How does molecular weight relate to water solubility?

Molecular weight has a significant effect on water solubility due to the relationship between molecular size, polarity, and the ability to interact with water. Substances that are highly soluble in water tend to have lower molecular weights, allowing them to interact more effectively with water molecules.

As molecular weight increases, the overall size of the molecules also increases, which can lead to a decrease in solubility. Larger molecules often have larger, non-polar regions that disrupt the ability of the molecule to interact with the polar water molecules, making it harder for the solute to dissolve. Additionally, large molecules may possess more non-polar characteristics that diminish their affinity for the polar solvent water.

Therefore, as the molecular weight rises, the tendency for solubility in water typically diminishes. This trend particularly applies to organic compounds and is influenced by the presence of functional groups. For example, small organic molecules with polar functional groups (like alcohols or carboxylic acids) can be very soluble in water, while larger hydrophobic molecules (or molecules containing larger non-polar regions) typically exhibit lower solubility.