Acid-Base Theories
Let’s start our discussion of acids and bases by defining some terms that are essential to the topics that follow.
Arrhenius acids and bases are:
 
acid—a substance that increases the concentration of protons (H+) in water
 
base—a substance that increases the concentration of hydroxide ions in water (OH-)
 
These definitions are limited to aqueous solutions.
 
Brønsted and Lowry acids and bases as:
 
acid—a substance that donates a proton to another substance
 
base—a substance that accepts a proton
 
These definitions can also apply to reactions that are not aqueous, so they are more accurate.
 
Lewis acids and bases are:
 
acid—a substance that accepts an electron pair
 
base—a substance that donates an electron pair
 
Here are some other terms that you’ll need to be familiar with:
 
hydronium (H3O+)—H+ riding “piggyback” on a water molecule; water is polar, and the positive charge of the naked proton is greatly attracted to one of the negative electron pairs on adjacent oxygen
 
monoprotic—describes acids that can donate one H+
 
diprotic—describes acids that can donate two H+ ions
 
polyprotic—describes acids that can donate more than one H+ ion
 
amphiprotic—describes a substance that can act as either an acid or a base. This means it can either lose a proton or gain one. Water is amphiprotic: it can form either a hydroxide ion or a hydronium ion. Other examples of amphiprotic substances are , ,