Materials Included In Kit

Additional Materials Required

Prelab Preparation

Must be completed at least 4–5 hours in advance of the lab.

1. Cut the blotting paper along the dotted lines to make 30 rectangular pieces, each with an outline of a chameleon. Save the margin strip (see step 8).
2. Fill a 400-mL beaker with 300 mL of distilled or deionized water.
3. Measure a small amount (0.3–0.6 g) of red cabbage extract powder into a weighing dish.
4. Stir the red cabbage extract powder into the beaker of water.
5. Pour the red cabbage indicator solution into a plastic container.
6. Place no more than three rectangular pieces of blotting paper into the plastic container. Wait about 30 seconds to allow the blotting paper to absorb the indicator solution.
7. Wearing rubber gloves or using tongs, carefully remove the blotting paper pieces from the solution and lay them out on paper towels to dry.
8. Repeat steps 6–7 for the remainder of the blotting paper pieces. Note: Include the margin strip of blotting paper for instructor testing.
9. Allow the treated blotting paper chameleons to completely dry, about 4–5 hours.

See the Lab Hints section for preparation of household solutions.

Safety Precautions

Dilute hydrochloric acid and sodium hydroxide solutions are slightly toxic by ingestion or inhalation and corrosive to skin and eyes. Some household chemicals are toxic by ingestion or inhalation and are skin and eye irritants. Avoid contact of all solutions with eyes and skin and clean up spills immediately. All food-grade items that have been brought into the lab are considered laboratory chemicals and are for lab use only. Do not taste or ingest any material in the lab and do not remove any remaining food items after they have been used in the lab. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Dilute hydrochloric acid solution may be neutralized with base and then disposed of down the drain with an excess of water according to Flinn Suggested Disposal Method #24b. Dilute sodium hydroxide solution may be neutralized with acid and then disposed of down the drain with an excess of water according to Flinn Suggested Disposal #10. Any leftover dilute HCl and NaOH solutions may be combined, and then the final product checked with pH paper. If the final product is near neutral (pH 5–9), it can then be discharged down the drain with an excess of water. Red cabbage indicator solution may be disposed of down the drain with an excess of water according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 students to design one chameleon each. This laboratory activity can reasonably be completed in one 45- to 50-minute class period. The pre-laboratory assignment may be completed before coming to lab, and the analysis of results may be completed the day after the lab.
• The following household substances are suggestions for classifying acid–base solutions with the red cabbage indicator.

Ammonia, household
Antacid tablet
Baking powder
Baking soda
Club soda
Contact lens solution
Dishwasher detergent
Drain cleaner
Grapefruit juice
Laundry detergent
Lemon juice
Liquid hand soap
Mouthwash
Shampoo
Soft drinks
Vinegar
Vitamin C tablet
Water, distilled and tap

• Dissolve solid substances with a small amount of distilled or deionized water. Tablets may be crushed with a mortar and pestle or between layers of waxed paper. It is not necessary for all of the solid particles to be dissolved in order to test the substance.
• Household solutions may be placed in labeled containers such as plastic cups, small jars or beakers, well plates or test tubes for student access. Set up several material dispensing stations around the room to avoid congestion.
• Advise students regarding smelling chemicals in the lab. Substances with a strong odor such as ammonia should be kept in a container with a lid or in a stoppered test tube.
• The blotting paper turns blue after being placed in the indicator solution and dried, indicating the paper is slightly basic. For this reason, students may not be able to exactly match the colors produced on their chameleons with the colors on the Universal Indicator Chart. However, the general pattern described in the Background section can be followed to estimate pH values.
• The red cabbage indicator solution may produce an unpleasant odor over time. Do not store leftover solution.
• Test various solutions with the margin strip of treated blotting paper to determine which substances will produce a variety of colors. In our experience, the brightest colors were produced as follows: pinks by the HCl solution and lemon juice, lavender by grapefruit juice, blues by distilled water and antacid tablets, greens by liquid detergent and baking powder, and yellows by dishwasher detergent and the NaOH solution. (The NaOH solution actually produced a yellow spot ringed by green.)
• Students may experiment spotting the treated blotting paper from the front (chameleon side) and the back for more variation in color intensity.
• Bleach is not recommended for this activity. In our experience, a bright white spot was produced which tended to spread farther than most other solutions.
• Some of the colors produced may fade with time. Laminating the finished artwork will preserve the color intensity for a longer time period.

