Kristopher Caro
Saponification
Kristopher Caro
CHEM 3220 Experiment: Soap Making (Saponification)
In this experiment we prepare soap from animal fat (lard) or vegetable oil. Animal fats and vegetable
oils are esters of carboxylic acids; they have a high molecular weight and contain the alcohol, glycerol.
Chemically, these fats and oils are called triglycerides. The principal acids in animal fats and vegetable
oils can be prepared from the natural triglycerides by alkaline hydrolysis, called saponification. You
may also choose to add a scent to your soap by adding an essential oil. You can purchase the scent you
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saponification
or
hydroly sis
Triglycerides
(Fat or Oil)
Carboxylic
acid salts
(Soap)
HO
Glycerol
Figure 1: Chemical Process of Saponfication
The natural acids are rarely of a single type in any given fat or oil. In fact, a single triglyceride molecule
in a fat may contain three different acid residues (R1COOH, R2COOH, R3COOH), and not every
triglyceride in the substance will be identical. Each fat or oil, however, has a characteristic statistical
distribution of the various types of acids possible—.
1
Kristopher Caro
The fats and oils that are most common in soap preparations are lard and tallow from animal sources,
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number of double bonds in the carboxylic acid portion of the fat or oil determine the properties of the
resulting soap. For example, a salt of a saturated long-chain acid makes a harder, more insoluble soap.
Chain length also affects solubility.
Tallow is the principal fatty material used in making soap. The solid fats of cattle are melted with
steam, and the tallow layer formed at the top is removed. Soap makers usually blend tallow with
coconut oil and saponify this mixture. The resulting soap contains mainly the salts of palmitic, stearic,
and oleic acids from the tallow, and the salts of lauric and myristic acids from the coconut oil. The
coconut oil is added to produce a softer, more soluble soap. Lard (from hogs) differs from tallow (from
cattle or sheep) in that lard contains more oleic acid.
Tallow
CH3(CH 2)14COOH
CH3(CH 2)16COOH
Palmitic acid
Stearic acid
CH3(CH 2)7CH
CH(CH2)7COOH
Oleic acid
Coconut oil
CH3(CH 2)10COOH
Lauric acid
CH3(CH 2)12COOH
Myristic acid
Figure 2: Chemical Structures of Scented Oils
2
Kristopher Caro
Pure coconut oil yields a soap that is very soluble in water. The soap contains essentially the salt of
lauric acid with some myristic acid. It is so soft (soluble) that it will lather even in seawater. Palm oil
contains mainly two acids, palmitic acid and oleic acid, in about equal amounts. Saponification of this
oil yields a soap that is an important constituent of toilet soaps. Olive oil contains mainly oleic acid. It
is used to prepare Castile soap, named after the region in Spain in which it was first made.
Toilet soaps generally have been carefully washed free of any alkali remaining from the saponification.
As much glycerol as possible is usually left in the soap, and perfumes and medicinal agents are
sometimes added. Floating soaps are produced by blowing air into the soap as it solidifies. Soft soaps
are made by using potassium hydroxide, yielding potassium salts rather than the sodium salts of the
acids. They are used in shaving cream and liquid soaps. Scouring soaps have abrasives added, such as
fine sand or pumice.
3
Kristopher Caro
Supplies

