Final answer:
Classification of molecules depends on their interaction with water: hydrophilic molecules mix with water, hydrophobic molecules repel water, and amphipathic molecules have both hydrophilic and hydrophobic parts. The hydrophobic part of a molecule, like the fatty acid chains in a phospholipid, is the nonpolar region. To classify hydrocarbons, one must look at the molecular structure to determine if they are aliphatic or aromatic, and identify alkanes, alkenes, or alkynes accordingly.
Step-by-step explanation:
When classifying molecules as hydrophilic, hydrophobic, or amphipathic (amphiphilic), one must consider the interactions of the molecule with water. A hydrophilic molecule is 'water-loving' and tends to dissolve or mix with water, whereas a hydrophobic molecule is 'water-fearing' and tends to repel and avoid water. An amphipathic molecule contains both a hydrophilic region and a hydrophobic region, allowing it to interact with both water and lipid environments.
An example of an amphipathic molecule is a phospholipid. It has a hydrophilic 'head' due to a negatively charged phosphate group and hydrophobic 'tails' made up of uncharged fatty acid chains. When identifying the hydrophobic part of each molecule, you would circle the fatty acid chains in a phospholipid. Ranking these molecules based on hydrophobicity involves understanding that the more nonpolar a molecule or region of a molecule is, the more hydrophobic it is.
To determine if a molecule is aliphatic or aromatic, and further classify aliphatic hydrocarbons as alkane, alkene, or alkyne, the structure of the molecule needs to be examined. Aliphatic hydrocarbons are non-aromatic compounds that can be saturated (alkanes) with single bonds, unsaturated with double (alkenes) or triple bonds (alkynes). Aromatic hydrocarbons contain a ring structure with delocalized electrons.