Problem 78 - Chemistry The Science in Context

Question

Zinc hydroxide is amphiprotic. Write chemical equations showing how an aqueous suspension of this compound reacts to the addition of a strong acid and a strong base.

Step-by-Step Solution

Answer

Answer: The chemical reactions of zinc hydroxide with a strong acid (HCl) and a strong base (NaOH) are as follows: 1. Reaction with strong acid (HCl): Zn(OH)₂ + 2HCl → ZnCl₂ + 2H₂O 2. Reaction with strong base (NaOH): Zn(OH)₂ + 2NaOH → Na₂[Zn(OH)₄] + H₂O

Step 1: Reaction with a strong acid (HCl)

In this step, we will show how zinc hydroxide reacts with a strong acid, hydrochloric acid. Since zinc hydroxide is amphiprotic, it can act as a base in this reaction. The base reacts with the acid to form a salt and water. The balanced equation for the reaction of zinc hydroxide with hydrochloric acid is: Zn(OH)₂ + 2HCl → ZnCl₂ + 2H₂O

Step 2: Reaction with a strong base (NaOH)

In this step, we will show how zinc hydroxide reacts with a strong base, sodium hydroxide. Since zinc hydroxide is a weak acid, it can transfer a proton to the stronger base (NaOH). The reaction will result in the formation of a complex ion and water. The balanced equation for the reaction of zinc hydroxide with sodium hydroxide is: Zn(OH)₂ + 2NaOH → Na₂[Zn(OH)₄] + H₂O So, in conclusion, the chemical reactions of zinc hydroxide with a strong acid (HCl) and a strong base (NaOH) are as follows: 1. Reaction with strong acid (HCl): Zn(OH)₂ + 2HCl → ZnCl₂ + 2H₂O 2. Reaction with strong base (NaOH): Zn(OH)₂ + 2NaOH → Na₂[Zn(OH)₄] + H₂O

Key Concepts

Zinc Hydroxide

Zinc hydroxide, with the chemical formula \( \text{Zn(OH)}_2 \), is a compound that plays a fascinating role in chemistry due to its amphiprotic nature. This means that zinc hydroxide can act as both an acid and a base, depending on the situation. In other words, it has the ability to donate or accept protons (\( \text{H}^+ \)).
When interacting with strong acids or bases, zinc hydroxide illustrates its unique dual characteristics. In acidic environments, it behaves like a base. While in basic environments, it shows its acidic side. Because of this flexibility, zinc hydroxide is frequently used in studies involving acid-base reactions, providing excellent real-life examples of amphiprotic behavior, which is vital for understanding more complex chemical processes.

Acid-Base Reactions

Acid-base reactions are fundamental processes in chemistry, where an acid reacts with a base resulting in the formation of a salt and water. These reactions are central to various applications, ranging from industrial processes to biological systems. One of the key characteristics of acid-base reactions is that they involve the transfer of protons (\( \text{H}^+ \)) between the reacting species.

• In the reaction of zinc hydroxide with a strong acid like hydrochloric acid (\( \text{HCl} \)), zinc hydroxide acts as a base since it accepts protons. This forms zinc chloride (\( \text{ZnCl}_2 \)) and water.
• Conversely, when zinc hydroxide reacts with a strong base such as sodium hydroxide (\( \text{NaOH} \)), it acts as an acid by donating protons. This results in the formation of a complex ion \( \text{Na}_2[\text{Zn(OH)}_4] \) and water.

These reactions highlight the amphiprotic nature of zinc hydroxide and showcase how it adjusts its behavior based on the reacting partner, making it a versatile component in acid-base chemistry.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They outline the reactants and products involved, providing a clear and concise way to express chemical processes. Each equation must be balanced to ensure the conservation of mass, meaning the number of atoms for each element must be the same on both sides of the equation.

In the case of zinc hydroxide's reactions, the chemical equations are formulated to reflect its amphiprotic interactions:

• The reaction with hydrochloric acid is balanced as follows: \[\text{Zn(OH)}_2 + 2\text{HCl} \rightarrow \text{ZnCl}_2 + 2\text{H}_2\text{O}\]Here, zinc hydroxide accepts protons from \( \text{HCl} \), pairing each hydroxide with a proton to form water.
• In the reaction with sodium hydroxide, the equation is: \[\text{Zn(OH)}_2 + 2\text{NaOH} \rightarrow \text{Na}_2[\text{Zn(OH)}_4] + \text{H}_2\text{O}\]In this case, zinc hydroxide donates a proton to the base, forming a complex ion.

These equations not only confirm the amphiprotic behavior of zinc hydroxide but also highlight the importance of balancing chemical reactions. This ensures that all atoms accounted for, illustrating the law of conservation of mass in chemistry. Balancing acts as a crucial tool in communicating and understanding chemical processes effectively.