How soap cleanses based on its structure?

Question

chemistry

Answer 1

Soaps are sodium or potassium fatty acids salts, produced from the hydrolysis of fats in a chemical reaction called saponification. Each soap molecule has a long hydrocarbon chain, sometimes called its 'tail', with a carboxylate 'head'. In water, the sodium or potassium ions float free, leaving a negatively-charged head.

Soap is an excellent cleanser because of its ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed.

Answer 2

Take a look at the typical structure of a soap or detergent molecule: soap/detergent molecules are typically comprised of a long hydrophobic (insoulble, water-avoiding) organic chain, with a hydrophilic (soluble, so they are attracted to water) group at one end. When you put soap in water, the hydrophobic ends want to get away from the water, while the hydrophilic end is attracted to the water. To resolve this conflict, the soap molecules group together into a structure called a micelle -- this is a "bubble" or a balloon-like structure with the hydrophilic ends on the outside, and the hydrophobic ends towards the center. This is why your bath water gets cloudy as you wash -- you are suspending micelles in the soapy water solution!

This micelle is very useful in removing oily/ greasy/ hydrophobic materials (otherwise known as dirt) from surfaces because the dirt is picked up and moves into the center of the micelle, where it is in a hydrophobic environment. The hydrophilic outer layer suspends the micelle in water, and allows you to rinse the dirt off the surface and down the drain. The micell also helps prevent the dirt from settling back onto the surface.

For more, check out the Wiki article.

Answer 3

Soap is made by reacting an alkali with a fatty acid, so you get a compound like sodium stearate. The stearate part of the molecule is like a fat, so it links to grease, and the sodium end is soluble in water, so soap removes grease. Without soap, greasy dirt can't be removed just with water.

Answer 4

It makes the water wetter
(reduces surface tension)
so it can get between the item being cleaned and the dirt
and facilitate the dirt being moved away from the item being cleaned