CHEMISTRY NOW: Getting Clean (Grades 9-12) Print

Objective:

Students will observe the interaction of immiscible liquids. Students will compare the results of adding various surfactants to a mixture of immiscible liquids. Students will understand how soaps clean.


Introduction Notes:

CHEMISTRY NOW: Getting Clean

 

 

 

Title:

 

 

Getting Clean

 

Subject/Topic:

 

 

Surfactants

 

Grades:

 

 

9-12

 

Standards

Alignment:

 

 

Science as Inquiry

Structure and Properties of Matter

Motion and Forces

 

 

Time Allowance:

 

 

1 hour

 

 

Overview and Purpose / Objective(s)

(information, concepts to be learned):

 

  1. Students will observe the interaction of immiscible liquids
  2. Students will compare the results of adding various surfactants to a mixture of immiscible liquids
  3. Students will understand how soaps clean.

 

 

VOCABULARY:

 

immiscible- when two or more substances will not mix together to form a homogeneous mixture

surfactant- a wetting agent, a substance that reduces the surface tension of a liquid and allows immiscible liquids to form a homogeneous mixture

hydrophobic –The non-polar end of a soap molecule that is water insoluble

hydrophilic – The polar end of a soap molecule that is water soluble

 

Materials:

 

-          Safety goggles

-          Small clear, plastic bottles with screw tops (soda or water bottles)

-          Water

-          Vegetable oil

-          Food coloring

-          Various substances to test such as:

                                                              i.      borax solution

                                                             ii.      hand soap solution

                                                             iii.      laundry detergent solution

                                                            iv.      ammonia solution

                                                             v.      dish detergent solution

-          Large test tubes with stoppers to fit

-          Squares of cloth with motor oil stains (6 per group or student)

-          Test tube rack

-          Droppers or pipettes

-          Colored pencils

 

ACTIVITY / ENGAGEMENT

(reinforcing lesson, making real-world connection)

 

This lesson is in three parts; each part can be used alone or with the others.

 

Part 1 – An investigation of immiscible substances

 

1. Begin by having each group of students assemble a “wave bottle” and investigate the characteristics of two immiscible liquids.

2. How to make a “wave bottle”:

a)      Obtain a small, clear, plastic bottle with a screw top.

b)      Fill it half full with water; add vegetable oil until almost full to the top.

c)      Add a few drops of food coloring to the bottle.

d)     Screw the cap on tightly.

e)      Shake the “wave bottle” and observe.

3. Have students investigate these two immiscible liquids and record their observations.

4. Discuss what the students have observed. Begin with some leading questions and then follow up:

         Where did the food coloring end up?

         What does this tell you about the food coloring’s properties?

         Why does the food coloring end up in only one of the liquids?

         Why do the liquids not mix?

         What happens when you shake the bottle vigorously?

         How can we get the two liquids to mix?

         In the case of dirty clothes, how can you relate what you have just done to challenges in getting clothes clean?

5. Introduce surfactants and briefly explain what these substances do. Surfactants are emulsifying agents that will allow two immiscible liquids to mix. Ask students –can you give an example of common surfactants? (Soaps and detergents are common surfactants. Many cleaning products are surfactants and this is one of the reasons they are able to clean clothing and surfaces.)

 

 

 

Part 2 – A study of surfactant molecules

 

Soap molecules are composed of long chains of carbon and hydrogen atoms. At one end of the chain is a configuration of atoms that like to be in water (hydrophilic). The other end shuns water (hydrophobic) but attaches easily to grease. In washing, the "greasy" end of the soap molecule attaches itself to the grease on a dirty plate, letting water seep in underneath. Particles of grease are pried loose and surrounded by soap molecules, to be carried off by a flood of water.

 

 
 

Thanks to ITACAnet.org

 

 

 

 

 

 

 

 

 

 

 

 

 

Ask students to identify which of the molecules in Picture 1 is a soap molecule. (You can give each student/student group its own copy). Then ask: How can you tell? Why does a soap molecule have to be polar? [For the teacher: A is chlorophyll, B is glucose, C is soap, D is glucose.]

 

Part 3 – Experimental Design

 

Discuss with students how they can design a valid experiment that allows them to investigate how surfactants work, including a determination of which works best, and what surfactants do to dirty clothes. Begin with a leading question as a review and follow-up questions:

 

  • - How does soap work?
  • - What kind of investigation can we do to observe the reaction of different surfactants with water and oil?
  • - Can you think of other ways to get these two liquids to mix?

 

Note:  Lab safety equipment should be used, and safety protocols followed. Goggles should be worn at all times. Caution students about working with vegetable oil:  although it is not a dangerous liquid, it will leave grease stains on their clothing and it is hard to clean up if spilled. Some detergents and soaps can be skin irritants, especially if students have sensitive skin.

 

Let students know that they will be given 6 large test tubes with stoppers. Have the following available for the students:

 

water

borax solution

hand solution

dish detergent solution soap solution

laundry detergent solution

ammonia

cloths with motor oil stains on them

 

1. Ask the students to create an experiment in which they will be testing the effectiveness of substances as surfactants. Be sure that the students (in groups or working individually) write the experiment down on the included data sheets BEFORE conducting the experiment.

 

2. Discuss their experimental design as a class.  Did they include a control? Did they use good experimental design?

 

Concluding Discussion:

 

After the students have finished their investigation, students should be able to describe how the surfactants affected their dirty cloths. Discuss with students the properties of these surfactants and why these substances are used as cleaners.

 

Extension Activities:

 

1. Students may also want to investigate other ways to get the liquids to mix, like heating or vigorous shaking.

2. They might also investigate some common household substances such as baking soda, flour, saltand sugar, since immiscible liquids are often mixed during cooking.

3. Students might want to learn to make their own soap. There are many online resources available (links below).

4. Students might investigate how surfactants are helpful in cleaning up after oil spills (see link below).

 

Additional Resources:

         http://www.flinnsci.com/Sections/Safety/safety.asp

         http://dictionary.reference.com/browse/immiscible

         http://scifun.chem.wisc.edu/HomeExpts/layeredliquids.htm

         http://dwb.unl.edu/chemistry/labs/LABS12c.html

         http://www.newton.dep.anl.gov/askasci/chem00/chem00600.htm

         http://chemistry.about.com/od/cleanerchemistry/a/how-soap-cleans.htm

         http://www.sintef.no/static/ch/environment/lab/Oil-spill.htm

 

 


Student Worksheet for “Mixing the Immiscible”

 

 

Experiment Title: __________________Date: _______Name: _______________

 

Student Hypothesis: _________________________________________________

 

Materials:

-          Safety goggles

-          Small clear, plastic bottles with screw tops (soda or water bottles)

-          Water

-          Vegetable oil

-          Food coloring

-          Various substances to test such as:

                                                              i.      borax solution

                                                              ii.      hand soap solution

                                                             iii.      laundry detergent solution

                                                           iv.      ammonia solution

                                                             v.      dish detergent solution

-          Large test tubes with stoppers to fit

-          Test tube rack

-          Droppers or pipets

-          Colored pencils

 

Safety Precautions:

 

________________________________________________________________

 

________________________________________________________________

 

Procedure:

 

Wear Safety Goggles for all lab work.

1. ___________________________________________________________

2. ___________________________________________________________

3. ___________________________________________________________

4. ___________________________________________________________

5. ___________________________________________________________

6. ___________________________________________________________

7. ___________________________________________________________

8. __________________________________________________________

9. ___________________________________________________________

10. ___________________________________________________________

 

Data and Observations:

 

 

 

 

 

 

 

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