Problem 142 - A Complete Resource Book in Chemistry for JEE Main

Question

The IUPAC name of the coordination compound \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) is \([2005]\) (a) potassium hexacyanoferrate (III) (b) potassium hexacyanoferrate (II) (c) tripotassium hexacyaniron (II) (d) potassium hexacyanoiron (II)

Step-by-Step Solution

Answer

The IUPAC name is potassium hexacyanoferrate (III).

Step 1: Identify the Central Metal and Its Oxidation State

The central metal ion in the coordination compound \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) is iron (Fe). We need to determine its oxidation state. Each cyanide (CN) ligand carries a charge of -1. Since there are 6 CN ligands, the total negative charge contributed by them is -6.

Step 2: Calculate the Oxidation State of Fe

The compound is overall neutral, and the three potassium ions contribute a total charge of +3. Therefore, the oxidation state \( x \) of Fe can be found using the equation: \( 3 + (x - 6) = 0 \). Solving this gives \( x = +3 \). Thus, the oxidation state of Fe in the compound is +3.

Step 3: Construct the IUPAC Name

The IUPAC name is structured as "cation anion." The cation in the compound is potassium (K), and the anion is formed by the metal complex \([\mathrm{Fe}(\mathrm{CN})_{6}]^{3-}\). The prefix for the six cyanide ligands is "hexa," and since the oxidation state of Fe is +3, we use the term "ferrate" with the oxidation state in Roman numerals. Thus, the IUPAC name is "potassium hexacyanoferrate (III)."

Key Concepts

Coordination Compounds

Coordination compounds are fascinating structures formed when central metal ions bind with molecules or ions known as ligands. These compounds are unique because the metal ions do not simply sit alone; instead, they share their centers with ligands through coordinate covalent bonds. The nature and number of these ligands typically determine the properties and reactivity of the coordination compound. For example, in the compound \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), the central metal ion is iron (Fe). The cyanide (CN) groups act as ligands and coordinate with the iron, creating a coordinate complex. Since the cyanide ion carries a negative charge, it neutralizes part of the charge from the metal ion. Understanding these interactions is key to naming and identifying properties of coordination compounds in chemistry.

Oxidation State Determination

Determining the oxidation state of the central metal in a coordination compound involves a methodical approach. The oxidation state represents how many electrons a metal has gained or lost upon forming the compound. It's crucial because it affects the compound's chemical behavior.

Let’s figure out how to determine this using the example \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\). The compound includes three potassium ions, each with a +1 charge, and six cyanide ligands, each carrying a -1 charge. Together, this makes a total ligand charge of -6. Since the overall compound is neutral, the oxidation state of iron must counterbalance these charges. The equation: \(+3 + (x - 6) = 0\), where \(x\) is the oxidation state of Fe, solves to \(+3\). Calculating the oxidation state like this helps ensure the compound stays electrically neutral, critical for correct naming and understanding its reactivity.

Naming Conventions in Chemistry

Naming coordination compounds systematically ensures clear communication among scientists. The International Union of Pure and Applied Chemistry (IUPAC) sets the guidelines, making nomenclature precise and standardized.

To properly name the compound \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), start with identifying the cation, which is potassium (K). Then, name the anion, which includes the complex itself: the metal and its ligands. For the ligands, use number prefixes like "hexa" for six cyanide ions.

Next, consider the central metal ion's oxidation state. Since it is iron (Fe) and in the anion form, we use the term "ferrate." Adding the oxidation state in Roman numerals as (III) gives important information. This comes together as "potassium hexacyanoferrate (III)." Such systematic naming helps to easily understand and convey the composition and structure of complex coordination compounds.