Problem 44 - Chemistry: The Central Science

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?

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction of potassium oxide (K₂O) with water (H₂O) is: \[K_{2}O + H_{2}O \rightarrow 2KOH\]. The net ionic equation is: \[O^{2-}(aq) + H_{2}O(l) \rightarrow 2OH^{-}(aq)\]. The base in this reaction is the oxide ion \(O^{2-}\), the acid is water (H₂O), and the spectator ion is the potassium ion \(K^{+}\).

Step 1: Write the balanced chemical equation for the reaction of K₂O with water.

First, we need to write the balanced chemical equation for the reaction of potassium oxide with water. Potassium oxide (K₂O) reacts with water (H₂O) to form potassium hydroxide (KOH). The balanced chemical equation is: \[K_{2}O + H_{2}O \rightarrow 2KOH\]

Step 2: Write the ionic equation for the reaction.

Now, we need to write the ionic equation for the reaction. To do this, we break down the compounds into their constituent ions. Remember that K₂O and KOH are strong electrolytes, which means they completely dissociate into their constituent ions in water. H₂O is a weak electrolyte and does not dissociate into ions. The ionic equation is: \[2K^{+}(aq) + O^{2-}(aq) + H_{2}O(l) \rightarrow 2K^{+}(aq) + 2OH^{-}(aq)\]

Step 3: Write the net ionic equation for the reaction.

To write the net ionic equation, we remove spectator ions, which are ions that remain unchanged throughout the reaction. In this case, the \(K^{+}\) ions are spectator ions. The net ionic equation is: \[O^{2-}(aq) + H_{2}O(l) \rightarrow 2OH^{-}(aq)\]

Step 4: (b) Identify the base in the reaction.

According to the Bronsted-Lowry definition, a base is a proton acceptor. In this reaction, the \(O^{2-}\) ion is the one that accepts protons (hydrogen ions) from water molecules to form hydroxide ions (OH⁻). Therefore, the base in this reaction is the oxide ion \(O^{2-}\).

Step 5: (c) Identify the acid in the reaction.

An acid is a proton donor, according to the Bronsted-Lowry definition. In this reaction, water (H₂O) donates a proton (hydrogen ion) to the oxide ion to form hydroxide ions. Therefore, the acid in this reaction is water (H₂O).

Step 6: (d) Identify the spectator ion in the reaction.

A spectator ion is an ion that does not participate in the reaction and remains unchanged. In this case, the potassium ion \(K^{+}\) is a spectator ion, as it is present on both sides of the equation and does not participate in the reaction.

Key Concepts

Net Ionic Equations

Net ionic equations highlight the chemical species that actually participate in a reaction, slicing through the complexity of full ionic equations to expose the essence of a chemical change. Imagine a bustling marketplace—while many people are wandering around, only some are actually engaging in the act of buying and selling. Similarly, in a chemical reaction, while many ions might be present, only some undergo a transformation.

A net ionic equation is written by first identifying and removing the spectator ions from the full ionic equation. These are the ions that appear on both sides of the equation and remain unchanged. What's left are the reactants that truly undergo change—forming the net ionic equation. For instance, when potassium oxide dissolves in water, the essential chemical event is the oxide ion reacting with water to produce hydroxide ions, depicted as: \[O^{2-}(aq) + H_{2}O(l) \rightarrow 2OH^{-}(aq)\].

The value of net ionic equations is profound in the realms of chemistry and education, as they provide a clear view of the core chemical interaction, free from the potentially confounding presence of spectator ions.

Bronsted-Lowry Acid-Base Theory

In a vast ocean of acid-base theories, the Bronsted-Lowry concept shines as a beacon, defining acids as proton donors and bases as proton acceptors. This elegant idea transcends mere formulas, capturing the dynamic exchange of protons in chemical reactions. In the scenario where potassium oxide dissolves in water, we witness the oxide ion (\(O^{2-}\)) in a dance, gracefully accepting protons from water molecules, reveling in its role as a base to emerge as the hydroxide ion (\(OH^{-}\)).

To illustrate, water itself can act as an acid, as it relinquishes protons to the oxide ion, confirming the fluidity of the Bronsted-Lowry theory. This theory is not just esoteric knowledge but forms the backbone of our understanding of many chemical processes, from industrial applications to biological systems.

Spectator Ions

Spectator ions are like the quiet observers at a magic show, present but not part of the act. They witness the chemical reaction without participating, unchanged in both form and charge. Identifying them is crucial when sifting through the full ionic equation to derive the net ionic equation, thereby streamlining it to its most fundamental components.

In the dissolution of potassium oxide in water, the potassium ion (\(K^{+}\)) is uninvolved in the transformation that occurs. It's a classic spectator ion, perched on the sidelines, appearing identically on both reactant and product sides of the equation. Recognizing these ions is not merely an academic exercise—it is central to understanding chemical reactivity and the driving forces behind reactions.

Chemical Equation Balancing

Balancing chemical equations is akin to assuring that both sides of a scale hold equal weight, embodying the law of conservation of mass. In chemical equations, we meticulously adjust the coefficients to ensure that the number of atoms for each element remains steadfast on both sides. The elegance of a balanced equation lies in its symmetry, echoing the natural order of the universe, where nothing is created or destroyed, merely transformed.

Take for example, the reaction of potassium oxide with water, which has been carefully balanced as: \[K_{2}O + H_{2}O \rightarrow 2KOH\].

Mastering the art of balancing equations not only safeguards the integrity of stoichiometric calculations but also underpins a solid foundation in the study of chemistry, fostering an appreciation of the meticulous nature of chemical phenomena.