Explain the mechanism of the cleaning action of soaps

Soap molecules form micelles around an oil droplet (dirt) in such a way that the hydrophobic parts of the stearate ions attach themselves to the oil droplet and the hydrophilic parts project outside the oil droplet. Due to the polar nature of the hydrophilic parts, the stearate ions (along with the dirt) are pulled into water, thereby removing the dirt from the cloth. Cleansing action of soaps : Soaps contain two parts, a large hydrocarbon which is a hydrophobic (water repelling) and a negative charged head, which is hydrophillic (water attracting). In solution water molecules being polar in nature, surround the ions & not the organic part of the molecule. When a soap is dissolved in water the molecules gather together as clusters, called micelles. The tails stick inwards & the head outwards. The hydrocarbon tail attaches itself to oily dirt. When water is agitated, the oily dirt tends to lift off from the dirty surface & dissociates into fragments. The solution now contains small globules of oil surrounded detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus the oily dirt is removed from the object The mechanism of cleansing action of soap: 1)A molecule of soap has two dissimilar ends. The hydrophobic end of the hydrocarbon chain is water repellent, while the hydrophilic end is polar and water soluble due to presence of carboxylate anion. Thus a soap molecule may be represented as: 2)W...

Cleaning Action of Soap: A soap molecule consists of two dissimilar parts: (i) A short ionic part comprising the carboxylate salt, –COO– Na+. This is the polar end. This is water soluble (i.e., hydrophilic or water attracting) and, therefore, remains attached to water. (ii) A long hydrocarbon chain which is the non-polar end. This end is hydrophobic (i.e., water repelling) and is soluble in oil and grease. When soap is dissolved in water, it forms a colloidal suspension. In this colloidal suspension, the soap molecules cluster together to form micelles and remain radially suspended in water with the hydrocarbon end towards the centre and the ionic end directed outward. This is shown in the figure. The dirt particles always adhere to the oily or greasy layer present on the skin or clothes. When a dirty cloth is dipped into a soap solution, its nonpolar hydrocarbon end of micelles attach to the grease or oil present in dirt and polar end remains in water layer. The mechanical action of rubbing subsequently, dislodges the oily layer from the dirty surface shaping it into small globules. A stable emulsion of oil in water is formed. The emulsified oil or grease globules bearing the dirt can now be readily washed with water.

When soap is dissolved in water, it forms a colloidal suspension. In this colloidal suspension, the soap molecules cluster together to form micelles and remain radially suspended in water with the hydrocarbon end towards the centre and the tonic end directed ontward. The dirt particles always adhere to the oily or greasy layer present on the skin or clothes. When a dirty cloth is dipped into a soap solution, its non-polar hydrocarbon end of micelles get attached to the grease or oil present in dirt and polar end remains in water layer. The mechanical action of rubbing subsequently, dislodges the oily layer from the dirty surface shaping it into small globules. A stable emulsion of oil in water is formed. The emulsified oil or grease globules bearing the dirt can now be readily washed with water.

The organic part of natural soap is a negatively-charged, polar molecule. Its hydrophilic (water-loving) carboxylate group (-CO 2) interacts with water molecules via ion-dipole interactions and hydrogen bonding. The hydrophobic (water-fearing) part of a soap molecule, its long, nonpolar hydrocarbon chain, does not interact with water molecules. The hydrocarbon chains are attracted to each other by dispersion forces and cluster together, forming structures called micelles. In these micelles, the carboxylate groups form a negatively-charged spherical surface, with the hydrocarbon chains inside the sphere. Because they are negatively charged, soap micelles repel each other and remain dispersed in water. Grease and oil are nonpolar and insoluble in water. When soap and soiling oils are mixed, the nonpolar hydrocarbon portion of the micelles break up the nonpolar oil molecules. A different type of micelle then forms, with nonpolar soiling molecules in the center. Thus, grease and oil and the 'dirt' attached to them are caught inside the micelle and can be rinsed away. Helmenstine, Anne Marie, Ph.D. "How Soap Works." ThoughtCo, Aug. 27, 2020, thoughtco.com/how-dos-soap-clean-606146. Helmenstine, Anne Marie, Ph.D. (2020, August 27). How Soap Works. Retrieved from https://www.thoughtco.com/how-dos-soap-clean-606146 Helmenstine, Anne Marie, Ph.D. "How Soap Works." ThoughtCo. https://www.thoughtco.com/how-dos-soap-clean-606146 (accessed June 15, 2023).