Final answer:
The carbon chain of a soap molecule that repels water is known as the hydrophobic tail. Soap molecules have amphipathic characteristics, with a hydrophilic head that interacts with water and a hydrophobic tail that avoids it.
Step-by-step explanation:
In relation to water solubility, the carbon chain of a soap molecule is known as the hydrophobic tail. Soap molecules are formed with a two-part structure: one end is the hydrophilic head, which is attracted to water, and the other is the hydrophobic tail, which repels water.
These molecules are amphipathic because they have both a water-attracting (hydrophilic) and a water-repelling (hydrophobic) part. In a soap molecule, like sodium stearate, the hydrophobic tail is typically a long hydrocarbon chain, while the hydrophilic head contains a negatively charged group such as a carboxylate ion.