Gloves

Goggles

Two Erlenmeyer flasks

Glass stirring rod

Two 250 mL beakers

Buchner funnel

Vacuum filtration system

Hot plate

Ice bath

Timer

8.25 grams of sodium hydroxide

28 mL of de-ionized water

35 grams of oil/fat
4
Kristopher Caro
Figure 3: Table of Supplies
5
Kristopher Caro
Procedure 1
Note: Wear gloves and goggles as sodium hydroxide is caustic.
1. Dissolve 3.25 g of sodium hydroxide in 8
mL of water in s 25 mL Erlenmeyer flask.
2. Swirl to help dissolve the solution.
3. Set aside and allow cooling to room
temperature.
4. In a beaker, add 25 grams of your oil (or
fat) and heat gently to about 40 ° C. If
using a fat it should be melted.
5. Combine the sodium hydroxide solution
and oils.
6. Stir the mixture until it starts to harden
(about 15-20 minutes). Once the mixture
Figure 4: Preparation of Erlenmeyer flask
starts to harden then stir for 5 minutes at 15 minute intervals. At the point when it starts
to harden you can also add any ‘essential oil’ ingredients to scent your soap.
6
Kristopher Caro
7. Once the soap is relatively firm (your
stir marks will remain for several
seconds) pour raw soap into your
prepared molds or keep it in the beaker.
After a few days the soap can be turned
out of the mold. If the soap is very soft,
allow it to cure for a few days to firm
the outside.
8. Eventually remove the soap and set the
bar out to cure and dry. This will allow
the bar to firm and finish saponification.
(This can actually take days to cure
Figure 5: Initial product of saponification
properly—the longer you wait the less
unreacted sodium hydroxide that will be present.
7
Kristopher Caro
Procedure 2
Note: Wear gloves and goggles, this is a very caustic solution!
1. Prepare a solution of about 5 g of sodium hydroxide dissolved in a mixture of 20 mL of
distilled water and 20 mL of 95% ethanol.
2. Place about 10 g of lard (or oil of your choice) in a 250-mL Beaker.
3. Add the sodium hydroxide solution to the flask.
4. Heat the mixture to about 120 °C.
5. Stir or swirl the Beaker frequently.
6. The soap often begins to precipitate
from the boiling mixture within about
20 minutes. If it appears that some of
the alcohol and water is evaporating
from the flask, you may add up to 10
mL of a 50% water/alcohol mixture to
replace the solvent that is lost.
Figure 6: Boiling the initial product
8
Kristopher Caro
7. Heat the mixture for a total of 25
minutes.
8. Place 100 mL of saturated sodium
chloride solution in a 250-mL
beaker.
9. Transfer the saponified mixture
from the Erlenmeyer flask to the
beaker.
10. Stir the mixture while cooling the
beaker in an ice-water bath.
11. Collect the prepared soap on a
Buchner funnel by vacuum
Figure 7: Lavender-scented product
filtration on filter paper.
12. Wash the soap with two 40-mL portions of ice cold distilled water to remove any excess
sodium hydroxide.
13. Continue to draw air through the filter for a few minutes to partially dry the product.
14. Allow the remaining sample to dry in your locker until the next period and then weigh
your product.
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Kristopher Caro
Soap Properties Experiment
Emulsifying Properties
1. Shake 5 drops of mineral oil in a test tube containing 5 mL of water. A temporary
emulsion of tiny oil droplets in water will be formed.
2. Repeat the same test, but this time add a small piece of the soap you have prepared before
shaking. Allow both solutions to stand for a short time.
3. Compare the appearance and the relative stabilities of the two emulsions.
4. Record your observations on the Report Sheet.
Hard Water Properties
1. Place about one-third spatula full of the soap you have prepared in a 50-mL beaker
containing 25 mL of water.
2. Warm the beaker with its contents to dissolve the soap.
3. Pour 5 mL of the soap solution into each of 5 test tubes (nos. 1, 2, 3, 4, and 5).
4. Test no. 1 with 2 drops of a 5% solution of calcium chloride (5% CaCl2), no. 2 with 2
drops of a 5% solution of magnesium chloride (5% MgCl2), no. 3 with 2 drops of a 5%
solution of iron(III) chloride (5% FeCl3), and no. 4 with tap water. The no. 5 tube will be
used for a basicity test, which will be performed later.
5. Record your observations on the Report Sheet.
Alkalinity
1. Test soap solution no. 5 with a wide-range pH paper.
2. What is the approximate pH of your soap solution? Record your answer on the Report
Sheet.
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Kristopher Caro
Report Sheet
Preparation
Describe the appearance of your soap.
Observation of the hard water reaction
No. 1 + CaCl2__________________________________________________________
No. 2 + MgCl2__________________________________________________________
No. 3 + FeCl3___________________________________________________________
No. 4 + tap water________________________________________________________
Alkalinity
pH of your soap solution (no. 5)
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Kristopher Caro
Post-Lab Questions
1. When you made soap, first you dissolved vegetable oil in ethanol. What happened to the
ethanol during the reaction?
2. What are the two main disadvantages of soaps versus detergent?
3. Soaps that have a pH above 8.0 tend to irritate some sensitive skins. Was your soap good
enough to compete with commercial preparations?
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Kristopher Caro
Works Cited
http://hoeggerfarmyard.com/the-farmyard/soap-making/
http://peanuthaymoe.wordpress.com/2013/04/09/soap-making-lab/
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Kristopher Caro
Index
beaker, 6, 7, 9, 10
flask, 6, 8, 9
oil, 1, 2, 3, 4, 6, 8, 10, 13
saponification, 1, 3, 7
soap, 1, 2, 3, 6, 7, 8, 9, 10, 11, 12, 13, 14
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