Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

Noble gases are sparingly soluble in water, owing to (a) hydrogen bonding (b) dipole-dipole interactions (c) dipole-induced dipole interactions (d) induced dipole-instantaneous dipole interactions

Step-by-Step Solution

Answer

(d) induced dipole-instantaneous dipole interactions

Step 1: Understand Noble Gases

Noble gases are a group of elements that have full valence electron shells, making them extremely stable and non-reactive. Examples include helium (He), neon (Ne), and argon (Ar). They are characterized by their lack of chemical reactivity and are usually found in gaseous form.

Step 2: Solubility of Gases in Water

The solubility of gases in water generally depends on the interactions between the gas molecules and the water molecules. In the case of non-polar gases like noble gases, typical interactions such as hydrogen bonding and dipole-dipole interactions do not apply.

Step 3: Analyze Each Option

Let's analyze each option: (a) Hydrogen bonding would require the gas to form bonds with hydrogen atoms, which noble gases do not do. (b) Dipole-dipole interactions apply to polar molecules, and noble gases are non-polar. (c) Dipole-induced dipole interactions involve a polar molecule inducing a dipole in a non-polar molecule, which is not primarily how noble gases dissolve in water. (d) Induced dipole-instantaneous dipole interactions (also known as London dispersion forces) occur between non-polar molecules like noble gases and are the main contribution to the solubility of noble gases in water.

Step 4: Conclusion

The solubility of noble gases in water is predominantly due to induced dipole-instantaneous dipole interactions, which are weak and account for the slight solubility of these gases. This is because noble gases are non-polar and can only interact with water through these temporary, weak forces.

Key Concepts

Induced dipole-instantaneous dipole interactions

These interactions, also known as London dispersion forces, occur between non-polar molecules, such as noble gases. Although noble gases are chemically inert and do not readily react with other substances, they can still experience temporary attractions.
When a non-polar molecule like a noble gas approaches another molecule, the electron distribution within the noble gas can become temporarily uneven. This slight shift forms a temporary dipole.
This temporary dipole can induce a dipole in a neighboring molecule, leading to a weak attraction between the two molecules. These forces are very weak compared to other types of intermolecular forces like hydrogen bonds or ionic bonds.
Despite their weakness, these dispersion forces are crucial for understanding why non-polar gases, including noble gases, can dissolve slightly in water.

Non-polar gases

Noble gases are examples of non-polar gases, characterized by their stable, complete electron shells. Because of this complete electron configuration, they exhibit little to no tendency to engage in chemical reactions, making them very stable.
Non-polar gases do not have regions of positive or negative charge, producing little in the way of permanent attractions that are typical of polar molecules.

• This lack of charge means non-polar gases don't readily interact with water via dipole-dipole or hydrogen bonding.
• Instead, their solubility in water is influenced predominantly by weak interactions, like the induced dipole-instantaneous dipole interactions.

Their solubility is usually very low compared to more reactive or polar gases. This is why gases like helium and neon seem to dissolve reluctantly in water.

Solubility in water

Solubility in water refers to the ability of a substance to dissolve in water, forming a solution. Water is a highly polar solvent and is excellent at dissolving ionic and polar substances due to strong dipole-dipole and hydrogen bonding interactions.
Non-polar gases such as noble gases, however, do not mix well with water. They don't have the complementary charge distributions that interact strongly with water.

• Instead, their presence in water is mostly due to weak forces, such as induced dipole-instantaneous dipole interactions.
• This minimal solubility can often be observed in the form of bubbles formed when noble gases escape from water after the decrease in pressure, such as when shaking a water bottle.

Understanding the nature of these interactions is key to grasping why some gases dissolve more readily than others in water.