Question

As \(\mathrm{K}_{2} \mathrm{O}\) dissolves in water, the oxide ion reacts with water molecules to form hydroxide ions. (a) Write the molecular and net ionic equations for this reaction. (b) Based on the definitions of acid and base, what ion is the base in this reaction? (c) What is the acid in the reaction? (d) What is the spectator ion in the reaction?

Short answer

(a) Molecular: \( \mathrm{K}_{2} \mathrm{O} + \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{KOH} \); Net ionic: \( \mathrm{O}^{2-} + \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{OH}^- \). (b) Base: \( \mathrm{O}^{2-} \). (c) Acid: \( \mathrm{H}_{2} \mathrm{O} \). (d) Spectator ion: \( \mathrm{K}^+ \).

Step-by-step solution

Write the molecular equation

When potassium oxide \( \mathrm{K}_{2} \mathrm{O} \) dissolves in water, it forms potassium hydroxide \( \mathrm{KOH} \). The molecular equation is: \( \mathrm{K}_{2} \mathrm{O} + \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{KOH} \).

Develop the net ionic equation

To develop the net ionic equation, consider the ionization of \( \mathrm{KOH} \) in water: \( \mathrm{KOH} \rightarrow \mathrm{K}^+ + \mathrm{OH}^- \). Since the \( \mathrm{K}^+ \) ions do not participate in the reaction, the net ionic equation focuses on the reaction of the oxide ion with water: \( \mathrm{O}^{2-} + \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{OH}^- \).

Identify the base in the reaction

According to the Brønsted-Lowry definition, a base is a proton acceptor. In this reaction, \( \mathrm{O}^{2-} \) accepts protons from water to form hydroxide ions, making \( \mathrm{O}^{2-} \) the base.

Identify the acid in the reaction

Water (\( \mathrm{H}_{2} \mathrm{O} \)) donates a proton to the oxide ion (\( \mathrm{O}^{2-} \)) to form hydroxide ions (\( \mathrm{OH}^- \)). Therefore, \( \mathrm{H}_{2} \mathrm{O} \) acts as the acid in the reaction.

Identify the spectator ion

In this reaction, \( \mathrm{K}^+ \) ions are present in the balanced equation but do not participate in the net ionic equation as they do not change during the reaction. Thus, \( \mathrm{K}^+ \) is the spectator ion.

Key concepts

Acid-Base Reactions

When discussing chemical reactions, acid-base interactions are a fundamental concept. In the context of the exercise, we examine how potassium oxide (\( \mathrm{K}_{2} \mathrm{O} \)) dissolves in water, leading to an acid-base reaction. This specific reaction type involves the transfer of protons between chemicals, which can result in the formation of water and salts.

The reaction follows the equation: \( \mathrm{K}_{2} \mathrm{O} + \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{KOH} \). Here, potassium oxide acts with water to form potassium hydroxide. This process involves the oxide ion \( \mathrm{O}^{2-} \) reacting with water to create hydroxide ions \( \mathrm{OH}^- \), causing a shift in proton distribution.

By focusing on these proton exchange processes, we can understand the essential nature of acid-base reactions and how they contribute to new compound formations.

Spectator Ions

In the realm of ionic equations, spectator ions play a unique role. These ions are present during chemical reactions but do not directly participate in the transformation. Rather, they remain unchanged throughout the chemical process. Recognizing spectator ions is important to simplify reactions into their essential components.

In our example, when \( \mathrm{K}_{2} \mathrm{O} \) dissolves in water, the potassium ions \( \mathrm{K}^+ \) are present in the system but don't change or affect the actual reaction mechanism.

The net ionic equation, after removing these stationary spectators, highlights the main reaction: \( \mathrm{O}^{2-} + \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{OH}^- \). By identifying these non-reactive ions like \( \mathrm{K}^+ \), we can focus on the core details, making the chemical reaction simpler and clearer to analyze.

Brønsted-Lowry Theory

Named after scientists Johannes Brønsted and Thomas Lowry, the Brønsted-Lowry theory is integral to understanding acid-base reactions. According to this model, an acid is a proton donor, while a base is a proton acceptor.

In the given reaction, water (\( \mathrm{H}_{2} \mathrm{O} \)) acts as the Brønsted-Lowry acid by donating a proton to the oxide ion (\( \mathrm{O}^{2-} \)). This turns the oxide ion into the base, as it accepts protons to form two hydroxide ions \( \mathrm{OH}^- \).

Understanding this theory helps clarify roles within reactions, allowing students to predict and comprehend the nature of substances when they encounter acid or base scenarios. By recognizing these proton exchanges, one grasps not just the process but also the broader implications of these reaction types in chemistry.