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Saponification
Problem
How is soap made? How does soap clean soiled articles? How does soap made in the laboratory compare to
commercially-prepared soap?
Introduction
Soap is something that we regularly buy in the grocery store and use daily. This was not always the case.
Queen Isabella of Spain (1451 - 1504) claimed that she had bathed twice in her entire life, once when she was
born and again on her wedding day. Queen Elizabeth I of England (1558 - 1603) took a bath every three
months whether she ”needeth it or no”. Cleopatra, the beautiful queen of Egypt bathed in fragrant oils. The oils
softened her skin, and the perfumes were needed to camouflage the odors produced by the bacteria on her skin.
Soap was known in ancient Rome – a soap factory was revealed among the ruins of ancient Pompeii – but this
soap was too harsh to use on skin.
The use of soap and water as we know it began in London when people realized that poor personal hygiene was
part of the cause of cholera and typhoid epidemics. In 1846, the British government passed a Public Baths and
Wash Act. It provided public baths and laundries for the working class of London. The idea rapidly spread
throughout Europe and the United States.
Soap is produced when a fat (or oil) is mixed and heated with sodium hydroxide, commonly known as lye, in a
chemical process called saponification. Solid soap is the sodium salt of a fatty acid. Soft soap is a mixture of
soap and glycerol. Liquid soap is the potassium salt of a fatty acid.
In this experiment you will synthesize soap and then analyze its properties through several different chemical
tests.
Work in these concept terms/definitions into your introduction.
Concepts: saponification reaction, chemical synthesis reaction, sodium hydroxide, ethyl alcohol, alkaline,
neutralize, soap, fat-lard-or oils, hard water, calcium chloride, precipitate, emulsifying agent, disperses,
suspension, micelles polar compounds, nonpolar compounds, phenolphthalein,
Prelaboratory Assignment
 Read the Introduction and Procedure before you begin.
 Answer the Prelaboratory Questions.
1. You will prepare a sodium hydroxide solution in this experiment. If 8.0 grams of NaOH are
dissolved in enough water to make 25.0 mL of solution, what is the molarity of that solution?
M(mol/L) = moles of solute/Liter of solution
2. Why are many organic molecules nonpolar and, therefore, not water soluble? What property of a
soap molecule gives it an affinity for water?
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Materials
Apparatus
Spatula or spoon
250-mL beaker
10-mL graduated cylinder
Heating unit
Stirring rod
3 small test tubes (13 x 100mm) and stoppers
Test tube rack
Safety goggles
Lab apron
Centigram or milligram balance
Disposable pipets
Reagents
Oil or fat (choose one)
Cottonseed oil
Coconut oil
Tallow
Lard
Vegetable shortening
Ethyl Alcohol
Solid NaOH pellets
Phenolphthalein
Commercial soap
Commercial detergent
0.5 M CaCl2 solution
Safety
1. Wear safety goggles and a lab apron at all times in the laboratory.
2. No food or drink is allowed in the laboratory at any time.
3. Be very careful when heating the soap mixture and especially when adding the ethyl alcohol. Ethyl alcohol
is flammable.
4. Sodium hydroxide is caustic. Be careful not to get it on your skin or clothing.
Procedure
Part 1
Making the Soap
1. Weigh out 15-20 g of your selected oil or fat. Transfer it to a clean 250 mL beaker.
2. To the beaker add 7-8 grams of solid sodium hydroxide pellets and 25 mL of tap water.
3. Measure 10 mL of ethyl alcohol using a graduated cylinder. Add this to the 250 mL beaker
containing the fat and NaOH solution.
4. Heat the mixture carefully on the heating unit, stirring it constantly for at least 20 minutes. The solution
should be hot but not boiling. As you heat carefully drip in 10 mL of additional ethyl alcohol. Note: If you
are using a flame for heating be careful to keep the alcohol away from the flame. As the mixture is heated,
it will bubble and foam. Be careful to regulate the burner by
moving it as necessary to prevent the mixture from overflowing.
5. At the end of 20 minutes, add 25 mL of water and continue heating and stirring for an additional 10 minutes.
Allow the mixture to cool.
6. Remove the coagulated soap mass with a spoon or spatula. Place it on several layers of paper towel and pat
it dry. Using the towel, shape it into a bar or a ball. Observe and record its appearance and smell.
7. Allow the soap to air dry until the next laboratory session.
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Part 2
Testing the Soap
1. Place 5 mL of water in each of three test tubes. Add a small portion of your soap to the first test tube.
Stopper the tube and shake vigorously to test the foaming action of your soap. Repeat this process using
commercial soap in the second test tube and commercial detergent in the third test tube. Record your
observations. Clean out the test tubes. Measure the height of the foam the soap created.
2. Place 5 mL of water in each of three test tubes. Add 8-10 drops of vegetable oil to each tube. Note that the
oil forms a separate layer on top of the water. Stopper and shake the first tube. Allow the tube to stand for a
few minutes and observe again. Add a small portion of your soap to the first test tube. Stopper the tube and
shake. Allow the tube to stand a few minutes. Record your observations. Repeat this process using
commercial soap in the second test tube and commercial detergent in the third test tube. Record your
observations. Clean out the test tubes. Measure the height of the foam the soap created.
3. Place 5 mL of water in each of three test tubes. Add a small portion of your soap to the first test tube.
Stopper the tube and shake to dissolve the soap. Add 10-15 drops of CaCl2 solution to the soap solution.
Shake and record the results. Repeat this process using commercial soap in the second test tube and
commercial detergent in the third test tube. Record your observations. Clean out the test tubes. Measure
the height of the foam the soap created.
1, 2, & 3 create a data table and graph to show the results of the foaming action.
4. Place 5 mL of water in each of three test tubes. Add a small portion of your soap to the first test tube.
Stopper the tube and shake to dissolve the soap. Add 2-3 drops of phenolphthalein indicator solution.
Shake and record your observations. Repeat this process using commercial soap in the second test tube and
commercial detergent in the third test tube. Record your observations. Clean out the test tubes. Note the
color change if any.
Cleaning Up
1. Dispose of the soap in the solid waste container.
2. Clean out the test tubes as directed by your teacher. Wash all glassware and return it to its proper location.
3. Wash your hands thoroughly before leaving the laboratory.
Analysis and Conclusions
Complete the Analysis and Conclusions section for this experiment and attach to the data chart and graph.
1. How do the sudsing actions of the soaps and detergent compare?
2. How do the oil breakup capabilities of the soaps and detergent compare?
3. Calcium chloride releases calcium ions into the water. This makes the water ”hard”. How do the results of
the soaps and detergent compare in hard water?
4. How do the pH values of the commercial soap and detergent compare with your soap? If phenolphthalein
turns pink that means a base is present.
Create a data chart and graph that shows the results of the foaming action of your soap from part 2 (1, 2, &
3 only)
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Something Extra-Research
1. Check the labels of commercial soaps and detergents. Determine how they are different. What makes a
detergent a better choice for use in hard water?
2. Making homemade soap can also be done using lard and ashes from a fire. The ashes of burned wood
contain sodium and potassium oxides. What happens when these oxides react with water?
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