- The preparation of soap from fat and lye has been, historically, a household task. Only in the last century has the making of soap become a commercial undertaking. Our ancestors made soap by boiling animal fats with the lye obtained from leaching wood ashes. In this experiment, we will make soap by the same process, called saponification, but will use modern ingredients.
- In the process of making soap, animal fat, which is a triglyceride, is hydrolyzed by the action of a strong base, such as sodium hydroxide, and heat. The resulting products are soap and glycerol:
CAUTION: Safety goggles must be warn throughout this experiment. This lab is intended to be done in a school lab, with adult supervision. Sodium hydroxide is very caustic, and can cause severe burns to the skin, especially when hot.
- This is an investigative lab of the SAPONIFICATION process. If you wish to make soap in volume, search the web for a web page dealing with the making of soap as a craft.
MATERIALS NEEDED:
*80 ml of 6 Molar NaOH solution
15 grams of lard
75 ml of distilled water
**300 ml hot sodium chloride solution
100-ml graduated cylinder
Wire screen
Ring stand
Ring
Wire gauze
Burner
Tongs
Stirring rod
400-ml beaker
250-ml beaker* To make 6 molar sodium hydroxide, dissolve 19.2 grams of NaOH in enough water to make a total volume of 80 ml.
** This is just a saturated solution of NaCl.PROCEDURE:
1. Obtain 80 ml of 6 molar NaOH and 15 grams of lard, and place 40 ml of the NaOH solution and the lard in a 400-ml beaker.
2. Heat to boiling, on a standard ring stand set-up, then continue boiling the mixture over the lowest flame that will sustain the boiling process. Stir the mixture constantly to avoid spattering. If Spattering occurs, remove the flame and continue stirring the mixture. Replace the flame and continue heating after the spattering stops.
3. Continue boiling and stirring for about 20 minutes, or until it appears that most of the water has been evaporated. Then carefully add the remaining 40 ml of NaOH solution and continue boiling for an additional 20 minutes, or until most of the water has boiled off. DO NOT LET IT BOIL DRY.
4. As the crude soap cools, a waxy solid should form. Add to it about 25 ml of distilled water and about 100 ml of hot, saturated sodium chloride solution. Stir the mixture, breaking up lumps with your stirring rod. Decant the wash solution by pouring it through a wire screen, which will trap small soap particles.
5. Repeat the wash process twice. After the final washing, press the soap between two sheets of paper towlling to expel as much water as possible.
YOU HAVE MADE LYE SOAP.
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- In the process of making soap, animal fat, which is a triglyceride, is hydrolyzed by the action of a strong base, such as sodium hydroxide, and heat. The resulting products are soap and glycerol:
SAPONIFICATION
PREPARATION OF SOAP
INTRODUCTION: