SOAPS

Soaps are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats and oils, or their fatty acids, by treating them chemically with a strong alkali.

First, i will explain the composition of fats, oils and alkalis, then the soapmaking process.

Fats and Oils

The fats and oil used in soapmaking come from animal or plant sources. Each fat or oil is made up a distinctive mixture of several different triglycerides.

In a triglyceride molecule, three fatty acid molecules are attached to one molecule of glycerine. There are many types of triglyceride; each types consists of its own particular combination of fatty acids.

Fatty acids are the components of fats and oils that used in making soap. They are weak acids composed of two parts;

A carboxylic acid group consisting of one hydrogen atom, two oxygen atoms, and one carbon atom, plus a hydrocarbon chain attached to the carboxylic acid group. Generally, its made up a long straight chain of carbon atom each carrying two hydrogen atoms.



Alkali

An alkali is a soluble salt of an alkali metal like sodium or potassium. Originally, the alkalis used in soapmaking were obtained from the ashes of plant, but they are now made commercially. Today, the term alkali describe a substance that chemically is a base(the opposite of an acid) and that reacts with and neutralizes an acid.

The common alkalis used in soapmaking are sodium hydroxide(NaOH), also called caustic soda; and potassium hydroxide(KOH), also called caustic potash.

How Soaps are Made

Saponification of fats and oils is the most widely used soapmaking process. This method involves heating fats and oils and reacting them with a liqiud alkali to produce soap and water (neat soap) plus glycerine.

The other major soapmaking process is the neutralization of fatty acids with an alkali. Fats and oils are hydrolyzed (split) with a high-pressure steam to yield crude fatty acids and glycerine. The fatty acids are then purified by distillation and neutralized with an alkali to produce soap and water (neat soap).

When the alkali is sodium hydroxide, a sodium soap is formed. Sodium soaps are "hard" soaps. When the alkali is potassium hydroxide, a potassium soap is formed. Potassium soaps are softer and foun in some liqiud hand soap and shaving creams.

The carboxylate end of the soap molecule is attached to water. It is called the hydrophilic (water-loving) end. The hydrocarbon chain is attracted to oil and grease and repelled by water. It is known as the hydrophilic (water-hating) end.

How Water Hardness Affects Cleaning Action
Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts - mostly those of calcium (Ca) and Magnesium (Mg), but sometimes also iron (Fe) and manganese (Mn). The mineral salts react eith soap to form an insoluble precipitate known as soap film or scum.

Soap film does not rinse away easily. It tends to remain behindand produces visible deposits on clothing and makes fabrics feels stiff. It also attaches to the insides of bathtubs, sinks and washing machines.

Some soap is used up reacting with hard water to form the film. This reduces the amount of soap available for cleaning. Even when clothes are washed in soft water, some hardness minerals are introduced by the soil on clothes. Soap molecules are not very versatile and cannot adapted to today's varietyof fibres, washing temperatures and water condition.