NEET Chemistry Notes Chemistry in Everyday Life -Soaps
Soaps
Soaps
These are the sodium or potassium salts of higher fatty acids and are prepared by alkaline hydrolysis of fats or oils. Fats or oils are esters of higher fatty acids.
Types of Soaps
- Toilet Soaps These are prepared by using better grades of fats and oils and care is taken to remove excess alkali, colour, perfumes.
- Transparent Soaps These are made by dissolving the soap in ethanol and then evaporating the excess solvent.
- Medicated Soaps These contain substances of medicinal value.
- Shaving Soaps These contain glycerol to prevent rapid drying. A gum called rosin is added while making them.
- Laundry Soaps These contain fillers like sodium rosinate, sodium silicate, borax cftid sodium carbonate.
Cleansing Action of Soap
On applying soap to a dirty wet cloth, the hydrocarbon part (non-polar part) of soap dissolves in grease or dust while the polar carboxylate part is directed towards water.
Thus, an emulsion is formed between grease particles and water molecules, which appears in the form of foam.
On washing the cloth with excessive water, these dirt or dust or grease particles are washed away from the surface of cloth along with soap and the cloth becomes clean.
Advantages
Soaps are biodegradable cleansing agents, therefore they do not cause pollution.
Disadvantages
Soaps do not work in hard water because hard water contains calcium and magnesium ions.
These ions form insoluble calcium and magnesium soaps respectively.
Synthetic Detergents
Alkyl benzene sulphonates are the synthetic detergents. These are also called syndets. The detergents are classified into following three types on the basis of ionic charge present at the soluble end of their chain.
Anionic Detergents
These are the sodium sate of sulphonated long chain alcohols or hydrocarbons. Anionic part of these detergents is involved in the cleansing action. These are formed by neutralising alkyl benzene sulphonic acids with alkali.
Anionic detergents are also used in toothpastes.
Cationic Detergents
Cationic detergents are quarternary ammonium salts of amines with acetates, chlorides or bromides as anions, e.g.
These are used in hair conditioners and are expensive, therefore these are of limited use.
Non-ionic Detergents
They do not contain any ion in their constitution. When stearic acid reacts with polyethylene glycol, non-ionic detergent is formed.
They are used in liquid dishwashing detergents.
Advantages
Detergents can be used both in soft and hard water as they give foam even in hard water.
Disadvantages
In detergents, hydrocarbon chain is highly branched, so bacteria cannot degrade this easily. In other words we can say, these are non-biodegradable.
Effluents containing such detergents reach to the rivers, ponds, etc. These persist in water even after sewage treatment and cause foaming in rivers, ponds and streams and their water gets polluted. Hence, detergents with straight chain hydrocarbons are preferred over branched chain as they are biodegradable and prevent pollution.