Oil and water don't mix because of their different molecular structures. Water is a polar molecule, meaning it has a slightly positive and slightly negative end. Oil, on the other hand, is a nonpolar molecule, lacking this charge separation.
The Science Behind It
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Polar vs. Nonpolar: Water molecules are strongly attracted to each other due to their polarity, forming hydrogen bonds. These bonds create a strong cohesive network. Oil molecules, being nonpolar, don't interact with these water-water bonds. They're simply repelled.
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Like Dissolves Like: This principle governs solubility. Polar substances dissolve in polar solvents, and nonpolar substances dissolve in nonpolar solvents. Since oil is nonpolar and water is polar, they are incompatible. To dissolve in water, oil would need to disrupt water's hydrogen bonds, which requires significant energy and doesn't occur naturally. This is why oil floats on water.
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Examples: Think of trying to mix salad dressing. The oil separates from the vinegar (mostly water) because of this difference in polarity.
Simple Explanation for Class 5
Imagine water molecules like tiny magnets, all sticking together. Oil molecules are like smooth marbles—they don't stick to the magnets. Because they can't interact, they stay separate.
References supporting this explanation:
- The statement, "Oils and fats not have any polar part and so for them to dissolve in water they would have to break some of water's hydrogen bonds," directly explains the incompatibility between oil (nonpolar) and water (polar) due to the strong hydrogen bonds in water.
- Multiple sources confirm the “like dissolves like” principle, highlighting that polar solvents dissolve polar substances, and nonpolar solvents dissolve nonpolar substances. Oil, being nonpolar, does not dissolve in the polar solvent, water.
