Problem 136 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the properties (A) reducing (B) oxidizing (C) complexing, the set of properties shown by \(\mathrm{CN}^{-}\)ion towards metal species is (a) \(\mathrm{A}, \mathrm{B}\) (b) B, C (c) \(\mathrm{C}, \mathrm{A}\) (d) A, B, C

Step-by-Step Solution

Answer

The properties shown by \( \mathrm{CN}^{-} \) are complexing, so the answer is (b) B, C.

Step 1: Understanding the Roles of CN−

The cyanide ion, \( \mathrm{CN}^{-} \), is well known for its ability to function in multiple roles when interacting with metals. Primarily, \( \mathrm{CN}^{-} \) is known as a strong ligand in coordination chemistry, where it shows complexing properties. It means that it can donate electron pairs to metal ions to form metal complexes.

Step 2: Assessing Reducing Properties

The ability of a species to be a reducing agent is based on its tendency to donate electrons. The \( \mathrm{CN}^{-} \) ion does not commonly act as a reducing agent, as it prefers to hold onto its electrons and form stable complexes with metals instead. This implies it is not typically reducing in nature.

Step 3: Evaluating Oxidizing Properties

An oxidizing property refers to the ability of a species to accept electrons. The \( \mathrm{CN}^{-} \) ion is not commonly known for this property. It does not have a strong tendency to gain electrons because it forms stable complexes by donating electrons to metal centres, indicating a lack of oxidizing characteristics.

Step 4: Identifying Complexing Properties

As previously mentioned, the \( \mathrm{CN}^{-} \) ion is a strong complexing agent, frequently used to form stable metal complexes through the donation of electron pairs to metal ions. Complexing is a characteristic property of \( \mathrm{CN}^{-} \).

Key Concepts

Reducing Properties

Reducing properties refer to the ability of a substance to act as a reducing agent. A reducing agent donates electrons during a chemical reaction. It gets oxidized itself in the process. In the context of coordination chemistry, a molecule's reducing capabilities can significantly impact its interactions with metal ions.
\( \mathrm{CN}^{-} \) ion, however, is not typically known for its reducing properties. Due to its powerful affinity for forming stable complexes with metals through the donation of electron pairs, it does not readily part with its electrons. This means that it has a low tendency to act as a reducing agent. Therefore, when working with \( \mathrm{CN}^{-} \) ions in coordination chemistry, it is important to remember that their primary role is not to donate electrons for reduction.

Oxidizing Properties

Oxidizing properties describe a substance’s ability to act as an oxidizer and accept electrons. An oxidizing agent receives electrons during a chemical reaction and becomes reduced. In coordination chemistry, these properties determine how well a molecule can interact by gaining electrons.
However, the \( \mathrm{CN}^{-} \) ion does not exhibit strong oxidizing properties. In contrast to substances that gain electrons, \( \mathrm{CN}^{-} \) prefers to hold its electron configuration steady. This behavior supports its role as an electron-pair donor rather than an acceptor.

• It forms stable complexes with metals by donating, not accepting, electrons.
• Therefore, \( \mathrm{CN}^{-} \) is unlikely to participate in reactions as an oxidizing agent.

This is important to remember when anticipating reactions and working with this ion in coordination compounds.

Complexing Agent

A complexing agent is a molecule or ion capable of forming a coordinate bond by donating electron pairs to metal ions. This is a defining feature in coordination chemistry, where the formation of stable metal complexes is crucial.
The \( \mathrm{CN}^{-} \) ion is renowned for its role as a strong complexing agent. It possesses a significant ability to donate its electron pairs, leading to the formation of stable complexes with transition metals. This is achieved via coordinate covalent bonds, which are crucial in the creation of metal complexes:

• It will bond with a metal ion by sharing its electronics through these coordinate bonds.
• This ability to stabilize metals is central to its role in many chemical reactions and industrial processes.

In summary, the complexing qualities of \( \mathrm{CN}^{-} \) make it essential in a variety of coordination chemistry applications.