Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

The oxidation number of \(\mathrm{Fe}\) in \(\mathrm{Fe}_{3} \mathrm{O}_{4}\) is (a) \(+2\) (b) \(2 / 3\) (c) \(+3\) (d) \(8 / 3\)

Step-by-Step Solution

Answer

The oxidation number of \(\text{Fe}\) in \(\text{Fe}_3\text{O}_4\) is \(\frac{8}{3}\) (d).

Step 1: Understanding Compound Composition

The compound is magnetite, denoted as \( ext{Fe}_3 ext{O}_4\). It consists of iron (Fe) and oxygen (O) atoms. In this structure, the iron exists in two different oxidation states.

Step 2: Assign Known Oxidation State

Oxygen typically has an oxidation number of \(-2\). Given there are 4 oxygen atoms, their total contribution to the charge is \(4 \times (-2) = -8\).

Step 3: Set Up Oxidation Number Equation for Iron

The compound \( ext{Fe}_3 ext{O}_4\) is neutral overall, so the sum of all oxidation numbers must be zero. Let the oxidation number of iron be \(x\). For 3 iron atoms, their total contribution is \(3x\). Thus, the equation becomes \(3x - 8 = 0\).

Step 4: Solve for Iron's Oxidation Number

Rearranging the equation \(3x - 8 = 0\) gives us \(3x = 8\). Solving for \(x\) yields:\[x = \frac{8}{3}\]

Step 5: Analyze the Result

The calculated oxidation number for iron in \( ext{Fe}_3 ext{O}_4\) is \(\frac{8}{3}\), which matches one of the provided options.

Key Concepts

Iron (Fe)

Iron is a versatile and essential element found throughout the earth's crust, not only in nature but also in many everyday items. Iron's symbol, Fe, stands for its Latin name, 'ferrum'. Iron is primarily known for its use in construction and manufacturing as part of alloys like steel.

• Iron is a transition metal, meaning it can exhibit different oxidation states.
• Its electrons can be relatively easily removed, added, or shared in chemical reactions.
• Iron's ability to change its charge makes it critical in numerous chemical processes.

Understandably, in chemistry, iron's behavior in reactions often includes losing or gaining electrons, leading to its variable oxidation states. These properties make iron valuable in both industrial and biological applications.

Magnetite (Fe3O4)

Magnetite, often seen as a magical natural magnet, is actually an iron mineral composed of iron ions and oxide ions. Its chemical formula is \( \mathrm{Fe}_3 \mathrm{O}_4 \), representing its unique complex structure.

• Considered one of the first materials recognized for its magnetic properties.
• Each magnetite unit comprises three iron ions combined with four oxide ions.
• The iron ions are found in two different oxidation states: Fe²⁺ and Fe³⁺.

Such a composition allows magnetite to effectively reduce iron ores in blast furnaces, a critical step in metalworking. Furthermore, its ferrimagnetic properties make it invaluable in various industrial applications.

Oxidation States of Transition Metals

Transition metals, including iron, are special on the periodic table. They have d-orbitals that allow these metals to adopt multiple oxidation states.

• These metals can lose different numbers of electrons depending on reaction conditions.
• This flexibility contributes to their wide range of chemical behaviors and reactions.
• Common oxidation states for iron include +2 and +3, contributing to its reactivity.

Understanding this versatility is key when predicting outcomes in chemical reactions. In the case of magnetite, iron's oxidation states combine to form a stable and magnetically responsive compound.

Chemical Equations

Chemical equations offer a concise way to represent chemical reactions. They show reactants transforming into products while obeying the law of conservation of mass.

• A complete equation showcases all participants and balances all elements involved.
• They provide insights into the stoichiometry of reactions.
• Interpreting equations requires understanding atom and charge balance.

A clear understanding of chemical equations helps chemists predict reaction products and comprehend processes at a molecular level. Involvement of transition metals like iron often means considering various possible products due to multiple oxidation states.

Calculating Oxidation Number

Calculating the oxidation number is a fundamental skill for understanding chemical reactions. Oxidation numbers denote an atom's electron count in a compound relative to the neutral atom.

• Oxidation numbers help identify electron transfer in redox reactions.
• Each element in a compound contributes differently to the total oxidation state.
• Rules for determining oxidation numbers ensure consistent application.

For instance, in magnetite \( \mathrm{Fe}_3 \mathrm{O}_4 \), calculating the oxidation number for iron ensures correct stoichiometry. Using the knowledge that oxygen is typically -2, chemists balance charges to maintain neutrality in compounds.