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Micelles to the Rescue - How Soap Transports Debris

Grades: 9-12
Author: Ryan Kiddey
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC- 1542358.


Abstract

Soap is an important part of our daily life, however how soap works is a mystery to many students and it's often taken for granted. This lesson is designed for a teacher to use within context of a larger unit on mixtures and solutions. The lesson will teach students how to make a primitive soap, understand the basic chemistry behind soap, conceptualize how soap removes debris via micelle aggregation, and identify what hard water is and its effect on micelle aggregation.


Objectives

What should students know as a result of this lesson?

  • Students will be able to identify the basic ingredients of a soap.
  • Students will be able to describe a colloid.
  • Students will be able to describe the molecular structure of a micelle.
  • Students will be able to describe how intermolecular attractions, such as ion-dipole forces, allow soap to work.
  • Students will be able to contrast hard water and soft water.
  • Students will be able to describe how polymer scientists are synthesizing micelles to be used as medical transporting vessels.

What should the students be able to do as a result of this lesson?

  • Students will be able to create homemade soap.
  • Students will be able to identify whether or not their water is hard or soft.
  • Students will be able to draw a micelle formed by soap and label its major structures.
  • Student will be able to design an experiment to test the effectiveness of their soap.
  • Students will be able to assess why hard water affects the aggregation of soap micelles.

Materials

Day One – Soap Making Activity

  • Crisco – 20 g
  • NaOH (aq) – 6M, 10 mL
  • Beaker – 100 mL
  • Styrofoam cup
  • Graduated cylinder – 25 mL
  • Glass stirring rod
  • Hot plate
  • Two thermometers
  • Universal pH indicator paper
  • Dropper

Day Two – Hook Activity and Lesson

  • Beaker – 2000 mL (8)
  • Beaker – 100 mL (one per group)
  • Calcium Chloride, CaCl₂, 100 grams
  • Black Pepper, ground
  • Generic dish soap
  • Olive Oil mixed with a little dirt, 100 mL
  • Disposable cooking pans (4)
  • Tap water

Day Three – Experiment with Soap

  • Olive Oil, 1 mL
  • Distilled water, 100 mL
  • Homemade soap
  • Commercial soap
  • Test tubes (7)
  • Test tube stoppers (7)
  • China Marker
  • Test tube rack
  • Hot plate
  • Cold Bath
  • Calcium Chloride, CaCl₂ 0.1 M, 10 mL
  • Balance
  • Forceps
  • pH paper
  • Pipet (2)
  • Watch glass
  • Cotton swab

Procedures

Lesson Summary

Introduction

Soap is an important part of our daily life, however how soap works is a mystery to many students and often taken for granted. This lesson is designed for a teacher to use within context of a larger unit on mixtures and solutions. The lesson will teach students how to make a primitive soap, understand the basic chemistry behind soap, conceptualize how soap removes debris via micelle aggregation, and identify what hard water is and its effect on micelle aggregation.

Lesson Delivery

This lesson is meant to take place for three separate sessions. It's been broken down by session one, two, and three. However, these sessions do not need to be taught consecutively. The teacher can implement session one a few weeks before they begin session two and three. This will give the soap time to cure and its pH to decrease to a level that is less hazardous.

Alternative Option to Making Soap

If a teacher does not feel comfortable having their students use a high molarity of sodium hydroxide or would like to deliver this lesson in three consecutive days, there is another option. You can prepare a liquid soap and call it “homemade” by grating 2 grams of Ivory bar soap and placing it in 1 L of water. Stir the solution vigorously for 5 minutes and let sit for 15 minutes until the 2 grams of Ivory soap dissolve. Place the liquid soap in droppers for each group to use during session three.

Lesson

Session One:

During session one students will follow a soap making procedure. Students will have very limited knowledge of chemistry because this lab will be performed very early in the semester. The focus should be on learning basic lab skills. When the lab is complete, each group will have its own cup of soap which will cure for four to six weeks. This will lower the pH of the soap as well as give students time to learn enough chemistry to fully understand “Micelles to the Rescue: How Soap Removes Debris.” See “Alternative Option to Making Soap” if you do not feel comfortable having students make soap.

