Problem 98 - Chemistry The Molecular Science

Question

Determine whether each statement is true or false. If it is false, correct the statement. (a) In \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{4}\right]\), platinum has a \(4+\) charge and a coordination number of six. (b) In general, \(\mathrm{Cu}^{2+}\) is more stable than \(\mathrm{Cu}^{+}\) in aqueous solutions.

Step-by-Step Solution

Answer

(a) False, coordination number is eight; (b) True.

Step 1: Analyzing Statement (a)

Let's start with statement (a): In \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{4}\right]\), the statement suggests that platinum has a 4+ charge and a coordination number of six. First, determine the coordination number by analyzing how many ligands are attached to the platinum. There are four \(\mathrm{NH}_3\) molecules and four \(\mathrm{Cl}\) ions, making a total of 8. Thus, the coordination number is 8, not 6. To find the oxidation state of platinum, assume \(\mathrm{NH}_3\) is neutral and each \(\mathrm{Cl}\) provides a \(-1\) charge, so the net charge from \(4\times (-1) = -4\). To balance, Pt must be \(+4\). Thus, this part of the statement is correct, but the coordination number part is false.

Step 2: Evaluating Statement (b)

Referring to statement (b): \(\mathrm{Cu}^{2+}\) is generally more stable than \(\mathrm{Cu}^{+}\) in aqueous solutions, primarily due to higher hydration energy and greater stability conferred by its full \(d\) sub-shell configuration in water solutions. This aligns with the known chemistry of copper ions. Thus, this statement is considered true.

Step 3: Correcting and Concluding the Exercise

In review, the two parts are assessed as follows: Part (a) of the statement is false because the coordination number is incorrectly stated as six, it should be eight. However, the charge of \(+4\) on platinum is correct. Thus, the correct statement is: "In \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{4}\right]\), platinum has a \(4+\) charge and a coordination number of eight." Part (b) is correct as written.

Key Concepts

Coordination Number

The coordination number is a fundamental concept in coordination chemistry, representing the number of ligand donor atoms attached to the central metal ion. In coordination compounds like \([\mathrm{Pt}(\mathrm{NH}_3)_4\mathrm{Cl}_4]\), it is determined by counting all the ligands bonded to the central metal.
For example, in the exercise, platinum is surrounded by four ammonia molecules and four chloride ions, giving it a coordination number of 8.
This number is important because it influences the geometry and stability of the coordination complex.

• Common geometries include linear, square planar, and octahedral.
• The coordination number can affect the overall color and reactivity of the compound.

Oxidation State

The oxidation state reflects the charge of a metal ion within a coordination complex, indicating the number of electrons lost or gained by the atom.
It is determined based on the charges of the surrounding ligands and the overall charge of the compound.
In the example of \([\mathrm{Pt}(\mathrm{NH}_3)_4\mathrm{Cl}_4]\),
each chloride contributes a \(-1\) charge and ammonia is neutral, leading to a \(+4\) oxidation state for platinum to balance the negative charges of the chlorides.

• The oxidation state is crucial in understanding the reactivity and properties of the metal.
• It can also indicate the type of chemical bonding in the complex.

Stability of Ions

Ion stability in coordination chemistry often depends on factors like hydration energy, electron configuration, and external conditions such as temperature and pressure.

For copper ions, \(\mathrm{Cu}^{2+}\) is generally more stable than \(\mathrm{Cu}^{+}\) in aqueous solutions. This is due to the greater hydration energy provided by the full \(3d\) sub-shell of \(\mathrm{Cu}^{2+}\), which stabilizes the ion in water.

• Higher oxidation states generally have more hydration energy, leading to greater stability.
• Stable ions tend to form more robust and less reactive complexes.

Aqueous Solutions

Aqueous solutions are water-based environments where coordination compounds often dissolve. The solubility and behavior of metal ions in such solutions depend on several factors:

• Hydration effects: Higher hydration energy typically leads to increased stability of the ion in solution.
• pH of the solution: It can alter the ionic forms and stability of complexes.
• Presence of other ions: Can lead to complex formation and precipitation effects.

For copper ions, as stated in the problem, \(\mathrm{Cu}^{2+}\) is more stable than \(\mathrm{Cu}^{+}\) due to its greater hydration energy.

Copper Ions

Copper ions such as \(\mathrm{Cu}^{+}\) and \(\mathrm{Cu}^{2+}\) are integral to many types of coordination compounds and reactions.
The two oxidation states have distinct properties:

• \(\mathrm{Cu}^{2+}\) is more commonly found due to its higher stability in aqueous environments.
• \(\mathrm{Cu}^{+}\) is less stable and often prone to disproportionation, where it can change into \(\mathrm{Cu}^{2+}\) and copper metal.

Understanding the nature of these ions is crucial for predicting reactivity and designing synthesis involving copper-based compounds.

Platinum Complexes

Platinum complexes are a significant class of coordination compounds with various applications including in catalysis and medicine.
The exercise provides an example with \([\mathrm{Pt}(\mathrm{NH}_3)_4\mathrm{Cl}_4]\), showcasing typical characteristics:

• Platinum often forms square planar complexes due to its preference for specific geometric arrangements.
• The coordination number and oxidation state influence properties such as catalytic activity.

Understanding these properties helps in designing platinum-based drugs and catalysts with desired activities.