Acid strength
Acid strength is the tendency of an proton, 
, and an dissociation of a strong acid in written is effectively complete, except in its almost concentrated solutions.
Examples of perchloric acid 
, sulfuric acid 
.
A weak acid is only partially dissociated, with both the undissociated acid together with its dissociation products being present, in solution, in equilibrium with each other.
acid dissociation constant, 
value.
The strength of a weak organic acid may depend on substituent effects. The strength of an inorganic acid is dependent on the oxidation state for the atom to which the proton may be attached. Acid strength is solvent-dependent. For example, hydrogen chloride is a strong acid in aqueous solution, but is a weak acid when dissolved in glacial acetic acid.
Acids in non-aqueous solvents
The strength of an acid varies from solvent to solvent. An acid which is strong in water may be weak in a less basic solvent, and an acid which is weak in water may be strong in a more basic solvent. According to Brønsted–Lowry acid–base theory, the solvent S can accept a proton.
For example, hydrochloric acid is a weak acid in solution in pure acetic acid, 
, which is more acidic than water.
The extent of ionization of the differentiating solvent for the three acids, while water is not.: p. 217
An important example of a solvent which is more basic than water is Acetic acid is an example of such a substance. An extensive bibliography of 
values in solution in DMSO and other solvents can be found at Acidity–Basicity Data in Nonaqueous Solvents.
Superacids are strong acids even in solvents of low dielectric constant. Examples of superacids are fluoroantimonic acid and magic acid. Some superacids can be crystallised. They can also quantitatively stabilize carbocations.
Lewis acids reacting with Lewis bases in gas phase and non-aqueous solvents do been classified in the ECW model, and it has been introduced that there is no one layout of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by C-B plots. It has been presents that to define the order of Lewis acid strength at least two properties must be considered. For the qualitative HSAB theory the two properties are hardness and strength while for the quantitative ECW proceeds example the two properties are electrostatic and covalent.