Arrhenius Theory introduced in 1887 by Swedish scientist Svante Arrhenius, is used to describe the behavior of acids and bases in aqueous solutions. This theory states that a material that releases hydroxide ions (OH^–) in water is an Arrhenius base, and a substance that releases hydrogen ions (H⁺) in water is an Arrhenius acid.

This article will thoroughly explain the Arrhenius theory, along with instances of Arrhenius bases, Arrhenius acids and Arrhenius theory of electrolytic dissociation.

What is Arrhenius Theory?

Arrhenius theory was introduced by a Swedish chemist Svante Arrhenius in 1884. This theory takes into account how acids and bases dissociate in water to explain their behaviour in aqueous solutions.

According to this theory, the substances dissociate in water to produce electrically charged atoms called ions, which are either hydrogen ions or hydroxide ions in general.

Arrhenius Theory of Acid and Base

Arrhenius theory particularly focus on the acidic or basic behavior of a substance. As per this theory, the substances that dissociate in water to release hydrogen ions (H⁺) are called acids, whereas the substances that dissociate in water to release hydroxide ions (OH^–) are called bases.

In simple terms, this theory states that acids are hydrogen-containing compounds whereas the bases are hydroxide containing compounds.

Examples of Arrhenius acids include: Hydrochloric acid, Sulfuric acid, and Carbonic acid and the examples of Arrhenius bases include: Sodium hydroxide, Potassium hydroxide, and Magnesium hydroxide.

Read More, Acid, Bases and Salts.

Arrhenius Acid

Arrhenius Acids are the substances that release hydrogen ions (H⁺) in water. Mineral acids like hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃) are the most prevalent types of Arrhenius acids. In water, these acids split apart to release hydrogen ions and create hydrated ions.

The general equation of Arrhenius acid undergoing dissociation in water is given by:

HA (aq) → H⁺ (aq) + A^– (aq)

Examples of Arrhenius Acid

• Hydrochloric acid is the most common example of Arrhenius acid. The equation of HCL dissociating in water is given as:

HCl + H₂O → H₃O⁺ + Cl^–

In this reaction, one hydrogen ion (H⁺) is released when hydrochloric acid (HCl) dissociates in water, creating a hydrated hydrogen ion (H₃O⁺). Another name for the hydrated ion is the hydronium ion (H₃O⁺). There is no change in the chloride ion (Cl^–) within the solution.

• Carbonic acid (H₂CO₃) is another important illustration of an Arrhenius acid. When carbon dioxide is dissolved in water, carbonic acid is produced. The equation of this reaction is as follows:

H₂CO₃ + H₂O → H₃O⁺ + HCO₃^–

In this reaction, two hydrogen ions (H⁺) are released when carbonic acid (H₂CO₃) dissociates in water, creating a bicarbonate ion (HCO₃^–).

Arrhenius Base

Arrhenius Base are the substances that release hydroxide ions (OH^–) when dissociated in water. Strong bases like potassium hydroxide (KOH) and sodium hydroxide (NaOH) are the most prevalent Arrhenius bases. In water, these bases separate to produce hydrated ions and hydroxide ions.

The general equation of Arrhenius base undergoing dissociation in water is given by:

BOH (aq) → OH^– (aq) + B^– (aq)

Examples of Arrhenius Base

• Sodium hydroxide is the most common example of an Arrhenius base. The equation of this reaction is given as:

NaOH + H₂O → Na⁺ + OH^– + H₂O

In this reaction, a hydrated sodium ion (Na⁺) and a hydrated hydroxide ion (OH^–) are formed when sodium hydroxide (NaOH) dissociates in water. The hydroxyl ion (OH^–) is another name for the hydrated ion. In the solution, there is no change in sodium ions.

• Ammonia (NH₃) is another example of an Arrhenius base. In water, ammonia slightly dissociates to release hydroxide ions. In water, it separates as follows:

NH₃ + H₂O → NH₄⁺ + OH^–

In this reaction, ammonia (NH₃) breaks down into ammonium ions (NH₄⁺) and hydrated hydroxide ions (OH-) in water.

Note: Sodium hydroxide and other strong bases release a greater quantity of hydroxide ions than ammonia does. Because of this, ammonia is categorized as a weak base by the Arrhenius theory.

Reaction Between Arrhenius Acid and Base

A neutralization reaction occurs when an Arrhenius acid and an Arrhenius base interact. The hydroxide ions (OH⁻) from the base and the hydrogen ions (H⁺) from the acid which mix to generate water in a neutralization process. Furthermore, the negative ion from the acid and the positive ion from the base combine to create a salt.

