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Soap, Detergent and stain removers.


Information in this section was supplied by explainthatstuff  at

 Often we use the words "soap" and "detergent" interchangeably, but really they're quite different things. A detergent is a chemical substance you use to break up and remove grease and grime, while soap is simply one kind of detergent. Soap has a long history and was originally made from purely natural products like animal fat and wood ash.

Today, detergents are more likely to be a mixture of synthetic chemicals and additives cooked up in a huge chemical plant and, unlike traditional soap, they're generally liquids rather than solids. Detergents are used in everything from hair shampoo and clothes washing powder to shaving foam and stain removers. The most important ingredients in detergents are chemicals called surfactants



One of the organic chemical reactions known to ancient man was the preparation of soaps through a reaction called saponification. Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and a crude soap.

The saponification reaction In the industrial manufacture of soap. Tallow (fat from animals such as cattle and sheep) or vegetable fat is heated with sodium hydroxide. Once the saponification reaction is complete, sodium chloride (common salt) is added to precipitate the soap. The water layer is drawn off from the top of the mixture and the glycerol is recovered using vacuum distillation. The crude soap obtained from the saponification reaction contains sodium chloride, sodium hydroxide, and glycerol. These impurities are removed by boiling the crude soap curds in water and re-precipitating the soap with salt. After the purification process is repeated several times, the soap may be used as an inexpensive industrial cleanser. Sand or pumice may be added to produce a scouring soap. Other treatments may result in laundry, cosmetic, liquid, and other soaps.

Detergents. (A simple explanation).      

The most important ingredients in detergents are chemicals called surfactants-a word made from bits of the words surface active agents.

How surfactants work You might think water gets you wet! well it does. But it doesn't get you nearly as wet as it could. That's because it has something called surface tension. Water molecules prefer their own company so they tend to stick together in drops. When rain falls on a window, it doesn't wet the glass uniformly; instead, it sticks to the surface in distinct droplets that gravity pulls down in streaks.

To make water wash better, we have to reduce its surface tension so it wets surfaces more uniformly. And that's exactly what surfactants do. The surfactants in detergents improve water's ability to wet things, spread over surfaces, and seep into dirty clothes fibres.


Surfactants also do another important job. The have a hydrophobic end and a hydrophilic end, that means that one end of their molecule is attracted to water, while the other end is attracted to dirt and grease. So the surfactant molecules help water to get a hold of grease, break it up, and wash it away.



A Brief History:

600BC: Historians think people have been making soap for around 2000 years, even since the time of the Phoenicians (an early Mediterranean civilization).

1790: Soap remains an expensive luxury until a French chemist Nicolas Leblanc (1742-1806) finds a cheaper way of making it using salt.

1800s: Soap making becomes popular in the United States of America, where people mix the ingredients in large "soap kettles". Soap kettles are used for most soap-making until World War II.

1916: German chemist Franz Gunther develops the first surfactant for detergents from coal tar.

1930s: Detergents based on surfactants are introduced in the United States.

1950s: Synthetic detergents are developed to counter soap shortages caused by World War II and soon overtake traditional soap to become our favourite chemical cleaners.

1960s/1970s: Concerns about water pollution from detergents building up in rivers and seas lead to the development of the first biodegradable surfactants.


Stain Removers: (A general guide). 

Whether it is lemon juice from your fridge, detergent bleach from your laundry cupboard or chemical solvent from your local hardware shop, all stain removers operate in one of four basic ways:

1. Dissolve the Stain Using a Solvent. The most common and universal solvent is water and many stains, especially if caught fresh, can be lifted off simply by flushing with or soaking in water. However, some stains contain substances that will not dissolve in water, for example grease stains like butter. These will require organic solvents, such as alcohol. In general, "like dissolves like" - thus, a stain made from hydrocarbons (e.g. motor oil) can be removed by a hydrocarbon solvent (eg. petrol). Limonene is an organic molecule that is found in citrus fruits (e.g. oranges and lemons) which dissolves a lot of grease stains and certain kinds of fruit stains - it can even work on inks, graffiti, candle wax and gum. So lemon juice is a good stain remover to try in many situations.

2. Dissolve the Stain Using a "Surfactant" An alternative to using an organic solvent is to lift the stain off with the help of a "surfactant", such as soap or detergent - these surround the stain molecules and make it easier for water to detach them from the fabric and carry them away in the rinse. So, in the grease stain example in (1), instead of using alcohol which might damage the fabric, you could apply some detergent to the grease stain first. However stains which have dried may not respond to soap and detergent with water and may need to be treated with the appropriate solvent. Synthetic surfactants, such as sulfonates, are used more often than soap nowadays as they do not react with hard water to form calcium deposits ("soap scum"). However, they are far more toxic to the environment and are not biodegradable.

3. "Attack and Destroy" the Stain Particles. If the stain cannot be easily dissolved, then it may need to be "chopped up" through the process of oxidation. Oxidising agents, such as peroxides, chlorine bleach and borax, break up the bonds holding the stain molecules together, so enabling the solvent to flush them away more easily. Biological and enzyme detergents often provide this action on stains, especially food-related stains - they work by releasing enzymes that act as a catalyst to speed up the chemical reactions which digest the proteins and fats in the stains. However, these reactions are generally slow.

4. "Hide" the Stain As a last resort, it is possible to make a stain "invisible" if you cannot remove it from the fabric. Thus, although the stain molecules remain embedded in the fabric, they are rendered colourless so that you can no longer see them. Bleach works in this way: by disrupting the bonds between the chromophore molecules (which absorb light at specific wavelengths and so "produce" colour), the optical properties of the molecule are changed and thus they become "colourless" to our eyes and we say that the stain has been removed. In actual fact, it is still there but we just can't see it. Unfortunately, bleach does not distinguish therefore it will also remove colour from the fabric that the stain is embedded in - thus it can really only be used for white fabrics. However, a very mild solution of bleach (Peroxide bleach rather than chlorine bleach) can sometimes be used with care on coloured fabrics.





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