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MadSci Network: Edible/Inedible Experiments Archive

How to Make Soap

Area of Science: Chemistry
Meant for Grade 10-12 (age 15-17).
This experiment is inedible.
An adult should be present.

Overview:
Make soap from lard.

Equipment:

  1. Lard or some sort of fat.
  2. 6N Sodium Hydrozide (NaOH)
  3. NaCl / table salt
  4. Ethanol - alcohol
  5. Glass beaker and stirring rod.
  6. Bunsen burner or other means of heating solution.
  7. Mold for making soap bars.

Safety:
Gloves, labcoat and appropriate eyeware should be worn when handling the 6N NaOH. It should be used in a well-ventilated area, preferably in a fume hood. DO NOT BREATHE THE FUMES. Wash with vinegar should you get some on your skin (have some vinegar handy before starting the experiment) - DO NOT wash with water! (Thank you, Erick)

How to do the experiment:
1.Place 10 grams of lard (or any other fat, such as oil or butter) in a beaker

2.SLOWLY AND CAREFULLY (have an adult do this...this stuff is dangerous) add 15mL of 6N sodium hydroxide

3.Add 50mL of ethyl alcohol

4. Gently heat this mixture under low heat, stirring with a glass stirring rod until the base has completely reacted with the lard (about 20 to 30 minutes)

5.After all of the base has reacted, add 20mL of water and stir

6.Cool the mixture. Add 12g of sodium chloride (table salt) to 50mL of water. Pour the cooled mixture of base and lard into the NaCl mixture (not the other way around)

7. Let this new mixture cool completely. The solid cake that forms is the soap (whats left, if you do it out chemically, is glycerol)

Explanation:
From MadSci File 851500145.Ch:

Re: Information on soap

Area: Chemistry
Posted By: Samuel Conway, Senior Staff Chemist, Avid Therapeutics,Philadelphia, PA
Date: Tue Jan 14 18:30:32 1997
Message ID: 851500145.Ch

"Soap" is nothing more than the sodium salt of a long chain fatty acid:

                         CH3-(CH2)n-COONa
                          ^^^^^^     ^^^
                     'fatty part'   'water soluble' end
The idea behind it is that the hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Thus, it allows water to remove normally-insoluble matter.

I can't say that I am an expert on its history; however, if you are old enough to remember "The Beverley Hillbillies", Granny was always cooking "lye soap" by the ce-ment pond. She would boil lye (sodium hydroxide) and lard (animal fat) in a big pot. The mushy mass left behind, when dry, would congeal into soap which Jethro said would "take off the dirt and a little bit of skin, too." That was probably because Granny did not understand stoichiometry and put too much lye in it.


Experiment submitted on Tue Jan 28 03:30:14 1997 by:
Name: Jeremy Myers
Email: softlord@pobox.com
Institution: Urban Academy, NY
Position: Student


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