Question

Write a balanced net ionic equation for the reaction of the amphoteric oxide \(\mathrm{ZnO}\) with: (a) Hydrochloric acid (b) Aqueous sodium hydroxide; the product is \(\mathrm{Zn}(\mathrm{OH})_{4}{ }^{2}\)

Short answer

Net ionic equations: \( \mathrm{ZnO + 2H^+ \rightarrow Zn^{2+} + H_2O} \) and \( \mathrm{ZnO + 2 \ OH^- + H_2O \rightarrow Zn(OH)_4^{2-}} \).

Step-by-step solution

Identify Reactants and Products

First, recognize that the amphoteric oxide ZnO can react with both acids and bases. The two reactions we need to consider are the reaction of ZnO with hydrochloric acid (HCl) and with aqueous sodium hydroxide (NaOH). Upon reacting with HCl, ZnO will form ZnCl₂ and water. With NaOH, ZnO reacts to form Zn(OH)₄²⁻.

Write Balanced Molecular Equation

For each reaction, write the balanced molecular equation. - Reaction with HCl: \[ \mathrm{ZnO (s) + 2HCl (aq) \rightarrow ZnCl_2 (aq) + H_2O (l)} \]- Reaction with NaOH: \[ \mathrm{ZnO (s) + 2 \ NaOH (aq) + H_2O (l) \rightarrow Na_2[Zn(OH)_4] (aq) } \]

Identify Ionic Species

For the reaction with HCl, identify which compounds dissociate into ions in solution. ZnCl₂ dissociates into Zn²⁺ and 2 Cl⁻ ions, and the same applies for the Na₂[Zn(OH)₄] in NaOH solution to dissociate into 2 Na⁺ and Zn(OH)₄²⁻.

Write Complete Ionic Equation

Convert the molecular equations to complete ionic equations by separating the soluble ionic compounds into their respective ions:- For HCl reaction: \[ \mathrm{ZnO (s) + 2H^+ (aq) + 2Cl^- (aq) \rightarrow Zn^{2+} (aq) + 2Cl^- (aq) + H_2O (l)} \]- For NaOH reaction: \[ \mathrm{ZnO (s) + 2 \ Na^+ (aq) + 2 \ OH^- (aq) + H_2O (l) \rightarrow 2 \ Na^+ (aq) + Zn(OH)_4^{2-} (aq)} \]

Remove Spectator Ions and Write Net Ionic Equation

Eliminate the spectator ions (ions that appear on both sides of the equation) to write the net ionic equations:- For ZnO with HCl, remove Cl⁻: \[ \mathrm{ZnO (s) + 2H^+ (aq) \rightarrow Zn^{2+} (aq) + H_2O (l)} \]- For ZnO with NaOH, remove Na⁺: \[ \mathrm{ZnO (s) + 2 \ OH^- (aq) + H_2O (l) \rightarrow Zn(OH)_4^{2-} (aq)} \]

Key concepts

Amphoteric Oxide

Amphoteric oxides are unique chemical species that have the ability to react with both acids and bases. This dual reactivity is a distinct characteristic that differentiates them from other oxides. One of the most common examples is zinc oxide ( \( \text{ZnO} \) ).
When \( \text{ZnO} \) reacts with acids such as hydrochloric acid, it behaves as a base, forming a salt and water. Conversely, when \( \text{ZnO} \) reacts with bases like sodium hydroxide, it acts as an acid, forming complex ions like \( \text{Zn(OH)}_4^{2-} \) .
This behavior is essential in various chemical processes and industrial applications, making amphoteric oxides invaluable in fields such as metallurgy and catalysis. They serve as key components in reactions that require control over acidity or basicity, showcasing their versatile nature.

Balanced Equation

A balanced chemical equation is crucial for accurately representing a chemical reaction. It ensures that the same number of each type of atom is present on both sides of the equation. This adherence to the conservation of mass allows us to predict the amounts of products and reactants involved in a reaction.
Take the interaction between \( \text{ZnO} \) and HCl: \[ \text{ZnO (s) + 2HCl (aq) \rightarrow ZnCl₂ (aq) + H₂O (l)} \] This equation is balanced because there are equal amounts of Zn, H, Cl, and O atoms on both sides, fulfilling the law of conservation of mass. A correctly balanced equation forms the basis for writing more complex equations, like ionic and net ionic equations.
Balancing equations requires practice and understanding of both chemical reaction types and stoichiometry. Ensuring the equation is balanced is the first step in analyzing any chemical reaction.

Spectator Ion

In a chemical reaction, spectator ions are those that do not participate directly in the chemical change. They exist in the same form in both reactants and products, essentially "watching" the reaction without taking part.
For example, in the reaction of \( \text{ZnO} \) with NaOH, the sodium ion ( \( \text{Na}^+ \) ) acts as a spectator ion. It appears as \( \text{Na}^+ \) on both sides of the complete ionic equation:
\[ \text{ZnO (s) + 2 Na}^+ (aq) + 2 OH^- (aq) + H_2O (l) \rightarrow 2 Na^+ (aq) + \text{Zn(OH)}_4^{2-} (aq)} \]
By identifying and removing these spectator ions, we simplify the reaction down to its net ionic form, highlighting the actual chemical transformation. This simplification is vital for understanding the fundamental changes occurring in a reaction.

Chemical Reaction

A chemical reaction involves the transformation of substances through the breaking and forming of bonds, which results in new products. Reactions can vary in complexity but are based on fundamental principles of chemistry.
When zinc oxide ( \( \text{ZnO} \) ) reacts with hydrochloric acid or sodium hydroxide, a chemical change occurs. In these reactions, zinc oxide is transformed into different products depending on whether it interacts with an acid or a base. This transformation is the essence of a chemical reaction.
Identifying the type of reaction, such as synthesis, decomposition, single displacement, or double displacement, can help in predicting and understanding the behavior of the substances involved. Thorough analysis of a chemical reaction involves balancing the equation, recognizing compound dissociation in ionic reactions, and simplifying to the net ionic equation, ensuring a comprehensive understanding of the transformation taking place.