Materials Included In Kit

Additional Materials Required

Safety Precautions

Shampoo is considered non-hazardous although it may be an eye irritant. Universal indicator solution contains denatured ethyl alcohol which is moderately toxic by ingestion and inhalation and is a body tissue irritant. Avoid contact with eyes, skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Disposal

All solutions may be flushed down the drain with water.

Teacher Tips

• This kit contains materials for a class of 24 students working in pairs.
• All shampoo samples included in this kit have been diluted with deionized water in a 50:50 ratio for ease of transferring the shampoo with pipets. Therefore the result from the Percent Solids Test 1 will be only ½ what it should be. To correct for this, students are told to multiply their percent solids value by two.
• Shampoo samples are provided that offer a range of test results. Unfortunately, shampoo formulations are constantly changing and results may vary from the results provided.
• Sample data are provided below for shampoo samples 1–5; however, the data given are in approximate range values. Exact data for each shampoo sample 1–5 are not provided as the shampoo brands and formulations may vary.
• In the percent solids test (Test 1), the shampoo samples should be completely dry before weighing. The technique for accomplishing this is called drying to a constant mass. The sample should be dried, cooled, and weighed; then re-dried, re-cooled, and re-weighed. If the two masses are off by more than ~0.05 grams, then the drying procedure should be continued until a constant mass is obtained.

Answers to Questions

1. Answers will vary.
2. Answers will vary.
3. A control is necessary in all tests in order to demonstrate that the results of the experiment are not caused by some hidden factor.
4. Answers may vary, although there will most likely be no solids in the control.
5. The hair is strongest under slightly acidic conditions (pH 4–6). The scales on the cuticle lie flat, light is reflected more coherently, and thus the hair appears shiny and lustrous.
6. At a higher pH (>7), the scales of the cuticle will fluff up, light will scatter, and hair will look dull.
7. Answers will vary.
8. Answers will vary, but most will be in the acceptable range.
9. Answers will vary.
10. Answers will vary.
11. Answers will vary; however, people associate foaming ability to cleansing ability which may or may not be a necessary correlation.
12. Answers will vary; however, it is likely there will be no correlation.
13. A micelle is a spherical cluster of soap molecules. The nonpolar tails point inward and surround the nonpolar oil while the polar heads point outward, allowing the whole micelle to be dissolved and rinsed away in the polar water.
14. The control tube with just oil and water has two distinct layers, with the oil forming a smooth, homogeneous layer above the water. The test sample tube with oil, shampoo, and water also has two layers. However, the oil in the top layer is emulsified and broken up into tiny bubbles. The water in the bottom layer is cloudy since some of the surrounded oil droplets are pulled into the water layer.
15. Answers will vary, although it is likely that no differences among the five shampoos will be observed.
16. Answers will vary; however, ability to cut grease would be more important for people with very oily or dirty hair.
17. The detergent (or surfactant) in the shampoo removes the grease and oil from the hair while the conditioners in the shampoo replace some of the lubricant.
18. Answers will vary.
19. Answers will vary; however, since the greatest dry weight component is most likely the surfactant, there will most likely be a direct correlation.
20. Answers will vary.
21. Answers will vary.
22. Possible answers may include cost per ounce, special formulations, product packaging, best-selling brand name, or color.
23. Results with tap water would vary depending on the hardness of the water. Student answers will vary; however, they may hypothesize that there would be less foaming, different pH, or perhaps a less pleasant fragrance.

Discussion

Suggested Guidelines for Evaluating Shampoo Formulation

Test 1. Percent Solids

The percent solids value is an indicator of the actual amount of non-volatile solid material, called “dry weight.” Thus, a higher percent solids means that there is less filler solvent while a lower percent solids indicates more filler solvent. What is the solid material that is left? Refer to Table 1 in the student handouts to see that the solid material is a mixture of many ingredients, with the majority of the weight attributed to the surfactant, the cleaning agent in the shampoo. Shampoo formulations vary in their percentage of solids. A good shampoo will usually have at least 18% solids and possibly as much as 30%.

Sample data for two shampoos are given in Table 2 Example. Shampoo samples provided in this kit range from 10–29% solids. Note: The samples must be thoroughly dry before the final weighing. This may require overnight drying.  

Test 2. pH

pH adjusters are added to shampoos to maintain a slightly acidic pH of about 4–6, although it is common for pH to go as high as 7 (neutral pH). Shampoo samples provided in this kit range from pH 4.5 to pH 7.0.

