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Experiment_718_Making Soap - Saponification_1_1_1

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    Student Name 


    Laboratory Date: 

    Date Report Submitted: 



    Student ID 


    Experiment Number and Title 

    Experiment 718:  Making Soap - Saponification 



    Experiment 718:  Making Soap - Saponification 


    Section 1:  Purpose and Summary 


    Make lye soap from sodium hydroxide and olive oil via the saponification reaction. 



    Soapmaking is an ancient technique which includes the mixing of water, a solution formed from burned wood ashes and fats and/or oils.  The chemical reaction for soapmaking is called saponification.  The modern technique to form solid soap uses plant oils and/or animal fat and sodium hydroxide to form solid bars or potassium hydroxide to form liquid soap.  The saponification reaction breaks the oil or fat molecule into glycerin and a sodium or potassium salt of the long hydrocarbon chains that have a carboxylate end functional group.   


    There are many kinds of fats and oils, both animal and vegetable. Fats are usually solid at room temperature, but many oils are liquid at room temperature.  The physical state of these fats and oils depends on the degree of unsaturation in the molecule.  The more double bonds, the more likely the fat or oil will be a liquid at room temperature.  Liquid cooking oils originate from corn, peanuts, olives, soybeans, and many other plants. For making soap, all different types of fats and oils can be used – anything from lard which comes from animal fat to exotic tropical plant oils like palm and coconut oils. 


    In this lab, you will test various fats and oils for their degree of saturation by reacting any double bonds in the fat or oil with bromine.  Remember, that unsaturated carbon-carbon double and triple bonds can react with halogens to form halogenated hydrocarbons. 


    Addition Reaction Example: 

    Alkene or Alkyne + Br2  → Bromoalkane 



    Saponification Reactions:  

    Fat + Lye → Soap + Glycerol 



    Additionally, you will explore water that has a high concentration of dissolved minerals which is called hard water.  The minerals that can be part of hard water minerals can include calcium (Ca2+), magnesium (Mg2+), and/or iron(III) Fe3+ ions.  These dissolved ions make it harder for soap to make a lather and be effective in solubilizing fats and dirt and removing them from your skin.  These ions combine with the soap and precipitate into hard-water scum.  You can also see dissolved minerals when they precipitate on your sink and bath/shower components as a white precipitate called scale.  If your water comes from a water well, you may see this more often than if you get water from a municipal water source.  Some people get around this problem, by using a water softener which removes the ions in the water by replacing them with sodium ions (Na+). 


    Section 2:  Safety Precautions and Waste Disposal 


    Safety Precautions: 


    Be sure to exercise caution when dispensing the 9 M NaOH. If the chemical comes into contact with your skin, immediately rinse with water for a minimum of fifteen minutes and notify your instructor.  


    Personal Protective Equipment (PPE) required: safety goggles, lab coat, closed-toe shoes.   


    Waste Disposal: 

    After completing parts 1 and 2 of this experiment, rinse all glassware in the laboratory sink with soap solution and rinse completely with laboratory water. 


    After completing part 3, pour contents of test tubes into the organic waste container in the fume hood. 



    Section 3: Procedure 


    Part 1:  Making Soap 


    Materials: warm olive oil (preheated by instructor in crockpot), 9 M sodium hydroxide solution, stearic acid 


    Equipment: tall 250 mL beaker, stirring plate and magnetic stir bar, plastic disposable pipets, silicone soap mold 


    1.  Your instructor has a container of olive oil, preheated to 35°C, at a central location in a crock pot. Pour 100 ml of the warm oil into a tall 250 mL beaker.  Add a magnetic stir bar to the beaker. 

    2. Add 30 ml of 9 M sodium hydroxide solution to the beaker carefully and slowly to the beaker.  Don’t let the sodium hydroxide splash on you or the counter. 

    3. Start the magnetic stirrer on low and don’t let the solution splash out of the beaker.  You must stir for 20-45 minutes. The mixture will slowly become smoother and more opaque; it should thicken to a pudding-like consistency.  


    While you wait for this stirring to complete, you may do the DETERGENT/SOAP AND HARD WATER and DEGREE OF SATURATION portions of the lab. 

    4. Add approximately 1 teaspoon of stearic acid. This will serve as a hardener for the liquid soap. Stir on the magnetic stirrer for 5 more minutes.  Remove the stir bar and return to the stockroom.  

    5. Pour into chosen mold shape. Label with your names and lab section number with masking tape on the silicone soap mold. 

    6. After pouring into the mold, the process will continue on its own. The soap will heat up and liquefy again, then cool off slowly, harden and dry. So, the soap must be left undisturbed for at least 12 hours. You will pick up your finished soap in lab next week. 



