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There are three components to this lesson, outlined below. Complete the activities 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?”
Part I: Determining the pH of shampoo samples
Using the shampoo samples given to you by your teacher, determine the pH of each of the samples. You can determine pH by using a method familiar to you, such as using pH strips or probes. Record the pH of your shampoo samples below or on a sheet of paper:
Part II: Treating hair samples in solutions of varying pH
Complete the following activity in your lab group and answer the questions that follow.
- Obtain 4 wooden splints; 4 test dishes; 20 strands of the same type of hair; and 4 strips of tape.
- Clean the 4 dishes in pH neutral solution and rinse thoroughly with distilled water. (Be sure to clean all glassware after each use so that the samples are not contaminated.)
- Label the test dishes pH 2.0, pH 6.0, pH 10.0, and pH 12.0. Add 10 mL of the appropriate pH solution to each of the dishes.
- Tape 5 strands of hair to each splint with one end fastened, and the other end free to be immersed in the test solutions. Label the ends of each splint with pH 2.0, pH 6.0, pH 10.0, and pH 12.0.
- Put each splint into the corresponding solution. Allow the hair to be exposed for 10 minutes.
- Remove the hair sample and rinse with distilled water. Allow the strands to air dry.
- Grasp the ends of the pH 2.0 sample and pull gently. Record observations of the following in the data table: texture (e.g., rough, smooth) and resilience (hairs’ ability to stretch and contract without breaking).
- Observe the hair under the microscope. Sketch what you see and record notable observations in the table (e.g., texture, smoothness).
- Repeat for other samples.
Effect of pH on Hair Resilience
|| Sketch of Hair
- The hair sample treated in what pH was the most resilient after treatment?
- The hair sample treated in what pH was the least resilient after treatment?
- Based on test results, what seems to be the best pH range for hair?
- Describe further research that would better determine the optimal pH range for hair care products.
- How would you answer the central question of the lesson now: “How does understanding the chemistry of hair care, including the role of pH, help in the development of better hair care products?”
Part III: Online exploration of hair care
Go to the Exploratorium’s website, Better Hair through Chemistry (http://www.exploratorium.edu/exploring/hair/). Read the introduction, page two, and page three and answer the following questions:
- What are some factors that impact the condition of hair?
- What could be causing your hair to be limp?
- What are the differences between hair follicles and hair shafts?
- When you cut yourself, can your skin heal? If so, why?
- If you damage your hair (e.g., by using the wrong types of hair care products) can it heal?
- What is the outermost layer of the hair shaft called?
- What is the role of the cuticle?
- What happens to cuticles in acidic solutions?
- What happens to cuticles in basic solutions?
- What happened to the author’s hair when she put it in an acidic solution? In a basic solution?
- Does that match what happened to your hair in this lesson’s activity?
- According to the article, how does shampoo work?
- Which is better for your hair, detergent or soap? Why?
- What does rinsing in acidic solution (e.g., vinegar) do for your hair?
- Does this article support the results of your in-class activities? Why or why not?