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The self-ionization of water (also autoionization of water, autoprotolysis of water, autodissociation of water, or simply dissociation of water) is an ionization reaction in pure water or in an aqueous solution, in which a water molecule, H 2 O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH −.
For example, water undergoes autoprotolysis in the self-ionization of water reaction. 2 H 2 O ⇌ OH − + H 3 O + For example, ammonia in its purest form may undergo autoprotolysis: 2 NH 3 ⇌ NH − 2 + NH + 4. Another example is acetic acid: 2 CH 3 COOH ⇌ CH 3 COO − + CH 3 COOH + 2
In chemistry, molecular autoionization (or self-ionization) is a chemical reaction between molecules of the same substance to produce ions. If a pure liquid partially dissociates into ions, it is said to be self-ionizing. [1]: 163 In most cases the oxidation number on all atoms in such a reaction remains unchanged.
K w is the equilibrium constant for self-ionization of water, equal to 1.0 × 10 −14. Note that in solution H + exists as the hydronium ion H 3 O +, and further aquation of the hydronium ion has negligible effect on the dissociation equilibrium, except at very high acid concentration. Figure 2.
Adiabatic ionization is a form of ionization in which an electron is removed from or added to an atom or molecule in its lowest energy state to form an ion in its lowest energy state. [16] The Townsend discharge is a good example of the creation of positive ions and free electrons due to ion impact.
3.6 Self-ionization. ... Download as PDF; Printable version; ... Water is an inorganic compound with the chemical formula H 2 O. It is a transparent, ...
The self-ionization of water can be ignored. This assumption is not, strictly speaking, valid with pH values close to 7, half the value of pK w, the constant for self-ionization of water. In this case the mass-balance equation for hydrogen should be extended to take account of the self-ionization of water.
The water molecule is amphoteric in aqueous solution. It can either gain a proton to form a hydronium ion H 3 O +, or else lose a proton to form a hydroxide ion OH −. [5] Another possibility is the molecular autoionization reaction between two water molecules, in which one water molecule acts as an acid and another as a base.