Soap Micelles Lift Oil

Also called

soap · micelle · detergent · cleansing action of soap · hydrophilic head · hydrophobic tail · emulsion · oil and water do not mix · sodium salt of fatty acid · hard water scum · calcium ions in hard water · lather · saponification · साबुन · मिसेल · कठोर जल

Topics

• A soap molecule is the sodium or potassium salt of a long-chain fatty acid, such as sodium stearate.
• Its ionic –COO⁻Na⁺ end is hydrophilic (dissolves in water); its long hydrocarbon tail is hydrophobic (dissolves in oil).
• Oil and water do not mix, so water alone cannot remove an oily stain from cloth.
• In soapy water the tails bury themselves in the oil while the heads stay out in the water.
• The soap molecules form a spherical cluster, a micelle, with the oil trapped at its centre.
• Micelles stay suspended as an emulsion; rinsing water carries them, and the dirt, away from the cloth.
• Hard water contains Ca²⁺ and Mg²⁺ ions, which react with soap to form an insoluble white curd, scum.
• Detergents are ammonium or sulphonate salts of long chains; they do not form scum, so they work in hard water.

About this model

A GLB file of about 311 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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