Q. 49 C5.0( 3 Votes )
Explain the cleansing action of soap. Draw diagrams to illustrate your answer.
Inside water, these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. This is achieved by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of the micelle. The ionic ends in the micelles remain attached to water. When the dirty clothes are agitated in soap solution, the oily dirt particles entrapped by soap micelles get dispersed in water and the clothes get cleaned.
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Soaps are prepared by treating the esters of fatty acid with alkali. Sometimes common salt is also added to it. Why is common salt added during this process?All In One Science
Have you ever observed while cleaning cloth that foam is formed with difficulty and an insoluble substance (scum) remains after washing with water? This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. Hence, you need to use a larger amount of soap. This problem is overcome by using another class of compounds called detergents as cleansing agents. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.
(i) How will you test the hardness of water?
(ii) Why soap forms scum (insoluble substance) with hard water?
(iii) How one can overcome the problem of scum formation? What values do you identify in this context?All In One Science