Problem 123 - A Complete Resource Book in Chemistry for JEE Main

Question

Buckminsterfullerene is prepared by (a) Vapourisation carbon by resistive heating (b) Passing an arc discharge between carbon electrodes in a tube containing helium at 100 torr (c) The pulsed laser vapourisation of graphite (d) None of these

Step-by-Step Solution

Answer

The pulsed laser vapourisation of graphite (option c) is the correct method.

Step 1: Understanding the Problem

The question asks for the method used to prepare Buckminsterfullerene, which is a form of carbon also known as C60. This involves knowing the specific conditions under which Buckminsterfullerene can be synthesized.

Step 2: Reviewing Given Options

Let's evaluate each of the given options: (a) Vapourisation carbon by resistive heating, (b) Passing an arc discharge between carbon electrodes in a tube containing helium at 100 torr, (c) The pulsed laser vapourization of graphite, and (d) None of these. We'll identify which, if any, is a known method for preparing Buckminsterfullerene.

Step 3: Evaluating Option (a)

Vapourisation carbon by resistive heating is a general process for heating materials but isn't specifically known to be used for generating Buckminsterfullerene. Therefore, option (a) is not the preparation method for Buckminsterfullerene.

Step 4: Evaluating Option (b)

Buckminsterfullerene was originally synthesized by passing an arc discharge through graphite electrodes in an inert atmosphere, such as helium. Option (b) closely aligns with this known method. However, let's check other options to confirm it's the best answer.

Step 5: Evaluating Option (c)

Pulsed laser vaporization of graphite is another method specifically used to produce C60. This involves using a high-energy laser to vaporize graphite, leading to the formation of Buckminsterfullerene. Option (c) is actually a valid and known method, possibly even more relevant than option (b).

Step 6: Confirming Correct Answer

Upon review, both options (b) and (c) can lead to the production of C60. However, option (c) describes a more direct and specific method known for creating Buckminsterfullerene, especially in laboratory conditions after the method's initial discovery.

Key Concepts

Carbon Vaporization Methods

Carbon vaporization refers to the process of converting carbon into vapor through the application of heat or energy. This forms the basis for creating various carbon structures, including Buckminsterfullerene, commonly referred to as C60. There are several methods to achieve this, with differing techniques based on the application of energy.

One common method is **resistive heating**, which involves passing an electric current through carbon materials to raise their temperature until vaporization occurs. However, this process is too general and lacks the specificity needed to synthesize C60 effectively.

Two more specialized techniques are used, notably in the synthesis of Buckminsterfullerene. These are the **arc discharge method** and **pulsed laser vaporization**, each providing unique conditions under which carbon can vaporize and subsequently form fullerenes.

Arc Discharge in Helium

Arc discharge in helium is a well-established method for synthesizing fullerenes, including Buckminsterfullerene (C60). This technique involves creating an electric arc between two carbon electrodes in an atmosphere of helium gas. The discharge generates high temperatures, leading to the vaporization of carbon from the electrodes.

The presence of helium is crucial because it acts as an inert gas, preventing unwanted reactions and allowing the carbon vapor to cool slowly as it forms Buckminsterfullerene. The helium atmosphere at 100 torr helps in controlling the rate of cooling and the overall stability of the formed fullerene structures.

**Benefits of the Arc Discharge Method include:**

• High efficiency in producing C60.
• Ability to produce a mixture of fullerenes, allowing research into different carbon structures.

This method, historically significant for the discovery of fullerenes, continues to be used due to its effectiveness.

Pulsed Laser Vaporization of Graphite

The pulsed laser vaporization technique is another prominent method for synthesizing Buckminsterfullerene. It involves using a high-energy laser pulse to vaporize graphite. This process is highly controlled and efficient, making it ideal for producing C60 in laboratory settings.

The **laser delivers intense energy** to the graphite, causing rapid heating and subsequent vaporization. As the carbon vapor cools, the atoms rearrange into the stable C60 structure. This method can be performed under vacuum or in the presence of inert gases like helium.

**Advantages of Pulsed Laser Vaporization include:**

• Precise control over energy input and timing, enhancing reproducibility.
• Clean process with minimal contamination, making it ideal for producing high-purity C60.

The ability to precisely control the conditions of vaporization has made this method especially useful in research and development of carbon-based materials, including fullerenes.