Question

Zinc hydroxide is an amphoteric substance. Write equations that describe \(\mathrm{Zn}(\mathrm{OH})_{2}\) acting as a Bronsted-Lowry base toward \(\mathrm{H}^{+}\) and as a Lewis acid toward \(\mathrm{OH}^{-} .\)

Short answer

When Zinc hydroxide (Zn(OH)₂) acts as a Bronsted-Lowry base toward H⁺ ions, the equation is: \( Zn(OH)_{2} + H^{+} \rightarrow Zn(OH)_3^- \). And, when Zn(OH)₂ acts as a Lewis acid toward OH⁻ ions, the equation is: \( Zn(OH)_{2} + 2OH^{-} \rightarrow Zn(OH)_{4}^{2-} \).

Step-by-step solution

Recalling the Definitions of Bronsted-Lowry Base and Lewis Acid

In order to write the equations, it is necessary to understand the meaning of Bronsted-Lowry base and Lewis acid. - A Bronsted-Lowry base is a substance that can accept a proton (H+ ion) in a chemical reaction. - A Lewis acid is a substance that can accept a lone pair of electrons, forming a coordinate covalent bond.

Writing the Equation for Zn(OH)2 as a Bronsted-Lowry Base

When Zn(OH)2 acts as a Bronsted-Lowry base, it accepts a proton (H+ ion) and subsequently forms Zinc hydroxide ion (Zn(OH)₃⁻). The equation can be written as: \[ Zn(OH)_{2} + H^{+} \rightarrow Zn(OH)_3^- \]

Writing the Equation for Zn(OH)2 as a Lewis Acid

When Zn(OH)2 acts as a Lewis acid, it accepts a lone pair of electrons from the hydroxide ion (OH⁻). As a result, a new bond with the hydroxide ion is formed, producing the Zinc hydroxide complex ion (Zn(OH)₄²⁻). The equation for this reaction can be written as: \[ Zn(OH)_{2} + 2OH^{-} \rightarrow Zn(OH)_{4}^{2-} \] In conclusion, the two equations that describe Zn(OH)2 acting as a Bronsted-Lowry base toward H+ ions and as a Lewis acid toward OH- ions are: 1. Bronsted-Lowry base: \( Zn(OH)_{2} + H^{+} \rightarrow Zn(OH)_3^- \) 2. Lewis acid: \( Zn(OH)_{2} + 2OH^{-} \rightarrow Zn(OH)_{4}^{2-} \)

Key concepts

Bronsted-Lowry Base

A Bronsted-Lowry base is a substance that accepts a proton, which is a hydrogen ion \( H^+ \). This concept forms part of the Bronsted-Lowry theory, which focuses on proton transfer reactions. In this framework:

• Acids donate protons.
• Bases accept protons.

Zinc hydroxide \( \text{Zn(OH)}_2 \) acting as a Bronsted-Lowry base accepts a proton to form zinc hydroxide ion \( \text{Zn(OH)}_3^- \). The process is expressed by the equation:\[ Zn(OH)_{2} + H^{+} \rightarrow Zn(OH)_3^- \]This reaction showcases the ability of \( \text{Zn(OH)}_2 \) to transform into a more complex ion by gaining a proton. Understanding this helps in recognizing how substances interact in various chemical environments.

Lewis Acid

A Lewis acid is defined by its ability to accept a pair of electrons. This definition widens the scope of acid-base reactions beyond those involving protons. According to the Lewis theory:

• Acids are electron pair acceptors.
• Bases are electron pair donors.

When \( \text{Zn(OH)}_2 \) acts as a Lewis acid, it accepts an electron pair from the hydroxide ion \( OH^- \), leading to the formation of a complex ion \( \text{Zn(OH)}_4^{2-} \). The reaction can be written as:\[ Zn(OH)_{2} + 2OH^{-} \rightarrow Zn(OH)_{4}^{2-} \]Through this interaction, \( \text{Zn(OH)}_2 \) becomes part of a more stable structure by forming a coordinate covalent bond. This property highlights the versatility and reactive nature of zinc compounds in different reactions.

Coordinate Covalent Bond

A coordinate covalent bond is formed when one atom provides both electrons for the bond. This type of bonding is crucial in complex ion formation and often involves Lewis acids and bases.

• The donor provides a lone pair of electrons.
• The acceptor allows the pair to complete its valence shell.

In the reaction of \( \text{Zn(OH)}_2 \) with \( OH^- \), the hydroxide ion donates a pair of electrons to zinc, resulting in the complex ion \( \text{Zn(OH)}_4^{2-} \). This demonstrates how coordinate covalent bonds enable the formation of intricate chemical structures. By facilitating electron sharing, these bonds play a key role in the behavior and properties of many compounds.