- The Arrhenius theory defines acids and bases specifically in aqueous solutions.
- An Arrhenius acid increases the concentration of hydronium ions (\(H_3O^+\)).
- An Arrhenius base increases the concentration of hydroxide ions (\(OH^-\)).
- The correct definition for an Arrhenius base is a substance that increases \(OH^-\) concentration in water: \(\boxed{\text{A substance that increases } OH^- \text{ concentration when it is dissolved in water.}}\)
Explanation
- Analysis of the Arrhenius Definition
The Arrhenius theory, proposed by the Swedish chemist Svante Arrhenius in 1887, provides a specific framework for identifying acids and bases based on their behavior in aqueous solutions. According to this theory, an acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions (\(H^+\)), often represented as hydronium ions (\(H_3O^+\)). Conversely, an Arrhenius base is defined as a substance that, when dissolved in water, increases the concentration of hydroxide ions (\(OH^-\)).
- Evaluating the Options
To determine the correct definition, we evaluate the provided options against the standard Arrhenius theory:
- "A substance that increases \(H_3O^+\) concentration when it is dissolved in water" describes an Arrhenius acid.
- "A substance that increases \(OH^-\) concentration when it is dissolved in water" correctly identifies an Arrhenius base.
- "A compound that donates protons" is the definition of a Brønsted-Lowry acid.
- "A compound that accepts protons" is the definition of a Brønsted-Lowry base.
Therefore, the second option is the correct Arrhenius definition of a base.
- Conclusion
Based on the definition established by Svante Arrhenius, a base is a substance that increases the hydroxide ion concentration when dissolved in water. Thus, the correct definition is the second option: a substance that increases \(OH^-\) concentration when it is dissolved in water.
Examples
In a laboratory setting, when you add sodium hydroxide (NaOH) to water, it dissociates completely into sodium ions (\(Na^+\)) and hydroxide ions (\(OH^-\)). Because the addition of NaOH significantly increases the concentration of \(OH^-\) ions in the solution, NaOH acts as an Arrhenius base. This concept helps chemists predict the pH level and reactive properties of solutions in various industrial and medicinal applications.