Problem 17 - Chemistry: An Atoms-Focused Approach

Question

Which ion is the counter ion in the coordination compound \(\mathrm{Na}_{2}\left[\mathrm{Zn}(\mathrm{CN})_{4}\right] ?\)

Step-by-Step Solution

Answer

Answer: The counter ion in the coordination compound \(\mathrm{Na}_{2}\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]\) is \(\mathrm{Na}^{+}\).

Step 1: Identify the coordination complex and its charge

First, we need to identify the coordination complex in the given compound. In the given compound, the coordination complex is \(\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]\). Now let's determine the charge of the coordination complex. Zn has a charge of +2, while each CN ligand has a charge of -1. Since there are four CN ligands, the total charge of the complex is +2 - 4 = -2. The coordination complex is \(\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]^{2-}\).

Step 2: Identify the counter ion

Now that we know the charge of the coordination complex, we can identify the counter ion. The counter ion is the ion that balances the charge of the complex. In this case, we have Na ions in the compound. Each Na ion has a charge of +1. To balance the -2 charge of the coordination complex, we need to have two Na ions, or \(\mathrm{Na}^{+}\) ions in the compound. Therefore, the counter ion in the coordination compound \(\mathrm{Na}_{2}\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]\) is \(\mathrm{Na}^{+}\).

Key Concepts

Counter Ions

Counter ions in coordination compounds are those ions that help to neutralize the charge of the complex part of the compound. Let's break this down for a better understanding. In our example, we have Na in the coordination compound \( \mathrm{Na}_{2}\left[\mathrm{Zn}(\mathrm{CN})_{4}\right] \). When a coordination complex, such as \( \left[\mathrm{Zn}(\mathrm{CN})_{4}\right]^{2-} \), is formed, it carries a net charge from the ligands and the metal ion. The counter ions, in this case \( \mathrm{Na}^{+} \), provide the necessary charge to balance this.

• Counter ions are not part of the ligand set.
• They balance the electrostatic charge of the complex.
• In this example, two sodium ions are needed to achieve neutrality.

Understanding counter ions is crucial as it helps demonstrate why certain ionic compounds are stable and neutral overall. They occur outside the coordination sphere and help maintain electrical neutrality in the compound.

Charge Balance in Complexes

In coordination chemistry, maintaining the balance of charge in a complex is key to stability. Let's dive into what this means. Each component of a coordination compound - the central metal ion and its surrounding ligands - carries a specific charge. In our case, the complex \([\mathrm{Zn}(\mathrm{CN})_{4}]^{2-}\) is comprised of a \(\mathrm{Zn}^{2+}\) ion and four \(\mathrm{CN}^{-}\) ligands.

If we do the math:

• Zn contributes +2 to the charge.
• Each CN contributes -1, for a total of -4 from four CN ligands.
• The net charge on the complex is +2 - 4 = -2

This -2 charge is what we aim to balance with counter ions, which in this case is achieved by introducing two Na ions with a charge of +1 each. Correct charge balancing ensures that complex ions remain intact and effectively neutral overall in solution.

Coordination Chemistry

Coordination chemistry involves the study of complex formations around a central metal atom or ion, which interacts closely with molecules or ions known as ligands. This field explores the structure, bonding, and reactivity of these complexes. The coordination number denotes the number of ligand positions around the central metal, which signifies the number of straight lines you can draw from the center connecting to each ligand.

In our example, the coordination number of Zn is 4, which matches the number of \(\mathrm{CN}^-\) ions. These ligands form a coordination complex \([\mathrm{Zn}(\mathrm{CN})_{4}]^{2-}\), bonding to the zinc via coordinate covalent bonds.

• Coordination compounds have varied applications, from oxygen transport in blood to catalysts in industries.
• Central to coordination chemistry is the electronic effect of ligands which influences the metal ion properties.
• This concept aids in designing compounds with specific functionality and stability.

Understanding coordination chemistry helps clarify many real-world chemical processes, particularly those involving transition metals and their compounds in various oxidation states.