Integrated Science – Dr. May
Soap Making Laboratory
Soaps are made by reacting animal or vegetable fats or oils with sodium
hydroxide. Fats are called triglycerides and are chemicals made up of one molecule of
glycerine (glycerol) and three molecules of long chain fatty acids (C4 to C22).
Glycerol
HOCH2

HOCH2

HOCH2
Fatty Acid (Oleic Acid) (9-octadecenoic acid) (C18H34O2)
CH3(CH2)7CH=CH(CH2)7COOH
Fats are formed by the reaction between fatty acids and glycerol. The reaction
products between organic acids and alcohols are called esters.
Olive Oil (C57H105O6)
CH3(CH2)7CH=CH(CH2)7COOCH2

CH3(CH2)7CH=CH(CH2)7COOCH2

CH3(CH2)7CH=CH(CH2)7COOCH2
To make soap we react the fat with sodium hydroxide to break the fat apart to
produce the sodium salt of the acid and glycerol.
CH3(CH2)7CH=CH(CH2)7COOCH2

CH3(CH2)7CH=CH(CH2)7COOCH2

CH3(CH2)7CH=CH(CH2)7COOCH2
+
3 NaOH

3 CH3(CH2)7CH=CH(CH2)7COO Na+
Soap (C18H33O2Na)
This process is called saponification.
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HOCH2

HOCH2

HOCH2
+
Choose a recipe:
Recipe Number One (1)
Recipe Number Two (2)
50 grams coconut oil
29 ml 7.5 M sodium hydroxide solution
50 grams Crisco
22 ml 7.5 M sodium hydroxide solution
Recipe Number Three (3)
Recipe Number Four (4)
50 grams lard
22 ml 7.5 M sodium hydroxide solution
50 grams of olive oil
22 ml 7.5 M sodium hydroxide solution
Recipe Number Five (5)
Recipe Number Six (6)
50 grams peanut oil
21 ml 7.5 M sodium hydroxide solution
50 grams corn oil
21 ml 7.5 M sodium hydroxide solution
Recipe you choose
Number __________
Mass of your 100 ml reaction beaker
_________________ grams
Add 50 grams for your fat
_________________ grams
Mass of beaker plus fat
_________________ grams
Volume of 7.5 M sodium hydroxide
_________________ ml
The steps we will use in the laboratory to make soap will be as follows.
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2.
3.
4.
5.
6.
7.
Weigh the correct amount of fat into a 100 ml beaker
Place the beaker and fat onto a hot plate and heat to 55oC.
Using a 100 ml graduated cylinder, obtain the 7.5 M NaOH from Dr. May
Immediately pour the NaOH solution into the warm fat and begin stirring
Stir for the first 15 minutes then once each 15 minutes until it “traces”.
Label a plastic mold for your soap with your name and recipe number.
The soap should stay in the mold for 2-3 days and can be used in three weeks.
As you begin stirring the mixture, it will be thin and watery. As the ingredients
react, the mixture becomes thick and turns opaque. “Tracing” is a term describing
the thickness of the mixture. When a drop of soap from your stirring rod is dripped on
the surface it should leave a “trace” or little mound. You can also draw a small line
in the surface of the soap. If the line remains, the soap has “traced”.
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