Amazing Reaction: Soap and Detergent

Soap

Actually soap plays an essential role in our daily life. Soap is salt of compound known as fatty acid. Soap is formed from the reaction between an alkali and a fatty acid. Soap molecules consist of a long hydrocarbon chain, which composed of carbon and hydrogen with a carboxylic acid group. The carboxylic acid group is ionic bonded to a metal ion either a sodium or potassium. Soap is a sodium salt fatty acid if the alkali used is sodium, while for potassium salt fatty acid if the alkali used is potassium hydroxide.

Alkali + fatty acid → Sodium/potassium hydroxide (soap) + water

The general formula of soap is RCOO-Na or RCOO-K, while R is a long-chained alkyl group. The hydrocarbon end is nonpolar but is soluble in nonpolar substances such as oils and fats, while the ionic end, which made up of salt of carboxylic acid, is soluble in water. The most common used fats and oils are tallow, coconut oil and palm oil. Soap can actually prepared by heating fat or oil together with alkali through saponification, which is a hydrolysis process of ester by alkali. There are some example of soap sodium palmaitate [CH₃(CH₂)₁₄COO^-Na⁺], sodium stearate [CH₃(CH₂)₁₆COO^-Na⁺], sodium laurate [CH₃(CH₂)₁₀COO^-Na^-].

Detergent

Detergents are cleansing agents that are used together with water to remove dirt while soap and detergent are considered as two different materials. Detergent is a salt that is produced from the reaction between an alkali and a sulphonic acid. It is the sodium salt of sulphonic acid. Synthetic detergents are made from hydrocarbons that are obtained as by-products of petroleum. Example of detergent : sodium alkyl sulphate. The preparation of sodium alkyl sulphate detergent can be by neutralization reaction between an alkyl sulphonic acid with a hydroxide solution.

Soap VS Detergent

Soaps and detergents contain a surfactant as their active ingredient. This is an ionic species consisting of a long, linear, non-polar tail with a cationic or anionic head and a counter ion. While the tail is insoluble in water but the head is soluble in water. Therefore this make the surfactant molecules a wetting agent whereas the tail migrate to align themselves with water interface, which lowering the surface tension at the point so that it can penetrates the fabrics. In additions, it allows those oily particles to form an emulsion with the water. The tail of surfactant molecules surround those oily particle, thus micelle is form. The polar ends of the molecules are on the outside of cluster and the non-polar ends are in the middle.

There are some different between soaps and detergents. One of the different between soaps and detergent is that soaps cannot be used in hard water, which contains a higher amount of magnesium and calcium ions. This is because the magnesium and calcium ions will form a reaction with the soap anions, thereby forming a non-soluble precipitate known as scum. While detergent does not form scum in hard water because the hydrophilic end of the detergent will not form a ionic bond with the magnesium and calcium ions in hard water. Besides, detergent is more effective as compare to soap because detergent can form bubbles in both hard water and soft water.

As we know, both of soaps and detergent are very useful and important to us. But do you know that the content of chemical ingredients inside soaps and detergent can actually causing effect to us? Do you know what the chemical ingredients are? Commonly, sodium lauryl sulfate and sodium laurate sulfate are used in the soaps and detergent and even the shampoos. One of the reason choosing both chemical is because they are cheap. Both chemicals are very effective foaming agent or known as surfactants. The main causes of the effect are skin irritating, hormone imbalance, eyes irritation, protein denaturing and carcinogenicity. We will discover the effect in long term of using those chemical. Therefore try to use some organic or natural product of soaps and detergent to have a healthy lifestyle.

Reference :