Arrhenius Acids and Bases: Definitions and Dissociation in Water

Arrhenius Theory of Acids and Bases

Introduction to Arrhenius Definitions

The Arrhenius theory, developed by Svante Arrhenius in the late 19th century, provides foundational definitions for acids and bases in aqueous solutions. This theory is essential for understanding the behavior of acids and bases in water, a key topic in GOB Chemistry.

• Arrhenius Acid: A substance that increases the concentration of hydrogen ions ($H^+$) when dissolved in water.

• Arrhenius Base: A substance that increases the concentration of hydroxide ions ($OH^-$) when dissolved in water.

• Key Ions: The hydrogen ion ($H^+$) and the hydroxide ion ($OH^-$) are fundamental to the concept of acids and bases.

• Arrhenius definitions are limited to aqueous solutions and do not describe acid-base behavior in non-aqueous media.

Example of Arrhenius Acid Dissociation:

• $\text{HCl} \rightarrow \text{H}_2\text{O} \rightarrow \text{H}^+ + \text{Cl}^-$

Example of Arrhenius Base Dissociation:

• $\text{NaOH} \rightarrow \text{H}_2\text{O} \rightarrow \text{Na}^+ + \text{OH}^-$

Dissociation of Compounds in Water

Practice Problems: Identifying Ions Formed

When ionic compounds dissolve in water, they dissociate into their respective ions. The following practice questions illustrate this process for several compounds.

Practice 1: Dissociation of Sr(OH)2

• Compound: Strontium hydroxide, Sr(OH)2

• Dissociation Equation:

$\text{Sr(OH)}_2 \xrightarrow{\text{H}_2\text{O}} \text{Sr}^{2+}~(aq) + 2~\text{OH}^-~(aq)$

• Ions Formed: $\text{Sr}^{2+}$ and $\text{OH}^-$

Practice 2: Dissociation of H2SO4

• Compound: Sulfuric acid, H2SO4

• Dissociation Equation:

$\text{H}_2\text{SO}_4 \xrightarrow{\text{H}_2\text{O}} 2~\text{H}^+~(aq) + \text{SO}_4^{2-}~(aq)$

• Ions Formed: $\text{H}^+$ and $\text{SO}_4^{2-}$

Practice 3: Dissociation of HBO2

• Compound: Metaboric acid, HBO2

• Dissociation Equation:

$\text{HBO}_2 \xrightarrow{\text{H}_2\text{O}} 3~\text{H}^+~(aq) + \text{BO}_2^-~(aq)$

• Ions Formed: $\text{H}^+$ and $\text{BO}_2^-$

Summary Table: Dissociation of Selected Compounds

Compound	Dissociation Equation	Ions Formed
Sr(OH)2	$\text{Sr(OH)}_2 \rightarrow \text{Sr}^{2+} + 2~\text{OH}^-$	$\text{Sr}^{2+}$, $\text{OH}^-$
H2SO4	$\text{H}_2\text{SO}_4 \rightarrow 2~\text{H}^+ + \text{SO}_4^{2-}$	$\text{H}^+$, $\text{SO}_4^{2-}$
HBO2	$\text{HBO}_2 \rightarrow 3~\text{H}^+ + \text{BO}_2^-$	$\text{H}^+$, $\text{BO}_2^-$

Key Terms and Concepts

• Dissociation: The process by which an ionic compound separates into its constituent ions when dissolved in water.

• Aqueous Solution: A solution in which water is the solvent.

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

Additional info: The Arrhenius definition is foundational but has limitations, as it does not account for acid-base reactions outside of aqueous solutions or those involving species other than $H^+$ and $OH^-$. Later theories, such as Brønsted-Lowry and Lewis definitions, expand upon these concepts.