Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following is a correct representation of tetraamminecopper(II) hexacyanoferrate(II)? (a) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{2}\) (b) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{2}\) (c) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) (d) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\)

Step-by-Step Solution

Answer

The correct representation is option (a).

Step 1: Identify and Understand Each Component of the Complex

First, identify the two parts of the given chemical name: 'tetraamminecopper(II)' is a metal complex with copper and ammonia ligands, and 'hexacyanoferrate(II)' involves a metal complex of iron and cyanide ligands. The Roman numerals indicate the oxidation states for copper (II) and iron (II). In chemical notation, tetra indicates four ammonia molecules, and hexa indicates six cyanide ions.

Step 2: Determine the Charge of Each Component

For the complex \([\text{Cu}(\text{NH}_3)_4]^{2+} \), copper in the +2 oxidation state is surrounded by four neutral ammonia molecules, giving a net charge of +2. For \([\text{Fe}(\text{CN})_6]^{4-} \), iron is in the +2 state, cyanide ions each with a -1 charge result in an overall charge of -4 for the hexacyanoferrate complex.

Step 3: Balance the Charges

The correct chemical formula should reflect an overall neutral charge. If \([\text{Cu}(\text{NH}_3)_4]^{2+} \) and \([\text{Fe}(\text{CN})_6]^{4-} \) are to form a neutral compound, the charges must balance out. Thus, three copper complexes (each +2) will balance with two iron complexes (each -4), resulting in a neutral combination programmatically written as \([\text{Cu}(\text{NH}_3)_4]_3[\text{Fe}(\text{CN})_6]_2 \).

Step 4: Match with Given Options

Compare the correctly balanced formula \([\text{Cu}(\text{NH}_3)_4]_3[\text{Fe}(\text{CN})_6]_2 \) to the options provided. Match it to the option (a), which is \([\text{Cu}(\text{NH}_3)_4]_3[\text{Fe}(\text{CN})_6]_2 \).

Key Concepts

Complex Ions

Complex ions are fascinating entities within coordination chemistry. They typically consist of a central metal ion bonded to one or more molecules or ions, known as ligands. These ligands donate electron pairs to the metal, forming coordinate covalent bonds. This creates a stable complex with unique properties.
In our exercise, we encounter two types of complex ions:

• The first is tetraamminecopper(II) with copper as the central metal surrounded by four ammonia molecules.
• The second is hexacyanoferrate(II) where iron is surrounded by six cyanide ions.

Recognizing the components of a complex ion is crucial because it helps us understand their geometry and reactivity. Furthermore, these complexes can have diverse biological, industrial, and medical applications, ranging from catalysis to medical diagnostics.

Oxidation States

Oxidation states are numerical values assigned to elements within a compound, indicating the number of electrons gained or lost. They help chemists determine electron distribution in chemicals, crucial for constructing correct chemical formulas.
In the current exercise, the importance of oxidation states is underscored:

• Copper in tetraamminecopper(II) exhibits a +2 oxidation state. This means it has lost two electrons.
• Similarly, iron in hexacyanoferrate(II) also has a +2 oxidation state, signifying two lost electrons.

These oxidation states are essential in balancing chemical equations. They ensure that the net charge of the compound reflects an overall balance of positive and negative charges, achieving a neutral chemical formula.

Chemical Formulas

Chemical formulas are the pictorial representation of a compound's composition. They provide insightful details about the elements present and their quantities. Crafting an accurate chemical formula depends significantly on understanding complex ions and their charges.

• Each formula should exhibit zero net charge when representing a neutral compound. For our complex, the charge balance came from combining three copper complexes, each bearing a +2 charge, with two iron complexes at -4 each.
• The expression \[ [\mathrm{Cu}(\mathrm{NH}_3)_4]_3[\mathrm{Fe}(\mathrm{CN})_6]_2 \] precisely follows this charge balancing, yielding a stable and neutral compound.

Grasping how to write and interpret chemical formulas is vital in chemistry. It allows scientists to communicate the makeup of compounds succinctly and correctly, ensuring accurate replication and understanding during experiments and theoretical studies.