(a) What are soaps and detergents?

(b) Why do they differ in their actions ?

(c) Explain their cleansing actions.

(a) Soap — It is the sodium or potassium salt of an organic fatty acid. It reacts with hard water forming scum, which is why ordinary soap is wasted.

CaSO₄ + 2NaSt (soap) ⟶ CaSt₂ (scum) + Na₂SO₄

Detergents — They are the sodium salts of alkyl sulphonic acids. Detergents contain a sulphonic acid group (-SO₃H) instead of a carboxylic group (-COOH).

(b) Soaps reacts with hard water forming scum, which is why ordinary soap is wasted.

Detergents can lather even with hard water. Due to the solubility of their calcium and magnesium salts in water, they do not form scum.

(c) Soap or detergent molecules form clusters called micelles when dissolved in water. The molecules arrange themselves with their tails inward and their heads outward. During the cleansing process, the hydrocarbon tail of the detergent attaches to oil and dirt. When water is stirred, the oil and dirt separate into smaller fragments. This allows other tails to attach to the fragmented oil and dirt. The detergent molecules surround these small oil and dirt globules. The negatively charged heads in the water prevent the globules from recombining into larger aggregates. As a result, when clothes are rinsed with water, the oil and dirt are effectively removed.