Problem 28 - A Complete Resource Book in Chemistry for JEE Main

Question

The compound used for the preparation of \(U F_{6}\) in the enrichment of \({ }_{92} \mathrm{U}^{235}\) is (a) \(\mathrm{HF}\) (b) \(\mathrm{CaF}_{2}\) (c) \(\mathrm{ClF}_{3}\) (d) \(\mathrm{AlF}_{3}\)

Step-by-Step Solution

Answer

The compound used is (a) HF.

Step 1: Identify the desired compound

The problem asks for the compound used in the preparation of Uranium Hexafluoride ( UF_6 ), which is vital in the enrichment process for Uranium-235 ( U^{235} ).

Step 2: List potential compounds and their possible use

The compounds provided are HF (Hydrogen Fluoride), CaF_2 (Calcium Fluoride), ClF_3 (Chlorine Trifluoride), and AlF_3 (Aluminum Fluoride). We need to determine which of these are typically used to form UF_6 .

Step 3: Analyze each option

HF - a source of fluoride ions, commonly used for introducing fluoride in reactions. CaF_2 - used as a stable source of fluoride but not directly for the preparation of UF_6 . ClF_3 - used as a fluorinating agent but not specifically for UF_6 preparation. AlF_3 - mainly used in aluminum smelting, not for uranium enrichment.

Step 4: Determine the correct compound for U F_6 preparation

HF is commonly used in the preparation of UF_6 due to its ability to provide fluoride ions effectively and is a key component in the chemical reaction that produces UF_6 from uranium compounds.

Key Concepts

Chemical Reactions in Nuclear Chemistry

In nuclear chemistry, reactions often involve elements that are radioactive, like uranium. This means these reactions are not just about rearranging atoms, they also might change the nucleus of the atom. Uranium is a heavy element used in nuclear reactions because of its ability to undergo fission, which is splitting of the nucleus. These nuclear transformations release a large amount of energy and are fundamental in nuclear power plants and atomic bombs.

A key aspect of these reactions is the conversion of uranium into different chemical forms such as uranium hexafluoride ( U F_6 ). This compound is crucial because it is used in the uranium enrichment process needed for nuclear reactors and weapons. Enriching uranium involves increasing the percentage of uranium-235, which is the isotope necessary for sustaining nuclear chain reactions. To accomplish this, uranium must be in a gaseous state, and converting it into U F_6 is the way to make it gaseous at reasonable temperatures.

Fluoride Compounds in Uranium Enrichment

Fluoride compounds play a vital role in transforming uranium into a form suitable for enrichment. The primary fluoride compound used for this purpose is Hydrogen Fluoride ( HF ).

- HF is crucial because it reacts with uranium oxide to produce uranium hexafluoride, the necessary form of uranium for the enrichment process. - Calcium Fluoride ( CaF_2 ) is very stable but does not efficiently produce U F_6 from uranium compounds. - Chlorine Trifluoride ( ClF_3 ) and Aluminum Fluoride ( AlF_3 ) don't serve the purpose well, as they are used in other industrial applications like smelting and general fluorination.

In the reaction, HF acts as the source of fluorine, allowing it to bond with uranium. This bond formation leads to the production of U F_6 , which is essential for the uranium enrichment process.

Uranium-235 Enrichment Process

The enrichment of uranium-235 is a pivotal process in nuclear chemistry. Naturally, uranium consists mostly of uranium-238 and a small percentage of uranium-235. However, for nuclear power or weapons, more uranium-235 is required.

The enrichment process involves several stages:

• The uranium must first be converted into a gaseous form, which is U F_6 . This is achieved by reacting uranium oxides with HF , resulting in uranium hexafluoride.
• Once gaseous, this U F_6 is then processed through centrifuges. These centrifuges spin at high speeds, separating isotopes primarily based on mass differences.
• The lighter uranium-235 isotopes are separated from the heavier uranium-238 isotopes.
• This enrichment can then tailor the concentration of uranium-235 to the needed specifications for its intended use, whether it is for reactor fuel or something else, like medical isotopes.

Understanding the enrichment process is critical, as it not only aids in energy production but also has implications for national security.