Soap [local] is made by reacting fats, such as stearol, with KOH to produce potassium stearate( or sodium stearate if NaOH is used). Sodium stearate is a salt formed by the reaction between fatty acid (stearol) and NaOH. Stearate is a deprotonated fatty acid having a negative charge. Part of the stearate is hydrophilic (mixing with water) and part of it is hydrophobic (mixing with nonpolar substances such as grease). Soap is rendered ineffective in hard water since calcium or magnesium ions form a precipitate with the stearate. Soap is a anionic surfactant i.e.the deprotonated fatty acid is negatively charged. Saponification is a process that involves the action of an alkaline substance such as NaOH on fat. In saponification the fat is first broken into glycerine and fatty acids. The fatty acids are neutralized to produce soap and water. In making soap it is important not to use too much lye or there will be lye in the soap which is very hard on the skin (and eyes). A saponification number is a conversion factor allowing calculation of the grams of lye needed for 1 ounce or 1 gram of a specific type of fat. Two labs are provided that provide directions on how to make soap under the experimental section. Information about the history of soap and soap making is in the history section.
