Question

Classify each of the following as an Arrhenius acid, an Arrhenius base, or a salt: (a) \(\mathrm{HNO}_{3}(a q)\) (b) \(\mathrm{KNO}_{3}(a q)\) (c) \(\mathrm{KOH}(a q)\) (d) \(\mathrm{K}_{2} \mathrm{CO}_{3}(a q)\)

Short answer

(a) Arrhenius acid; (b) Salt; (c) Arrhenius base; (d) Salt.

Step-by-step solution

Analyze the Compound for Acid

Examine each compound to see if it releases hydrogen ions (H^+) in water. (a) \( \mathrm{HNO}_{3}(a q) \): Nitric acid dissociates to form \( H^+ \) and \( \mathrm{NO}_{3}^- \), making it an Arrhenius acid.(b) \( \mathrm{KNO}_{3}(a q) \): This compound does not produce \( H^+ \) ions in water, so it is not an Arrhenius acid.(c) \( \mathrm{KOH}(a q) \): Does not release \( H^+ \) ions, this is a base rather than an acid.(d) \( \mathrm{K}_{2} \mathrm{CO}_{3}(a q) \): Does not produce \( H^+ \) ions.

Check for Base Formation

Evaluate if the compound produces hydroxide ions (OH^-) in aqueous solution.(a) \( \mathrm{HNO}_{3}(a q) \): Does not produce \( OH^- \) ions, so it is not an Arrhenius base.(b) \( \mathrm{KNO}_{3}(a q) \): Does not produce \( OH^- \) ions, so it is neither an Arrhenius base nor an acid.(c) \( \mathrm{KOH}(a q) \): Dissociates to form \( K^+ \) and \( OH^- \), making it an Arrhenius base.(d) \( \mathrm{K}_{2} \mathrm{CO}_{3}(a q) \): Forms \( 2K^+ \) and \( \mathrm{CO}_{3}^{2-} \) but does not release \( OH^- \) directly.

Determine if it is a Salt

Determine if the compound is a salt by checking if it consists of a metal cation and a non-metal anion.(a) \( \mathrm{HNO}_{3}(a q) \): It's an acid, not a salt.(b) \( \mathrm{KNO}_{3}(a q) \): Consists of \( K^+ \) and \( \mathrm{NO}_{3}^- \). This is a salt.(c) \( \mathrm{KOH}(a q) \): It's a base; not classified as a salt in this context.(d) \( \mathrm{K}_{2} \mathrm{CO}_{3}(a q) \): Consists of \( K^+ \) and \( \mathrm{CO}_{3}^{2-} \). This is a salt.

Key concepts

Acid-Base Classification

When discussing acid and base classification in chemistry, it's important to understand the Arrhenius theory. This theory helps classify substances by their ability to release ions in water. According to Arrhenius:

• Acids release hydrogen ions \(H^+\) in aqueous solutions.
• Bases provide hydroxide ions \(OH^-\) when dissolved in water.
• Salts are compounds that arise from the neutralization between acids and bases, typically consisting of a metal cation and a non-metal anion.

Let's see this in action with examples from the original exercise. For instance, nitric acid \(\mathrm{HNO}_{3}(aq)\) releases \(H^+\) in water, classifying it as an Arrhenius acid. In contrast, potassium hydroxide \(\mathrm{KOH}(aq)\) releases \(OH^-\) ions, marking it as an Arrhenius base. Meanwhile, compounds like potassium nitrate \(\mathrm{KNO}_{3}(aq)\) and potassium carbonate \(\mathrm{K}_{2} \mathrm{CO}_{3}(aq)\) do not release \(H^+\) or \(OH^-\) directly, making them salts due to their composition of ions.

Dissociation in Water

The process of dissociation in water is a fundamental concept in understanding how acids, bases, and salts behave. When a compound dissociates, it breaks down into its constituent ions in an aqueous solution. This dissociation is pivotal for classifying chemicals in the Arrhenius system.
For example, when nitric acid \(\mathrm{HNO}_{3}(aq)\) is dissolved in water, it dissociates to form \(H^+\) and \(\mathrm{NO}_{3}^-\). Similarly, potassium hydroxide \(\mathrm{KOH}(aq)\) dissociates into \(K^+\) and \(OH^-\) ions. This dissociation into ions is what allows these substances to demonstrate their acidic or basic properties.
A key point to note is that not all compounds result in \(H^+\) or \(OH^-\) ions. For instance, while potassium carbonate \(\mathrm{K}_{2} \mathrm{CO}_{3}(aq)\) dissolves to give \(2K^+\) and \(\mathrm{CO}_{3}^{2-}\), the lack of \(H^+\) or \(OH^-\) ions from direct dissociation classifies it as a salt, even though it may alter the solution's pH slightly if the carbonate ion acts as a weak base.

Chemistry Education

Understanding the Arrhenius theory and the concept of dissociation in water is essential to mastering the basics of chemistry. These theories lay the groundwork for more advanced topics in chemistry education, such as understanding reaction mechanisms and predicting the outcomes of chemical reactions.
Integrating these concepts into your studies can provide a clearer picture of how substances interact in aqueous environments. It helps clarify why certain substances behave as they do, like why acids are corrosive or why bases can neutralize them.

• Experimentation: Performing simple experiments with acids, bases, and salts can deepen understanding.
• Concept Application: Practice classifying compounds by their reactions in water to solidify understanding.
• Theoretical Comprehension: Work through exercises that require determining \(H^+\) or \(OH^-\) ion release for classification accuracy.

By focusing on these foundational concepts, students can build a strong base for future chemistry learning, making complex subjects more accessible and manageable.