The main difference between Arrhenius and Bronsted Lowry acids and bases is their definitions. In the Arrhenius model, an acid is a substance that dissociates in water to produce hydrogen ions (H⁺) as the only positive ions in solution. An Arrhenius base is a substance that dissociates in water to produce hydroxide ions (OH⁻) as the only negative ions in solution. However, in the Brønsted-Lowry model, an acid is a substance that can donate a proton (H⁺ ion) to another substance, and Brønsted Lowry base is a substance that can accept a proton (H⁺ ion) from another substance.
Arrhenius and Bronsted Lowry are two prominent theories in chemistry that help understand the nature of acids and bases. These theories provide different perspectives on what defines an acid and a base.
Key Areas Covered
1. What are Arrhenius Acids and Bases
– Definition, Features
2. What are Bronsted Lowry Acids and Bases
– Definition, Features
3. Similarities Between Arrhenius and Bronsted Lowry Acids and Bases
– Outline of Common Features
4. Difference Between Arrhenius and Bronsted Lowry Acids and Bases
– Comparison of Key Differences
5. FAQ: Arrhenius and Bronsted Lowry Acids and Bases
– Frequently Asked Questions
Key Terms
Arrhenius Acids, Arrhenius Bases, Bronsted Lowry Acids, Bronsted Lowry Bases
What are Arrhenius Acids and Bases
The Arrhenius model is one of the earliest theories to describe the behavior of acids and bases in aqueous solutions. The Swedish chemist Svante Arrhenius proposed it in 1884. According to the Arrhenius model:
An acid is a substance that dissociates in water to produce hydrogen ions (H⁺) as the only positive ions in the solution. This dissociation process is as follows:
Acid (A) → H⁺(aq) + Anion (A⁻)
In this equation, “A” represents the acid, and “Anion” is the negatively charged ion resulting from the dissociation. Arrhenius acid can increase the concentration of H⁺ ions in an aqueous solution.
A base is a substance dissociating in water to produce hydroxide ions (OH⁻) as the only negative ions in the solution. The dissociation process can be represented as follows:
Base (B) → OH⁻(aq) + Cation (B⁺)
Here, “B” represents the base, and “Cation” is the positively charged ion formed during dissociation. The key feature of an Arrhenius base is its capacity to increase the concentration of OH⁻ ions in an aqueous solution.
Neutralization Reaction in the Arrhenius Model
One of the foundational concepts in the Arrhenius model is the neutralization reaction. This reaction is as follows:
Acid (H⁺) + Base (OH⁻) → Water (H₂O) + Salt
The production of water is a direct result of the combination of H⁺ and OH⁻ ions to form H₂O molecules, while the remaining ions form a salt. This reaction is fundamental to our understanding of acid-base reactions and their importance in various chemical and industrial processes. The Arrhenius model is limited in its applicability because it primarily focuses on behavior in aqueous solutions. It does not account for the behavior of acids and bases in non-aqueous solvents. It also does not account for situations where hydrogen ions (H⁺) and hydroxide ions (OH⁻) are not the only species involved.
What are Bronsted Lowry Acids and Bases
The Bronsted Lowry model was formulated independently by Danish chemist Johannes Brønsted and English chemist Thomas Lowry in 1923. It is a broader and more comprehensive theory for defining acids and bases compared to the Arrhenius model.
In the Bronsted-Lowry model, an acid is defined as a substance capable of donating a proton (H⁺ ion) to another substance. This definition is not restricted to aqueous solutions and can be applied to a wide range of chemical reactions in various solvents. A base, according to the Bronsted Lowry model, is a substance that can accept a proton (H⁺ ion) from another substance. Just like with acids, this definition is not limited to aqueous systems and is applicable to a broad spectrum of reactions.
Proton Transfer in Bronsted Lowry Model
The key feature of the Bronsted Lowry model is the concept of proton transfer. In an acid-base reaction, an acid donates a proton (H⁺) to a base, resulting in the formation of a new acid and a new base. This process can be represented as follows:
Acid₁ (Hₓ) + Base₂ → Base₁ (Hₓ) + Acid₂
In this equation, “Acid₁” donates a proton to “Base₂,” leading to the formation of “Base₁” and “Acid₂.”
