Why Can’t Soap Cleanse Our Clothes?

Soap is the result of the mixture of potassium salts of fatty acids which is obtained from vegetable oils or animal fats and which is reacted with an alkali such as potassium hydroxide. This process of reacting the potassium salts of fatty acids with an alkali is known as saponification.

The saponification process is mostly practiced and performed for the making of soap industrially. This process involves the process of heating animal fats or vegetable oil and reacting with an alkali in order to give the result of soap and water mixed with glycerine. The another part of the process is neutralization of fatty acids with an alkali. The fats and oils are hydrolyzed with a high-pressure steam to produce fatty acids and glycerine. After that, the fatty acids is purified by distillation and neutralization with an alkali to yield soap and water.

If the alkali is sodium hydroxide, then, the sodium soap will be formed. Sodium soaps are made in solid form. Thus, they are also known as ‘hard’soaps. In contrast, if the alkali is potassium hydroxide, then, the soap formed will be smoother and is found in liquid form. This type of soaps is usually found in liquid-hand soaps and shaving cream. The carboxyl group present at the end of the soap molecule is attracted towards the water which is hydrophilic while the other end of the soap molecule which is a hydrocarbon chain is attracted to oil and grease which are non-polar substances rejected by water molecules. This end is known as the hydrophobic end.

Although,soap is a cleaning agent, the cleaning action of soap is affected by water hardness. Soap is proved to be less efficient in cleaning when dissolved in hard water. The water is labeled as hard water due to the presence of mineral salts such as Calcium ions and Magnesium ions which contributes to the formation of the insoluble precipitate also known as scum when soap reacts with these mineral salts. The scum formed on clothes makes the fabric stiff and thus causes a visible stain to deposit on clothes. Moreover, scum attaches to the internal parts of washing machines.

The reaction of soaps with hard water decreases the amount of soap present to be used for the cleaning action. However, if soap is let to react with soft water, the soil on stains and dirts on the clothes shows the presence of mineral salts which eventually reduces the effectiveness of soap in the cleaning action. Therefore, soap is inflexible to be used for laundry purposes, especially in a variety of fibres, washing temperatures and water conditions nowadays.