The general equation of an Arrhenius acid (HA) and an Arrhenius base (BOH) reaction is as follows:

HA(aq) + BOH(aq) → H_2​O(l) + BA(aq)

Where,

• HA stands for the Arrhenius acid.
• BOH stands for the Arrhenius base.

In the above equation, H⁺ and OH^– combine to make water, and the combination of the positive ion from the base (B⁺) and the negative ion from the acid (A⁻) results in the formation of salt.

Read More, Arrhenius Equation

Arrhenius Theory of Electrolytic Dissociation

Arrhenius Theory of Electrolytic dissociation states that the aqueous solution of acid conducts electricity when a substance called electrolyte is dissolved in the solution, which further dissociates into ions and conducts electricity.

Dissociation is the process of dissolving substances into smaller parts that can reassemble in other circumstances. The compound’s molecules disintegrate into ions (electrically charged particles) in an ionic or electrolytic dissociation process that involves the addition of an electrolyte or solvent.

Water being a neutral substance does not conduct electricity. But when an electrolyte (such as salt) is dissolved in water, it conducts electricity. This process is known as “Electrolytic Dissociation“.

The electrolytic dissociation of a substance further depends on the nature of the electrolyte. The electrolytes are of basically two types namely:

• Strong Electrolytes
• Weak Electrolytes

Strong Electrolytes

Strong Electrolytes are those that can totally breakdown into their corresponding ions even in mild circumstances.

• Its dissociation constant is also large, indicating a high degree of dissociation.

• Electrical conductivity is very high in this kind of electrolytes.

Weak Electrolytes

Weak electrolytes can only partially dissociate in an aqueous solution.

• Low ionization and a lower dissociation constant value are characteristics of these electrolytes.

• Electrical conductivity is poor in them.

Read More, Strong and Weak Electrolytes

Limitations of Arrhenius Theory

Following are the limitations to the Arrhenius’s theory:

• This theory does not apply to non-aqueous or gaseous processes of acids and bases; it is only relevant to their aqueous solutions.

• Only compounds with the formulas HA for acids or BOH for bases can use this theory. As the acidic characteristics of CuSO₄, AlCl₃, CO₂, and SO₂ cannot be represented by the formula HA, the theory is unable to explain them. Similarly, because amines, Na₂CO₃, and NH₃ cannot be represented by the formula BOH, the theory is unable to explain their fundamental features.

• This hypothesis is unable to account for the basic and acidic properties of NH₃ and HCl in non-aqueous media such as acetone, benzene, and gaseous states.

• The Arrhenius hypothesis states that protons (H⁺) are free to exist in aqueous solutions. H⁺ ions, on the other hand, are constantly hydrated and exist as hydronium ions (H₃O⁺) in aqueous solutions.

Summary of Arrhenius Theory

We can summarize the whole Arrhenius’s theory in the following points:

• Any substance that raises the concentration of (H⁺) in an aqueous solution is an Arrhenius acid.

• Any substance that raises the concentration of (OH^–) in aqueous solution is an Arrhenius base.

• In an aqueous solution, (H⁺) ions instantly combine with water molecules to generate (H₃O⁺) hydronium ions.

• An Arrhenius acid and base often react to generate water and salt in an acid-base or neutralization reaction.

Arrhenius Theory – Frequently Asked Questions

What does Arrhenius Theory of Electrolytic Dissociation mean?

Arrhenius Theory of Electrolytic dissociation states that the aqueous solution of acid conducts electricity when a substance called electrolyte is dissolved in the solution.

What is Arrhenius Theory of Electrolytes known as?

Arrhenius Theory of Electrolytes is known as the Arrhenius Theory of Dissociation.

What are the Advantages of Arrhenius Theory?

Advantages of Arrhenius Theory are:

1. Explains acid-base neutralization.
2. Defines acids and bases.
3. Explains electrolyte conductivity.
4. Simple and foundational for understanding acid-base reactions.

What are the Main Postulates of Arrhenius Theory?

Arrhenius Theory postulates are:

• Acids produce H⁺ ions in water.
• Bases produce OH⁻ ions in water.
• Acid-base reactions involve H⁺ and OH⁻ ions forming water.

What is the Weakest Acid?

The weakest known acid is carborane acid, specifically H(CHB₁₁C₁₁).

What are Examples of Strong Acids?

The strongest acids include:

• Fluoroantimonic acid (HSbF₆).
• Magic acid (FSO₃H·SbF₅).
• Carborane acids.
• Hydrochloric acid (HCl) in concentrated form.
• Perchloric acid (HClO₄).

What is Arrhenius Theory of Neutralization Reactions?

The Arrhenius Theory states that an Arrhenius acid reacts with an Arrhenius base and Arrhenius acid to form water and a salt in the context of neutralization reactions.