Explain the cleaning action of soap. Why does soap not work in hard water?
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Solution
Cleaning action of soap
A soap molecule is composed of sodium or potassium salt of a long-chain carboxylic acid.
It is divided into two parts: a lengthy hydrocarbon tail and a negatively charged head. The hydrocarbon tail is hydrophobic which means it is insoluble in water and repels water, but the polar end is water-soluble and hydrophilic.
Because dirt is non-polar, the polar end of the soap molecule dissolves in water while the nonpolar end connects it to the dirt molecule when applied to a wet dirty surface. Micelles are spherical clusters formed as a result of this process.
The hydrophobic tails of micelles reside in the center of the cluster, whereas the ionic ends are on the surface, ion-ion repulsion keeps the micelle in the solution as a colloid and prevents it from forming a precipitate. As a result, an emulsion is generated, which aids in the dissolution of debris in water before being cleansed with running water and because of the presence of Magnesium and Iron in hard water, soap does not perform.
So due to the presence of Magnesium and Iron in hard water, soap doesn't work in hard water
