Preparation of Soap “Saponification” and the Study of Biological Fats 2015





      How is soap made and used? The purpose of this lab is to make a small batch of soap, test the soap's properties, and related the soap to biological characteristics. Triglycerides may undergo hydrolysis and/or bond breaking via heat (i.e. boiling) both in basic and acidic solutions to produce fatty acids and glycerol. Hydrolysis of "triacylglyceride" in a base solution (making soap) is called saponification.  The Na+ salts of these, long-chain fatty acids are soaps.  The best soaps are those in which the fatty acid salt is saturated.  Potassium (K+) can be used as a Na+ substitute in the soap making process. Soaps and detergents are similar in that they both contain a long hydrocarbon chain and a highly ionic or polar end.  Calcium chloride (CaO2) in hard water may hinder the ability of soap in that the Ca++ may replace the Na+ and make the molecule less attracted to water (ie. Ca(C18H35O2)) and less effective as a cleaning agent; Ma++ has a similar effect. Soap's general characteristic is that it emulsifies or separates oily material from a watery environment and is basic due to the -OH or saponification process.  The ionic ends of soap are water soluble and thus attracted to water; while the hydrocarbon chain is not soluble in water and thus attracted to oil/dirt.  When water is used to rinse, the hydrophilic ionic end "drags" the oil/dirt with the water because it is also attached to the hydrophobic hydrocarbon chain that is attracted to the oil/dirt.  Indicators such as phenolphthalein will turn a basic solution red-pink.  The amphiphilic properties of soap can be found in the human body in the form of bile salts from the liver and phospholipids in cellular membranes. The hypothesis is that if soap can be made, then tests for "soap-like" characteristics can be performed to confirm the soap’s lipid-like qualities.




Procedure: Making the Soap


  1.  Weigh about 20 g of Crisco using an electronic scale.


  2.  Place the Crisco in a 250 mL beaker and heat slowly in order to melt the fat.  When fat is melted remove from burner for about 5 minutes.


  3. Wearing gloves and goggles. Using a 50 or 100 mL beaker, add about 20 mL 6M sodium (or potassium, whatever will be available) hydroxide solution: Caution: The solution  

      will irritate skin. Note: Clean the beaker right away after using it for the NaOH (KOH) with soap and water.


  4. Return the 250 mL beaker with the fat and hydroxide solution to the heat source and boil the mixture while stirring with a glass stirring rod.  Keep gloves and goggles on.


  5. Continue stirring for ~15 minutes or until the liquid appears to be gone; place heater on a lower setting towards the end of the boiling process.


      It is important to remain stirring to prevent "spattering".  “Foaming” is alright, just don’t let it foam too many times.


  6. Remove beaker from the heat (with glove hand) and allow to cool.  The soap is ready if it appears as a white granular semi-liquid material.  Wait for about 3-5 minutes to



  7.  Add 30 mL of 30% sodium chloride solution and break up any lumps with the glass rod. This will help remove remaining glycerol and excess sodium

       hydroxide (or potassium hydroxide); plus, insure that the fatty acids have Na+’s (K+’s).


  8. Place a funnel lined with filter paper onto the other 250 mL beaker.


  9. Decant "filter" the soap solution by carefully pouring it into the lined funnel and allowing the liquid to pass through.


10. Wash the soap one more time with 20 mL of 30% sodium chloride solution by pouring the solution onto the soap that is still in the filter lined funnel. Again, to remove

       remaining glycerol and excess sodium hydroxide (potassium hydroxide); plus, insure that the fatty acids have Na+’s (K+’s).