Students will do hands-on activities and read information online in order to answer the central question of this lesson: How does understanding the chemistry of hair care, including the role of pH, help in the development of better hair-care products?
It is important for high-school students to begin to appreciate the importance of scientific research. Increased scientific knowledge is what continues to spur technology; at the same time, as the base of scientific knowledge increases, technology advances. In this lesson, students will investigate how scientific research helps to develop the most effective types of hair-care products.
The ultimate goal of this lesson is for students to answer the central question: How does understanding the chemistry of hair care, including the role of pH, help in the development of better hair-care products? In order to do this, students will do hands-on activities with shampoo and hair samples, as well as read an online article about the pH of hair care products.
This lesson is most appropriate for an introductory chemistry course. Prior to this lesson, students should have been introduced to acids, bases, and the pH scale. This lesson complements previous instruction on acids and bases by providing a real-world context in which students investigate the impact of scientific research on hair-care products.
First, ask the following questions to focus students on the topics of hair and hair care:
- Have you ever wondered why your hair looks good one day and terrible the next?
- Is there anything that you try to do to fix your hair on a "bad hair day?"
- What are some of the products you use on your hair on a regular basis?
- How do these products impact the condition of your hair?
- Have you ever done something to your hair that really changed it?
Then help students focus on the science of hair care by asking this question:
- What do you think acids and bases might have to do with hair care products?
Briefly review acids, bases, and pH and continue talking about these in terms of hair care. Ask the following questions:
- What is pH?
- What are acids?
- What are bases?
- What are some methods to test pH?
- What role do you think pH plays in terms of hair care?
- Do you think it's more likely that an acidic, basic, or neutral product is best for your hair?
Finally, write the central question for this lesson somewhere where all students can see it: How does understanding the chemistry of hair care, including the role of pH, help in the development of better hair-care products? Let students know that the rest of this lesson will involve experimenting and reading information online to answer this question.
The Development is divided into three sections, all outlined for the students on the student sheet. Distribute the Effect of pH on Hair Resilience student sheet at this time.
Part I: Determining the pH of Shampoo Samples
This part relies on shampoo samples that the students brought in from home. List the names of the shampoos and have students vote to decide the favorite brands of the class.
Break students into lab groups. Give each lab group a set of shampoo samples for which they will determine pH; distribute the samples so they all get tested. Students will record the pH of their samples on their student sheets.
Note: Have students determine pH by using a method familiar to them. For example, using pH strips or probes. Also, it would be a good idea to have students wear safety goggles during this activity.
After the pH of all samples has been recorded, ask the following questions:
- Were most shampoos acidic or basic? (Most should've been acidic.)
- What about the shampoos you voted as your favorites? Were they acidic or basic?
Based on this activity, ask students to come up with an initial answer to the central question of the lesson: How does understanding the chemistry of hair care, including the role of pH, help in the development of better hair-care products?
Part II: Treating Hair Samples in Solutions of Varying pH
This part of the lesson involves testing hair samples in solutions of different pH. Distribute a hair sample to each group (20 strands of the same type of hair; they will eventually divide the sample into 4 groups of 5 strands each) and have students complete the activity by following the procedure on the student sheet.
Note: The test is subtle but shows expected results if done correctly. Observations of hair in each pH sample should include:
- pH 2.0: hard; smooth; not resilient; breaks easily
- pH 6.0: not as hard; smooth; very resilient; resists breaking
- pH 10.0: rough; not very resilient; tends to break easily
- pH 12.0: very rough; not resilient; tends to break very easily
When all students are finished with the activity, discuss the questions they answered on their student sheets (refer to Effect of pH on Hair Resilience: Answer Key for the questions from the student worksheet with suggested responses).
Part III: Online Exploration of Hair Care
In this section of the lesson, students will go to the Exploratorium's website, Better Hair through Chemistry. Here they will read the introduction, page two, and page three and answer questions on their student sheets. When they're finished, discuss the questions in class (refer to Effect of pH on Hair Resilience: Answer Key for the questions from the student worksheet with suggested responses).
Ask students the following questions:
- What is your final answer to the central question: How does understanding the chemistry of hair care, including the role of pH, help in the development of better hair-care products? (Students should understand that a pH that is too high or too low can adversely affect hair resilience. They should be able to explain that researchers continue to test substances to attempt to determine desirable characteristics, including desirable pH.)
- Describe how scientific research plays a role in the development of hair-care products over time. (Students should understand that research provides new information that leads to the development of better hair-care products over time. They should understand that this research is ongoing, partly accounting for the new hair-care products they see advertised.)
Students could create an advertisement for a shampoo. This could be a shampoo that's currently on the market, or one that they create. The focus of the advertisement should be on the science of the shampoo: What about the chemistry of the shampoo makes it good?
Students should include the following in their advertisements:
- Name of the shampoo
- Information about the chemistry of the shampoo (e.g., pH), and how this impacts the quality of the shampoo
- Sufficient background information about the chemistry (e.g., pH), so that general audiences can understand the advertisement
Students can read articles about the science of hair care, including How Hair Coloring Works, at How Stuff Works.
In his winning essay for the 2008 AAAS/Subaru Essay Writing Competition for K-12 Teachers, "Bad Hair Day," teacher Simon Holdaway shares another hair-related classroom idea.