Teacher Tips

• This activity is an excellent and fun way to introduce acids and bases along with their application in industry, health and the environment.
• Strong acid and base solutions are electrolytes, that is, they conduct electricity well due to the presence of ions. Pure water contains no ions, and therefore does not conduct electricity.
• The Indicator Sponge—A Discrepant Event Demonstration Kit (Flinn Catalog No. AP6160) is a great way to amaze your students and challenge their thinking skills regarding acids and bases. For a life science application, try Help from MOM Demonstration Kit (Flinn Catalog No. FB1857).
• To obtain the optimum result for colors, use a 0.02% solution of red cabbage indicator.

Answers to Prelab Questions

1. Complete the following chart by identifying the substance listed as acidic, basic or neutral.
   {13463_Answers_Table_2}
2. Describe the hazards and precautions associated with using hydrochloric acid and sodium hydroxide solutions.

   Hydrochloric acid and sodium hydroxide solutions are slightly toxic by ingestion or inhalation and corrosive to skin and eyes. Avoid contact of all solutions with eyes and skin and clean up spills immediately. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

3. Describe the precautions associated with food-grade items that have been brought into the laboratory.

   All food-grade items that have been brought into the lab are considered laboratory chemicals and are for lab use only. Do not taste or ingest any material in the lab and do not remove any remaining food items after they have been used in the lab.

Sample Data

Answers to Questions

1. Obtain a Universal Indicator Red Cabbage Extract Color Chart. Note: One chart can be shared by several students. Complete the table above by comparing the color of the test solutions spotted on the blotting paper to the colors on the chart. Estimate as closely as possible the pH of each solution tested. A yellow-green to yellow color indicates a pH greater than 11.
2. Which of the solutions tested are acidic? What evidence supports this?

   Hydrochloric acid solution, grapefruit juice, and vinegar are acidic. They produced pink to lavender colors after reacting with the indicator solution, representing pH values less than 7.

3. Which of the solutions tested are basic? What evidence supports this?

   Sodium hydroxide solution, antacid, dishwasher soap, and liquid dish soap are basic. They produced colors corresponding to pH values greater than 7.

4. Are any of the solutions tested neutral or nearly neutral (pH 6–8)? If so, which one(s)?

   Distilled water tested neutral.

5. Based on the results, which solutions would be considered strongly acidic? Which are strongly basic?

   The acids with the lowest pH were HCl solution and vinegar. The bases with the highest pH were NaOH solution and dishwasher detergent.

6. Compare your results with those of other students. (a) In what types of products are most household bases found? What characteristics do bases have in common? (b) In what types of products are most household acids found? What characteristics do acids have in common?

   (a) Most household bases are found in cleaning solutions such as soap, drain cleaner, and ammonia. Bases feel slippery and have a bitter taste. (b) Most household acids are found in juices and soft drinks. Acids taste sour and sting if they come in contact with broken skin.

Introduction

Chameleons are known for their ability to change color. Certain chemicals, called indicators, also change color in solution depending on how acidic or basic the solution is. Creatively change the color of a paper “chem”-eleon treated with red cabbage indicator solution by using a variety of common household substances.

Concepts

• Acids vs. bases
• Indicators
• pH scale

Background

Citric acid, stomach acid, acid rain—just a few acids in our everyday life! Acids are compounds that release hydrogen ions (H⁺, the same as a proton) in solution. Acids are corrosive, sting if they contact broken skin, and taste sour. (Note: Taste should never be used to identify a lab chemical, and chemicals should not be touched with the bare skin.)

Bases are compounds that release hydroxide ions (OH^–) in solution. Bases feel slippery as solutions, are corrosive and have a bitter taste. Remember, however, that touch and taste should never be used to test for the presence of a base or any chemical.

