Preparation of Soap “Saponification” and the Study of Biological Fats
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 A: 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. Add about 15 mL 6M sodium (or potassium, whatever will be available) hydroxide solution: Caution: The solution will irritate the skin.
4. Return the 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 until the liquid appears gone (~15 minutes.); place it 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 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 cool.
7. Add 25 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 (see diagram) 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 25 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).
Procedure B: Comparing Commercial Soap with Yours
After the filtering process is done (~24 hours), remove the filter paper with the dry soap from the funnel. The process of making soap, saponification, is now complete. Using a sharp edge (ie scalpel, knife, razor blade), try to finely chop your soap into very small pieces.
Control: Using Commercially Prepared Known Soap
1. Dissolve a "pinch" of commercially prepared soap (flakes) in 5 ml of distilled water in a test tube. Label tube with tape “C” for control.
2. Add a four (4) drops of phenolphthalein solution (a pH indicator).
3. Shake the tube gently. A color change of “pink” will indicate that the solution is "basic".
Independent Variable: Using Pre-made Soap
4. Repeat 1-3 by dissolving a small portion of your soap in 5 ml of distilled water in a test tube. Label tube with tape “V” for variable.
5. Observe and record/describe the results of the Phenolphthalein Test here:
Hard Water Test:
Control: No Hard Water
1. Make a solution by dissolving a "pinch" of commercially prepared soap (flakes) in 15 mL of distilled water in a test tube. Label tube with tape “C-d-s” for control.
2. Shake the tube (thumb over top) 10 times. Note the results pertaining to the amount of bubbles produced because of your shaking.
Independent Variable: Using Hard Water
3. Make a solution by dissolving a "pinch" of commercially prepared soap (flakes) in 15 mL of hard water from the tap in a test tube. Label tube with tape “V-h-s” for variable. (Use 10 mL of distilled water with 6 drops of .1 M calcium chloride solution if water from tap is unavailable)
4. Shake the tube (thumb over top) 10 times. A reaction of a few bubbles being produced and a cloudy appearance is what your results should show.
5. Repeat 1-4 by making solutions from a small portion of your soap (using distilled water and then hard water). However, for the C-d-s label, call it, “C-d-h” and for the V-h-s label, call it, “V-h-h” (C = control ; V = variable / d = distilled; h = hard water tap / s = soap; h = homemade soap.
6. Observe and record/describe the results of the Hard Water Test here:
Vegetable Oil Test:
Control: No Soap
1. Obtain 10 ml of distilled water in a test tube. Label tube with tape “C” for control.
2. Using your graduated cylinder, add 5 ml of vegetable oil to the test tube.
3. Add 20 drops of Sudan IV (this will stain lipids red)
4. Invert the tube (thumb over top) 10 times.
5. Note the layering and staining affect of oil.
Independent Variable: Using Soaps
6. Repeat the procedure (1-5) above, but also place a "pinch" of commercially prepared soap flakes into the test tube. However, label it “S” for soap and for the next test tube, label it “H” for homemade soap.
7. Observe and record the results.
8. Repeat the procedure (1-5) above, but also place a small portion of your soap into the test tube.
9. Observe and record/describe the results of the Vegetable Oil Test here: