Question

Oxidation states of the metal in the minerals haematite and magnetite, respectively, are (A) II, III in haematite and III in magnetite (B) II, III in haematite and II in magnetite (C) II in haematite and II, III in magnetite (D) III in haematite and II, III in magnetite

Short answer

The correct oxidation states are III in haematite and II, III in magnetite, which corresponds to option (D).

Step-by-step solution

Understanding Hematite

Hematite is an iron oxide with the formula Fe2O3. To understand the oxidation state of iron in hematite, recognize that oxygen almost always has an oxidation state of -2. Since there are three oxygen atoms, their total oxidation state is -6. The compound must be neutral, so the two iron atoms combined must have an oxidation state of +6 to balance the -6 from oxygen. This means each iron atom must be in a +3 oxidation state in hematite.

Understanding Magnetite

Magnetite has the chemical formula Fe3O4, which can also be written as FeO·Fe2O3, meaning there is one Fe(II) and two Fe(III) within the structure. In FeO, iron has an oxidation state of +2. In Fe2O3, as established previously in hematite, each iron has an oxidation state of +3. So, in magnetite, both Fe(II) and Fe(III) are present.

Analyzing the Options

Combining the information obtained from the previous steps, we can conclude that iron in hematite (Fe2O3) is in the +3 oxidation state and in magnetite (Fe3O4) it exists in both +2 and +3 oxidation states. Therefore, the correct answer among the given options is the one that reflects these oxidation states.

Key concepts

Hematite

Hematite, a common iron oxide, holds significance both as a gemstone and an ore of iron. Its chemical formula is written as Fe2O3, denoting the presence of two iron (Fe) atoms and three oxygen (O) atoms in each molecule. Given that oxygen has a consistently assigned oxidation state of -2, we can determine the oxidation state of iron in hematite. The total oxidation state for the three oxygen atoms is -6, leaving the two iron atoms to balance this charge with a combined +6 oxidation state. Hence, each iron atom in hematite must have an oxidation state of +3 to neutralize the molecule, contrasting with other iron oxides where the oxidation state of iron may differ.Understanding the oxidation state in minerals like hematite is crucial for its identification and industrial processing, as it directly influences physical properties such as color, density, and magnetic behavior. Hematite is typically non-magnetic and is characterized by a reddish-brown streak, which is useful for miners and geologists in the field.

Magnetite

Magnetite, another iron oxide, is not only an iron ore but also a mineral with interesting magnetic properties. It has the chemical formula Fe3O4, which can be viewed as a combination of FeO and Fe2O3. This combination hints at the presence of iron in two distinct oxidation states within a single mineral. Specifically, one iron atom is in the +2 oxidation state (Fe(II)), while the other two are in the +3 oxidation state (Fe(III)).

The coexistence of two iron oxidation states is what imparts magnetite with its characteristic magnetism, distinguishing it from hematite. Iron's varying oxidation states influence the arrangement of electrons in their orbitals, modifying how these minerals interact with magnetic fields. For students and professionals working with minerals, the magnetic character of magnetite provides a quick identification tool and plays a role in the extraction and processing of the mineral. Its magnetic qualities also make it useful in various industrial applications, such as in magnetic recording media.

Chemical Formula

Understanding the chemical formula of a compound is foundational in chemistry. It indicates the types and quantities of atoms present in a molecule. The chemical formulas for hematite (Fe2O3) and magnetite (Fe3O4) tell us not only the proportion of iron to oxygen but also offer clues about their structure and chemical characteristics.

The significance of mastering the interpretation of chemical formulas, for students, extends beyond solving textbook exercises. It is vital for predicting the behavior of compounds in reactions, understanding their properties, and analyzing their roles in various contexts, from biological systems to technological applications. A solid grasp of chemical formulas aids in visualizing the geometric arrangement of atoms in three-dimensional space, enhancing the comprehension of complex chemical phenomena.

Balancing Oxidation States

The concept of balancing oxidation states involves ensuring that the total charges in a compound add up to zero, which is a requirement for chemical stability. Oxidation states provide insight into the electron distribution among atoms in a molecule, revealing information about potential chemical reactions. For example, the balancing of oxidation states in hematite and magnetite helps in understanding why these compounds form and how they behave chemically.

When students learn to determine oxidation states and balance them, they harness a critical analytical tool used across various chemical disciplines. It forms the basis for redox reactions, which are fundamental to processes such as combustion, metabolism, and electrochemical cells. Through balancing oxidation states, one can deduce the feasible pathways for chemical transformations and evaluate the likelihood of certain products forming in a reaction.