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    Making Soap Experiments

    This experiment is courtesy of 

    Elementary Lesson for Making Soap

    Developers:

    David Crotty
    Franklin Elementary
    Pennsauken, NJ

    Mike Gavaghan
    Separations Technology
    Rohm & Haas Company
    Spring House, PA

    Faith Lipford
    Separations Technology
    Rohm & Haas Company
    Spring House, PA

     

    Grade Level:

    5 through 8

     

    Discipline:

    General Science, Chemistry

     

    Goals:

    Upon completion of this lesson, the student will:

    1. recognize and use chemical indicators in the lab.

    2. recognize the need for safety while doing chemical experiments.

    3. understand the need for following precise directions.

     

    Objectives:

    Upon completion of this lesson, the student will be able to:

    1. use pH paper to determine if soap is acidic or alkaline.

    2. define saponification and emulsion

    3. manufacture a soap sample.

    4. compare the relative strength of their sample against commercial soap products

     

    Background:

    Evidence of soap making dates back to the Egyptians and Babylonians. However, due to the harshness of homemade soaps and the expense of early commercial products, humans have been using soaps to clean clothes and themselves for a relatively short period of time.

    Homemade soaps were usually made from kitchen fats or lard. The fats were broken down using ash soaked in water. The soaking ash produced the needed hydroxide. The samples the students will manufacture will be made from the same process.

    Saponification is a process in which a fat molecule is broken down by sodium hydroxide (lye) into four smaller molecules; three of the new molecules are soap and one is glycerol. The glycerol molecule keeps the soap moist. Emulsion is a temporary mixing of two insoluble liquids such as oil and water.

     

     

    Activity 1: Making Soap

     

    Teacher Preparation:

    SAFETY NOTE: Both ethyl and isopropyl alcohol are flammable. Sodium hydroxide is caustic. Use care with these chemicals. Students should be familiar with lab safety procedures before beginning this experiment (see page 4). Make sure there is no open flame in the room. Use goggles, gloves, aprons, or lab coats.

     

    For the class: (the following will provide enough solutions for 50 experiments)

    1. Prepare sodium hydroxide and alcohol solution. Place 120g of sodium hydroxide (sodium hydroxide is available at hardware stores under the name Lye. Avoid using liquid drain cleaners) in a glass container. Add enough water to make 500 ml of solution. Stir to dissolve. Add 500 ml of either ethyl or 70% isopropyl alcohol (available at drug stores). (Wear safety glasses when you prepare this solution. It can cause serious damage to the eye.)

    2. Prepare fat: Solids such as Crisco work best. Melt approximately 1 kg of Crisco or another vegetable shortening into a container suitable for heating. Heat fat to 40 to 45 degrees C. The fat must stay in liquid form until distributed to the students.

     

    For each group:

    Container with at least 100g of either table salt or kosher salt.
    Balance scale.
    Heating tray or electric burner.
    20ml of sodium hydroxide/alcohol solution
    20ml of melted fat or oil.
    Soup can
    Glass custard cup or container to fit into the mouth of the soup can (see diagram 1).
    Safety goggles and aprons.
    Wooden stirrers.
    Two aluminum pie plates, inverted and stapled (see diagram 2).
    Cheese cloth.
    Small cup (4 oz.) ice water.

     

    Diagram 1 How to make a water bath

    Diagram 2 Burner safety cover

    Procedure:

    1. Divide class into groups of 4. Have students wear gloves and goggles.

    2. Distribute sodium hydroxide/alcohol solution.

    3. Distribute melted fat.

    4. Add fat to custard cup. Place on water bath.

    5. Pour sodium hydroxide/alcohol solution into fat while stirring with wooden stick.

    6. Continue heating and stirring until a small sample can be completely dissolved in a test tube filled half way with water.

    7. While stirring the solution have another student weigh 90g of salt into a container, using a balance scale.

    8. Dissolve salt in 300ml of water.

    9. Pour the soap solution directly into the salt water. The soap will separate and float.

    10. Using a rubber band place cheesecloth over another jar. Pour the salt solution and soap through the cheesecloth. Allow solution to drain. Pour 4 oz. of ice water on soap to remove the salt.

    11. Gently squeeze excess water from the cloth. Spread out the cheese cloth to allow the soap to dry. Some soap will dry faster than others, allow 1 to 3 days.

    12. Wash hands with soap and water. Avoid contact with eyes.

     

     

    Activity 2: Testing the Soap

     

    Materials:

    1. Homemade soap

    2. Various commercial soaps and detergents, i.e.. liquid dish detergent, bar soap, soap flakes (Borax), powdered laundry detergent, etc.

    3. Small clear containers to hold 50ml of sample.

    4. Test tubes (2 per test solution).

    5. pH paper and/or phenolphthalein (phenolphthalein an acid/base indicator can be made from Ex-Lax tablets. Grind one tablet and mix with one liter of luke-warm water).

    6. Calcium chloride (available at supermarkets and hardware stores as Driveway Heat or ice melt) and Epsom salt (magnesium sulfate).

    For the class:

    The students will test their soap products using hard water. ( Hard water is that which contains Ca and Mg ions.) To make water hard add � teaspoon of both calcium chloride and epsom salt to two liters of water.

    NOTE: Since your water supply may be "hard", it might be a good idea to use deionized water to make all solutions for this activity. You can usually purchase this inexpensively in a supermarket. Many people buy deionized water for use in steam irons.

     

    Procedure:

    Dissolve 1g of test soap in 50 ml of luke-warm water.

    Pour 10ml of each solution into either a test tube or a small clear container. Into a similar container pour10ml of plain water to act as a control.

    3. Test each sample with both pH paper and phenolphthalein.

    4. Add 5 drops of cooking oil to the test tube. Shake. Record observation.

    5. In another test tube add 10ml of soap solution. Add 5ml of hard water. Shake.

    Using a ruler measure the amount of foam created by each sample.

     

    Worksheet

    Solution #

    pH

    phenolphthalein

    emulsion

    foam (cm)

             
             
             
             
             
             
             
             
             

     

    Teacher notes:

    - Enter the solution number in column 1

    - Using pH paper will allow students to determine pH between 1 and 14

    - Phenolphthalein will turn the solution a shade of red if the pH is above 8.5

    - For the emulsion column have students describe the conditions within the test tube. For example, did the oil mix? Has the solution become cloudy? Is there a layer of foam? Is there a layer of scum on top of the water?

    - Have students measure the amount of foam above the water line with a ruler.

    Safety Rules for the Home/School Chemistry Lab

    1. Work with an adult.
    2. Wear eye protection.
    3. Do not touch your eyes or face while doing an experiment.
    4. When something spills, clean it up immediately.
    5. Label all containers with the name of the content.
    6. When you have finished an experiment, put all equipment away.
    7. Before leaving your lab area, wash your hands.
    This experiment is courtesy of 



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