The alkaline solution ( %) is added into the kettle, a little in excess. The mixture is boiled by passing steam through it. The oil gets hydrolysed after several hours of boiling. This process is called Saponification ii) Salting out of soap: Common salt is then added to the boiling mixture.
Soap is finally precipitated in the tank. After several hours the soap rises to the top of the liquid as a ‘curdy mass’. The neat soap is taken off from the top. It is then allowed to cool down.
Effect of hard water on soap Hard water contains calcium and magnesium ions (Ca + and Mg + ) that limit the cleaning action of soap. When combined with soap, hard water develops a thin layer (precipitates of the metal ions) called ‘scum’, which leaves a deposit on the clothes or skin and does not easily rinse away. Over time, this can lead to the deterioration of the fabric and eventually ruin the clothes. On the other hand, detergents are made with chemicals that are not affected by hard water.
Why ordinary soap is not suitable for using with hard water? Ordinary soaps when treated with hard water, precipitate as salts of calcium and magnesium. They appear at the surface of the cloth as sticky grey scum. Thus, the soaps cannot be used conveniently in hard water .
. . Detergents Development of synthetic detergents is a big achievement in the field of cleansing. These soaps possess the desirable properties of ordinary soaps and also can be used with hard water and in acidic solutions.
These are salts of sulphonic acids or alkyl hydrogen sulphates in comparison to soap, which are salts of carboxylic acids. The detergents do not form precipitates with Ca + and Mg + present in hard water. So, the cleansing action of detergents is better than that of soaps. Preparation of detergents Detergents are prepared by adding sulphuric acid to the processed hydrocarbon obtained from petroleum.
This chemical reaction result in the formation of molecules similar to the fatty acid in soap. Then, an alkali is added to