Problem 20 - Chemistry The Central Science In Si Units

Question

The most important oxides of iron are magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4}\), and hematite, \(\mathrm{Fe}_{2} \mathrm{O}_{3} .\) (a) What are the oxidation states of iron in these compounds? (b) One of these iron oxides is ferrimagnetic, and the other is antiferromagnetic. Which iron oxide is more likely to be ferrimagnetic? Explain.

Step-by-Step Solution

Answer

(a) Magnetite has Fe in +2 and +3, while hematite has Fe in +3. (b) Magnetite is more likely ferrimagnetic due to mixed oxidation states.

Step 1: Evaluate Oxidation States in Magnetite

Magnetite \(\mathrm{Fe}_3\mathrm{O}_4\) can be represented as a combination of \(\mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{3+}\). In the compound, iron occurs in two oxidation states: two atoms of iron in the +3 state and one atom in the +2 state. This can be expressed as \([\mathrm{Fe}^{3+}_2\mathrm{Fe}^{2+}]_2\mathrm{O}_4\).

Step 2: Evaluate Oxidation States in Hematite

In hematite \(\mathrm{Fe}_2\mathrm{O}_3\), all the iron atoms are in the +3 oxidation state. This can be represented as \(2\mathrm{Fe}^{3+} + 3\mathrm{O}^{2-}\). Both irons have the same oxidation state of +3.

Step 3: Identify Ferrimagnetic Properties

Ferrimagnetism occurs when magnetic moments of atoms on different sublattices oppose one another, often leading to a net magnetic moment due to an imbalance. In magnetite \(\mathrm{Fe}_3\mathrm{O}_4\), this situation exists due to the presence of both \(\mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{3+}\) ions, resulting in ferrimagnetism.

Step 4: Identify Antiferromagnetic Properties

Antiferromagnetic materials have opposing magnetic moments that completely cancel each other out, resulting in no macroscopic magnetism. Hematite \(\mathrm{Fe}_2\mathrm{O}_3\) is a classical example, largely because all \(\mathrm{Fe}^{3+}\) ions have an opposite alignment with complements, effectively nullifying any external magnetic field.

Step 5: Determine Which Ore is Ferrimagnetic

Since magnetite \(\mathrm{Fe}_3\mathrm{O}_4\) contains both \(\mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{3+}\), creating an imbalance necessary for ferrimagnetism due to their coexisting different oxidation states, it makes magnetite the more likely candidate for ferrimagnetic properties.

Key Concepts

Oxidation States

Iron can exist in different oxidation states, particularly in iron oxides such as magnetite and hematite.
The oxidation state is crucial in determining the chemical and physical properties of these compounds.
In an oxidation state, the number of electrons an atom gains or loses is represented by a number, often indicated by Roman numerals. For example:

• In magnetite \( \mathrm{Fe}_3\mathrm{O}_4 \), iron occurs in two oxidation states: +2 and +3. Specifically, it consists of two iron atoms with an oxidation state of +3 and one iron atom with an oxidation state of +2.
• In hematite \( \mathrm{Fe}_2\mathrm{O}_3 \), all iron atoms are in the +3 oxidation state, meaning every iron atom loses three electrons, resulting in more complete oxidation.

Understanding the variations in oxidation states helps clarify the degree of oxidation in iron oxides, affecting how these compounds behave in chemical reactions and influence magnetic properties.

Ferrimagnetism

Ferrimagnetism is a fascinating property observed in certain materials where there are two or more types of ions with magnetic moments that align in opposite directions.
This opposing alignment does not completely cancel out, leading to a net magnetic moment.
This phenomenon is particularly observed in magnetite \( \mathrm{Fe}_3\mathrm{O}_4 \), where the presence of both \( \mathrm{Fe}^{2+} \) and \( \mathrm{Fe}^{3+} \) ions creates unequal opposing magnetic moments.In such materials:

• Different ions reside in unique sublattices within the crystal structure, and their magnetic spins align antiparallel to each other.
• The magnetic moment imbalance results in a significant net magnetization, making these materials magnetically active.

The property of ferrimagnetism is crucial for various applications, such as data storage devices, transformers, and certain types of sensors, due to their ability to maintain magnetization.

Antiferromagnetism

Antiferromagnetism is a magnetic phenomenon where the magnetic moments of atoms or ions within a material align in opposite directions, leading to a cancellation of their macroscopic magnetic effect.
In other words, these materials do not exhibit any net magnetization externally due to the perfect antiparallel alignment of their spins.
One renowned example of an antiferromagnetic material is hematite \( \mathrm{Fe}_2\mathrm{O}_3 \).In antiferromagnetic substances:

• The magnetic sublattices have equal numbers of opposite spins, resulting in a complete neutralization of magnetic moments.
• The absence of an external magnetic moment makes them useful in applications requiring minimal magnetic interference.

Understanding antiferromagnetism is essential for developing advanced magnetic materials with specific thermal and electrical properties, desirable in scientific and industrial applications.