Problem 151 - A Complete Resource Book in Chemistry for JEE Main

Question

In the coordination compound \(\mathrm{K}_{4}\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]\), the oxidation state of nickel is (a) \(-1\) (b) 0 (c) \(+1\) (d) \(+2\)

Step-by-Step Solution

Answer

The oxidation state of nickel is 0.

Step 1: Recognize the coordination compound formula

The coordination compound given is \( \mathrm{K}_{4}\left[\mathrm{Ni}(\mathrm{CN})_{4}\right] \). It consists of the coordination complex \([\mathrm{Ni}(\mathrm{CN})_{4}]\) and four potassium ions (\(\mathrm{K}^+\)).

Step 2: Understand the role of potassium ions

In this compound, the potassium ions (\(\mathrm{K}^+\)) are present to balance the overall charge of the coordination complex. Each potassium ion has a charge of \(+1\), and since there are four potassium ions, they contribute a total charge of \(+4\).

Step 3: Determine the charge of the complex

The overall compound is neutral, meaning the sum of the charges must be zero. Therefore, the charge of the complex \([\mathrm{Ni}(\mathrm{CN})_{4}]\) must be \(-4\) to counterbalance the \(+4\) from the four \(\mathrm{K}^+\) ions.

Step 4: Calculate the charge of the ligands

Cyanide (\(\mathrm{CN}^-\)) is the ligand in the complex and each \(\mathrm{CN}^-\) carries a charge of \(-1\). With four \(\mathrm{CN}^-\) ligands present, the total charge contributed by the ligands is \(-4\).

Step 5: Calculate the oxidation state of nickel

Let the oxidation state of nickel be \(x\). From Step 3, the charge of \([\mathrm{Ni}(\mathrm{CN})_{4}]\) is \(-4\). The equation is: \[ x + 4(-1) = -4 \] Simplifying this, we find \( x - 4 = -4 \). Solving for \(x\), we get \( x = 0 \). Therefore, the oxidation state of nickel in the compound is 0.

Key Concepts

Understanding Coordination Compounds

Coordination compounds are fascinating structures often formed by a central metal atom or ion surrounded by a certain number of ligands. Ligands are ions or molecules that can donate a pair of electrons to the metal, forming what is known as a coordinate bond. These compounds are quite prevalent in the field of chemistry, showcasing a wide range of colors and properties.
Coordination compounds can be complex, but they are essential for understanding various chemical reactions and processes. In the compound \( \mathrm{K}_{4}\left[\mathrm{Ni}(\mathrm{CN})_{4}\right] \), nickel acts as the central metal ion bonded to four cyanide ligands.

• The central ion (nickel in this case) is often a transition metal.
• Ligands surround the central ion and donate electrons.
• The overall charge of the compound is balanced by ions outside the brackets, such as potassium ions \( \mathrm{K}^+ \).

Coordination compounds are integral in various fields, including biochemistry, where similar complexes help transport gases like oxygen in the body.

Diving into Nickel Chemistry

Nickel, a versatile transition metal, plays a crucial role in the realm of coordination chemistry. Known for its ability to form complexes with various ligands, nickel exhibits several oxidation states, typically ranging from \(+2\) to \(-2\), although \(0\) oxidation state is possible too. In our compound \( \mathrm{K}_{4}\left[\mathrm{Ni}(\mathrm{CN})_{4}\right] \), nickel holds an oxidation state of \(0\).

Nickel’s electron configuration \([\mathrm{Ar}] 3d^{8} 4s^{2}\) allows it to adapt its bonding situation by losing different numbers of electrons, stabilizing the compound with neutral or charged ligands.

• Nickel's ability to bond with ligands like cyanide shows its flexibility as a transition metal.
• The oxidation state of nickel drastically impacts the compound's properties, such as color and reactivity.
• Nickel complexes often display vibrant colors due to d-d electron transitions.

Nickel coordination compounds are widely used in applications from catalysis to electrochemistry, showcasing their significance beyond just academic interest.

The Role of Ligand Charge

To understand the stabilizing forces in coordination compounds, it is crucial to consider the charge of ligands. Ligands like cyanide, denoted by \( \mathrm{CN}^- \), are crucial in determining the overall charge and stability of a coordination compound. In our compound \( \mathrm{K}_{4}\left[\mathrm{Ni}(\mathrm{CN})_{4}\right] \), each cyanide ligand carries a charge of \(-1\).

The total charge contributed by the four cyanide ligands can be found by summing their individual charges: \(4 \times (-1) = -4\). This charge directly influences the oxidation state of the central metal ion.

• Cyanide is a common ligand that forms strong bonds with transition metals.
• The negative charge of ligands like \( \mathrm{CN}^- \) helps in stabilizing positively charged metal centers.
• The ligand charge contributes significantly to the overall electronic environment of the complex.

Understanding ligand charges equips us to predict the properties of coordination compounds. It also aids in balancing charges to predict correct oxidation states of metals within the complex.