Saponification Introduction



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Saponification
Introduction:
Making homemade soap is as old as the American colonies. It was a necessary skill in the early history of the United States, but held on a as tradition the Appalachian region until quite recently. Even today, soap is still made by some but it is considered a home industry and is usually sold at craft fairs and flea markets to increase family income. From a chemical point of view, a soap is a metallic salt of a higher carboxylic acid. The most common soap is the sodium salt of stearic acid. Soaps are made by boiling oils or solid fats with solutions of either sodium hydroxide or potassium hydroxide. The process of soap-making is called saponification.

Materials/Equipment:
NaOH pellets 400 mL beaker thermometers

Distilled Water 250 mL beaker Styrofoam cup

Lard 50 mL graduated cylinder

crayons hot plate

stirring rods balance gloves

Procedure: Part 1: Making the Soap


  1. Place a weight boat on the balance and hit tare. Add enough lard until the mass reads ~50 grams. Then repeat this again with a second weight boat.

  2. Then transfer the 100 grams of lard to the 400mL beaker. You WILL LOSE some!

  3. Begin heating the lard gently on the stove (level 3 only). Add in a thermometer.

  4. Place a new weight boat on the balance and hit the tare button. Add approximately 14 grams of NaOH. Transfer these pellets to the 250 mL beaker.

  5. In a graduated cylinder measure out 46.0 mL of distilled water. Slowly add the water to the 250 mL beaker containing the NaOH. Stir carefully until the all the NaOH is dissolved. KEEP the stirring rod in the solution and ADD one of your thermometers to monitor temperature. CAUTION: This solution process is strongly exothermic! The beaker will become very hot. Avoid splashing or splattering.

  6. Choose the crayon or crayons to be used in the coloring process. Strip off all the paper around the crayon. Beware: The color may fade or become brighter in the heating process.

  7. When the lard is about 75 degrees C. (This high temperature is necessary to melt the crayon quickly), Add the crayon (break it up first) to the hot lard and allow the crayon to completely melt into the lard. Stir with a stirring rod and keep this stirring rod in the mixture to avoid contamination. Once the crayon has melted, take off it off the stove to cool.


  1. Allow the lard-crayon mixture to cool to about 55 degrees C. While this mixture is cooling, check the temperature of the NaOH solution. It should be about 40 degrees C. (If the NaOH solution has cooled too much, gently heat it until it is about 40 degrees C. If it is still too hot, allow it to cool to 40 degrees C).

CAUTION: Note the temperatures carefully since too high a temperature may cause boiling and splattering, while too low will result in an unacceptably slow reaction rate.
9. Once both solutions are at the proper temperature (55 degrees C for the lard/crayon mixture and 40 degrees C for the NaOH solution), carefully pour the NaOH solution into the lard in a thin stream, while slowly and steadily stirring the mixture.

10. Continue to stir slowly for about 10 to 20 minutes or until the soap is the consistency of honey.

11. Before the soap solidifies, pour the mixture into a styrofoam cup. Write the name of someone in your group on the cup and place it in the fume hood. Allow soap to stand for 24 to 48 hours.
Part 2: Analyze your Soap

10. Examine the soap. The appearance should be smooth and creamy. Test the TOP part of the soap by touching it with a strip of moist pH paper. Wearing gloves, remove the soap from the cup. Now test the MIDDLE and the BOTTOM of the soap with pH paper. Record all the pH colors and corresponding values.



11. The soap may be taken home IF it passes the pH test and washing test (Ms. Townsend only).
Data Table:

Part

Observations

Lard/crayon mixture




NaOH/water mixture



First 10 min of mixing the two solutions




Last 10 min of mixing the two solutions




After 3 days



pH of TOP




pH of MIDDLE




pH of the BOTTOM







Saponification

ASIM

Revised: 2/06



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