Arrhenius Acid: Definition & Examples

Lesson Transcript
Instructor: Nissa Garcia

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

Arrhenius acid is a compound that raises the concentration of protons in an aqueous by adding hydrogen ions. Learn the significance of these acids through examples of their chemical reactivity. Updated: 11/02/2021

What Is an Arrhenius Acid?

What can make a solution be classified as an acid? There are many definitions from different scientists as to what an acid is. In 1884, the Swedish scientist named Svante Arrhenius came up with the definition of an acid, which is known as the Arrhenius acid.

Svante Arrhenius
Svante Arrhenius

Let us imagine an aqueous solution, which is a solution containing water. According to Svante Arrhenius, an acid is a compound that, when in an aqueous solution, increases the number of hydrogen ions (H+), which is a proton. This definition became known as the definition for an Arrhenius acid.

In the chemical equation below, it shows that when the acid, hydrochloric acid (HCl) is dissolved in water, the hydrogen (H) atom and the chlorine (Cl) atom dissociate from each other, and so, the concentration of H+ in an aqueous solution increases due to the release of H+ ions from HCl. The Arrhenius acid is HCl.

Equation 1 below shows the chemical compounds involved in the chemical reaction, and equation 2 shows the structure of these chemical compounds so you can visualize how the H and Cl atoms dissociate from each other in HCl.

Arrhenius Acid: Increases Hydrogen (H+) Ions in an Aqueous Solution
Arrhenius acid reaction

When an Arrhenius acid is in water, the acid releases hydrogen ions (H+), which are protons, in water, so it protonates water. When water is protonated, it results in the production of hydronium (H3O+) ions. In the chemical equation shown, it shows that the Arrhenius acid, HCl, protonates water (H2O). As a result, the hydrogen atom from HCl transfers to H2O, and this results in the hydronium ion (H3O+) and the chlorine ion (Cl-). Equation 1 below shows the chemical compounds involved in the chemical reaction, and equation 2 shows the structure of these chemical compounds so you can visualize how the acid protonates water.

Arrhenius Acid: Increases Hydronium (H3O+) Ions in an Aqueous Solution
Arrhenius acid in water

Hydrogen (H+) and hydronium (H3O+) ions, in the case of Arrhenius acids, are interchangeable terms. So, we can say that an Arrhenius acid is a compound that increases the hydrogen (H+) or hydronium (H3O+) concentration in an aqueous solution, making the solution more acidic.

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Examples of Arrhenius Acids

How do we know if a chemical compound is an Arrhenius acid or not? Arrhenius acids can be binary acids, which are made up of a hydrogen (H) atom and another nonmetallic element, and oxoacids, which are acids made of hydrogen (H), oxygen (O) and at least one other atom.

If we look at the periodic table, binary acids can be formed between hydrogen and elements from group 16 and 17. In the illustration below, the elements that are boxed in red are the ones that typically bond with hydrogen to form binary acids. For instance, hydrogen (H) bonds with fluorine (F) to form the binary acid hydrofluoric acid (HF).

Elements in Group 16 and 17 That Form Binary Acids
Group 16 and 17

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