Problem 40 - A Complete Resource Book in Chemistry for JEE Main

Question

In Kjeldahl's method of estimation of nitrogen, copper sulphate acts as (a) catalytic agent (b) silver spiral (c) hydrolyzing agent (d) oxidizing agent

Step-by-Step Solution

Answer

Copper sulphate acts as a catalytic agent in Kjeldahl's method, so the correct answer is (a).

Step 1: Understanding Kjeldahl's Method

Kjeldahl's method is a process used to estimate the nitrogen content in a compound. It involves three main steps: digestion, neutralization, and titration. Copper sulphate is used during the digestion process.

Step 2: Role of Copper Sulphate in Digestion

During digestion, the nitrogen in the organic compound is converted to ammonia. Copper sulphate is added as it helps in the efficient and complete digestion of the sample by acting as a catalyst.

Step 3: Identifying the Correct Option

A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. Therefore, in the context of Kjeldahl's method, copper sulphate acts as a catalytic agent, which corresponds to option (a).

Key Concepts

Nitrogen Estimation

Understanding how much nitrogen is in a substance is crucial for various applications. One of the most common methods to achieve this is through Kjeldahl's method, named after Johan Kjeldahl. This method allows us to measure the nitrogen content comprehensively and accurately. In Kjeldahl's approach:

• Digestion: The organic material containing nitrogen is broken down using a strong acid. This process converts nitrogen into ammonium ions.
• Neutralization: The digested sample is then neutralized with a base to release the ammonia.
• Titration: Finally, the released ammonia is distilled and titrated to quantify the nitrogen content.

Knowing the nitrogen content, especially in fertilizers or food products, is vital since it can indicate protein levels. Accurate nitrogen estimation can help in determining quality and nutritional value. This holistic process ensures the nitrogen content is not only assessed but also quantified accurately.

Copper Sulphate Role

During the digestion phase of Kjeldahl's method, copper sulphate plays an essential role. Its main function is to act as a catalyst. A catalyst, such as copper sulphate in this case, significantly increases the rate of the chemical reaction without being consumed.
This means only a small quantity is needed to affect the process, making it cost-effective and efficient. Copper sulphate helps:

• Enhance Efficiency: Speeds up the breakdown of the organic compound, ensuring a complete conversion to ammonia.
• Stabilize Reaction: Provides consistent and reproducible results.

Thus, copper sulphate ensures that the nitrogen estimation process is both rapid and thorough. Its presence guarantees that the sample digestion occurs smoothly and as fully as possible, which is crucial for obtaining accurate results.

Chemical Digestion Process

In the context of Kjeldahl's method, the chemical digestion process is the initial step where the real magic happens. This step transforms nitrogen from its organic form into a form that's easier to measure, namely ammonium ions. Here's how digestion works:

• Strong Acid Use: Typically, sulfuric acid is used as it provides an acidic environment necessary to break down the organic matter.
• Heating: The application of heat accelerates the breakdown process, ensuring the complete conversion of nitrogen to ammonium ions.

A successful digestion is critical, as incomplete digestion will lead to inaccurate nitrogen estimation. The process is meticulously controlled to ensure full conversion while minimizing any form of nitrogen retention within the zero order of the compound.
This foundational step guarantees that subsequent stages, like neutralization and titration, can proceed efficiently and produce reliable data.