Soggy soap
PHOTO: S.R. RAGHUNATHAN
Why do soaps, particularly washing soaps become soggy during rainy season?
S.G. ATHREYA
Chennai
Washing soaps are manufactured by the saponification of oils or fats with an alkali such as sodium hydroxide. During saponification the free fatty acids present in the oil, are neutralized and converted into their corresponding sodium salts.
In order to neutralize the fatty acids completely, a slight excess of alkali than its stoichiometric requirement is added.
Moreover, a sizable percentage of sodium silicates are also added in the washing soap, which serve as wetting agent as well as filler.
The alkali present in slight excess in the final product is hygroscopic in nature. Hygroscopy is the ability of a substance to take water molecules from the surrounding environment through either absorption or surface adsorption process.
Sodium silicates contain sodium oxide component, which can be easily hydrolyzed into sodium hydroxide in presence of moisture.
During rainy season or under higher humidity the alkali components become hygroscopic, which in turn leads to partial dissociation and/or precipitation of fatty acid components in the surface.
This makes the soap soggy.
Dr. M KANAGASABAPATHY
Assistant Professor, Department of Chemistry
Rajus’ college
Rajapalayam
Tamil Nadu
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