To express the concentration of hydrogen ions in solution, a term called pH (potential of hydrogen) is used. The pH scale ranges from 0–14. If the concentration of H⁺ ions is greater than the concentration of OH^– ions, then the substance is considered acidic and has a pH value lower than 7. Conversely, if the concentration of OH^– ions is greater than the concentration of H⁺ ions, then the substance is basic and has a pH value greater than 7. If the H⁺ and OH^– ion concentrations are equal (as in pure water, H₂O), the substance is neutral, with a pH value of 7. Figure 1 provides pH values for some common substances.

Although acids as a group or bases as a group may have common characteristics, they are not all alike. Some weak acids, such as citric acid found in fruit juices, are safe to consume, while stronger acids corrode metals and destroy human tissue. Likewise, some weak bases are used for bathing, while some strong bases are very caustic to living tissue. The strength of an acid or base depends on the amount of ions produced in solution. A strong acid, such as hydrochloric acid, HCl—found in the stomach—donates a greater number of H⁺ ions to a solution than a weak acid, such as lactic acid found in milk. In a similar manner, strong bases donate more OH^– ions to a solution than weak bases. Household ammonia is a weaker base than sodium hydroxide, NaOH, which is found in drain cleaner.

Red cabbage contains a water-soluble pigment called anthocyanin. A solution prepared from red cabbage extract acts as an indicator because it will react with various solutions and change color depending on the pH of the solution. Strongly acidic solutions will react with anthocyanin to produce a reddish-pink color. The pigment will react with strongly basic solutions to produce a greenish-yellow color and with neutral solutions to produce a bluish-purple color.

Experiment Overview

The purpose of this activity is to estimate the pH of several common household chemicals by “spotting” the chemical onto paper chameleons treated with red cabbage indicator solution. Beautifully unique artwork may be created in the process!

Materials

Prelab Questions

Read the Background and Safety Precautions sections, then answer the following questions.

1. Complete the following chart by identifying the substance listed as acidic, basic or neutral.
   {13463_PreLab_Table_1}
2. Describe the hazards and precautions associated with using hydrochloric acid and sodium hydroxide solutions.
3. Describe the precautions associated with food-grade items that have been brought into the laboratory.

Safety Precautions

The dilute hydrochloric acid and sodium hydroxide solutions used in this lab are slightly toxic by ingestion or inhalation and corrosive to skin and eyes. Some household chemicals are toxic by ingestion or inhalation and are skin and eye irritants. Avoid contact of all solutions with eyes and skin and clean up spills immediately. All food-grade items that have been brought into the lab are considered laboratory chemicals and are for lab use only. Do not taste or ingest any material in the lab and do not remove any remaining food items after they have been used in the lab. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Obtain a blotting paper chameleon, paper towels, and eight cotton swabs.
2. Obtain a sample of 0.1 M hydrochloric acid solution.
3. Dip one end of a cotton swab into the HCl solution. Dab excess solution on a paper towel if necessary.
4. Lightly dab the wet end of the cotton swab on a corner of the blotting paper outside the outline of the chameleon. Do not “spot” the solution too close to the outline, as the liquid may spread.
5. Observe and record the color change in the results table on the “Chem”-eleon Indicator Worksheet.
6. Obtain a sample of 0.1 M sodium hydroxide solution.
7. Repeat steps 3–5 with the NaOH solution, using the other end of the cotton swab.
8. Repeat steps 3–5 six more times with a variety of household chemical solutions (including beverages) provided by your instructor, using a fresh cotton swab end each time. Be sure to record the solutions tested. Reserve a few cotton swabs for your final artwork.
9. Choose three to six solutions to create your colorful “chem”-eleon. Use a variety of dots, lines and other patterns. Always use a fresh cotton swab end to avoid contamination of chemical solutions. Note: Removing some of the dry cotton from the end of a clean swab may help create a smaller spot or line of color.
10. Allow the chem-eleon to dry on a fresh paper towel, and then cut along the outline with scissors.
11. Consult your instructor for appropriate disposal procedures for leftover solutions. Used cotton swabs, scrap blotting paper and paper towels may be disposed of in the regular trash.

Student Worksheet PDF

13463_Student1.pdf