Question

What is the Arrhenius definition of a base?

Short answer

An Arrhenius base increases OH⁻ ions in water.

Step-by-step solution

Understanding the Arrhenius Definition

Arrhenius definition is a concept in chemistry used to categorize substances based on their behavior in water.

Identifying a Base by Arrhenius Definition

According to Arrhenius, a substance is a base if it increases the concentration of hydroxide ions (OH⁻) when dissolved in water.

Key concepts

Hydroxide Ions

Hydroxide ions, denoted as OH⁻, are fundamental to the concept of bases in chemistry. These ions consist of one oxygen atom bonded to one hydrogen atom, carrying a negative charge. Hydroxide ions play a crucial role in many chemical reactions, particularly in determining the basicity of a solution.

In aqueous solutions, the presence of hydroxide ions typically signals the basic nature of a substance. When a base dissolves in water, it releases hydroxide ions into the solution, increasing its basicity. The concentration of these OH⁻ ions is often used to measure the pH levels, affecting the solution's acidity or alkalinity.

Many common chemical bases, such as sodium hydroxide ( NaOH ), are known for their ability to dissociate in water, consistently producing hydroxide ions. As more OH⁻ ions accumulate in the solution, the pH level rises, making the environment more basic.

Arrhenius Definition

The Arrhenius definition of bases is a fundamental principle in acid-base chemistry. Proposed by Svante Arrhenius in the late 19th century, this definition is used to categorize substances based on their behavior in water.

According to the Arrhenius definition, a substance qualifies as a base if it can increase the concentration of hydroxide ions (OH⁻) when dissolved in water. This rise in OH⁻ concentration is key to classifying compounds like NaOH as Arrhenius bases.

This concept emphasizes the role of water in the behavior of chemical substances. By focusing on the release of hydroxide ions, the Arrhenius definition provides a clear and straightforward way to understand what makes a chemical a base within aqueous solutions.

• Key example: Sodium hydroxide releases OH⁻ ions.
• Focus on behavior in water.
• Clear criteria for classification.

Water Dissociation

Water dissociation is an essential process in chemistry, particularly in understanding acid-base behavior. In its simplest form, water dissociates into hydrogen ions (H⁺) and hydroxide ions (OH⁻). This equilibrium can be represented by the equation:

\[ H_2O(l) \rightleftharpoons H^+(aq) + OH^-(aq) \]

In pure water, the concentration of hydrogen ions is equal to the concentration of hydroxide ions, resulting in a neutral pH of 7. However, when substances like Arrhenius bases are introduced to water, they disrupt this equilibrium by producing additional hydroxide ions.

This additional production of OH⁻ ions by a base is what defines its basic properties. Understanding water dissociation helps explain why the introduction of a base raises the pH and decreases the acidic nature of a solution.

• Equilibrium state in pure water.
• Introduction of bases alters this balance.
• Role in defining acidity and basicity.