Problem 3 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the follwoing reaction occurs in the combustion zone of the blast furnace during the extraction of iron? (a) \(\mathrm{CO}_{2}+\mathrm{C} \longrightarrow 2 \mathrm{CO}\) (b) \(\mathrm{CaO}+\mathrm{SiO}_{2} \longrightarrow \mathrm{CaSiO}_{3}\) (c) \(\mathrm{C}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}\) (d) \(\mathrm{FeO}+\mathrm{CO} \longrightarrow \mathrm{Fe}+\mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

The correct reaction in the combustion zone is (c) \( \mathrm{C} + \mathrm{O}_{2} \to \mathrm{CO}_{2} \).

Step 1: Identifying the Combustion Zone

In a blast furnace, the combustion zone is characterized by the reaction of coke (carbon) with oxygen to produce gaseous products. This is where chemical energy from the coke is transformed into thermal energy.

Step 2: Analyzing Reaction Options

Let's analyze the reactions:a) \( \mathrm{CO}_{2} + \mathrm{C} \to 2\mathrm{CO} \): This is a reduction reaction, not a combustion, occurring in the lower part of the furnace.b) \( \mathrm{CaO} + \mathrm{SiO}_{2} \to \mathrm{CaSiO}_{3} \): This is a slag formation reaction, not related to the combustion zone.c) \( \mathrm{C} + \mathrm{O}_{2} \to \mathrm{CO}_{2} \): This is a classic combustion reaction, where carbon combusts with oxygen to form carbon dioxide.d) \( \mathrm{FeO} + \mathrm{CO} \to \mathrm{Fe} + \mathrm{CO}_{2} \): This is a reduction reaction, converting iron oxide to iron.

Step 3: Selecting the Correct Reaction

The reaction that occurs in the combustion zone involves burning carbon fuels like coke to produce heat. From the options, only option (c) \( \mathrm{C} + \mathrm{O}_{2} \to \mathrm{CO}_{2} \) represents a combustion reaction.

Key Concepts

Extraction of Iron

Iron extraction is a critical industrial process used to procure this essential metal from its ores. The primary ore of iron is hematite, but other ores like magnetite can also be utilized. The extraction process predominantly occurs in a blast furnace, where iron ore undergoes various chemical transformations to form pure iron.
The first crucial step involves crushing the iron ores to smaller pieces to facilitate ease of handling and reaction.
Once prepared, these ores are introduced into a blast furnace in combination with limestone and coke. The mixture is heated at high temperatures, enabling the conversion of iron oxide in the ore to molten iron.
Iron is then separated from impurities and further refined to achieve the desired level of purity and quality.

• The limestone aids in removing impurities by forming 'slag', a by-product that's tapped off and discarded.
• Coke provides both the carbon needed for reduction reactions and serves as a vital source of heat when combusted.

Extraction of iron via a blast furnace is an efficient process that produces large quantities of iron ready for various applications.

Combustion Reaction

Combustion reactions are exothermic processes that provide energy essential in many industrial operations. In the context of a blast furnace, the combustion reaction plays a vital role in providing the heat required for other reactions.
The primary combustion reaction involves coke reacting with oxygen to form carbon dioxide. This reaction (\[\mathrm{C} + \mathrm{O}_{2} \to \mathrm{CO}_{2}\]) releases a substantial amount of heat, critical for maintaining the temperature needed for iron extraction.
What distinguishes combustion reactions, especially in a blast furnace, is the conversion of chemical energy from fuels like coke into thermal energy. Here are key characteristics of combustion reactions:

• They involve oxygen and a combustible material, usually a hydrocarbon or carbon like coke.
• They release energy in the form of heat and sometimes light.
• The products are typically carbon dioxide and water, though in the case of coke, it’s mostly carbon dioxide.

These reactions are pivotal in various processes, allowing industries to harness energy for a myriad of applications.

Blast Furnace Zones

The interior of a blast furnace is intricately organized into different zones, each serving a unique function during the iron extraction process. Understanding these zones is crucial for effective furnace operation and optimal iron production.
The blast furnace can be segmented into four main zones:

• **Combustion Zone**: Here, coke combusts with oxygen, generating high temperatures necessary for reducing iron oxide to iron. This zone is critical for initiating endothermic (heat-absorbing) processes higher up in the furnace.
• **Reducing Zone**: Reduction reactions take place in this zone. Iron oxides are transformed into iron through reactions with carbon monoxide, a by-product of combustion.
• **Slag Formation Zone**: In this area, limestone reacts with impurities to form slag. This slag is vital for trapping and removing impurities from iron.
• **Stoving Zone**: As materials descend through the furnace, residual heat dries off moisture content and pre-heats the feedstock before it enters lower, hotter zones.

Each zone contributes to the overall efficiency of the blast furnace, ensuring that chemical transformations occur at the right temperatures and conditions to maximize iron output.