They dissolve many metals and turn blue litmus paper red. Chemical compounds called bases or alkalis neutralize acids. Many acids occur naturally and some are essential for life. Acids are also used widely in industry, and they are a part of a large number of foods and beverages. But many acids are poisonous, and strong acids can cause severe burns.
Chemists use several definitions to describe the behavior of acids.
A hydrogen atom consists of one proton, which has a positive electric charge, and one electron, which has a negative charge. A hydrogen ion is the proton that remains when a hydrogen atom loses its electron. In solution, the proton is closely associated with solvent molecules, forming hydronium ions. However, acids are most broadly defined as compounds that are electron pair acceptors. This definition describes all acids, including those that have no hydrogen that they can release and that cannot serve as proton donors.