Acids and Bases are a group of chemical compounds with specific chemical properties. These are defined in terms of 2 theories :
• Arrhenius theory • Lowry-Brønsted theory
Arrhenius theory
I call this the two gun theory.
The ACID shoots out an H+.
The BASE shoots out an OH-.
Acid An acid is a substance that produces hydrogen ions (H+);
also called hydronium ions (H3O+) when it dissolves in water.
or more detailed :
Base A base is a substance that produces hydroxide ions (OH-) when it dissolves in water.
Lowry-Brønsted theory
I call this the one gun and target theory.
The acid is the gun.
The base is the target.
The acid (gun) shoots out an H+ at a base (target).
An acid is a proton (H+ ion) donor.
A base is a proton (H+ ion) acceptor.
The Lowry-Brønsted theory leads to what is called conjugate acid-base pairs.
When the acid donates an H+ to a base, the acid itself becomes its own conjugate base.
And the base, upon receiving the H+, becomes it's own conjugate acid.
In the Lowry-Brønsted theory, there is no mention of water needing to be present.
Further, a base does not need to have an OH- present. A compound just needs to be able to accept an H+ to be called a base.