Test 3. Foaming Ability

Foaming agents are added to shampoos to aid in the formation of lather. This lather helps to carry the dirt into the water layer so that it easily rinses out. In addition, consumers like a shampoo that lathers up a great deal. Shampoo samples provided in this kit give a foam level ranging from 40–80 millimeters in the test tube.

Test 4. Grease-Cutting Ability

The grease-cutting ability test performed in this lab was a qualitative test to determine if the shampoo has the ability to “cut grease” or, in other words, to wash the oil into the water layer. (Comparisons among the five shampoos will not be made as no quantitative measurement was made.) How does shampoo “cut grease”? Micelle formation was discussed in the background information of this lab. Encourage students to review this background information before answering Questions 11–15.

Students should observe that all of the shampoo samples emulsify the oil. They will observe emulsification as tiny bubbles in the oil layer and as cloudiness in the water layer. It is your option as to how many shampoo samples the students test. Students will not be able to rank the shampoo samples for this test. The flashlight is suggested to help the students to see the cloudiness (turbidity) in the water layer.

Test 5. Fragrance

While this tends to be a very individual preference, fragrance may often be a key reason that some people choose a shampoo. Encourage students to describe the fragrance using very specific fragrance descriptors (e.g., sweet, floral, fruity, minty, herbal, woody, medicinal, citrus, coconut) rather than using simply “good” or “bad.”

Test 6. Home Project (Optional)

In addition to the activity described in the procedure, you may allow your students to run Tests 1–5 on their own favorite brand or brands of shampoo. Discussion may follow on what additional factors may have influenced them to purchase this product such as fragrance, product packaging, cost per ounce, best-selling brand name or ease of opening bottle. Allow an open-ended discussion to encourage the students to evaluate brands and form judgments about the “worth” of different shampoos.

References

Consumer Reports 1992, June, pp 395–403.

Holmes, A. Ed. Product Testing Activities by Consumer Reports; Prentice Hall: Englewood Cliffs, NJ, 1993; pp 15:1–8.

Sarquis, M. Ed. Dirt Alert—The Chemistry of Cleaning; Terrific Science: Middletown, OH, 1995; pp 39–44.

Sarquis. M. Ed. Fat Chance—The Chemistry of Lipids; Terrific Science: Middletown, OH, 1995; pp 47–56.

Selinger, B. Chemistry in the Marketplace, 4th ed.; Harcourt Brace Jovanovich: Sydney, Australia, 1994; pp 110–113.

Snyder, C. H. The Extraordinary Chemistry of Ordinary Things; John Wiley & Sons: New York, 1992; pp 571–577.

Introduction

Extra body! Healthy looking, shiny hair! Removes buildup without drying! Moisturizes! Fortifies! Nourishes! Protects! These are just some of the claims of shampoo ads. Are they true? What really makes a shampoo good? Understanding hair and how shampoos function will allow you to answer these questions for yourself.

Concepts

• Chemical function
• pH
• Surfactant

Background

Let’s take a look at hair. The primary function of the more than 150,000 individual strands of hair on the average human head is protection. Hair helps insulate the body and maintain a constant body temperature. Hair also helps provide some protection from UV radiation. Specialized hair such as eyelashes and eyebrows help protect the eyes from mechanical injuries and foreign particles.

Hair is distributed over most of the body with a few exceptions such as the palms of the hands and the soles of the feet. The length, thickness, type and color of hair varies with the different body parts and different genetics. Gender also plays a role since the average growing phase of a hair lasts about six years in women and about three to four years in men. The length attained, if uncut, is 70 to 80 cm for women and 40 to 50 cm for men. Growth then ceases and the hair follicle lies dormant for 3–6 months. After this time it starts to produce a new hair which pushes out the old hair, a process termed shedding. A typical adult will shed about 100 hairs each day and, at any given time, about 90% of hair follicles are actively growing.

A strand of hair consists of two primary parts, the shaft and the root (see Figure 1). The shaft is the visible portion of the hair that is above the surface of the skin and is a lifeless structure composed of a hard fibrous protein called keratin. The hair strand grows from the root, which is the portion of the hair that is implanted in the skin and is the growing, living part of the hair. This living root is embedded within a microscopic sac called a hair follicle. The rapidly dividing cells in the tissue, or papilla, of a hair follicle receive nutrients from blood vessels at the deep end of the follicle. As the cells divide and grow, they push upward toward the surface. As they move away from nourishment, the cells become filled with keratin, then dry, harden and eventually die.

The keratinized remains make up the developing cortex, which is the elongated central core of a strand of hair. The cortex forms the bulk of the strand and contains the hair coloring pigment, melanin. Different amounts of the pigment account for different colors of hair from light blonde to black. Absence of the pigment produces white or gray hair. Redheads differ in that their hair contains a unique iron-based pigment which indeed makes their hair “rusty” in color.

