According to the Bronsted-Lowry definition, acids are hydrogen donors.

The most common Lewis bases are anions, and therefore, have unpaired valence electrons which may be donated to Lewis acids. The concept of donating and/or accepting hydrogens refers to the Bronsted-Lowry definition of acids. A Bronsted-Lowry acid donates hydrogens.

There are three primary classifications of acids and bases.

Arrhenius acids yield protons when dissolved in solution, while Arrhenius bases yield hydroxide ions.

Brønsted-Lowry acids are protone donors, while Brønsted-Lowry bases are proton acceptors.

Lewis acids are electron acceptors, while Lewis bases are electron donors.

An acid that dissociates completely in solution is considered a strong acid due to its high Ka value.

Remember: amphoteric means that the substance can act as either an acid or a base. Using the Bronsted-Lowry definition of acids and bases (acids donate hydrogens and bases accept hydrogens) we find that is the only compound that can give up a hydrogen (and be left with ), or accept a hydrogen (and become ).

According to the Bronsted-Lowry definition, bases are hydrogen acceptors.

According to the Arrhenius definition, acids increase the concentration of hydrogen ions in a solution.

Acids are soluble in water substance, but remember, only water gets the liquid (l) phase label. Since acids are almost always dissolved in water, we use the (aq) subscript at the end of the chemical formula to indicate its phase.

An acidic solution will always have a hydronium concentration greater than . A basic solution will always have a hydroxide concentration greater than . If the hydroxide concentration is equal to the hydronium concentration, the solution is neutral.

The opposite of the above conditions can also be noted. If the hydronium concentration is less than , then the solution will be basic. An example of this is a solution where the hydronium ion concentration is . Since this value is far less than , this will be a basic solution.

According to theArrhenius definition, bases increase the concentration of hydroxide ions in a solution.

An amphoteric substance is one that can act either as an acid or a base. Amino acids are good examples of amphoteric substances; they have a carboxylic acid group that can be acidic, and an amino group that can be basic.