Preparing Homemade Soap

This lab can be used with an IPC class or a chemistry class in conjunction with studying acids and bases.

• observe the saponification process
• compare a homemade soap with a commercial soap
• expand lab skills

BACKGROUND

People have been using soap to clean their clothes and themselves for a relatively short time.  As recently as 1850, bathing regularly was not a common practice.  Homemade soaps were harsh, and manufactured commercial soaps were expensive, costing five times the price of a quart of milk.

Early soaps were produced by using the same procedure you will use. The process, known as saponification, involves the hydrolyzing of ester bonds in triglycerides (fats) with metal hydroxides such as NaOH or KOH. The early source of the hydroxide was a solution made from soaking ashes in water and the source of the fat was lard from animals and general kitchen fat.

Finer commercial soaps were prepared by varying the kinds of fat. The reaction occurs when the large triglyceride molecule is broken into four smaller parts by the sodium hydroxide. Three of these smaller molecules are soap molecules and the other is a glycerol molecule, which keeps the soap moist.

The key to understanding how a soap possesses cleaning power is found in examining the molecular structure of soap. The soap has a nonpolar hydrocarbon end that is attracted to the nonpolar grease or oil. The other end is polar and is attracted to water. This allows a soap to dissolve in both water and nonpolar substances. So, the soap surrounds the grease or oil with its nonpolar end (emulsifies) and the other end is picked up by the water and washed away.

In this experiment, you will saponify the fat of your choice and examine the properties of your product, then compare this to a commercial soap you have around the house.

MATERIALS

PROCEDURE

1. Prepare 20 grams of the fat of your choice by melting away any solid fat.
2. Allow the mixture to cool to about 45o C.
3. Heat a mixture of 20 mL of 6 M NaOH and 20 mL of ethyl alcohol to about 35o C.
4. When the ingredients are at the proper temperatures, slowly pour the NaOH solution into the melted fats while stirring constantly with the plastic spoon.
5. Stir until the saponification reaction is complete. This process should take about 5 - 10 minutes and produce a thick substance.
6. If you wish to add a scent to your soap, add about 1 mL of any essential oil, ground cloves or cinnamon at this time.
7. Pour the soap slowly and evenly into a mold.

Allow the soap to set for 1 - 3 days.

Notice the sudsing action of your soap when washing out the beaker.

SAFETY

• ALWAYS wear safety goggles for this lab.
• NaOH is corrosive and can cause severe burns.
• Ethanol is flammable and should be kept away from flame.