Question

What are the sodium salts of sulfonic acid?
(A) Soap
(B) Detergents
(C) Hard water
(D) Soft water

Answer 1

Hint: In the above question, it is asked which of the following options are sodium salts of sulfonic acid. For this, we have studied the composition of each substance. Sodium salts of sulfonic acid are hydrophilic groups which get attached to the dirt and make it soluble in water. They have cleansing property even in hard water.

Complete step by step solution:
Soaps are made from natural ingredients, such as plant oils (coconut, vegetable, palm, pine) or acids derived from animal fat. Detergents, on the other hand, are synthetic, man-made derivatives.
Soap and detergent molecules contain a hydrophobic (water-insoluble) part, such as a fatty acid or a rather long chain carbon group, such as fatty alcohols or alkylbenzene. The molecule must also contain a hydrophilic (water-soluble) group, such as $ {\text{ - COONa}} $ in case of soap or a sulfo group, such as $ {\text{ - OS}}{{\text{O}}_{\text{3}}}{\text{Na}} $ , $ {\text{ - S}}{{\text{O}}_{\text{3}}}{\text{Na}} $ or a long ethylene oxide chain in nonionic synthetic detergents.
Hard water is the water which contains appreciable quantities of minerals such as calcium and magnesium.
Soft water is water which contains only sodium ions.
Hence, we can conclude that detergents are sodium salts of sulfonic acid.
Hence, option B is the correct option.

Note:
Soap usually reacts with water. While detergents are free-rinsing which means they don’t leave a residue whereas soap needs a clear water wash after application or it will leave a film.
Hard water is the enemy of soap. In hard water conditions soaps form scum. This scum can deteriorate fabrics and eventually ruin clothes or other surfaces. However, detergents can work in any level of water hardness since they usually react less, as compared to soap, to the many minerals which are present in hard water.