester project?
Work with us on data science and visualisation projects, and deploy your project as an app on top of Graph Search.
Concept
Self-ionization of water
Summary
The self-ionization of water (also autoionization of water, and autodissociation of water) is an ionization reaction in pure water or in an aqueous solution, in which a water molecule, H2O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH−. The hydrogen nucleus, H+, immediately protonates another water molecule to form a hydronium cation, H3O+. It is an example of autoprotolysis, and exemplifies the amphoteric nature of water.
The self-ionization of water was first proposed in 1884 by Svante Arrhenius as part of the theory of ionic dissociation which he proposed to explain the conductivity of electrolytes including water. Arrhenius wrote the self-ionization as H2O H+ + OH-. At that time, nothing was yet known of atomic structure or subatomic particles, so he had no reason to consider the formation of an H+ ion from a hydrogen atom on electrolysis as any less likely than, say, the formation of a Na+ ion from a sodium atom.
In 1923 Johannes Nicolaus Brønsted and Martin Lowry proposed that the self-ionization of water actually involves two water molecules: H2O + H2O H3O+ + OH-. By this time the electron and the nucleus had been discovered and Rutherford had shown that a nucleus is very much smaller than an atom. This would include a bare ion H+ which would correspond to a proton with zero electrons. Brønsted and Lowry proposed that this ion does not exist free in solution, but always attaches itself to a water (or other solvent) molecule to form the hydronium ion H3O+ (or other protonated solvent).
Later spectroscopic evidence has shown that many protons are actually hydrated by more than one water molecule. The most descriptive notation for the hydrated ion is H+(aq), where aq (for aqueous) indicates an indefinite or variable number of water molecules. However the notations H+ and H3O+ are still also used extensively because of their historical importance. This article mostly represents the hydrated proton as H3O+, corresponding to hydration by a single water molecule.
Official source
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Ontological neighbourhood
Related courses (15)
CH-160(g): Advanced general chemistry
Cet enseignement vise l'acquisition des notions essentielles relatives à la structure de la matière, aux équilibres et à la réactivité chimiques. Le cours et les exercices fournissent la méthodologie
CH-160(f): Advanced general chemistry
Cet enseignement vise l'acquisition des notions essentielles relatives à la structure de la matière, aux équilibres et à la réactivité chimiques. Le cours et les exercices fournissent la méthodologie
ENV-200: Environmental chemistry
This course provides students with an overview over the basics of environmental chemistry. This includes the chemistry of natural systems, as well as the fate of anthropogenic chemicals in natural sys
Related lectures (32)
Water Quality Modelling: Equilibrium Phases
Explores equilibrium phases in water quality modelling, illustrating with examples of mineral precipitation and pH adjustment.
Acids and Bases: pH and Buffer Solutions
Explains acids, bases, pH scale, buffer solutions, and conjugate pairs.
Acids and Bases: Definitions and Equilibrium
Explains acid-base definitions, equilibrium constants, pH scale, conjugate pairs, and buffers.