Cleansing Agents

Cleansing agents are, in the most general sense, substances used to remove stain, dirt or clutter from a surface, and they fall into two broad categories: those that occur naturally (soaps) and those that are synthetically developed (detergents). A key practical problem motivates why detergents were developed at all, alongside soaps that had already existed for a very long time: soaps are water-soluble and work well in ordinary water, but hard water contains dissolved salts of calcium and magnesium, and these react with soap in solution to precipitate an insoluble calcium or magnesium salt of the fatty acid -- a scum -- that sticks to fabric rather than washing dirt away, effectively deactivating the soap. This problem can be partly managed with washing soda (Na2CO3), which precipitates the dissolved calcium (and magnesium) salts out of hard water as carbonates before the soap is even used, which is why washing soda is described as helping soap's cleaning action by 'softening' the water first. Synthetic detergents were designed spec …