Soap Making Lab

Introduction: Soap-making is an age-old, relatively simple process. In this laboratory activity, “homemade” soap will be prepared, then tested to determine its pH and to see how well it lathers and cuts through grease. These properties of the “homemade” soap will be compared to those of a commercial soap sample to see how well it performs.

Background: One of the organic chemical reactions known to ancient man was the preparation of soaps through a reaction called saponification. Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap. Once the saponification reaction is complete, sodium chloride is added to precipitate the soap. The water layer is drawn off the top of the mixture and the glycerol is recovered using vacuum distillation.

Materials:

Olive oil
Peanut oil
Calcium chloride solution, 0.1 M, CaCl₂, 20 mL
Commercial soap sample, 2g
Ethyl alcohol, 95%, CH₃CH₂OH, 25 mL.
Sodium chloride, NaCl, 25 g
Sodium hydroxide pellets, NaOH, 2.5 g.
Water, distilled or deinonized, 300 mL.
Water, tap, 300 mL.
Hot plate
PH paper test strips, 2
Ruler
Stirring rod
Stoppers, to fit the test tubes, 2
Test tubes, 16´ 125 mm, 2
Test tube rack
Thermometer
Vacuum filtration apparatus
Watch glass
Weighing dish

Safety Precautions:

Ethyl alcohol is a flammable liquid and a dangerous fire risk. Addition of denaturant makes the product poisonous-it cannot be made non-poisonous. Sodium hydroxide is a corrosive solid; skin burns are possible. Considerable heat is evolved when sodium hydroxide pellets are added to water. It is very dangerous to eyes; wear eye protection plus gloves when handling and using sodium hydroxide. Do not use the soap prepared in this lab to wash hands because it may contain excess base which is severely corrosive to the skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Procedure:

1. Prepare a water bath by filling a 600-mL beaker about half full with tap water. Place this beaker on a hot and bring the water to a temperature of about 80-85⁰C. This will be the warm-water bath.

2. Prepare 150 mL of ice-cold water by placing 150mL of distilled or deionized water in a 250-mL beaker. Partially submerge this beaker in a large container of ice water ( the ice bath) and allow the water to cool until step 8.

3. Prepare a 25% sodium chloride solution by adding 25g of sodium chloride to 100mL of cool distilled or deionized water in a 400-mL beaker. Submerge this beaker in the ice bath prepared in step 2 and allow it to cool until step 8.

4. Add 2.5g of sodium hydroxide pellets to 25mL of 95% ethyl alcohol in a 125-mL Erlenmeyer flask. Swirl the flask to get as much of the sodium hydroxide to dissolve as possible, but most of it will not dissolve.

5. Add 5mL of oil to the 125-mL Erlenmeyer flask and swirl.

6. Submerge the flask in the warm-water bath and heat it for 20 minutes. While heating, stir the solution frequently with a stirring rod. Watch the flask carefully to make sure that it does not boil over. Turn down the temperature of the hot plate if necessary to prevent the contents of the flask from boiling over into water bath.

7. While the flask is heating, set up the vacuum filtration apparatus.

8. After heating the flask for 20 minutes and once a white soapy film has developed, pour the contents of the flask into the cooled 25% sodium chloride solution. Leave any remaining sodium hydroxide pellets behind in the flask. Stir this mixture vigorously. Submerge the beaker in the ice-bath and allow it to cool to room temperature.

9. Collect the precipitate by vacuum filtration and wash it three times with the ice-cold water from step 2. Observe the physical characteristics of your soap such as color, texture, and smell. Record your observation

10. Allow the filtered soap to air-dry overnight. Observe its physical characteristics again after drying. Record your observations.

11. Observe the physical characteristics of a commercial soap sample. Record your observations.

Analysis:

Test 1: Determination of pH

12. Place about 0.5g of your soap sample into a test tube labeled “homemade soap.” Use forceps to handle the soap sample until the pH has been determined.

13. Place about 0.5g of a commercial bar soap into a second test tube labeled “ commercial soap.”

14. Add 10 mL of distilled or deionized water to each test tube and stopper the test tubes. Shake both tubes to dissolve the soap in the water.

15. Immerse a stirring rod into each test tube. Remove the stirring rod and touch the wet end of the rod to a strip of pH paper.

16. Compare the resulting color to the chart on the container of pH paper to determine the pH of the solution. Record the pH of both samples. Note: If the pH of the soap sample is above the pH of the commercial soap sample, do not handle the soap with your bare hands for the remaining test. Instead, use forceps to handle the soap.

17. Save these soap solutions for test 2

Test 2: Lathering ability

18. Use the same samples used in test1.

19. Stopper both test tubes and shake each one vigorously 25 times. Record your observations of the lathering abilities. Allow both test tubes to sit until the liquid below the soap bubbles appear clear (about one minute).

20. Record the amount of lather formed by measuring the height of the lather in cm above the water with a ruler.

Test 3: Behavior in “Hard” water

21. Place about 0.5g of your soap sample into the test tube labeled “homemade soap”

22. Place about 0.5g of a commercial bar soap into the test tube labeled “ commercial soap”

23. Add 10 mL of a 0.1 M calcium chloride solution to each test tube and stopper the test tubes. The calcium chloride solution is similar to “hard” water.

24. Shake each test tube vigorously 25 times. Record your observations.

Test 4: Ability to cut through grease

25. Drip about 1 mL of oil onto a watch glass with a pipet. Rub the oil on the watch glass with a cotton swab.

26. Hold the watch glass over the sink or a large beaker. Using a pipet, rinse the watch glass with water. Allow the water to run down the watch glass in an attempt to rinse the oil. Record your observations.

27. Rub a small piece of homemade soap on the watch glass. Again run water over the watch glass to rinse the oil/soap mixture. Record your observations. Note: If the pH of your soap sample was above the pH of the commercial soap sample, use forceps to handle the soap.

28. Repeat steps 25-27, this time using the commercial soap sample to clean the watch glass. Record your observations.

Questions: Provide answers on a separate sheet of paper

1. Based on your data, does the homemade soap behave like the commercial soap sample? How is it similar? How is it different?

2. Compare your homemade soap to a soap that was made from a different oil by a different group. How do these soaps compare?

3. Why do soaps made from different oils have different properties, even if the properties are slightly different?

4. Generate a list of properties that are important when buying a commercial soap product. (Hint: Think of what brands you buy and why you buy them.)

5. Do you think your homemade soap would sell as is? Why or why not?

6. If your goal (as a soap chemist) is to make a soap that is marketable and appealing to the general public, what changes would you make to your “homemade” soap?

Name:

Data Tables

Observations of Soap Sample

	Commercial Soap	Homemade Soap
Smell
Color
Texture
Other observations

Test1: Determination of pH

	Commercial Soap	Homemade Soap
pH