Problem 133 - A Complete Resource Book in Chemistry for JEE Main

Question

Addition of high proportions of manganese makes steel useful in making rails of railroads, because manganese 1\. gives hardness to steel 2\. helps the formation of oxides of iron 3\. can remove oxygen and sulphur 4\. can show highest oxidation state of \(+7\). (a) \(1,2,3\) (b) 1,3 (c) 2,4 (d) \(1,3,4\)

Step-by-Step Solution

Answer

The correct answer is (b) 1,3.

Step 1: Understand the Properties of Manganese in Steel

Manganese is a key component in steel production due to its impact on the hardness of steel. It is known to improve the toughness and wear resistance, which helps in making durable materials like railroad rails.

Step 2: Analyze Reason 1 - Gives Hardness to Steel

Assess Reason 1 by recognizing that manganese's ability to add hardness and toughness to steel is essential in applications such as railroad rails. This makes Reason 1 valid in the context.

Step 3: Analyze Reason 2 - Helps Formation of Oxides of Iron

Review Reason 2, which states that manganese aids in the formation of iron oxides. However, this is not a common reason manganese is added to steel; rather, it is known for deoxidizing by removing oxygen and preventing iron oxides.

Step 4: Analyze Reason 3 - Can Remove Oxygen and Sulphur

Examine Reason 3, which states that manganese can remove these elements. This is correct, as manganese effectively acts as a deoxidizer and desulfurization agent in the steelmaking process.

Step 5: Analyze Reason 4 - Can Show Highest Oxidation State of +7

Evaluate Reason 4, noting that manganese can exist in several oxidation states, the highest being +7. However, this property is not crucial for its use in strengthening steel.

Step 6: Identify Correct Options Based on Analysis

The correct answer should include valid reasons linked to the usefulness of manganese in steel for railroad rails. Among reasons analyzed, 1 and 3 are consistent, while 2 and 4 are not directly relevant.

Key Concepts

Hardness of Steel

The hardness of steel refers to its ability to resist deformation and wear, which is a crucial property for many industrial applications. Manganese enhances the hardness of steel by increasing its toughness and wear resistance. This makes the metal suitable for high-stress applications, ensuring it can withstand the rigors of everyday use without deforming.

Steel's hardness is particularly important in the construction of railroad rails. These rails must bear heavy loads and endure constant friction from train wheels. By incorporating manganese into the steel composition, the rails gain the necessary strength and durability to perform effectively under such conditions.

Manganese achieves this by improving the formation of martensite during steel quenching, a process that increases hardness. This enhanced hardness ensures that the materials last longer and maintain their integrity over time.

Deoxidizing in Steel Production

Deoxidizing is a vital part of steel production that involves removing oxygen from steel to improve its quality. Oxygen can form unwanted oxides in steel, leading to weaker and less reliable product outcomes. Manganese plays a crucial role in this process as a deoxidizer.

• It reacts with the oxygen present in the molten steel, forming manganese oxides instead of more harmful iron oxides.
• This reaction helps in producing cleaner steel, with fewer impurities that could compromise its strength.
• Manganese also assists in desulfurization, removing sulfur contaminants that can lead to brittleness.

By contributing to both deoxidizing and desulfurization, manganese ensures that the final steel product has a desirable quality. The reduction of these impurities leads to steel that is more robust and overall more reliable.

Railroad Rails

Railroad rails are an exceptional application of steel, requiring materials that can endure substantial weight, weather fluctuations, and persistent wear from train traffic. The inclusion of manganese in steel for railroad rails has transformed their durability and efficiency.

• Manganese-enhanced steel rails provide exceptional toughness, ensuring they do not wear down easily despite constant use.
• The combination of hardness and toughness ensures the rails can handle extreme conditions without sustaining damage.
• Such properties contribute to safe and efficient railway transport by reducing the frequency of rail replacements and associated maintenance costs.

This makes manganese an indispensable element in ensuring railroad rails meet the demanding requirements of modern railway systems.