Which property describes how a chemical partitions between octanol and water, indicating hydrophobicity?

• A. Partition coefficient: n-octanol/water
• B. Flash point
• C. Odor threshold
• D. Decomposition temperature

Answer: (A)

Hydrophobicity is shown by how a chemical distributes itself between a nonpolar phase and water at equilibrium. The measure that captures this distribution is the octanol/water partition coefficient, often written as Kow or logP. It tells you how much of the substance prefers the octanol phase versus the water phase. A higher Kow means the compound is more lipophilic and tends to partition into octanol (more hydrophobic), while a lower Kow means it stays more in water (less hydrophobic). This concept is key for predicting things like membrane permeability and environmental fate.

Other properties described by the options—flash point relates to flammability, odor threshold to sensory detection, and decomposition temperature to chemical stability—not to how a compound divides between octanol and water.