Problem 61 - Chemistry An Atoms First Approach

Question

Write equations for the stepwise formation of each of the following complex ions. a. \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\) b. \(\mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\)

Step-by-Step Solution

Answer

Formation of \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\): 1. \(\mathrm{Ni}^{2+} + \mathrm{CN}^- \rightarrow \mathrm{NiCN}^{+}\) 2. \(\mathrm{NiCN}^{+} + \mathrm{CN}^- \rightarrow \mathrm{Ni}(\mathrm{CN})_{2} \) 3. \(\mathrm{Ni}(\mathrm{CN})_{2} + \mathrm{CN}^- \rightarrow \mathrm{Ni}(\mathrm{CN})_{3}^{-}\) 4. \(\mathrm{Ni}(\mathrm{CN})_{3}^{-} + \mathrm{CN}^- \rightarrow \mathrm{Ni}(\mathrm{CN})_{4}^{2-}\) Formation of \(\mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\): 1. \(\mathrm{V}^{3+} + \mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow \mathrm{V}(\mathrm{C}_{2}\mathrm{O}_{4})^{+}\) 2. \(\mathrm{V}(\mathrm{C}_{2}\mathrm{O}_{4})^{+} + \mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow \mathrm{V}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2}^{-}\) 3. \(\mathrm{V}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2}^{-} + \mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow \mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\)

Step 1: Identify the central metal ion and the ligands

In both complex ions, we can identify the central metal ion and the ligands as follows: a. \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\): The central metal ion is \(\mathrm{Ni}^{2+}\) and the ligand is \(\mathrm{CN}^{-}\). b. \(\mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\): The central metal ion is \(\mathrm{V}^{3+}\) and the ligand is \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\). ##Step 2: Determine the number of ligands coordinating the central metal ion##

Step 2: Determine the number of ligands coordinating the central metal ion

Count the number of ligands that coordinate the central metal ions in the given complex ions: a. In \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\), there are 4 ligands \(\mathrm{CN}^-\) coordinating the \(\mathrm{Ni}^{2+}\) ion. b. In \(\mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\), there are 3 ligands \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\) coordinating the \(\mathrm{V}^{3+}\) ion. ##Step 3: Write the equations for the stepwise formation of the complex ions##

Step 3: Write the equations for the stepwise formation of the complex ions

Write the equations showing the step-by-step binding of the ligands to the central metal ions: a. Formation of \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\): 1. \(\mathrm{Ni}^{2+} + \mathrm{CN}^- \rightarrow \mathrm{NiCN}^{+}\) 2. \(\mathrm{NiCN}^{+} + \mathrm{CN}^- \rightarrow \mathrm{Ni}(\mathrm{CN})_{2} \) 3. \(\mathrm{Ni}(\mathrm{CN})_{2} + \mathrm{CN}^- \rightarrow \mathrm{Ni}(\mathrm{CN})_{3}^{-}\) 4. \(\mathrm{Ni}(\mathrm{CN})_{3}^{-} + \mathrm{CN}^- \rightarrow \mathrm{Ni}(\mathrm{CN})_{4}^{2-}\) b. Formation of \(\mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\): 1. \(\mathrm{V}^{3+} + \mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow \mathrm{V}(\mathrm{C}_{2}\mathrm{O}_{4})^{+}\) 2. \(\mathrm{V}(\mathrm{C}_{2}\mathrm{O}_{4})^{+} + \mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow \mathrm{V}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2}^{-}\) 3. \(\mathrm{V}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2}^{-} + \mathrm{C}_{2}\mathrm{O}_{4}^{2-} \rightarrow \mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}\)

Key Concepts

Central Metal Ion

In the fascinating world of chemistry, a central metal ion serves as the heart of a complex ion. Think of it as a core that attracts various ligands around it to form a stable structure. In our exercises, we have two central metal ions:

• Nickel (\(\mathrm{Ni}^{2+}\)) in \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\).
• Vanadium (\(\mathrm{V}^{3+}\)) in \(\mathrm{V}(\mathrm{C}_{2} \mathrm{O}_{4})_{3}^{3-}\).

These central metal ions have positive charges which play a crucial role in attracting negatively charged ligands. By holding these ligands together, they form what are known as coordination complexes. Understanding the role of the central metal ion helps you to appreciate how these intricate structures are formed. It's like piecing together a puzzle where the metal ion is the piece that other pieces revolve around.

Ligands

Ligands are like the loyal companions that surround the central metal ion, binding to it through coordination bonds. They are usually ions or molecules with lone pairs of electrons. Unlike normal friends, these companions donate these electron pairs to the metal ion's empty orbitals to form a strong bond. In our examples:

• Cyanide (\(\mathrm{CN}^{-}\)) serves as the ligand for Nickel in \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\).
• Oxalate (\(\mathrm{C}_{2} \mathrm{O}_{4}^{2-}\)) acts as the ligand for Vanadium in \(\mathrm{V}(\mathrm{C}_{2} \mathrm{O}_{4})_{3}^{3-}\).

The number and type of ligands can significantly impact the properties of the resulting complex ion. Each ligand binding adds a layer of stability and can change how the entire complex behaves in a chemical reaction. Recognizing the interplay between ligands and the central metal ion helps explain the varied chemistry of complex ions.

Stepwise Formation

The formation of complex ions doesn't happen all at once; it's a step-by-step dance of chemistry called stepwise formation. This process involves ligands attaching to the central metal ion one at a time, similar to threading beads on a string. Let's break it down with examples:

• For \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\), the process starts with Nickel and one Cyanide coming together to form \(\mathrm{NiCN}^{+}\). With each subsequent Cyanide ion added, the complex grows larger: \(\mathrm{Ni}(\mathrm{CN})_{2}\), \(\mathrm{Ni}(\mathrm{CN})_{3}^{-}\), and finally \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\).
• Similarly, Vanadium and Oxalate join forces gradually: starting with \(\mathrm{V}(\mathrm{C}_{2} \mathrm{O}_{4})^{+}\), then \(\mathrm{V}(\mathrm{C}_{2} \mathrm{O}_{4})_{2}^{-}\), and culminating in \(\mathrm{V}(\mathrm{C}_{2} \mathrm{O}_{4})_{3}^{3-}\).

Each step is key and adds a new dimension to the complex, affecting properties like solubility, color, and the potential for further reactions. Understanding stepwise formation helps demystify how complex ions evolve and behave in different chemical environments.