Life Science Curriculum 8-12
Submitted by: Renato O'Neal
Institution: Azusa Pacific University
Title of Experiment: Preparation of Soap From Animal Fat
250 mL Beaker (1)
Stirring Rods (2)
Ring Stand (1)
Wire Gauze (1)
Watch Glass (1) or Asbestos Pads
Bunsen Burner (1)
Suction Funnel (1)
20 mL100% Ethanol
20 grams Animal Fat
20% Sodium Hydroxide
100 mL Saturated Sodium Chloride
Scientific Background of Experiment:
Soap making is an art founded long ago. This experiment will help you understand how soap removes dirt, from clothing and skin. Soap contains ester, which can be reacted with lye (sodium hydroxide) to form glycerol and soap. Ester contains various long chain organic species containing hydrogen and carbon. These groups are non-polar because of the electro negativities of hydrogen and carbon causing them to be hydrophobic, as well as, lipophilic, but since soap contains CO2- molecules it is also hydrophilic.
Dirt is often held to skin or clothing by oils. This is where soap comes in, soap molecules burry their lipophilic ends into the oil, and their hydrophilic ends stick out. When water comes the hydrophilic ends are attracted to the water and are pulled off whatever surface it may be. With in these oil particles that are lifted, they contains negative ends that contain the oil particles to form into sphere. The spheres are then removed when rinsed. This is how soap works in taking off dirt form clothes and skin.
1. Prepare Bunsen burner. Attach hose to gas outlet, as well as, burner. Place ring stand approximately 2.5 inches above burner, then place wire gauze on top of ring stand.
2. Prepare a 250 mL beaker. Add 20 grams of animal fat to beaker. Then place 20 mL of 100% ethanol in beaker, also adding 25 mL of 20% sodium hydroxide to beaker. Stir for approximately 1 minute.
3. Heat mixture. Place beaker on top of wire gauze. (CAUTION: Ethanol burns vary easily, and may explode. Keep flame away from the top of the beaker.
4. Allow heating till foam reaches half way to the top to the beaker, or higher. No odor of ethanol should be present, and a pasty mass should from at the bottom of beaker (this contains your soap).
5. Add 100 mL of saturated sodium chloride to beaker and stir for approximately 1 minute. At this point the soap will precipitate out. Filter the soap through a suction funnel and wash soap two times with small quantities of ice water.
6. Use the soap to wash you hands.
Misc. Helpful Information/ Hints/ Suggestions:
Allow enough time for the solution to burn and good amounts of foam to form.
Carefully watch students when ethanol is burning, because beaker might explode.
In order to see if you created good soap, look and feel the soap for grease, if it feels greasy, then unreacted lard is present. If the soap feels slippery then sodium hydroxide is present and this may cause redness or roughening of the skin.
J. White, Laboratory Experiments for General Chemistry. Department of biology and chemistry Azusa Pacific University, July 1999.