Preparation of Soap by Lipid Saponification
Introduction
Soaps are molecules containing a very long alkyl group, which is soluble in non-polar
substances (fats and oils), and an ionic end (the salt of a carboxylic acid), which is
soluble in water.
The cleaning action of soaps results from their ability to emulsify or disperse waterinsoluble materials (dirt, oil, grease, and so on) and hold them in suspension in water.
This ability comes from the molecular structure of soap. When soap is added to water
that contain oil or other water-insoluble materials, the soap surrounds the oily dirt
particles. The alky group, the long hydrocarbon chain, dissolves in the oily dirt, while
the ionic end dissolves in water. In simple terms the “oily” hydrocarbon end of the soap
attaches itself to the oily dirt particles. By surrounding the oily dirt particles the soap
makes the only the ionic water-soluble end expose to the water. As a result and new
compound is formed that can be dissolved easily in water. The oily particles are
dispersed throughout the water and may be rinsed away.
Experiment Procedure: The Preparation of Soap
Soaps are prepared by the alkaline hydrolysis (saponification) of fats and oils
This reaction, the basis of the soap industry, also provides a commercial source of
glycerol that is useful as antifreeze and as a tobacco moistening agent and is necessary in
the manufacture and production of nitroglycerine.
Part I: The Production of Soap
Procedure
Safety Alert: The dilute sodium hydroxide solution is corrosive and will vigorously attack
human tissue. Wash any contacted area of the skin with cool water. Inform your
instructor if your eyes are involved.
1. Put 2.0 ml of vegetable oil and 3.0 ml of dilute (6 M) sodium hydroxide solution
(NaOH) into a 100 ml beaker.
2. Cover the beaker with a watch glass and carefully boil the contents over a low
flame of a Bunsen burner or electric hot plate. There will be a significant amount
of spattering inside the beaker, and steam will escape from the pouring spout of
the beaker. Make certain the spout is directed away from you or your lab
partners. The boiling rate is more easily controlled if you hold the Bunsen burner
in your hand and direct the flame against the bottom of the beaker as needed to
maintain a steady but slow rate of boiling. Changing the heat setting on the
electric hot plate can make similar adjustments.
3. Heat the beaker until most of the water has evaporated and the contents are the
consistency of a thick foam (approximately 3 to 5 minutes). Take care not to char
the contents.
4. After heating is completed, remove the heat source and allow the beaker to cool
for 10 minutes before you remove the watch glass.
5. While the breaker is cooling, prepare a concentrated solution of sodium chloride
by mixing together 15 grams of sodium chloride (NaCl) and 55 ml of distilled
water. Stir the mixture to dissolve the solid.
6. After the heated beaker is cool, add 20 ml of the sodium chloride solution
prepared in Step 5 to the beaker. Loosen the solid in the beaker by stirring with a
spatula. Stir the mixture well, but do not beat it into froth. Decant the liquid from
the solid. Use a wire screen to keep the floating soap from leaving the beaker.
Dispose of the decanted liquid in the sink.
7. Repeat Step 6 again. Then, add the final 20 ml of sodium chloride solution and
stir, but this time filter the mixture through the funnel lined with 2 or 3 layers of
cheesecloth and allow the solid soap product to collect in the cheesecloth.
8. Remove the cheesecloth from the funnel and twist it into a ball to remove excess
liquid for the soap. Save the soap product for use in Part II: The Properties of
Soap.
Part II: The Properties of Soap
A. The Emulsifying Properties of Soap
As a result of soap’s molecular structure, soap is capable of emulsifying or dispersing
oil and similar water-insoluble substances.
Procedure for the Testing of Emulsifying Properties
1. Prepare a soap solution by dissolving about 1 gram of your soap product in 60 ml
of boiling water. This solution will be used throughout Part II.
2. Place 4 drops of mineral oil into each of two separate 15 cm test tubes.
3. Add 5 ml of distilled water to one test tube, 5 ml of the soap solution to the other
test tube.
4. Shake both tubes vigorously for 1 minute.
5. Observe the degree of oil emulsification in each tube as indicated by the presence
of suds and the absence of oil droplet in the liquid, or the absence of oil scum on
the inside of the test tube.
6. Record your results in Table A of the Data and Report, Using the following scale:
 = good emulsifier;  = fair emulsifier;  = poor emulsifier.
7. Dispose of the test tube contents in the sink.
B. The Behavior of Soap in Hard Water
The sodium and potassium salts of most carboxylic acids are water-soluble.
However, the calcium, magnesium, and iron salts are not. Thus, when soaps are
placed in hard water that contains such ions, an insoluble, curdy solid forms.
Most of us have seen these results in the form of a bathtub ring. This process
removes soap ions from solution and decreases the cleaning effectiveness of
soaps.
Procedure for Testing Soap in Hard Water Conditions
1. Place 5 ml of soap solution in each the three 15 centimeter test tubes.
2. Add 2 ml of 1% calcium chloride (CaCl2) to one soap-containing test tube.
Repeat this process, using 1% magnesium chloride (MgCl2) and 1% iron chloride
(FeCl3) solutions.
3. Mix the contents by inverting each tube and note whether or not a precipitate
forms. Indicate the amount of precipitate by the following scale:  = very large
amount of precipitate;  = large amount of precipitate;  = little or no amount of
precipitate.
4. Record your results in Table B.
5. Add 4 drops of mineral oil to each test tube and shake the mixture vigorously.
6. Observe and record (Table B) the emulsifying ability of the soap solution in each
of the test tubes as indicated primarily by the amount of suds formed. Use the
Following scale:  = heavy suds;  = light suds;  = little or no amount of suds.
7. Dispose of the test tube contents in the sink.
C. Alkalinity of Soap
Soaps undergo a hydrolysis reaction in water. As a result, soap solutions tend to be
alkaline.
Procedure for testing the pH of the Soap Solution
1. Test a small sample of your soap solutions with red litmus paper. Record the
results in Table C.
2. Test a small sample (20 drops) of your soap solution by adding 2 or 3 drops of
phenolphthalein indictors. Phenolphthalein is pink at a pH higher than about 8 on
the pH scale.
Data and Report Sheet
Properties of Soap Solution
Table A: Emulsifying Properties
Test Tube Contents
Emulsifying Ability
Oil and Water



Oil and Soap Solution



Table B: Behavior in Hard Water
Test Tube Contents
Amount of Precipitate
Soap Solution and CaCl2



Soap Solution and MgCl2



Soap Solution and FeCl3



Test Tube Contest
Emulsifying Ability
Soap Solution and CaCl2 plus oil



Soap Solution and MgCl2 plus oil



Soap Solution and FeCl3 plus oil



Table C: Alkalinity
Soap Solution
Reaction to red Litmus
Reaction to Phenolphthalein
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Questions
1. In an ion-exchange water softener, hard water ion such as Ca2+, Mg2+, and Fe3+
are replaced by sodium ions, Na+. How do the added Na+ ions influence the
behavior of the soap?
a. Na+ ions decrease their cleaning effectiveness
b. Na+ ions increase their cleaning effectiveness
c. Na+ ions have no effect on the cleaning effectiveness.
Explain your Answer:
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2. The soil found in most dirty ovens consists primarily of fats or oils. Some
popular oven cleaners are solutions of strong base. After the cleaner is applied, it
is allowed to sit for some time. Much of the baked-on grease and oil then wipes
away because it has been partially converted into which of the following?
a. Soap
b. An acid
c. Carbon
d. Carbon Dioxide gas
e. Sugar
Explain your Answer:
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