Question

Though covalent in nature, methanol is soluble in water, why? (a) Methanol is transparent like water. (b) Due to hydrogen bonding between methanol and water molecules. (c) Due to van der Waals forces between methanol and water. (d) Due to covalent attraction forces.

Short answer

Methanol is soluble in water due to hydrogen bonding between methanol and water molecules, which is the strongest intermolecular force among the options given.

Step-by-step solution

Understanding Methanol's Solubility

To determine why methanol is soluble in water, we need to understand the intermolecular forces at play between methanol (CH3OH) and water (H2O) molecules.

Evaluating Given Options

Option (a) suggests transparency as a reason for solubility, which is not correct, because solubility depends on intermolecular forces and not on visual properties. Option (c) mentions van der Waals forces which are present in all molecules, but they are weaker than hydrogen bonds in water-soluble substances. Option (d) suggests covalent attraction forces, which are within molecules and not between them. Option (b) suggests hydrogen bonding, which occurs due to the ability of methanol to act both as a hydrogen bond donor and acceptor, similar to water molecules, enabling strong intermolecular attractions.

Identifying the Reason for Solubility

Hydrogen bonds are the strongest type of dipole-dipole interaction and occur when a hydrogen atom covalently bonded to an electronegative atom like oxygen is attracted to another electronegative atom of a neighboring molecule. In the case of methanol and water, this intermolecular force is the reason for methanol's solubility in water.

Key concepts

Hydrogen Bonding

Hydrogen bonding is a type of strong intermolecular force that plays a critical role in the solubility of substances in water. It occurs when a hydrogen atom, which is covalently bonded to a highly electronegative atom such as oxygen, nitrogen, or fluorine, experiences an attractive force towards another electronegative atom on a different molecule. In methanol ((CH3OH)), the hydrogen atom bonded to the oxygen is partially positive due to oxygen's high electronegativity.

This allows methanol to interact closely with water ((H2O)), which also contains highly electronegative oxygen atoms bonded to hydrogen. These molecules are capable of 'recognizing' one another through these polar features, which leads to the formation of hydrogen bonds. It's like having matching puzzle pieces that are attracted to each other and form a connection. These connections allow methanol to dissolve in water effectively, enhancing its solubility.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion which act between neighboring particles (molecules, atoms, or ions). They are not as strong as the intramolecular forces that hold atoms together within a molecule, like the covalent bonds within the methanol molecule itself. However, they are pivotal in determining a substance's physical properties, such as boiling points, melting points, and solubility.

There are several types of intermolecular forces, such as London dispersion forces, dipole-dipole interactions, and hydrogen bonding. In the context of methanol's solubility in water, hydrogen bonding is the essential intermolecular force. Methanol molecules can line up with water molecules, forming a network of hydrogen bonds. This collective strength of multiple hydrogen bonds enables the methanol to mix uniformly with water.

Solvation Process

The solvation process is the interaction between a solute (like methanol) and the solvent (such as water) leading to the dissolution of the solute into the solvent. This process involves breaking the intermolecular forces within the solute and solvent, followed by the formation of new interactions between the solute and solvent molecules.

During the dissolution of methanol in water, water molecules surround the methanol molecules. The partially negative oxygen atoms in water align with the partially positive hydrogens in methanol, and vice versa. This arrangement results in the formation of a 'solvation shell' around the methanol molecules. This shell of water molecules stabilizes the methanol in the aqueous environment, allowing it to remain dissolved. The proper understanding of solvation is critical for grasping why certain substances dissolve in water while others do not.