Both soap and detergent are some type of salts. What is the difference between them?

Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water? List two problems that arise due to the use of detergents instead. of soaps.

Soaps are defined as the sodium salts of fatty acids Example:

C₁₇H₃₅COO^-Na⁺ Sodium stearate

C₁₅H₃₁COO^-Na⁺ Sodium palmitate

whereas detergents are sodium salts of a long chain benzene sulphonic acids. Example:

CH₃- (CH₂)₁₁ - C₆H₄ -SO3^- Na⁺

CH₃ – (CH₂)₁₀ – CH₂ – SO₄^– Na⁺

The action of soap in removing an oily spot from a piece of cloth is as follows:

When a dirty cloth having oily spot is put in water containing dissolved soap, the oil is not dissolved in water. The soap molecules are salts of sodium and potassium of long chain carboxylic acid. The acid end of soap is hydrophilic i.e. water loving , and gets dissolved in water and the carbon chain dissolves in oil. Soap molecules forms micelles structure in which one end of the soap molecule is attached to the oil droplet and the other end towards the water. The formation of soap micelles thus removes oil particles from the surface and the surface is cleaned.

If the water is hard, it reacts with calcium and magnesium ions which are present in hard water and results in formation of calcium and magnesium salts which doesn’t gives lather. The precipitate formed gets sticks to clothes and interferes in the cleaning of clothes. Therefore, soaps are not used for washing clothes when the water is hard.

The two problems that arise due to the use of detergents instead. of soaps

1. These are non-biodegradable substances and can’t be broken into simpler substances by microorganisms. They remain as such in the environment.

2. They creates pollution in environment and also harmful when eaten by any animal.