Problem 42 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The IUPAC name of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}\) is \(\ldots \ldots \ldots \ldots\)

Step-by-Step Solution

Answer

Hexamminecobalt(III) chloride.

Step 1: Identify the Complex Ion

The compound given is \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]\mathrm{Cl}_{3}\). We identify the complex ion within the square brackets: \([\mathrm{Co}(\mathrm{NH}_3)_6]^{3+}\). Here, \(\mathrm{Co}\) is the central metal ion, and \(\mathrm{NH}_3\) is a neutral ligand.

Step 2: Name the Ligands

The ligand \(\mathrm{NH}_3\) is named "ammine" in coordination chemistry. Since there are six \(\mathrm{NH}_3\) ligands, we use the prefix 'hexa' to indicate the number of ligands: 'hexammine'.

Step 3: Determine the Oxidation State of the Metal

In the compound \([\mathrm{Co}(\mathrm{NH}_3)_6] \mathrm{Cl}_3\), the overall charge is neutral. Each \(\mathrm{Cl}^-\) contributes -1 charge (total -3 charge), which means the complex ion must have a +3 charge to balance it. Therefore, the oxidation state of \(\mathrm{Co}\) is +3.

Step 4: Name the Metal Ion

Since the metal ion is cobalt and the oxidation state is +3, we name the metal as 'cobalt(III)' in the complex ion.

Step 5: Combine the Names

Combine the names from Step 2 and Step 4 to write the full IUPAC name of the coordination compound: 'hexamminecobalt(III) chloride'.

Key Concepts

IUPAC Nomenclature

IUPAC nomenclature is the universal system used to give a standard name to chemical compounds, ensuring consistency and clarity. When naming coordination compounds, like \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]\mathrm{Cl}_{3} \), we follow specific rules to reflect both the structure and composition of the complex.

Key steps in this process:

• Identify the central metal ion and its attached ligands within the coordination sphere – those elements enclosed in square brackets.
• Name the ligands first, using prefixes like "mono", "di", "tri" to indicate numbers, while factors like alphabetical order play a role when multiple ligands are present.
• Determine the oxidation state of the metal, indicated in Roman numerals.
• Finish with the name of the substance bearing the ionic charge outside the brackets, which could be an anion like chloride (\(\text{Cl}^-\)).

The coordination compound \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]\mathrm{Cl}_{3} \)is named 'hexamminecobalt(III) chloride'. This name comprises:

• 'hexammine': six ammonia ligands \(\left(\text{NH}_{3}\right)\) that bond to cobalt.
• 'cobalt(III)': the cobalt metal ion with its oxidation state of +3.
• 'chloride' marking the three chloride ions providing balance outside the coordination ion.

Following this structured methodology guarantees chemical names provide crucial insights into the composition and geometry of the complex.

Complex Ions

Complex ions are fascinating structures found in the field of coordination chemistry, involving a central metal atom bonded to molecules or anions known as ligands. These ligands can be neutral like \( \text{NH}_3 \) (ammine), or negatively charged, all immensely important for defining the properties of the compound.

A complex ion is always enclosed in square brackets, indicating the charged entity within. The metal, often a transition metal, serves as the central core. Ligands like ammine wrap around this metal through coordinate covalent bonds, where the ligand donates pairs of electrons to empty orbitals of the metal ion.

The arrangement, number, and kind of ligands influence the overall charge and stability of the complex. An example is the ion \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+} \),where cobalt is a central ion, stabilized and rendered distinct by six ammine ligands. Complex ions play a central role in multiple fields, from biological systems involving hemoglobin and chlorophyll to industrial catalysts, underscoring their importance. Their study enables a deeper understanding of molecular architecture and interactions in the chemical world.

Oxidation States

Oxidation states, also known as oxidation numbers, are essential in understanding the electron arrangement and charge of atoms in a compound. Particularly within complex ions, oxidation states indicate how electrons are distributed between different elements, guiding naming conventions and chemical behavior predictions.

Determine the oxidation state by considering the charge contributions of all ligands and the overall charge of the complex. For our example of \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]\mathrm{Cl}_{3} \):

• The chloride ions (\(\text{Cl}^-\)) contribute a total charge of -3 (3 x -1 each).
• The complex ion part \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+} \) must balance this with a +3 charge, conferring an oxidation state of +3 to cobalt as ammine is a neutral ligand.

Oxidation states are detailed in Roman numerals after the metal's name (such as "cobalt(III)"). These figures not only map out the electron disposition but also help define nomenclature, as seen in the name 'hexamminecobalt(III) chloride'.Understanding oxidation states is crucial because it opens windows into the redox behavior of compounds, their reactivity, and their role in wider chemical processes ranging from metallurgy to biochemistry.