Question

Iron is present in the earth's crust in many types of minerals. The iron oxide minerals are hematite \(\left(\mathrm{Fe}_{2} \mathrm{O}_{3}\right)\) and magnetite \(\left(\mathrm{Fe}_{3} \mathrm{O}_{4}\right) .\) What is the oxidation state of iron in each mineral? The iron ions in magnetite are a mixture of \(\mathrm{Fe}^{2+}\) and Fe \(^{3+}\) ions. What is the ratio of \(\mathrm{Fe}^{3+}\) to \(\mathrm{Fe}^{2+}\) ions in magnetite? The formula for magnetite is often written as \(\mathrm{FeO} \cdot \mathrm{Fe}_{2} \mathrm{O}_{3} .\) Does this make sense? Explain.

Short answer

The oxidation state of iron in hematite (Fe2O3) is +3. In magnetite (Fe3O4), the ratio of Fe³⁺ to Fe²⁺ ions is 2:1, and the formula FeO · Fe2O3 makes sense as it represents the balanced cationic and anionic charges in the compound, with FeO representing the part with Fe²⁺ ions and Fe2O3 representing the part with Fe³⁺ ions.

Step-by-step solution

Determine the oxidation state of oxygen in the minerals

In general, the oxidation state of oxygen in oxide compounds is -2. This means that in both hematite (Fe2O3) and magnetite (Fe3O4), oxygen atoms have an oxidation state of -2.

Determine the oxidation state of iron in hematite (Fe2O3)

We have 2 iron (Fe) atoms and 3 oxygen (O) atoms in hematite (Fe2O3). As we know that the oxidation state of oxygen is -2, the total negative charge from the oxygen atoms is -6. Since the compound is neutral, the total positive charge from the iron atoms must be +6. As there are 2 iron atoms, each iron atom must have an oxidation state of +3. Therefore, the oxidation state of iron in hematite is +3.

Determine the overall oxidation state of iron in magnetite (Fe3O4)

We have 3 iron (Fe) atoms and 4 oxygen (O) atoms in magnetite (Fe3O4). As we know that the oxidation state of oxygen is -2, the total negative charge from the oxygen atoms is -8. Since the compound is neutral, the total positive charge from the iron atoms must be +8.

Determine the ratio of Fe³⁺ to Fe²⁺ ions in magnetite

In magnetite, the iron ions are a mixture of Fe²⁺ and Fe³⁺ ions. Since the total positive charge from the iron atoms in magnetite is +8: Let x = number of Fe³⁺ ions Then, (3-x) = number of Fe²⁺ ions The total charge of Fe³⁺ ions = x * (+3) The total charge of Fe²⁺ ions = (3 - x) * (+2) Now, the sum of their charges should be equal to the total (+8) charge: x * (+3) + (3 - x) * (+2) = +8 By solving this equation for x, we get x = 2. This means that there are 2 Fe³⁺ ions and (3 - 2) = 1 Fe²⁺ ion in magnetite. Therefore, the ratio of Fe³⁺ to Fe²⁺ ions in magnetite is 2:1.

Check if the formula FeO · Fe2O3 makes sense for magnetite

We can rewrite this formula as: FeO · Fe2O3 = Fe(II)O + Fe(III)2O3 = Fe²⁺O²⁻ + 2Fe³⁺O²⁻*1.5 Both the cationic and anionic charges on both sides of the equation are balanced. Therefore, this formula makes sense for magnetite: - FeO represents the portion with Fe²⁺ ions (1 Fe²⁺ ion per formula unit). - Fe2O3 represents the portion with Fe³⁺ ions (2 Fe³⁺ ions per formula unit). This confirms that the formula FeO · Fe2O3 is consistent with the composition of magnetite.

Key concepts

Iron Minerals

Iron minerals are naturally occurring compounds in the Earth's crust that contain iron. They are key sources of iron, which is essential for numerous industrial processes. Among these minerals, the most notable are hematite and magnetite. Both are iron oxide minerals and are significant due to their iron content and applications.

Iron minerals come in various forms, but hematite and magnetite are the most commercially valuable. These minerals are preferred for their ease of extraction and high iron content. They are utilized extensively in the steel manufacturing industry and other sectors requiring large quantities of iron.

Hematite

Hematite is a common iron oxide mineral with the chemical formula \(\mathrm{Fe}_{2}\mathrm{O}_{3}\). It consists of iron and oxygen, where each molecule includes two iron atoms and three oxygen atoms. Due to its structure, hematite is often sourced for iron production because of its high iron content.

In terms of oxidation states, the iron atoms in hematite exist in the +3 oxidation state. This is because the total charge contributed by the three oxygen atoms is -6, requiring a +6 charge from two iron atoms to maintain neutrality. Therefore, each iron atom has a +3 charge, confirming its identity as Fe³⁺.

Magnetite

Magnetite, with the chemical formula \(\mathrm{Fe}_{3}\mathrm{O}_{4}\), is an intriguing iron oxide mineral distinctively known for its magnetic properties. It consists of three iron atoms and four oxygen atoms, forming a balanced yet complex mixture of oxidation states.

Interestingly, magnetite features a combination of both Fe²⁺ and Fe³⁺ iron ions. The overall positive charge required to balance the four oxygen atoms, which have a total charge of -8, is +8. This condition results in a mixture of iron ions: specifically, two Fe³⁺ ions and one Fe²⁺ ion per mineral formula unit.

The ratio of Fe³⁺ to Fe²⁺ in magnetite is therefore 2:1. This unique combination contributes to magnetite’s distinct properties and usefulness in various technological applications.

Iron Ions

Iron ions play a crucial role in determining the properties of iron minerals such as hematite and magnetite. The ions can exist in different oxidation states, mainly +2 and +3. These states influence how the minerals form and behave, including their magnetic and electric properties.

In magnetite, both types of iron ions contribute to its unique characteristics. Fe²⁺, or ferrous ions, and Fe³⁺, or ferric ions, are present in a well-defined ratio, creating fascinating chemical dynamics. Understanding these different ion configurations is essential for exploring the processing and use of these iron-containing materials.