Arrhenius Base: Definition, Theory & Examples

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  • 0:00 What Is an Arrhenius Base?
  • 2:02 How to Identify an…
  • 2:58 Examples of Arrhenius Bases
  • 3:24 Lesson Summary
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Lesson Transcript
Instructor: Nissa Garcia

Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

What makes a solution a base? There are many ways that bases are defined and described. A scientist named Svante Arrhenius came up with a concept of a basic solution, which we refer to as an Arrhenius base, which is the focus of this lesson.

What Is an Arrhenius Base?

In chemistry, a base is a substance that is slippery to the touch and has a pH greater than 7. If you were to eat a base (which you should not do) it would have bitter to the taste. A perfect example of a base is soap - when you touch soap, it feels slippery. Have you ever accidentally tasted soap? You may notice that it has a bitter taste.

These are some physical characteristics of bases, but what about the theory behind the behavior of bases when they are in a solution? There are many theories from different scientists that describe a base. One Swedish scientist, named Svante Arrhenius, came up with the theory of a base in 1884. Svante Arrhenius' definition of a base is what we now refer to as an Arrhenius base.

An Arrhenius base is a substance that, when dissolved in an aqueous solution, increases the concentration of hydroxide, or OH-, ions in the solution. An aqueous solution is a solution that has water present in it. Let's imagine dissolving a basic substance in water. According to Svante Arrhenius, when a base dissolves in an aqueous solution, it dissociates into ions and releases hydroxide ions.

Here we see that a base, sodium hydroxide, is added to an aqueous solution.

NaOH dissociates into sodium, Na+, and hydroxide, OH-, ions. Because the hydroxide ions are released in the aqueous solution, the hydroxide concentration increases; therefore, NaOH is an Arrhenius base.

Sodium hydroxide, when dissolved in an aqueous solution, releases hydroxide ions in the solution. Here we can see the chemical equation for this dissociation.

The water above the arrow means that the NaOH is added or combined with water and dissociates into sodium, a positive cation, and one or more negative hydroxide anions.

How to Identify an Arrhenius Base

How do we know if something is an Arrhenius base? We can tell based on its chemical formula. In the chemical formula, if a metal is followed by one or more hydroxide ions, then that is an Arrhenius base. How do we know if it is a metal? We can tell based on the position in the periodic table. Elements that are located to the left of the black line are metals.

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