Soaps and detergents
SOAPS ARE made by the process of saponification, where animal fat or plant oils are reacted with an alkali such as sodium hydroxide. Soaps are, therefore, the alkali metal (Na, K or Li) salts of fatty acids.
The oil or fat would represent the ester formed from the combination of glycerol with a fatty acid. When sodium hydroxide is added, the ester is hydrolysed to form glycerol, and the sodium ion replaces the hydrogen on the acid to form the sodium salt (a soap). If potassium hydroxide is used as the alkali, then a potassium salt (soap) would be formed.
E.g., Fat/Oil (Ester) + sodium hydroxide glycerol + sodium stearate (soap)
The process where the ester is broken down to form soap is similar to the hydrolysis reaction of esters.
Soapless detergents, on the other hand, are made from petroleum products treated with concentrated sulphuric acid. Here, crude oil is used instead of animal fats and vegetable oils.
HOW DO THE CLEANSING ACTION OF SOAP AND DETERGENTS DIFFER?
Soaps are not suitable for washing with hard water. Hard water contains dissolved ions (minerals) such as Ca2+ and Mg2+ which replace the sodium ion (Na+) in the soap molecule. This results in a precipitate called scum, which is insoluble and floats on the water surface. Using soap with hard water therefore reduces the cleansing action of the soap and results in loss, as more soap is needed to carry out the task. The presence of scum is also unsightly, as it sticks to clothes.
Detergents can clean effectively even in acidic mediums, as
they are made from the salts of strong acids (e.g., sulphuric acid). They are more soluble in water and have a stronger cleansing action. Unlike soap, less detergent would be needed as it is not being used up to form scum. The use of detergents would also result in conserving natural vegetable oils and animal fats, which can serve other purposes.
WHAT ARE THE ENVIRONMENTAL IMPLICATIONS OF USING SOAPS AND DETERGENTS?
Soaps are usually biodegradable since they are made from plant or animal products, while soapless detergents are nonbiodegradable products that can end up harming the environment. The phosphate levels in some of these detergents lead to pollution of water bodies as a result of nutrient enrichment. Nowadays, some detergents are made ‘phosphate-free’, which lessens their impact on waterways. Unfortunately, the fact that detergents are made from petroleum products will only serve to deplete these non-renewable resources.
HOW DO SOAPS/ DETERGENTS WORK?
The soap molecule has two ends: a head and a tail.
The polar part of the soap is hydrophilic (water-loving) and interacts with water, while the non-polar part is hydrophobic (water-hating) and interacts with the oil and grease. By this action, the oil is separated by the cleansing action of the soap.