CHEM 131 EXPERIMENT : SOAP MAKING (SOPANIFICATION)
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 (See chapter 18 of
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soap by adding an essential oil. You can purchase the scent you want to add or isolate it from
the natural source using a process of steam distillation (see ‘Natural Product Isolation’ procedure
at the end of this lab)
O
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O
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CH
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R 2COO- Na + + HO
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R 3COO- Na +
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R 2C
O
R 3C
Triglycerides
(Fat or Oil)
NaOH
saponification
or
hydroly sis
Carboxylic
acid salts
(Soap)
HO
Glycerol
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—.
The fats and oils that are most common in soap preparations are lard and tallow from animal
sources, and coconut, palm, and olive oils from vegetable sources. The length of hydrocarbon
chain and the 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. Soapmakers 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
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.
To Prepare for this lab:
The lab tech will supply some oils to use as well as some primitive molds but you may want to
purchase some ‘essential oil scents’ to add to your soap to make it more pleasant. You may also
want to purchase soap molds if you want your soap to have a fun shape.
You can buy essential oils and soap molds at Zenith Supply on 63rd and Roosevelt
http://www.zenithsupplies.com/
PROCEDURE—2 procedures are given. The first one is from a recommended soap making
website ‘Thesage.com’. This website will also give you ideas as to what oils to use and scents
(essential oils) that can be added. The second procedure is from an organic chemistry lab text.
You can do either one. Note that you can add an essential oil to scent your soap.
STANDARD PROCEDURE FROM THE ‘THE SAGE.COM’**

Note: wear gloves (and goggles of course) as sodium hydroxide is caustic.
Dissolve 3.25 g of sodium hydroxide in 8 mL of water in s 25 mL Erlenmeyer
flask. Swirl to help dissolve the solution. Set aside and allow cooling to room
temperature.

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.

Combine the sodium hydroxide solution and oils. Stir the mixture until it starts to
harden (about 15-20 minutes). Once the mixture 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.

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.

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 properly—the longer
you wait the less unreacted sodium hydroxide that will be present
** At thesage.com website you can determine the amount of sodium hydroxide to use by using
their ‘lye’ calculator. It’s based on using a 3:1 molar equivalence of hydroxide to triacyl
glyceride. You may also use any oil or mixture of oils you choose. Olive oil is known to work
fairly well.
PROCEDURE FROM ‘ORGANIC LAB TECHNIQUES’ PLK 2nd ed.
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. Wear Gloves, this is a very caustic solution!
Place about 10 g of lard (or oil of your choice) in a 250-mL Beaker and add the sodium
hydroxide solution to the flask. Heat the mixture to about 120 °C. Stir or swirl the Beaker
frequently.
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. Heat the mixture for a
total of 25 minutes.
Place 100 mL of saturated sodium chloride solution in a 250-mL beaker and transfer the
saponified mixture from the Erlenmeyer flask to the beaker. Stir the mixture while cooling the
beaker in an ice-water bath. Collect the prepared soap on a Buchner funnel by vacuum filtration
on filter paper (see pg 622 of your text). Wash the soap with two 40-mL portions of ice cold
distilled water to remove any excess sodium hydroxide. Continue to draw air through the filter
for a few minutes to partially dry the product. Allow the remaining sample to dry in your locker
until the next period and then weigh your product.
CHEM 131 LAB 7 (soap making) REPORT:
Name_________________________
Turn in report as a group
Due Monday Dec 13, lab checkout
1. (10 pts) Show your instructor your awesome bar(s) of soap.
Name ___________________________
Soap making lab
Pre Lab Questions- 5 pts: (Answers submitted individually at the beginning of
lab)
1)Write the balance equation for this reaction (use a C18 triaceylglyceride for you ‘oil’)
2) State what oil (or mixture of oils) that you will be using to make your soap