Problem 104 - A Complete Resource Book in Chemistry for JEE Main

Question

When water is allowed to freeze in the presence of Ar, \(\mathrm{Kr}\) or Xe under pressure, then (a) atoms noble gas (G) trapped in the crystal lattice of ice gives clathrates corresponding to the composition 8G. \(26 \mathrm{H}_{2} \mathrm{O}\) (b) these are called noble gas hydrates (c) both are correct (d) all are incorrect

Step-by-Step Solution

Answer

(c) both are correct

Step 1: Understanding the Problem

The problem asks about the composition and naming of certain compounds formed when noble gases are trapped in ice under pressure. These compounds are clathrates with a specified composition, and they are known by certain names.

Step 2: Analyzing the Composition

The composition given is 8G. 26 H₂O, where G represents a noble gas atom (such as Ar, Kr, or Xe). This indicates that 8 atoms of a noble gas are trapped in a structure formed by 26 water molecules, forming a clathrate.

Step 3: Understanding Noble Gas Clathrates

Clathrate hydrates are compounds in which water molecules form a cage-like structure that traps gas molecules. They are known when certain gases, like noble gases, get trapped within the lattice structure of ice under high pressure.

Step 4: Evaluating Statement (a)

Statement (a) claims that noble gas atoms (G) trapped in the crystal lattice of ice form clathrates with the given composition. This aligns with the definition of clathrate hydrates, making statement (a) correct.

Step 5: Evaluating Statement (b)

Statement (b) claims that these are called noble gas hydrates. This is correct terminology for clathrate hydrates involving noble gases.

Step 6: Choosing the Correct Answer

Both statement (a) about composition and statement (b) about naming are correct. Therefore, option (c) 'both are correct' must be the answer.

Key Concepts

Noble Gases

Noble gases are a group of chemical elements with very unique properties. They are all located in Group 18 of the periodic table and include well-known gases like Argon (Ar), Krypton (Kr), and Xenon (Xe). One of their standout characteristics is that they are chemically inert. This means they do not readily participate in chemical reactions with other elements. This quality comes from having complete valence electron shells, which makes them very stable.

Despite their reluctance to react chemically, noble gases can become trapped within structures like clathrate hydrates under certain conditions.

• Argon, Krypton, and Xenon are the noble gases involved in forming clathrates with ice.
• The trapping occurs under high pressure and low temperature conditions.

This is significant in the field of chemistry as it allows noble gases to exist in solid form, which is otherwise uncommon due to their gaseous nature at room temperature.

Crystal Lattice

A crystal lattice is a highly organized, repeating structure that extends in three dimensions. In the case of clathrate hydrates, this structure is formed by water molecules arranging themselves to create cage-like formations. The intricate pattern of the lattice is essential for trapping gas molecules like noble gases.

The process works by surrounding the gas with a symmetrical framework of water molecules, creating stable structures known as clathrates.

• Water molecules bond in a way that resembles a cage.
• This lattice is capable of trapping various guest molecules, including noble gases.

The fact that these gases are enclosed without forming direct chemical bonds is what distinguishes clathrates from other molecular compounds. The properties of the crystal lattice, like its geometric integrity, directly influence the ability to trap and hold noble gas atoms effectively.

High Pressure

High pressure plays a crucial role in the formation of clathrate hydrates. It is one of the key conditions required to transform water and gas mixtures into solid clathrates. At high pressure, the water molecules are forced into closer proximity, enhancing the possibility of forming the cage-like crystal structures.

This environment is essential for preventing the gases from escaping while the lattice forms.

• High pressure ensures that the necessary water molecule configurations are achieved.
• This results in stable clathrate formations with guest gas molecules locked inside.

Without high pressure, the possibility of noble gases escaping the lattice is higher, thus high pressure is critical for both the formation and stability of clathrates in the natural world and laboratory settings. This process underpins many scientific and industrial applications, including gas storage and environmental science.