Enveloping the cortex is a thin, translucent, scaly protein sheath called the cuticle. As the hair emerges through the skin, the cuticle is compressed with a roller action forming its shingle-like appearance (see Figure 2). Sebaceous glands lying in the skin near the follicle lubricate the emerging shaft with an oily sebum, which is a mixture of fats, cholesterol, proteins and inorganic salts. This secreted sebum gives the hair a gloss, keeps the scales of the cuticle lying flat, and prevents the strand from drying out. Too much oily sebum and the hair feels greasy and dirty; too little and it is dry, dull and brittle.

So what is the purpose of a shampoo? A shampoo must remove dirt from the hair and scalp as well as enough accumulated sebum to keep the hair looking clean and shiny, but not so much as to strip away all of the oil. This sounds like a tricky feat and does indeed require some balancing of ingredients.

Shampoo, therefore, is a mixture of several compounds in specific proportions, each with its own specific function (see Table 1). Water is by far the most abundant ingredient at 60%. The main active ingredient is a surfactant, such as sodium lauryl sulfate (see Figure 3), which provides the detergent action of the shampoo.


A surfactant is a long chain molecule with two distinct parts. One end is a nonpolar, hydrophobic (water-fearing) carbon chain, resembling a “tail.” The other end is a polar, ionic, hydrophilic (water-loving) “head.” The nonpolar tail has an attraction to the nonpolar materials like grease or oil while the polar head is attracted to the polar water molecules. This “like dissolves like” phenomenon allows the surfactant to form a micelle in a polar solvent like water. A micelle is a spherical cluster of soap molecules that forms a cluster around a grease or oil droplet with the nonpolar tails pointing inward to surround the nonpolar oil droplet. The polar heads form the sphere’s outer surface and thus allow the entire oil-containing droplet to be soluble in water and then to be rinsed away (see Figure 4). 

The surfactant in the shampoo will therefore disperse or break up the oil particles so they can float away in the water. As the surfactant surrounds the oil droplet, a permanent dispersion will form in the water. This dispersion is called an emulsion. While micelles are microscopic and thus too tiny for the naked eye to observe, emulsification of the oil droplets by the shampoo can be seen as tiny bubbles in the oil layer and as a cloudy phase in the water layer.

The other ingredients in a typical shampoo, while accounting for less than 10% of total weight, also serve important functions and should not be considered trivial. The acidity of a shampoo, for instance, has much to do with its ability to produce a good luster and strong, resilient hair. A strand of hair is stronger under slightly acidic conditions, such as a pH of about 4–6. Furthermore, the scales of the cuticle are affected by pH. Under basic conditions, the hair tends to swell up and fluff out. This condition causes reflected light to scatter, making hair look dull. Under slightly acidic conditions, the scales of the cuticle lie flat. Thus light is reflected more coherently and the hair has a pleasant luster (see Figure 5). For these reasons, a weak acid, such as myristic acid, is added as a pH adjuster.

Many shampoo formulations also contain small amounts of a conditioner, an oil-like material, which replaces at least part of the lubricant (sebum) that may be lost in the washing. The conditioner also makes the hair easier to comb and reduces the static of newly-shampooed hair. Foaming agents are added to aid in the formation of lather. Thickening agents are added to increase the viscosity of the shampoo, thus making the shampoo easier to apply and not so “water-like.” Finally, other shampoo additives include colorants, fragrances, preservatives, dandruff controllers, chelating agents and other ingredients specific to the shampoo’s intended market.

Using this kit, students will perform tests on five different shampoo samples, record and analyze data and then begin to form judgments about the different shampoos

Materials

Safety Precautions

Shampoo is considered non-hazardous although it may be an eye irritant. Universal indicator solution contains denatured ethyl alcohol which is moderately toxic by ingestion and inhalation and is a body tissue irritant. Avoid contact with eyes, skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Procedure

Test 1. Percent Solids
(Each group should do only one sample and share data with other groups.)

Prepare Control Sample

1. Weigh an evaporating dish on a balance. Record mass in Table 2.

2. Add about 3–4 grams of distilled water to the dish. Weigh and record in Table 2.
3. Dry the sample by exposing it to a heat lamp. A hot plate on low heat setting may also be used to drive off volatile matter.

