Caustic Chemicals Used in Soap Making

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Key Point.

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  • Caustic chemicals used in soap making: sodium hydroxide, potassium hydroxide.
  • The strong alkalis in soap do not harm the skin when they are sufficiently saponified with oils and fats.
  • Skin damage may be due to the roughness of the ingredients used in soap making.

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The main component of soap is the sodium salt of higher fatty acids, which is usually made by saponification of oils and fats with sodium (or potassium) hydroxide.

The only thing that makes soap is that NaOH or KOH is highly corrosive, but it is only raw material for soap; they are not present in soap (the saponification reaction has taken place); what is present is glyceryl stearate.

caustic chemicals used in soap making

Properties of Corrosive Chemicals

Sodium hydroxide (chemical formula: NaOH, alias caustic soda or lye).

A white crystal, at room temperature, is very corrosive. Quickly soluble in water, its aqueous service is highly alkaline and can transform phenolphthalein red and litmus option blue. Sodium hydroxide is an extremely typical antacid and of the essential drugs in the chemistry laboratory. Its remedy can be utilized as a washing-up liquid.

The remedy is a colorless and clear sodium alkali liquid, among the greatest bases, easily dissolves in water, response chemically with lots of natural and inorganic substances, is very corrosive and can burn human skin, and so on.

Sodium hydroxide is entirely ionized in water with sodium and hydroxide ions and can be neutralized with any protonic acid. Sodium hydroxide is one of the most important raw materials in manufacturing soap. A solution of sodium hydroxide is added to the oil and, in the right proportion, will certainly react and blend to make solid soap. This reaction uses the hydrolysis principle, and this kind of NaOH-catalyzed hydrolysis of esters is called saponification.

Sodium hydroxide will deliquesce when damp in the air. Sodium hydroxide is susceptible to deterioration in the air because of the encounter with airborne CO2.


Sodium hydroxide is utilized in a variety of production processes. In chemical manufacturing, sodium hydroxide offers an alkaline environment or is used as a stimulant. Waterdown solutions of NaOH are utilized as cleaning liquids in residential usage.

Potassium hydroxide (chemical formula: KOH, alias caustic potash).

White is strong, soluble in water and alcohol, yet insoluble in ether. Really hygroscopic as well as deliquescent in air, even more, responsive than sodium hydroxide. It can react with carbon dioxide to form potassium carbonate. So it will be made use of to soak up carbon dioxide.

It is strongly corrosive and typically made to make potassium carbonate. Strong potassium hydroxide is a white orthogonal crystal, offered in lumps and flakes, and gives off a great deal of heat when dissolved in water.

The Cleaning Principle of Soap

The molecular structure of soap can be divided into two parts. At one end is the polarly charged COO- (hydrophilic part), and at the other end is the non-polar carbon chain (lipophilic part). When the soap molecules enter the water, the polar hydrophilic part of the soap breaks the attraction between the water molecules. It reduces the surface tension of the water so that the water molecules are evenly distributed on the surface of the clothes or skin to be washed.

The oleophilic part of the soap penetrates deep into the oil, while the hydrophilic part dissolves in the water. After stirring, this combination forms smaller oil droplets, and their surface is covered with the hydrophilic part of the soap without regrouping into a large oil stain. This process, also known as emulsification, is repeated several times, and all the oil becomes very small droplets that dissolve in the water and can be easily rinsed away.

soap molecular structure


Sodium hydroxide and potassium hydroxide, used in soap making, are both strong bases and have strong corrosive properties. However, their alkalinity decreases because of the saponification reaction with oils and fats that turn them into soap. After 1-2 months, their alkalinity drops to even below 9, and they do not cause significant damage to the skin.

Generally speaking, commercially available soaps are made with industrial soda and normal-grade oils and fats, which take at least six months (in the case of industrial soda) to reduce their alkalinity. So in the quest for quicker soap production for sale, soap manufacturers add “artificial acids” to the soap ingredients to quickly neutralize the alkalinity, “artificial creams” to add moisturization, and “surfactants” to increase the lather. “However, these soaps with unnatural ingredients can affect the skin.

In the case of handmade soaps, the product should be left to dry for 6 to 8 weeks after it has been made and allowed to fully mature so that the fully saponified soap does not harm the skin.

Although sodium hydroxide and potassium hydroxide are caustic chemicals used in soap making, they do not affect human skin when reacted. However, for the health of yourself and your family, you need to choose a high-grade product when buying soap.

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Batte, H.D., Wright, A.J., Rush, J.W. et al. Phase Behavior, Stability, and Mesomorphism of Monostearin–oil–water Gels. Food Biophysics 2, 29–37 (2007). 

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