Why is oil hydrophobic?

Hydrophobicity is the property of the molecule that is repelled from the water. Hydrophobic molecules are generally non-polar in nature. Hydrophobic molecules form groups in the form of micelles. The water molecules form large angle on the hydrophobic molecule. Some of the hydrophobic molecules are fats, oils, alkanes, and any greasy substances. Hydrophobic substances have application in separating oil from water, managing the oil spills, and separating non-polar compounds from polar compounds. Hydrophobic compounds also exhibit the feature of lipophilic compounds except silicones.

When oil is added to water, the cohesive forces existing between the water molecules makes them to attract each other. All the water molecules come closer to each other as water is Polar in nature. As oil is non-Polar it does not have any charge on it. So, oil does not tend to mix with water and tends to move away from water molecules. The small oil droplets that were distributed on water when the oil is mixed with water combine to form large drop. The formation of large drop is initiated by the cohesive forces that exist between the water molecules. As the oil molecules appear to be avoiding the water molecules, oil is called as hydrophobic substance. The interaction between oil and water molecules is called as hydrophobic interaction.

The oils are fatty substances. Fats are comprised of few long fatty acids linked with glycerol molecule. The fatty acids are long carbon chains with a hydroxyl group at one end. The lengthy carbon chains of these fatty acids are non polar in nature and are bulky. As they are non-polar and bulky, oil is not attracted towards charged water molecules. Hence, fats and oils are hydrophobic. The bulky structure of the fatty acids and the non-polar carbon-hydrogen bonds makes them to be repelled by the water molecules. Moreover, the water molecules form hydrogen bonding with other water molecules and cluster together to push away the non-polar oil molecules. So, oil is hydrophobic in nature.

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