Session Two:

Session two consists of two hook activities and a PowerPoint lecture. It may take more than one class period to complete the activities in session two. The hook activities will expose students to the effect soap has on water. The first activity will contrast hard and soft water; the second will show the effect soap has on the surface tension of water. Discussions should follow after each hook activity. After the hook discussions students will be given a handout for taking notes. The handout matches the PowerPoint presentation. There is a vocabulary assignment that can be used as an in-class assignment or be assigned as homework.

Session Three:

Session three will give students an opportunity experiment with the soap they created earlier in the semester. Students will investigate how their homemade soap compares to store bought commercial soap. They will investigate how each soap lathers and their pH differences, how hard water effects each soap, and as how each removes grease. Students will also design their own experiment to see how temperature effects the effectiveness of soap. There are post lab questions for students to consider how businesses market their soap.

Engagement

Hook activities will require students to think critically about the effect hard water as on soap and how soap affects the surface tension of water. The soap lab (session three) will require students to design an experiment that tests temperature’s effect on the effectiveness of soap. Students will be pre-assessed on their knowledge of soap and how it transports debris. These activities will allow the instructor to identify areas where students need the greatest focus and refinement.

Exploration

When students are making their soap (session one) the instructor will teach laboratory techniques that foster student safety. Students will be required to write what they felt went well in the soap making process and what hazards they faced. (If a teacher does not feel comfortable having their students make soap, an alternative option is available. Please see Lesson Overview.) During the hook activities (session two) students will be required to explore the effects of hard water and surface tension. This will require them to answer questions pertaining to these activities and to share their findings with the class. During the lecture (session two) students will be given guided notes and be require to take notes during the lecture. During the soap experiment (session three) students will be required to collect data relating to their observations on how effective their soap is under certain conditions, compared to commercial soap. They will report their findings to the rest of the class.

Elaboration

The soap experiment lab (session three) will be the culminating activity for the entire lesson. The lab requires students to have a solid understanding of how soap works and how certain variables will affect the soap. Students will use the knowledge they gained from the lecture (session two) to help them analyze their findings. They will also be required to design an experiment to see what effect temperature has on soap. They will report their findings to the class.


Prerequisites

Students must have a basic understanding of intermolecular forces and how ionic compounds can disassociate into solution. Students must also understand basic molecular geometries in order to understand the formation of a micelle.


Best Teaching Practices

  • Using Analogies
  • Hands on/Minds on Learning
  • Real Life Situations and Problem Solving
  • Discrepant Events

Alignment with Standards

NGSS Standards:

Ohio Standards:

Chemistry: Structure and Properties of Matter

  • ionic intramolecular forces
  • polarity of molecules
  • intermolecular chemical bonding
  • solubility

Content Knowledge

Using basic laboratory equipment (hot plate)

Basic understanding of lab safety and working with bases

Basic understanding of molecular geometry

Solid understanding of intermolecular forces

Solid understanding of how a solution forms


Safety

Sodium Hydroxide is a powerful base and must be used with extreme caution. Students must wear gloves, safety goggles, and lab aprons while making the soap (session one) and when experimenting with the soap (session three). The pH may not fall to safe levels after the soap cures. Test the soap with pH paper to make sure it can be held by hand when attempting to experiment with it (session three). If the pH is higher than 8.5 students must wear gloves and use forceps when interacting with their homemade soap.

During one of the hook activities students will be putting their hands into a solution of calcium chloride. Make sure students rinse and wash their hands thoroughly after the activity.


Applications

Major corporations are experimenting with different techniques to make soaps and surfactants more effective. While visiting Lurbrizol Corporation in Cleveland the lesson designer had an opportunity to hear a surfactant chemist talk about her work with improving additives used in soaps and lotions. Additionally, research is being conducted at the University of Akron (UA) on polymer micelles. Researchers are studying nanocapsule polymer micelles that can be used as transport vehicles for drug delivery for cancer treatment. UA Researchers are currently attempting to develop an extended release application to this cutting edge nanocapsule technology.


Assessment

This lesson will tie into a large unit on mixtures and solutions. The concepts learned in this lesson will be a part of the overall unit exam. Moreover, students will be assessed on how well they perform on their post-lab activity during session three as well as the vocabulary assignment given on session two.


Other Considerations

Grouping Suggestions:

  • Since each group will be making their own soap during session one, these groups should not be split up on session three when they experiment on their homemade soap.

Pacing/Suggested Time:

  • See lesson overview

Printable PDF Worksheets

Session One:

Session Two:

Session Three:

Supplemental Materials:


Safety Disclaimer