Spring Blooms

Introduction

Now that spring has arrived, let April showers bring gorgeous May flowers. In this two-part demonstration, one set of flowers will explode into a rainbow of colors when sprayed with special misting solutions while a second set of flowers acts as a horticultural chameleon when the humidity is changed.

Concepts

• Acid–base indicators
• Le Chatelier’s principle

Materials

Safety Precautions

Phenolphthalein, thymolphthalein and universal indicator solutions contain alcohol and are flammable solutions. Household ammonia is a skin and eye irritant. Avoid contact with eyes and skin. Do not spray the chemicals on anyone or near any furniture. Cobalt chloride is moderately toxic by ingestion. It is also a possible skin irritant. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. 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. Indicators can be disposed by using Flinn Suggested Disposal Method #18b. Dilute aqueous ammonia can be poured down the drain with excess water according to Flinn Suggested Disposal Method #26b. The flowers may be disposed of according to Flinn Suggested Disposal Method #26a. The cobalt(II) chloride solution may be disposed of according to Flinn Suggested Disposal Method #27f.

Procedure

Part 1

1. Open up two facial tissues and place one on top of the other.
2. Fold one half over the other half along the seam of the tissue (see Figure 1).
   {13979_Procedure_Figure_1}
3. Cut the tissue in half along the seam. This gives four rectangular pieces, one on top of another (see Figure 2).
   {13979_Procedure_Figure_2}
4. Accordion pleat the tissue to form ¼-inch pleats—fold over a small ¼-inch portion of tissue, take this portion and fold it under, and continue in this manner until the entire facial tissue has been used. The result is an alternating over-and-under pattern (see Figure 3).
   {13979_Procedure_Figure_3}
5. Fasten the pleated tissues together in the middle with a green pipe cleaner (see Figure 4).
   {13979_Procedure_Figure_4}
6. Separate each of the four tissue pieces on both sides of the pipe cleaner by gently pulling each tissue ply away from the others. This will give a ruffled look.
7. Repeat steps 1–6 to prepare additional flowers.
8. Fill three spray bottles with different indicator solutions (see the Materials section).
9. Spray each flower with an indicator using a spray bottle. Alter nate between indicators and allow the flowers to air dry. Leave some flowers unsprayed to keep them white.
10. Place the dried flowers in a vase or other container.
11. Pour the ammonia solution into a different spray bottle.
12. Spray the flowers with the aqueous ammonia solution. Watch as the “treated” flowers change to their appropriate indicator colors.
13. Blowing on the flowers will cause the color to slowly disappear.

Part 2
Prepare each flower as follows:

1. Flatten out one sheet of filter paper and fold the filter paper three times to form a small wedge shape. The  wedge is ⅛ of a circle (step 1).
2. Fold the wedge about 4 cm from the tip. Fold the wedge in half, placing the pointed end on the inside of the fold (step 2). The wedge is now 1⁄16 of a circle.
3. Cut out a rectangle, about 10 cm by 15 cm, from the green tissue sheet. Fold the sheet in half twice (step 3).
4. Cut the folded tissue into the shape of a leaf, leaving the fold edge uncut (step 4).
5. Unfold the tissue—there should be four connected leaves. Cut the tissue in half, producing two sets of two leaves (step 5).
6. Bend the center of a green pipe cleaner over the bottom of the folded filter paper from step 2 and twist the pipe cleaner tightly three times (step 6).
7. Place one set of the leaves around the folded filter, then tightly twist the pipe cleaner around both.
8. Repeat step 7 using the other set of leaves.
9. Using your fingers, separate the pleats of the filter to form a robust “blossom.” Twist the remaining lengths of pipe cleaner around each other to make a stem (step 9).
10. Repeat steps 1–9 to prepare additional flowers.
11. Pour some of the 10% cobalt chloride solution into a shallow container or a spray bottle.
12. Hold the flower upside-down and dip it briefly into the solution or apply the 10% cobalt chloride solution from the spray bottle.
13. Dry the flower in the upside-down position. Use a blow dryer or hang by the stem to air dry. The flower is dry when it is blue in color. If it is humid, the flower may stay pink. When the humidity drops, the blue color will emerge.
14. Open the blossom, spray the flower with water using the mist sprayer, and the flower color will change from blue to pink.
15. Dry the flower and repeat the spraying process.

