The compounds that during ionization the cations generated are all hydrogen ion (H+) called acids. At 25℃, the pH value of the dilute solution is less than 7.
Acid is a general term for a class of compounds.
The narrow definition of an acid in chemistry is that the compounds during ionization in aqueous solution the cations generated are all hydrogen ion.
Most of these substances are soluble in water, while a few, such as silicic acid, are not soluble in water. Generally, the aqueous solution of acid can conduct electricity, and its conductivity is related to its ionization degree in water. Some acids exist in water as molecules and do not conduct electricity. Some acids dissociate into positive and negative ions in water and conduct electricity. More broadly defined, it's an acid that provides protons, if not, it is alkali.
According to the ionization degree of acid in aqueous solution, there are strong acid and weak acid. It is generally believed that strong acid completely disassociates in aqueous solution, such as hydrochloric acid and nitric acid. Weak acids partially ionize in aqueous solutions, such as acetic acid and carbonic acid. Strong acid: per chloric acid, hydrologic acid, sulfuric acid, hydro bromic acid, hydrochloric acid, nitric acid, iodic acid, etc. Medium strong acid: oxalic acid (oxalic acid), sulfite, phosphoric acid
, pyruvate, carbonic acid (considered as weak acid).