How does the miscibility of alcohols change with increasing molecular weight?

The correct answer is that the miscibility of alcohols decreases with increasing molecular weight due to the structural characteristics of alcohols. Alcohols contain a hydroxyl (-OH) group that is polar and can form hydrogen bonds with water, which is key for miscibility. In lower molecular weight alcohols, such as methanol and ethanol, the hydrophilic (water-attracting) properties of the -OH group dominate because the hydrocarbon chain is short, which minimizes the influence of the hydrophobic (water-repelling) carbon chain.

As the molecular weight of the alcohol increases, the length of the carbon chain increases as well, leading to an overall increase in the hydrophobic character of the molecule. This increase in non-polar character reduces the ability of the alcohol to interact favorably with water molecules, thereby decreasing its miscibility in water. For instance, when comparing hexanol and butanol, butanol is more soluble in water than hexanol because butanol has a shorter carbon chain, making it more polar overall.

Thus, as the molecular weight of alcohols increases, the hydrophobic hydrocarbon part of the molecule outweighs the hydrophilic -OH part, leading to decreased miscibility with water. This principle holds true until