AI Tutor
If you shake a bottle of salad dressing, the oil and vinegar mix for a moment, but within seconds they separate right back into two distinct layers.
Why do oils and fats stubbornly refuse to dissolve in water?

The Hydrophobic Nature of Lipids

Lipids are a diverse group of carbon-based biomolecules that are defined by one shared trait: they are hydrophobic, meaning they do not dissolve in water.
Water molecules are polar with partial electric charges that attract each other, whereas lipids are made almost entirely of nonpolar carbon-hydrogen bonds (Cβˆ’HC-H) that share electrons equally.
Because water molecules strongly pull toward one another, they squeeze out the nonpolar lipid molecules, forcing the oil to cluster together.
So how are these nonpolar molecules built at the atomic scale?

Anatomy of a Triglyceride

The most common lipids in food and animal storage are triglycerides, commonly known as fats and oils.
A triglyceride is assembled from one glycerol moleculeβ€”a three-carbon alcoholβ€”bonded to three long fatty acid chains.
Each fatty acid tail consists of a carboxyl group (βˆ’COOH-\text{COOH}) attached to a long hydrocarbon chain that stores large amounts of chemical energy.