Soap is an anionic surfactant. Soap is the sodium or potassium salt of higher fatty acids (containing more than 15 carbon atoms), which is saponified by fatty acids and sodium hydroxide or potassium hydroxide. For example, stearic acid is saponified with sodium hydroxide or potassium hydroxide to make soap. The reaction formula is as follows: c 1 7h35cooh+NaOH → c17h35coona+H2O stearate sodium hydroxide stearate (sodium soap) water c17h35cooh+KOH → c17h35cook+H2O stearate potassium hydroxide stearate (potassium soap) Hard soap is fatty acid and sodium hydroxide (burning? ) saponification, so it is also called sodium soap. Soft soap is saponified by fatty acid and potassium hydroxide, so it is also called potassium soap, which is used in cosmetics. Sodium soap is often used in printing and dyeing, so the description in this section is limited to sodium soap. 2. As far as sodium soap is concerned, there are many kinds because of the different fatty acids used. Part of its raw material is stearic acid, that is, animal fat, such as butter and sheep oil, and its chemical structure is saturated fatty acid. Some use palmitic acid, which is roughly made of vegetable oils such as palm oil and olive oil and is an unsaturated fatty acid. Soaps widely available in the market are generally made of stearic acid, which can be used for scouring, dyeing and post-treatment in printing and dyeing. Soft fatty soap is of high quality and is generally used for fabric finishing.