Every acid in the Bronsted Lowry model has a corresponding conjugate base, and every base has a corresponding conjugate acid. These conjugate pairs differ by the gain or loss of a proton. For example, if “Acid₁” donates a proton to “Base₂” to form “Base₁” and “Acid₂,” then “Base₁” is the conjugate base of “Acid₁,” and “Acid₂” is the conjugate acid of “Base₂.”
Moreover, the Bronsted Lowry model recognizes amphoteric species. Water is a classic example of an amphoteric substance because it can both donate and accept protons.
Neutralization Reaction in Bronsted Lowry Model
The neutralization reaction is a fundamental concept in the Bronsted-Lowry model. It involves the combination of an acid and a base to form water and a salt. This reaction is a specific example of proton transfer:
Acid (Hₓ) + Base (OHₓ) → Water (H₂O) + Salt
The neutralization reaction demonstrates the production of water due to the combination of H⁺ and OH⁻ ions to form H₂O, while the remaining ions form a salt.
Similarities Between Arrhenius and Bronsted Lowry Acids and Bases
- Both models agree that acids are substances that can release or donate protons (H⁺ ions) during chemical reactions.
- They also agree that bases are substances that can accept protons (H⁺ ions) during chemical reactions.
Difference Between Arrhenius and Bronsted Lowry Acids and Bases
Acids
In the Arrhenius model, acids are substances that release hydrogen ions (H⁺) when dissolved in water, thus increasing the concentration of H⁺ ions in the solution. However, in the Bronsted Lowry model, acids are substances that can donate protons (H⁺ ions) to another substance, known as a base. In this model, an acid is considered a proton donor.
Bases
The Arrhenius model defines bases as substances that release hydroxide ions (OH⁻) when dissolved in water, resulting in an increase in the concentration of OH⁻ ions in the solution. The Bronsted Lowry model defines bases as substances that can accept protons (H⁺ ions) from another substance, known as an acid. Here, a base is characterized as a proton acceptor.
Applicability
Moreover, the Arrhenius model is primarily applicable to reactions that occur in aqueous solutions, focusing on the behavior of acids and bases in water, whereas the Bronsted-Lowry model is more versatile and applicable to a broader range of chemical reactions, extending the definition of acids and bases to include reactions in non-aqueous solvents.
Amphoteric Substances
The Arrhenius model does not explicitly explain the concept of amphoteric substances, which can act as both acids and bases depending on the conditions, whereas the Bronsted Lowry model addresses the concept of amphoteric substances, recognizing that certain substances can function as both acids and bases, depending on the specific reaction and conditions.
Key Focus
In the Arrhenius model, the primary focus is on the ion concentration in the solution, particularly the concentration of H⁺ and OH⁻ ions. However, the Bronsted Lowry model shifts the focus to the transfer of protons (H⁺ ions) between substances, emphasizing proton transfer as the central feature of acid-base reactions.
FAQ – Arrhenius and Bronsted Lowry Acids and Bases
Is HCL a Bronsted or Arrhenius?
HCl is both a Bronsted-Lowry and Arrhenius acid because it donates a proton (H⁺) in the Bronsted-Lowry model and releases hydrogen ions (H⁺) in the Arrhenius model when dissolved in water.
Is KOH an Arrhenius base?
Yes, potassium hydroxide (KOH) is an Arrhenius base. This is because it dissociates in water to release hydroxide ions (OH⁻), thus increasing the concentration of OH⁻ ions in the aqueous solution.
Why is NH3 not Arrhenius?
NH3 (ammonia) is not considered an Arrhenius base because it does not produce hydroxide ions (OH⁻) when dissolved in water.
Conclusion
In the Arrhenius model, an acid is a substance that dissociates in water to produce hydrogen ions (H⁺) as the only positive ions in a solution. An Arrhenius base is a substance that dissociates in water to produce hydroxide ions (OH⁻) as the only negative ions in the solution. However, in the Brønsted-Lowry model, an acid is a substance that can donate a proton (H⁺ ion) to another substance. Meanwhile, Brønsted Lowry base is a substance that can accept a proton (H⁺ ion) from another substance.
Reference:
1. “Arrhenius.” Science Direct.
2. “Bronsted Lowry Theory.” Byju’s.
Image Courtesy:
1.“Bronsted lowry 3d diagram” By Minestrone Soup at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
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