Problem 74 - Chemistry The Molecular Science

Question

Write a chemical equation that illustrates how the hydrated \(\mathrm{Ni}^{2+}\) ion, \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\), acts as an acid in aqueous solution.

Step-by-Step Solution

Answer

\([ ext{Ni(H}_2 ext{O)}_6]^{2+} + \text{H}_2\text{O} \rightarrow [\text{Ni(H}_2\text{O)}_5(\text{OH})]^+ + \text{H}_3\text{O}^+\).

Step 1: Understanding the Acidic Nature

The hydrated nickel ion, \([ ext{Ni(H}_2 ext{O)}_6]^{2+}\), acts as an acid in aqueous solutions by donating a proton (H\(^+\)) from one of the water molecules attached to the nickel ion. This causes the formation of hydronium ion \(\text{H}_3\text{O}^{+}\) and a complex with one less water molecule.

Step 2: Formula Representation of Proton Donation

When \([ ext{Ni(H}_2 ext{O)}_6]^{2+}\) acts as an acid, it donates a proton to water, forming \(\text{H}_3\text{O}^{+}\) and \(\left[ ext{Ni(H}_2 ext{O)}_5( ext{OH})\right]^+\). This can be represented by the following chemical equation: \[[A ext{Ni(H}_2 ext{O)}_6]^{2+} + ext{H}_2 ext{O} \rightarrow [ ext{Ni(H}_2 ext{O)}_5( ext{OH})]^+ + ext{H}_3 ext{O}^+.\]

Step 3: Balanced Chemical Equation

Ensure that the equation is properly balanced in terms of charge and mass. In this situation, both the number of atoms of each element and the net charge are balanced: \((+2) + (0) = (+1) + (+1)\). So, we have the equation: \[[ ext{Ni(H}_2 ext{O)}_6]^{2+} + ext{H}_2 ext{O} \rightarrow [ ext{Ni(H}_2 ext{O)}_5( ext{OH})]^+ + ext{H}_3 ext{O}^+.\]

Key Concepts

Understanding Hydrated Ions

Hydrated ions form when ions interact with water molecules in an aqueous solution. The water molecules organize around the ion due to electrostatic interactions. In the case of the \([\text{Ni(H}_2\text{O)}_6]^{2+}\) ion, six water molecules surround the central nickel ion. This creates a structure where the nickel ion is at the center, and the water molecules act as a shield or cushion around it.

• Hydration stabilizes ions and affects their reactivity.
• The number of water molecules surrounding an ion can vary, but for transition metal ions like \(\mathrm{Ni}^{2+}\), it is commonly six.
• These interactions are essential as they define the ion's behavior and characteristics in solution.

Hydration helps ions remain suspended in the solution and significantly influences their chemical properties. Understanding this concept is crucial as it is often the key to predicting how these ions will react with other substances in a solution.

Exploring Proton Donation

Proton donation is a hallmark of acidic behavior in chemistry. It refers to the process where a molecule or ion donates a hydrogen ion (H\(^+\)) to another species. The hydrated nickel complex \([\text{Ni(H}_2\text{O)}_6]^{2+}\), acts as a weak acid.When it donates a proton to water, the water molecule accepts the proton and forms a \,\text{hydronium ion} \(\text{H}_3\text{O}^{+}\). The nickel complex loses one water molecule, converting into \([\text{Ni(H}_2\text{O)}_5(\text{OH})]^+\). This process is summed up by the chemical equation:\[ [\text{Ni(H}_2\text{O)}_6]^{2+} + \text{H}_2\text{O} \rightarrow [\text{Ni(H}_2\text{O)}_5(\text{OH})]^+ + \text{H}_3\text{O}^+ \]
Understanding proton donation is important because:

• It is a key process in many chemical reactions, especially those involving acids and bases.
• Proton transfer affects pH levels in solutions, which can influence the outcome of a reaction.
• It helps in predicting equilibrium states and determining the strength of acids.

Insights into Chemical Equilibrium

Chemical equilibrium is the state where the concentrations of reactants and products remain constant over time. This occurs when the forward and reverse reactions occur at the same rate. In the context of the hydrated nickel complex, after donating a proton, the system can reach equilibrium.Even though the equation:\[ [\text{Ni(H}_2\text{O)}_6]^{2+} + \text{H}_2\text{O} \rightleftharpoons [\text{Ni(H}_2\text{O)}_5(\text{OH})]^+ + \text{H}_3\text{O}^+ \]appears one-way, it can exist in dynamic equilibrium. This means the reverse reaction, where \([\text{Ni(H}_2\text{O)}_5(\text{OH})]^+\) accepts a proton to revert to \([\text{Ni(H}_2\text{O)}_6]^{2+}\), also occurs.Equilibrium concepts are vital because:

• They allow us to understand reaction completeness and yield.
• They are crucial in optimizing conditions in industrial chemical processes.
• The equilibrium constant provides insight into the ratio of products to reactants at equilibrium.

By studying equilibrium, chemists can manipulate and predict the outcomes of chemical reactions efficiently.