Phenol is more acidic than ethanol because (a) greater resonance stabilization of phenoxide ion (b) phenol has greater H-bonding than ethanol (c) phenol has larger molar mass (d) phenol has higher boiling point than ethanol

Understanding the acidity of different compounds is crucial in chemistry, and when it comes to phenol, resonance stabilization plays a key role in its greater acidity compared to ethanol. Resonance stabilization refers to the spread of negative charge over multiple atoms, creating a more stable electronic structure.

In phenol, when the hydroxyl hydrogen is lost, the resulting negative charge on the oxygen can be delocalized into the aromatic benzene ring. This means the lone pair on the oxygen can 'resonate' or spread out within the conjugated system of the ring, leading to more stability.

Why Does Resonance Affect Acidity?

The stable phenoxide ion that is formed when phenol loses a proton, compared to the ethoxide ion from ethanol, explains the higher acidity. Ethanol lacks such an extensive system for delocalization, which means its conjugate base is less stable and less willing to accommodate a negative charge.

Hydrogen bonding is an important concept when analyzing the properties of molecules, but it's not directly related to the question of acidity between phenol and ethanol. Both phenol and ethanol are capable of forming hydrogen bonds due to the presence of an -OH group; however, hydrogen bonding largely impacts boiling points and solubility, rather than acidity.

Hydrogen Bonding and Its Effects

The strength of hydrogen bonds can be significant in determining how molecules interact with one another, but when it comes to losing a hydrogen ion (a measure of acidity), this intermolecular force is not the determining factor. Thus, although hydrogen bonds are present in both phenol and ethanol, they do not explain why phenol is more acidic.

A common misconception is associating the molar mass of a compound with its acidity. While molar mass can indicate other properties such as boiling point or melt point, it doesn't have a direct correlation with acidity.

Take phenol and ethanol for instance — although phenol has a larger molar mass, this property does not contribute to its acidity. The focus for acidity should remain on the stability of the conjugate base, which, as discussed, is enhanced in phenol due to resonance stabilization, not its molar mass.

Boiling point signifies the temperature at which a liquid turns to vapor, and while it tells us something about the intermolecular forces at play, it does not directly relate to acidity. For example, even though phenol has a higher boiling point than ethanol, which is attributed to stronger intermolecular forces (like hydrogen bonding), this physical property is distinct from the chemical property of how easily a substance gives up a proton.

What Really Matters for Acidity?

We should focus on the nature of the conjugate base and its ability to stabilize negative charge. It's this stability that dictates the tendency of the original substance to act as an acid, not characteristics such as boiling point. Therefore, the higher boiling point of phenol is another unrelated property and not a factor in its greater acidity over ethanol.