Problem 57 - General Chemistry

Question

Write the equation for the acid ionization of the \(\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+}\) ion.

Step-by-Step Solution

Answer

The equation is \( \mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Zn}(\mathrm{OH})(\mathrm{H}_2\mathrm{O})_5^{+} + \mathrm{H}_3\mathrm{O}^+ \).

Step 1: Identify the Acid

The acid in this case is the hexa-aqua zinc ion, \( \mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+} \). This is a complex ion made of a zinc ion surrounded by six water molecules.

Step 2: Understand Ionization

Ionization refers to the loss of protons (\( \mathrm{H}^+ \)) from water molecules in the complex, forming a hydronium ion (\( \mathrm{H}_3\mathrm{O}^+ \)) in the process.

Step 3: Write the Ionization Reaction

The ionization of \( \mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+} \) involves the release of a proton (\( \mathrm{H}^{+} \)) from one of the water molecules, forming \( \mathrm{H}_3\mathrm{O}^{+} \) and \( \mathrm{Zn}(\mathrm{OH})(\mathrm{H}_2\mathrm{O})_5^{+} \). The equation is: \[ \mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Zn}(\mathrm{OH})(\mathrm{H}_2\mathrm{O})_5^{+} + \mathrm{H}_3\mathrm{O}^+ \].

Step 4: Check for Charge and Mass Balance

Ensure that both charge and mass are balanced in the equation. The reactants and products each have a net charge of \(+2\) and the same number of each type of atom.

Key Concepts

Zinc Complex Ion

Zinc complex ions are fascinating structures with zinc at their core. Typically, these ions involve a zinc ion surrounded by molecules or ions that coordinate with it, forming a stable complex. In the case of the hexa-aqua zinc ion, denoted as \( \mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+} \), zinc is bonded to six water molecules.
This setup is quite common among transition metals like zinc, where coordination chemistry plays a critical role in their chemical behavior. Complex ions are crucial because they often act as acids or bases in chemical reactions. The coordination of water molecules creates a situation where the release or acceptance of protons is more likely, allowing the ion to participate actively in acid-base chemistry.

• 6 water molecules coordinate with one zinc ion.
• The overall charge of this complex ion is \(+2\).
• Such complexes are essential in various chemical, biological, and industrial processes.

Understanding how these complex ions behave is crucial to predict their reactions, especially in solutions where they might interact with other ions or molecules.

Hydronium Ion Formation

Hydronium ions, represented as \( \mathrm{H}_3\mathrm{O}^+ \), are key players in acid-base chemistry. They form when a water molecule accepts an additional proton \( \mathrm{H}^+ \). This is a critical step in the ionization of the zinc complex ion \( \mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+} \).
This ionization process involves water molecules bonded to the zinc ion losing a proton. The proton binds to another water molecule in the solution, leading to the formation of \( \mathrm{H}_3\mathrm{O}^+ \).

• Hydronium ions contribute to the acidity of a solution.
• The process involves proton transfer from water, not zinc directly.
• Hydronium ions are essential in balancing charge and influencing the pH of the system.

When these hydronium ions appear in solution, they are the reason why the solution becomes acidic. Being aware of hydronium ion formation helps in understanding how acid-base reactions proceed in aqueous environments.

Proton Transfer

Proton transfer is a fundamental concept in understanding the reactivity and behavior of acids and bases. In the context of the zinc complex ion, proton transfer occurs when a water molecule in the complex releases a \( \mathrm{H}^{+} \) ion.
The proton then moves to bond with another water molecule, ultimately forming \( \mathrm{H}_3\mathrm{O}^{+} \). This movement of protons from one species to another is essential for defining acid behavior in chemistry.

• Proton transfer defines how acids release \( \mathrm{H}^+ \) ions.
• It accounts for the transformation of reactants into products in ionization reactions.
• Such a mechanism is central to many biological processes and industrial applications.

By tracking the journey of protons between substances, we gain insight into how reactions are balanced in terms of both mass and charge, which is vital for solving equations accurately and understanding chemical equilibria.