Advantages of Detergents Over Soaps

Soaps are not suitable when hard water is used. Detergents can be used with both hard and soft water. Detergents are more soluble in water than soaps. They also have a stronger cleansing action than soaps. Detergents don't need expensive vegetable oil for their preparation as they can be prepared from hydrocarbons of petroleum. They can be used in acidic solutions whereas soaps cannot be used (free fatty acids are precipitated).

A detergent is a cleaning agent. Detergents can be classified into one of two general categories: natural soaps (or just soaps) and synthetic detergents (or syndets). Both soaps and syndets have many similarities, particularly with regard to their molecular structures and the way they clean objects.

The structure of soaps and detergents

Both soaps and syndets consist of very long molecules. A model of such molecules is shown below:

CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CHCOO ⁻ , Na ⁺

The characteristic of all such molecules is that they have very different ends. The left end of the above molecule is said to be hydrophobic, meaning it "hates water." That end of the molecule is attracted by fats and oils, but not by water. The right end of the molecule above is said to be hydrophilic, meaning it "loves water." That end of the molecule is attracted by water but not by fats and oils.

Most of the dirt that collects on clothing, dishes, and our bodies is surrounded by a thin layer of oil. Simply washing an object with water is not a very effective way of getting the object clean because oil and water do not mix with each other.

But suppose that a detergent, either a soap or a syndet, is added to the wash water. In that case, detergent molecules line up with one end attached to the oily dirt and the other end attached to water molecules. When the object is scrubbed or agitated, the oil-covered dirt attached to detergent molecules, which are also attached to water molecules, is removed from clothing, dishes, or human skin. The dirt-detergent-water combination can then disappear down the drain.

Soaps

No one knows exactly when soap was discovered. It was apparently used by the Phoenicians as early as the sixth century B.C. Modern methods of soapmaking were not perfected, however, until late in the eighteenth century. In 1790, French chemist Nicholas Leblanc(1742–1806) invented a process for making caustic soda (sodium hydroxide) from common table salt (sodium chloride). His invention made it possible to manufacture soap inexpensively from ordinary raw materials.

Soap is made by heating together fats or oils with water solutions of sodium hydroxide (lye). Molecules of fats and oils are very long molecules, like the one shown above. They do not have the charged group at the end of the molecule (—COO ⁻ , Na ⁺ ) as shown in that structure, however. The charged group is obtained from the sodium hydroxide with which the fat or oil is mixed.

Anyone can make his or her own soap simply by boiling a fat and lye together in a metal pot. The soap produced, however, would normally not be very pleasant to use. It would probably contain some left-over lye, which is very harsh. Washing with lye soap gets things clean but can be very damaging to human skin.

Today, soaps contain a number of ingredients to make them more pleasant to use. These ingredients include perfumes and coloring agents. Soaps may also be whipped into a lather when they are still liquid, to make them float; pressed into very hard bars, to make them last longer; or treated in other ways to give them special properties.

Date: 2016-01-03; view: 821