Prepare Test Sample

4. Weigh another evaporating dish on a balance. Record mass in Table 2.
5. Add about 3–4 g of your assigned shampoo sample to the dish. Weigh and record in Table 2.
6. Dry the sample by exposing it to a heat lamp. A hot plate on low heat setting may also be used to drive off volatile matter.
7. Complete Tests 2–5 while this is drying.
8. When the sample is dry and the dish is cool, weigh the dish again and record its mass. Calculate percent solids using the equation provided on the data sheet.
9. Since the shampoo samples in this kit had been diluted 50:50 with water for ease of handling, multiply your percent solids value by two to get the actual percent solids value.
10. Complete Data Table 2 with data on the other shampoo samples from other student groups.

Test 2. pH

Prepare Control Sample

1. Add 10 mL of distilled water to a test tube.
2. Add five drops of universal indicator solution to the water.
3. Observe the color of the solution and determine its pH by using the pH reference card.
4. Record the pH value in Table 3.

Prepare Test Samples

5. Add 10 mL of distilled water to another test tube.
6. Add two drops of shampoo sample 1 to the test tube.
7. Add five drops of universal indicator solution to the test tube.
8. Observe the color of the solution and determine its pH by using the pH reference card.
9. Repeat steps 5–8 for the other four shampoo samples.
10. Record all the pH values in Table 3.
11. Clean out the test tubes for use in Test 3.

Test 3. Foaming Ability

Prepare Control Sample

1. Add 5 mL of distilled water to a test tube.
2. Covering the test tube opening with your thumb, vigorously shake the tube 25 times.
3. Did any foaming occur? Record your observations in Table 3.

Prepare Test Samples

4. Add 2 drops of shampoo sample 1 to a clean test tube.
5. Add 5 mL of distilled water to the test tube.
6. Covering the test tube opening with your thumb, vigorously shake the tube 25 times.
7. Allow the tube to sit for one minute.
8. Using a metric ruler, measure (in mm.) the level of foam above the water and record in Table 3.
9. Repeat steps 4–8 for the other four shampoo samples.
10. Clean out the tubes for use in Test 4.

Test 4. Grease-Cutting Ability

Prepare Control Sample

1. Add 10 mL of distilled water to a test tube.
2. Add 10 drops of corn oil to the water.
3. Covering the test tube opening with your thumb, invert the test tube several times to mix the layers.
4. Set the tube in the test tube rack and allow the layers to separate.

Prepare Test Samples

5. Add 10 mL of distilled water to a test tube.
6. Add 20 drops of shampoo sample 1 to the test tube. Cover the test tube opening with your thumb and mix by inverting the tube several times. (Do not vigorously shake the tube as too much foam will interfere with your ability to see the layers in step 7.)
7. Now, drop by drop, add 10 drops of corn oil to the tube, making careful observations as you add the oil.
8. Mix the layers by inverting the tube several times. Allow the tube to sit for about one minute.
9. Carefully observe the top oil layer in this tube. Compare it to the oil layer of the control and record your observations in Table 3.
10. Carefully observe the more dense water layer. Compare it to the water layer of the control and record your observations in Table 3.
11. If desired, hold the control tube and the sample tube up and shine the flashlight through the water layer. Do you observe any cloudiness in either tube? Record your observations in Table 3.
12. Repeat steps 5–11 for shampoo sample 2. Record your observations in Table 3.
13. Did you observe differences between shampoo samples 1 and 2? Do you think the other shampoos will show differences? Repeat this test on the other shampoo samples.
14. Clean out the test tubes for the next lab group.

Test 5. Fragrance

1. Test the fragrance by smelling a sample of distilled water. (Since each of the shampoo samples are made and diluted with distilled water, this should be considered your control.)
2. Test the fragrance by smelling each of the shampoo samples.
3. Describe the fragrance using fragrance descriptors (e.g., sweet, floral, fruity, minty, herbal, woody, medicinal, citrus, coconut) rather than using simply “good” or “bad.”
4. Record data in Table 3.

Test 6. Home Project (Optional)

1. Each student should bring in two small samples of shampoo. The shampoo should be labeled with a generic label that does not indicate the brand or type of shampoo.
2. Each student should keep track of the brand, type, price and bottle size of the shampoos that they bring in.
3. The teacher should distribute two different samples to each student.
4. At home, students wash their hair with both types of shampoo at the same time. In order to do this, students will part their hair down the center and use one type of shampoo on each side.
5. When the hair is dry, students should compare each side in terms of texture, ease of combing and body/appearance. Observations should be recorded in Table 4.
6. Class data should be combined in a large data table on the chalkboard. Comparisons of different brands of shampoos may be made and discussed.

Student Worksheet PDF

12797_Student1.pdf