    Part 2 Soap and Detergent Effectiveness in Hard Water 


    Materials:  A small amount of soap made from PART 1, commercial powdered detergent, pH paper, hard water solution, laboratory water 


    Equipment:  Two 150 ml beakers, masking tape, glass stir rod, 3 test tubes, test tube rack 


    1. Label one beaker “soap” and one beaker “detergent”.  Put 100 ml of laboratory water in each beaker.  Heat both beakers together on a hot plate. 

    2. Dissolve 2 g of the moist soap from Part 1 (use the leftover soap from your beaker in Part 1) in the boiling water of your beaker labeled “soap”.  Dissolved 1 g of the commercial powdered detergent in the beaker labeled “detergent”. 

    Use these two solutions to complete the data table. 

    3. Use pH paper and place the end of the paper into the solution in one of the beakers.  Test both beakers and compare the pH of the soap solution compared to the detergent solution. 

    4. Place 4 drops of mineral oil into each of 3 test tubes.  Add 5 ml of laboratory water into the first tube, add 5 ml of the soap solution into the second test tube, and add 5 ml of the detergent solution into the last test tube.  Place your finger over the end of the test tube or place a cork in the end, shake the test tubes, then visually inspect the tubes.  Record whether the solution emulsifies the oil.  If the solution can surround and emulsify the oil, you won’t see a layer of oil at the top of the test tube.  If the test tube looks the same top to bottom and side to side, then the oil, soap or detergent and water have formed a homogeneous mixture.  This is what an emulsified mixture looks like.  If the soap or detergent can’t surround the oil, you will see two layers:  oil on top and water on the bottom. 

    5.  Place 5 ml of soap solution into each of three test tubes.  Add 2 ml of 0.5% MgCl2 to the first tube, add 2 ml of 0.5% CaCl2 to the second test tube, and add 2 ml of 0.5% FeCl3 to the third test tube.  Shake these three test tubes and look for a precipitate (white, chunky floating particles).  Add 4 drops of mineral oil to each of the three test tubes.  Shake them again and look for emulsification (like step 4 above). 

    6.  Do the same process in three new test tubes with the detergent solution.  Add the ionic solutions from Step 5 (above) to each of the three test tubes as you did for the soap solution.  Check for precipitation.  Add 4 drops of mineral oil to each of the three test tubes.  Shake them again and look for emulsification (like Step 4 above).  Record all your observations on the data sheet below. 




      pH Observation Emulsified? (Y/N?)













    Laboratory water 







    Soap and Mg2+ ion 

    Soap and Ca2+ ion 

    Soap and Fe3+ ion 










    Precipitate (Y/N?) 

    Precipitate (Y/N?) 

    Precipitate (Y/N?) 


    Emulsified (Y/N?) 


    Emulsified (Y/N?) 

    Emulsified (Y/N?) 




    Detergent and Mg2+ ion 

    Detergent and Ca2+ ion 

    Detergent and Fe3+  ion 


















    Precipitate (Y/N?) 

    Precipitate (Y/N?) 

    Precipitate (Y/N?) 


    Emulsified (Y/N?) 


    Emulsified (Y/N?) 

    Emulsified (Y/N?) 



    Part 3:  Degree of Saturation of Various Fats and Oils 


    Materials:  Olive oil, melted shortening, 2% bromine (Br2) in dichloromethane, dichloromethane, pipet 


    Equipment: 2 test tubes, test tube rack 


    Add 2 drops of olive oil to 1 ml of dichloromethane in a test tube.  Add 2% Br2 in dichloromethane dropwise to the oil.  Shake the test tube until the color disappears.  Continue this process, and keep track of the number of drops, until you finally see the color stay in the solution.  Do the process again with a fresh test tube and melted shortening.  Compare how the two fats differ on the data table below. 



    Olive oil 


    No. of drops of bromine used 





    No. of drops of bromine used 





    Which fat is more unsaturated? 




    Post Lab Questions: 


    1.  Explain how soaps emulsify oils from your skin. 








    2.  Draw an emulsified oil in a micelle. 








    3.  How is a micelle similar to the bilayer of a cell wall?  How is it different? 









    4.  Soap doesn’t kill bacteria, so how does soap work to clean your hands? 








    5.  Draw the reaction of any alkene with Br2.   








    6.  Explain how the bromine test works to detect unsaturation. 








    7.  Which has more unsaturation: olive oil or shortening? 








    8.  What does unsaturation have to do with the physical properties of an oil (physical state at room temperature)? 








    9. Which is more basic: your soap or detergent? 








    10.  Which alkene below would be more unsaturated: 


    Alkene A- requires 10 drops of bromine in dichloromethane before you see color? 




    Alkene B - requires 20 drops of bromine in dichloromethane before you see color? 











    Experiment_718_Making Soap - Saponification_1_1_1 is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.

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