ChemLab #36 - Saponification, Making Soap
Date Submitted: Self-evaluation Score:   
Lab Group Members:
Introduction:   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 (lard), which is a triglyceride, is hydrolyzed by the action of a strong base (sodium hydroxide) and heat. The resulting products are soap and glycerol: CAUTION: Sodium hydroxide is very caustic, and can cause severe burns to the skin, especially when hot.

Materials:   80 ml of 6 Molar NaOH solution, 15 grams of lard, 300 ml hot sodium chloride solution, 100 ml graduated cylinder, wire screen, ring stand, ring, wire gauze, lab burner, large stirring rod, 400 ml beaker, 250 ml beaker
Pre Lab:
Prepare 6 molar sodium hydroxide: dissolve 19.2 g of NaOH in enough distilled water to make a total volume of 80 ml.

Prepare saturated solution of NaCl: dissolve 107 g of NaCl in 300 ml of distilled water (at room temperature).

Experimental Design:
  1. Place 15 grams of lard in a 400 ml beaker.
     
  2. Add 40 ml of the 6 M NaOH solution to the beaker. (Half of what you have prepared.)
     
  3. Heat to boiling − 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.
    CAUTION: clean up any splatter carefully − it is caustic!
  4. Continue boiling and stirring until MOST of the water has evaporated (about 20 minutes). DO NOT LET IT BOIL DRY.
     
  5. Carefully add the remaining 40 ml of NaOH solution and boil for an additional 20 minutes, or until MOST of the water has boiled off. DO NOT LET IT BOIL DRY.
     
  6. Remove the flame. As it cools, a waxy solid (the crude soap) should form. To wash, add about 100 ml of HOT saturated NaCl solution. Stir the mixture, breaking up lumps with your stirring rod.
     
  7. When most of the lumps have been broken up, decant the liquid (down the drain with running water).
     
  8. Repeat the wash process two more times.
     
  9. After the final washing, press the soap between two sheets of paper towel to expel as much water as possible.
     
  10. Press into "bar" shape and let dry.
     
  11. Clean and store ALL glassware.
Conclusion:     The bar of lye soap is your conclusion!