Strong Base Definition and Examples

Chemistry Glossary Definition of Strong Base

Sodium hydroxide is an example of a strong base. In water, it completely dissociates into its ions.
Sodium hydroxide is an example of a strong base. In water, it completely dissociates into its ions. LAGUNA DESIGN / Getty Images

Strong Base Definition

A strong base is a base that is completely dissociated in an aqueous solution. These compounds ionize in water to yield one or more hydroxide ion (OH-) per molecule of base.

In contrast, a weak base only partially dissociates into its ions in water. Ammonia is a good example of a weak base.

Strong bases react with strong acids to form stable compounds.

Examples of Strong Bases

Fortunately, there aren't very many strong bases.

They are hydroxides of the alkali metals and alkaline earth metals. Here is a table of the strong bases and a look at the ions they form:

BaseFormulaIons
sodium hydroxideNaOHNa+(aq) + OH-(aq)
potassium hydroxideKOHK+(aq) + OH-(aq)
lithium hydroxideLiOHLi+(aq) + OH-(aq)
rubidium hydroxideRbOHRb+(aq) + OH-(aq)
cesium hydroxideCsOHCs+(aq) + OH-(aq)
calcium hydroxideCa(OH)2Ca2+(aq) + 2OH-(aq)
barium hydroxideBa(OH)2Ba2+(aq) + 2OH-(aq)
strontium hydroxideSr(OH)2Sr2+(aq) + 2OH-(aq)

Note that while calcium hydroxide, barium hydroxide, and strontium hydroxide are strong bases, they are not very soluble in water. The small amount of compound that dissolves dissociates into ions, but most of the compound remains a solid.

The conjugate bases of very weak acids (pKa greater than 13) are strong bases.

Superbases

The Group 1 (alkali metal) salts of amides, carbanions, and hydroxides are called superbases. These compounds cannot be kept in aqueous solution because they are stronger bases than the hydroxide ion.

They deprotonate water.

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Helmenstine, Anne Marie, Ph.D. "Strong Base Definition and Examples." ThoughtCo, May. 18, 2017, thoughtco.com/definition-of-strong-base-604664. Helmenstine, Anne Marie, Ph.D. (2017, May 18). Strong Base Definition and Examples. Retrieved from https://www.thoughtco.com/definition-of-strong-base-604664 Helmenstine, Anne Marie, Ph.D. "Strong Base Definition and Examples." ThoughtCo. https://www.thoughtco.com/definition-of-strong-base-604664 (accessed December 17, 2017).