One of the most basic and yet important applications of chemistry in our everyday lives is soap. In fact, all types of cleaning agents, which includes soaps and detergents, are made from chemicals. Let us learn about these cleansing agents in some detail.
Cleansing agents are substances we use to get rid of stains, dust, foul smells, dirt etc from surfaces. These are the chemicals we use to decrease the surface tension on planes so that water can properly do its job. Cleaning with only water does not work effectively, as the surface tension is too high for cohesive forces to work.
Two very common cleansing agents in our daily lives are soaps and detergents. Let us learn about the chemical compositions of both, and how they actually function.
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Soaps are a common detergent. They are the most popular type of cleansing agents. Soaps are generally made by reacting an alkali (like sodium hydroxide) in liquid form with naturally occurring fats or fatty acids, produced from animals and plants. The process is known as saponification.
The molecular structure of soaps is made up of long chains of molecules. At one end we have the hydrophobic end (the tail), made of the hydrocarbon chain. These molecules repel water and attach itself to the oils and the grease. Then at the head of the chain, we have the water-loving, or the hydrophilic chain made up of anionic molecules.
Soaps have surface active agents, that are called surfactants. They basically reduce the surface tension of the water. The surfactants attach on one end to the water molecules, and this allows the water to better wet the surface. At the other end, surfactants attach themselves to oils and the dirt. Overall they allow the water to better clean the surface.
Types of Soaps
- Toilet Soaps: Toilet soaps use a higher quality of oils and fatty acids to give them better quality. Sometimes perfumes and colours are added for cosmetic purposes.
- Medicated Soaps: In these types of soaps we add antiseptics to the soap as an ingredient. The antiseptic is to help kill germs from the surface along with the dirt and dust.
- Floating Soaps; As the name suggests, these soaps float in the water instead of sinking like normal soaps. This is done by whipping air into the soap in the soap mixture before they set in their moulds.
- Shaving Soaps: These soaps must not dry to fast. So glycerol is added to it to keep it from drying. Also, we add a substance known as rosin to help the soap lather.
- Soap Chips: These are leftover pieces of soap that are left over in soap production. They can also be made by the scrapping of small pieces of soap from a thin sheet of soap.
The other type of cleansing agents is synthetic detergents. These are just like soaps, i.e. they have all the properties of soap. But they do not contain any soap at all, their chemical structure is completely different to soaps.
One of the biggest advantages of detergents over soaps is that they can work in any condition. They can work in normal water as well as hard water. They do not form any scum in hard water. Some detergents are even able to work in ice cold water.
Detergents are long chains of molecules similar to soaps. One of the types of molecules are hydrocarbons made of carbon and hydrogen atoms. These hydrocarbons are derived from fats, oils, fatty acids etc. The other ingredient will depend on the type of detergent. So let us take a look the types of detergents.
Types of Detergents
These are anion active synthetic detergents. There are sulphate salts of long chains of hydrocarbons. The anion active part is the cleansing agent. One common example is sodium alkyl sulphates. The preparation involves treating a long chain alcohol with a concentrated sulphuric acid. Then it is neutralized by Sodium hydroxide.
Anion detergents are the most common type of detergents. They are used in household work mostly, like washing clothes, mopping floors etc. We even use anionic detergents in toothpaste.
Cationic detergents are ammonia salts, usually of chlorides or acetates. They have a long chained molecular structure of hydrocarbons. And the active part of the molecule is a positive ion. i.e. cation. This explains the name cation detergents. A popular example is cetyltrimethylammonium bromide.
Cationic detergents also have bactericidal properties. One common use for them is in hair conditioners. Cationic detergents tend to be expensive and so they do not have many industrial uses.
As the name suggests they do not have any ions in their molecules, so they are uncharged. To produce nonionic detergents we react polyethene glycol with stearic acid. There are two main types of nonionic detergent polyoxyethylene and glycosidic.
Solved Question for You
Question: Detergents are better than soaps because:
- They wash better
- They absorb the hardness of water
- Are less affected by hard water
- None of the above
Answer: The correct option is C. Detergents are less affected than soaps by hard water. This is because the hydrocarbon chains in detergents do not precipitate with calcium, magnesium and other metal ions. So it does not form any scum.