Question

Identify the oxidation state of the metal in each of the following compounds: (a) \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{NO}_{2}\right)_{3}\) (b) \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{NO}_{3}\) (c) \(\mathrm{K}_{3}\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2} \mathrm{Cl}_{2}\right]\) (d) \(\mathrm{Cs}\left[\mathrm{CuCl}_{2}\right]\)

Short answer

(a) +3; (b) +1; (c) +3; (d) +1.

Step-by-step solution

Assign known charges

First, assign known charges to the ligands and counterions based on common oxidation states: - Nitrite (\(\text{NO}_2^-\)) has a charge of -1.- Ammonia (\(\text{NH}_3\)) is neutral.- Nitrate (\(\text{NO}_3^-\)) has a charge of -1.- Oxalate (\(\text{C}_2\text{O}_4^{2-}\)) has a charge of -2.- Chloride (\(\text{Cl}^-\)) has a charge of -1.- Potassium (\(\text{K}^+\)) has a charge of +1.- Cesium (\(\text{Cs}^+\)) has a charge of +1.

Calculate oxidation state for Co in (a)

For \(\mathrm{Co}\left(\mathrm{NH}_3\right)_3\left(\mathrm{NO}_2\right)_3\):- Ammonia ligands are neutral.- Each \(\text{NO}_2\) is -1, with three total giving -3.- Overall charge of the complex is 0 (no charge indicated).- Let the oxidation state of \(\text{Co}\) be \(x\).Equation: \[x + 0 + (-1)(3) = 0\]Solving:\[x - 3 = 0 \rightarrow x = +3\]Thus, Co's oxidation state is +3.

Calculate oxidation state for Ag in (b)

For \(\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right] \mathrm{NO}_3\):- Ammonia ligands are neutral.- \(\text{NO}_3^-\) acts as a counterion with -1 charge, balancing the complex to zero.Equation for \(\text{Ag}\):\[x + 0 = +1\] (since the whole complex has a +1 charge to balance the nitrate)Solving:\[x = +1\]Thus, Ag's oxidation state is +1.

Calculate oxidation state for Cr in (c)

For \(\mathrm{K}_3\left[\mathrm{Cr}\left(\mathrm{C}_2\mathrm{O}_4\right)_2 \mathrm{Cl}_2\right]\):- Potassium has a +3 total charge for three ions.- Two \(\text{C}_2\text{O}_4^{2-}\) provide a total of -4.- Two \(\text{Cl}^-\) provide a total of -2.- Overall charge of complex is determined by the three potassium cations making the whole complex neutral.- Let the oxidation state of \(\text{Cr}\) be \(x\).Equation:\[x + (-4) + (-2) = -3\] (since the counter charge of K is +3 for overall neutrality)Solving:\[x - 6 = -3 \rightarrow x = +3\]Thus, Cr's oxidation state is +3.

Calculate oxidation state for Cu in (d)

For \(\mathrm{Cs}\left[\mathrm{CuCl}_2\right]\):- Cesium has a +1 charge.- Two \(\text{Cl}^-\) provide a total of -2.- Overall charge of the complex must balance to zero.- Let the oxidation state of \(\text{Cu}\) be \(x\).Equation:\[x + (-2) = -1\] (to balance the Cs+)Solving:\[x - 2 = -1 \rightarrow x = +1\]Thus, Cu's oxidation state is +1.

Key concepts

Understanding Coordination Compounds

Coordination compounds are complex structures formed when central metal ions bind with molecules or ions called ligands. These compounds are integral to many biological systems and industrial processes. For example, hemoglobin in blood is a coordination compound that contains iron.

In coordination compounds, a metal ion is surrounded by an ensemble of ligands. These ligands can be neutral molecules or ions that donate at least one pair of electrons to the metal, forming a coordinate covalent bond.

Key characteristics include:

• Central Metal Ion: Acts as the electron acceptor in the coordination complex.
• Coordination Sphere: The metal ion and its surrounding ligands form the inner sphere, defining the geometry and reactivity of the compound.
• Coordination Number: Represents the number of ligand attachment points to the metal ion, influencing the shape of the complex.

Understanding coordination compounds is crucial for determining properties like oxidation states.

Role and Calculation of Oxidation States in Metal Ions

Metal ions in coordination compounds can have various oxidation states, affecting the overall characteristics of the compound. The oxidation state represents the hypothetical charge an atom would have if all bonds were ionic.

To determine the oxidation state of the metal ion:

• Assign known charges to the ligands and other ions in the compound based on common oxidation states.
• Use the compound's overall charge to set up an equation to solve for the metal's oxidation state.

For example, in a complex like o the ammonia ligand is neutral, and any nitrite group (\(\text{NO}_2^-\))is –1. By balancing these charges, you can find the oxidation state of the central metal.

The Significance of Ligands

Ligands play a significant role in forming coordination compounds, acting as the electron pair donor to the central metal ion. They influence the compound’s stability, reactivity, and geometry.

Types of ligands include:

• Neutral Ligands: Such as ammonia (\(\text{NH}_3\)), which does not impart additional charge.
• Charged Ligands: Including nitrate (\(\text{NO}_3^-\)), which affects the overall charge of the compound.
• Bidentate Ligands: Such as oxalate (\(\text{C}_2\text{O}_4^{2-}\)), which can attach to the metal ion at two points, providing more stability.

The nature of the ligand and its charge help determine the oxidation state of the metal and the compound’s overall balancing.

Balancing Chemical Equations in Coordination Chemistry

Balancing chemical equations is essential to represent accurately the stoichiometry of the reaction involving coordination compounds. It ensures that both mass and charge are conserved throughout the reaction.

When balancing the equations involving coordination compounds:

• Identify the oxidation state of each element in the compounds.
• Ensure that the number of atoms and the total charge on both sides of the equation are equal.
• Use stoichiometric coefficients to balance both the number of atoms and the charges.

For example, if a complex ion has a negative charge, it must be balanced by counter ions with positive charges in the equation to reflect neutrality in the overall reaction. This process aids in accurately identifying changes, such as in redox reactions or ligand exchanges.