Question

(a) Pyrolusite \(\left(\mathrm{MnO}_{2}\right)\) is a commercially important mineral of manganese. What is the oxidationstate of \(\mathrm{Mn}\) in this metal? (b) Name some reagents that might be used to reduce this ore to the metal.

Short answer

(a) The oxidation state of manganese (Mn) in pyrolusite (MnO2) is +4. (b) Some common reagents used to reduce MnO2 to manganese metal are carbon (C) or carbon monoxide (CO), aluminum (Al), and hydrogen gas (H2).

Step-by-step solution

(a) Finding the oxidation state of manganese in pyrolusite (MnO2)

To find the oxidation state of manganese (Mn) in MnO2, we will use the fact that oxygen has an oxidation state of -2. Let's denote the oxidation state of Mn as x. In MnO2, there are two oxygen atoms, each with an oxidation state of -2, giving a total oxidation state of -4 for the two oxygen atoms. The compound MnO2 is neutral, which means the sum of the oxidation states of all the elements in the compound should be equal to 0. Therefore, we can write an equation for the sum of the oxidation states of Mn and O: \(x + (-4) = 0\) Now, solve for x: \(x = 4\) The oxidation state of manganese (Mn) in pyrolusite (MnO2) is +4.

(b) Reagents used for the reduction of pyrolusite (MnO2) to manganese metal

To reduce MnO2 to the manganese metal (Mn), we can use various reagents that provide reducing conditions. Some common reducing agents used in metallurgy are: 1. Carbon (C) or carbon monoxide (CO): Pyrolusite can be mixed with carbon or coke and heated to high temperatures. Carbon or carbon monoxide can reduce MnO2 to manganese metal under these conditions: \( \mathrm{MnO}_{2} + \mathrm{C} \rightarrow \mathrm{Mn} + \mathrm{CO}_{2} \) or, \( \mathrm{MnO}_{2} + \mathrm{CO} \rightarrow \mathrm{Mn} + \mathrm{CO}_{2} \) 2. Aluminum (Al): Aluminum can act as a powerful reducing agent when mixed with MnO2 and heated to high temperatures. This process is called aluminothermic reduction: \( 3\mathrm{MnO}_{2} + 4\mathrm{Al} \rightarrow 3\mathrm{Mn} + 2\mathrm{Al}_{2}\mathrm{O}_{3} \) 3. Hydrogen gas (H2): At high temperatures, hydrogen can reduce MnO2 to manganese metal: \( \mathrm{MnO}_{2} + \mathrm{H}_{2} \rightarrow \mathrm{Mn} + \mathrm{H}_{2}\mathrm{O} \) These are some of the reagents that can be used to reduce pyrolusite (MnO2) to manganese metal.

Key concepts

Manganese

Manganese is a transition metal found in the middle of the periodic table. It is recognized for its versatility and ability to form a variety of compounds. This element is crucial for many industrial processes, particularly in the production of steel, due to its ability to improve hardness and strength properties. Manganese plays an essential role in biological systems as well, although in much smaller amounts.

• It is primarily sourced from manganese ores, such as pyrolusite, which contains manganese dioxide (MnO2).
• Manganese is present in several oxidation states, but the most common are +2, +3, +4, +6, and +7.
• The oxidation state in a compound helps determine the behavior and chemical response of manganese.

Pyrolusite, specifically, is an important commercial manganese mineral, often used as a precursor in extracting manganese for various applications.

Redox Reactions

A redox reaction, short for reduction-oxidation reaction, involves the transfer of electrons between two substances. It's a fundamental concept in chemistry that describes all chemical reactions in which there is a change in oxidation state. In the context of reducing pyrolusite to manganese, we leverage this principle.

• Oxidation refers to the loss of electrons, while reduction refers to the gain of electrons.
• In metallurgy, redox reactions are essential for extracting metals from their ores, like manganese from pyrolusite.

For instance, reducing agents like carbon or hydrogen can donate electrons to MnO2, thus reducing it and increasing the manganese oxidation state in the process.When manganese dioxide (\(\mathrm{MnO}_{2}\)) is reduced, its oxidation state decreases, transitioning from +4 to 0 in metallic form. This change is vital in the industrial extraction of pure manganese metal.

Metallurgy

Metallurgy is the science and technology of extracting metals from their ores and modifying the metals for use. It includes several complex processes, many of which involve chemical reactions and physical treatments. Reducing manganese ores like pyrolusite is a part of this extensive domain.

• One common method for extracting manganese from pyrolusite is the reduction process involving carbon or aluminum as reducing agents.
• This process transitions manganese from an ore state to its metallic form, ready for industrial applications.

During the metallurgical reduction of pyrolusite, different chemical equations demonstrate the agents' capabilities to drive manganese reduction:

Reduction Reagents

- **Carbon/Carbon Monoxide**: These are used to produce manganese from manganese dioxide, involving heating with carbon to produce manganese and carbon dioxide. - **Aluminum**: This employs a heat-driven process, called aluminothermic reduction, to transform manganese dioxide into manganese metal and aluminum oxide. - **Hydrogen gas**: This method relies on hydrogen's ability to react with manganese dioxide at high temperatures, also producing water vapor. These reduction processes are crucial in metallurgy, allowing for the conversion of manganese ore into a usable metal component critical in various applications, notably the steel industry.