Saponification

Introduction

The soaps that we use daily are, chemically speaking, salts of fatty acids. A fatty acid is made up of a hydrocarbonated chain of variable length, ended by a carboxylic acid functional group (-COOH). To produce soap, a mixture of fatty acids is be reacted with a base (a substance that captures protons, NaOH for example). The hydrogen atom of the carboxylic acid group is removed from the fatty acid, forming an anion. This anion will combine with the cation from the base in order to form the soap.

Since ancient times different sources of fatty acids have been used in the production of soap: animal fats, olive oil or other vegetable oils. These fatty acids are generally present in the form of triglycerides: three fatty acid chains are connected to a glycerol backbone. The reaction is then slightly different: the fatty acid chains separate from the glycerol backbone in a process called “transesterification”. Before the modern era, the substances acting as bases were generally ashes, soda or potash. The specific ingredients chosen, as well as their relative proportion, will influence the properties of the soap (hardness, cleansing, lather, and conditioning).

In this experiment, a mixture of vegetable shortening, and olive and coconut oils will be reacted with sodium hydroxide in a saponification reaction to produce soap. Milk, essential oils, and colorants will be added to improve the properties of soap.

Safety

DO NOT PIPET BY MOUTH. Use a pipetting aid. Carefully examine all glassware for cracks or chips. Ask for a replacement if you find any. Wear your safety glasses.

Prelab 

In our prelab notebook:

• Using a pencil, draw, by hand, the first 11 steps of the experimental procedure, using images and point form phrases. 
• Define hygroscopic.
• Construct a table containing olive and coconut oils, their melting points and their densities (use the Handbook of Chemistry and Physics).
• Construct a second table of the following fatty acids: linoleic acid, myristic acid, oleic acid, palmitic acid, stearic acid. Using the Handbook of Chemistry and Physics, provide their structures, include their melting point and their molar mass in the table.  Also, indicate whether the fatty acids are saturated, monousaturated or polyunsaturated. 
• Write a balanced equation that includes the chemical formulas and the structures of the reactants and the products of the saponification reaction. Use glycerol trioleate (an ester of oleic acid, sometimes called olein or triolein) and sodium hydroxide as the reactants.
  

Procedure

Record in ink directly in your lab notebook, in ink, all measurements (masses, volumes, temperatures, etc.). Use paper towels to protect your workstation from NaOH and fats.

1. In a 100 mL beaker, rapidly weigh 15.6 g of NaOH. Cover the beaker immediately with a watch glass as NaOH is hygroscopic! Immediately replace the lid on the bottle of NaOH. Perform this step in the fume hood because of the toxic fumes. 
2. Dissolve the NaOH completely in 35 mL of distilled water measured using a graduated cylinder. Mix thoroughly and let the solution cool. 
3. Tare a 600 mL beaker. Add 45 g of vegetable shortening and 30 g of coconut oil. 
4. Place the 600 mL beaker on a hot plate and melt the shortening and the coconut oil Stir with a magnetic stirring bar. Remove from the heating plate when the contents are liquid. 
5. Measure 35 mL of olive oil in a graduated cylinder and weigh. 
6. Add the olive oil to the liquid mixture of oils. Reweigh the graduated cylinder again to determine the mass of olive oil added. Before continuing, make sure that the reactants (NaOH and oil mixture) are almost at the same temperature, i.e. approximately 40-45°C. 
7. Add the NaOH solution gradually to the oil mixture, stirring constantly. Observe the saponification reaction.  The mixture should then take on a creamy and thicker texture. 
8. Measure 15 mL of milk in a graduated cylinder, and with stirring, add to the saponification reaction. Optionally, add a few milliliters of essential oils, colorant and any other desired ingredient. 
9. Grease two weighing boats with Vaseline and identify them. Weigh each one separately.
10. Transfer the soap to the weighing boats and let dry. 
11. Return to the lab at a later day and weigh the weighing boats containing the soap once again. 
12. Remove the soap from the weighing dishes and let dry completely.

Cleanup

Clean all other glassware with soap and water, and rinse well with tap water.  Once all the soap residue is gone, rinse once with distilled water.  There is no need to dry the inside of the glassware with a paper towel. Wipe the lab bench with moist paper towels, followed by a dry paper towel.