Problem 30 - A Complete Resource Book in Chemistry for JEE Main

Question

The reduction of calcined phosphate rock with coke and sand in an electric are furnace at \(1773 \mathrm{~K}\) gives a number of products including (a) silicon (b) calcium hydride (c) phosphorus (d) calcium oxide

Step-by-Step Solution

Answer

The products are (a) silicon and (c) phosphorus.

Step 1: Identify the Main Reaction Components

In the given problem, the main components reacting in the electric arc furnace are calcined phosphate rock (primarily consisting of calcium phosphate), coke, and sand. This reaction occurs at an elevated temperature of 1773 K.

Step 2: Determine the Likely Reaction Products

At high temperature, the reduction process with coke (a form of carbon) and sand (SiO2) usually results in the separation of elements. Carbon from the coke can reduce phosphorus compounds to produce phosphorus gas.

Step 3: Understand the Role of Silicon Dioxide (Sand)

The silicon dioxide primarily reacts with other components in the electric arc furnace. It can react to form elemental silicon, especially in the presence of a reducing agent like carbon from coke.

Step 4: Analyze the Calcium Compounds

Calcium phosphate is the primary component of calcined phosphate rock. Under the conditions of the furnace, it mainly decomposes and does not produce calcium hydride and rarely forms calcium oxide as final products because reduction favors the formation of gaseous products like phosphorus gas.

Step 5: Finalize the List of Key Products

Considering all reacted components and typical furnace conditions, phosphorus gas (c) is a common output. The reaction also allows the formation of elemental silicon (a) from the reduction of sand.

Key Concepts

Silicon Production

In the process of phosphate rock reduction, a fascinating transformation occurs in the electric arc furnace. Here, sand, which is primarily composed of silicon dioxide (\( ext{SiO}_2\)), plays a critical role. The operation takes place at a high temperature of 1773 K, where the furnace acts as a controlled environment for chemical reactions.

• Silicon dioxide, when heated, interacts with carbon from coke.
• This reaction is a type of reduction since oxygen is removed from silicon dioxide.
• The result is the formation of elemental silicon, usually in a pure form.
  

The silicon produced can have various applications, such as in electronics where silicon is a key component of semiconductors.

Phosphorus Gas Formation

One of the primary outputs of the phosphate rock reduction process is phosphorus gas. This is achieved through a complex reaction involving calcined phosphate rock and coke.

• Calcined phosphate rock is mainly made of calcium phosphate.
• During reduction, coke, acting as a carbon source, breaks down the phosphate component.
• This decomposition releases phosphorus in gaseous form, especially at the elevated temperatures in an electric arc furnace.
  

Phosphorus gas is important in different fields, including the manufacture of fertilizers and other chemicals. Its formation in the furnace underscores the powerful reducing capabilities of the setup.

High Temperature Reduction

The process of reducing phosphate rock involves extremely high temperatures to facilitate chemical reactions. The temperatures in an electric arc furnace can reach up to 1773 K, which is essential for several reasons.

• The high temperature ensures that the phosphate rock components are sufficiently reactive.
• It promotes the breakdown of chemical bonds, enabling the formation of new products.
• The heat also ensures the complete removal of oxygen from silicon and phosphorus compounds.
  

In industrial practices, maintaining such high temperatures is critical to ensure the efficiency and success of the reduction process, unlocking desired elements like silicon and phosphorus gas.

Electric Arc Furnace

An electric arc furnace (EAF) is instrumental in the reduction of phosphate rock. This sophisticated device uses electricity to generate an arc of heat, capable of reaching very high temperatures necessary for industrial reactions.

• It provides a controlled environment where temperature can be precisely regulated.
• The energy provided by the electric arc melts and reacts materials, facilitating the reduction process.
• Unlike other types of furnaces, EAFs are cleaner and allow easier recovery of gases like phosphorus.
  

This furnace is pivotal in minimizing impurities and enhancing the production of desired elements such as silicon and phosphorus gas. Its design and functionality make it a vital tool in metallurgical operations.