Introduction to acids

Acids are a general term for a class of compounds.
The narrow definition of an acid in chemistry is that the cations ionized in an aqueous solution are all hydrogen ion compounds. Proposed by Arrhenius, this theory is called Arrhenius acid-base theory.
The broad definition is: a substance that can accept electron pairs.
Most of these substances are easily soluble in water, and a few, such as silicic acid, are difficult to dissolve in water. The aqueous solution of acid is generally conductive, and its conductive properties are related to its ionization degree in water. Some acids exist as molecules in water and do not conduct electricity; Some acids dissociate into positive and negative ions in water, which can conduct electricity.
Acid-base proton theory: A broader definition, which considers that the reaction can provide protons is an acid, and vice versa is a base, this definition is called J. M. Bronsted-T. M. Lowry acid. This theory is called the acid-base proton theory.
Bronsted acidity is a concept in the proton theory of acid-base that represents the ability of a substance to release protons (H +). Specifically, if A substance HA, with the release of H + A, becomes a ⁻, its Bronsted acidity is the equilibrium constant for the response HA = H + a ⁻. The greater the equilibrium constant, the easier HA is to release protons, and the stronger its Bronsted acidity is.
Lewis acid-base theory: Proposed by American G. N. Lewis. This theory defines acids as acceptors of electron pairs, known as Lewis acids, more broadly. Acid-base reaction is the reaction of covalent bond between electron docking acceptor and electron pair donor.
Soft and hard acid-base theory: The soft and hard acid-base theory is an extension of Lewis's acid-base theory. In the soft and hard acid-base theory, acid and base are classified as "hard" and "soft" respectively.