Student Worksheet PDF

13979_Student1.pdf

Teacher Tips

• The kit contains enough chemicals and materials to perform the demonstration as written seven times. Up to 35 reusable flowers may be constructed from the materials included in the kit. After each demonstration, store the chemical solutions for subsequent presentations.
• Empty spray bottles from consumer products, such as window cleaners, can be used if thoroughly rinsed out.
• If desired, the entire demonstration can be performed with just one type of flower.
• This demonstration can be used to introduce the topics of acid–base indicators (Part 1) and Le Chatelier’s principle (Part 2), or presented at spring break as a seasonal review of these subjects.
• Silk flowers may also be used when doing a series of presentations. For best results, wash them between each use.
• The flowers can be dried and stored in zipper-lock bags to be reused later.

  Part 1

• Tissue flowers are easy to make and are useful when performing this demonstration for many participants.
• Meta- or para-nitrophenol, can be used to give a yellow color to the ammonia-treated flowers. Phenolphthalein, thymolphthalein, and nitrophenol solutions can also be combined in various ratios to give a variety of colors to these flowers.
• One spray bottle can be used for all the indicator solutions if it is thoroughly rinsed with deionized water between each change of solution.

  Part 2

• Place the flowers in different locations (e.g., near heating vents, the ceiling, a window, a closet). Record your observations for one week.
• You can illustrate the reversible pink–blue reaction of cobalt chloride using strips of filter paper instead of the paper flowers.

Answers to Questions

1. The solution all of the flowers were sprayed with in Part 1 was ammonium hydroxide. When you blow on the flowers, carbon dioxide combines with water and produces carbonic acid. Describe the colors of the flowers that were first soaked in the following indicator solutions, in an acid and in a base:
   1. Phenolphthalein

      In a basic solution, these flowers were white. In an acid, they were pink.

   2. Thymolphthalein

      In a base, these flowers were blue, but in an acid they were pink.

   3. Universal indicator

      In a base, these flowers were bluish-purple. In an acid, they were reddish-orange.

2. What is an acid–base indicator?

   An acid–base indicator is a chemical that changes color based on the pH of the solution.

3. What color were the flowers in Part 2 when they were wet? What color were they when they were dry?

   When the flowers in Part 2 were wet, they were a bright pink color. After the flowers had dried, they were blue.

4. What is Le Chatelier’s principle?

   Le Chatelier’s principle states that system that is at equilibrium will try to stay at equilibrium. Therefore, if change occurs in a system at equilibrium, the position of equilibrium will shift in a direction to reduce the effect of that change.

Discussion

Part 1
Indicators are weak organic acids or bases that change colors at various pH values. Indicator color changes are described in many chemistry books. Phenolphthalein solution gives a pink flower in basic solution and a colorless or white flower in an acidic environment. Thymolphthalein turns the flower a very light blue in basic solution. A stronger aqueous ammonia solution will give a deeper blue color. Universal indicator solution gives multicolored flowers, depending on the pH of the ammonia solution. When blowing on the flowers, carbon dioxide in breath combines with water to form carbonic acid. This lowers the pH, turning both the phenolphthalein- and thymolphthalein-soaked flowers colorless or white. Flowers tested with universal indicator will change to red, orange, or yellow, depending on the final pH.

Part 2
Anhydrous cobalt(II) chloride (CoCl₂) is blue and cobalt chloride hexahydrate (CoCl₂•6H₂O) is pink.

References

Special thanks to Penney Sconzo, Westminster Schools, Atlanta, Georgia, for providing Flinn Scientific with the instruction for the Part 1 activity. Special thanks also to Shirley Wehner, Flinn Scientific, for developing the instructions to create the flowers in Part 2.

Mattson, Bruce; Kubovy, Mary Alice; Hepburn, Jeff; Lannan, Joe. Chemistry Demonstration Aids That You Can Build. Flinn Scientific: Batavia, IL, 1997.