Arrhenius Acids And Bases

Adolfo Arranz

2 min read

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29-11-2024

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The Arrhenius definition of acids and bases, while not the most comprehensive model available, provides a fundamental understanding of these crucial chemical species. Proposed by Svante Arrhenius in 1884, this theory focuses on the behavior of substances in aqueous solution, laying the groundwork for more advanced acid-base theories.

Defining Arrhenius Acids and Bases

According to Arrhenius, an acid is any substance that increases the concentration of hydrogen ions (H⁺) when dissolved in water. This increase in H⁺ ions leads to a decrease in pH, making the solution more acidic. Common examples include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃). When these acids dissolve in water, they dissociate, releasing H⁺ ions into the solution:

• HCl(aq) → H⁺(aq) + Cl⁻(aq)

An Arrhenius base, conversely, is a substance that increases the concentration of hydroxide ions (OH⁻) when dissolved in water. This increase in OH⁻ ions leads to an increase in pH, making the solution more alkaline or basic. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are classic examples. Their dissociation in water is represented as:

• NaOH(aq) → Na⁺(aq) + OH⁻(aq)

Limitations of the Arrhenius Definition

While the Arrhenius theory is simple and useful for many common acids and bases, it has limitations. It fails to explain the acidic or basic properties of substances that do not contain hydrogen or hydroxide ions. For instance, ammonia (NH₃) acts as a base despite lacking OH⁻. Furthermore, the theory is restricted to aqueous solutions; it cannot account for acid-base reactions in non-aqueous solvents.

Addressing the Limitations: Beyond Arrhenius

The limitations of the Arrhenius definition led to the development of broader theories, such as the Brønsted-Lowry theory and the Lewis theory. These theories offer more comprehensive explanations of acid-base behavior and encompass a wider range of chemical reactions.

Conclusion

The Arrhenius definition provides a straightforward introduction to acids and bases, emphasizing the role of H⁺ and OH⁻ ions in aqueous solutions. While not a complete model, it serves as a crucial stepping stone in understanding acid-base chemistry and paves the way for a deeper exploration of these fundamental concepts using more comprehensive theories. Its simplicity makes it an excellent starting point for students learning about acids and bases for the first time.