The Chemistry of Spring Break

Introduction

Spring break is a time for students and teachers to cast off the winter doldrums and embrace the arrival of a bright new season. Entertain and amuse the students with this set of six demonstrations that celebrate the arrival of spring.

This set of six demonstrations includes:

1. The Blues of Winter Battle the Sunshine of Spring—Create a solution that mimics early spring. The solution starts out sunny yellow, turns blue and melancholy, then back to yellow and blue again and so on. The color oscillation will continue for about 10 minutes.
2. Spring Colors Arrive—Colorless solutions are combined to produce a brilliant rainbow of spring colors. The demonstration can be performed with accompanying music (i.e., “The Rainbow Connection”).
3. Bright Sun, Warmth and Leaves—A flask of sunny yellow solution, when shaken, produces a warm red color, that leads to the greens of spring foliage. The demonstration solution can be prepared once and reused over and over again.
4. Spring Blooms—Now that spring has arrived, let April showers bring gorgeous May flowers. Spray a misting solution onto colorless flowers and watch the flowers bloom into vibrant hues! The demonstration requires 30–50 minutes preparation time.
5. Weather-or-Not Flowers—A change in weather causes these flowers to dramatically switch identity. A striking blue petunia when the air is dry, the flower converts to a pink impatiens in a humid condition. This demonstration requires 20–30 minutes preparation time.
6. Fun in the Sun—As spring break approaches, all thoughts turn to... you guessed it, VACATION! In this overhead demonstration, students can sit back and watch as the sun slowly sets over the palm tree on their vacation beach.

The “Chemistry of Spring Break” can be presented in a variety of ways. All six demonstrations can be performed during one class period, one demonstration can be done for each day before spring break, or the demonstrations can be performed over several class sessions.

Supplemental Demonstrations
Instructions for three additional demonstrations on the “spring break” theme are included as supplements.

1. Easter Explosion—Place a beaker of green solution inside a plastic Easter bunny, add a yellow liquid and stand back! Foamy green ooze and stream will erupt out of the wabbit’s mouth and eyes.
2. Feeling Blue—No one is exempt from an occasional “bout with the blues.” Whether it is because “your favorite team just lost the big game” or “winter is getting you down”—we are all susceptible to temporary periods of brief sadness. Still, in time, the “weather changes” and so does our mood. The following demonstration provides a visual perception of how the “blues” come and go when our lives get a little shaken up.
3. Easter Egg in a Flask—Place a shelled, hard-boiled egg in the neck of an erlenmeyer flask, chill the flask with an ice water solution and presto! The egg is sucked into the flask. Remove the flask from the ice water bath, apply heat, and the egg pops out of the flask.

Concepts

• Oscillating reactions
• Reaction mechanisms
• Acid–base reactions
• pH indicators
• Oxidation-reduction
• Indicators
• Acid–base indicators
• Le Chatelier’s principle
• Colloids and precipitates
• Tyndall effect/light scattering
• Catalysts
• Decomposition reaction
• Pressure–temperature relationship at constant volume

Experiment Overview

The Blues of Winter Battle the Sunshine of Spring
Three colorless solutions are mixed to produce a yellow solution that suddenly turns blue and then yellow again. The solution will oscillate between yellow and blue for several minutes. This classic oscillating reaction will amaze students and teachers alike.

Spring Colors Arrive
A colorless solution is added to each of six beakers. A second colorless solution is added to each and the six solutions turn a different color of the rainbow. Add more of the first solution and the rainbow of colors disappears.

Bright Sun, Warmth and Leaves 
A solution is shaken, and the color of the solution turns from yellow to red to green and then back to yellow again. The sequence of color changes is reversible.

Spring Blooms
A collection of flowers turn different colors when sprayed with a “misting” solution. Students are impressed--why are various colors obtained with different indicators? Add an aesthetic touch of springtime to the classroom with this unusual demonstration of acid-base properties.

Weather-or-Not Flowers 
Create a variety of blooms, all with one flower! Use Le Chatelier’s principle to create a real horticultural chameleon.

Fun in the Sun
A simple chemical reaction produces a colloidal solution, resulting in a chemical “sunset.”

Materials

Safety Precautions

Hydrogen peroxide solution is an oxidizer and a skin and eye irritant. Potassium iodate is an oxidizer; the solution is acidified and contains sulfuric acid. Sulfuric acid is severely corrosive to eyes, skin and other tissue. Starch–malonic acid–manganous sulfate solution is a strong irritant, moderately toxic and corrosive to eyes, skin and respiratory tract. The reaction produces iodine in solution, in suspension and as a vapor above the reaction mixture. The solid iodine is toxic by ingestion and its vapor is toxic by inhalation. Iodine in solution is irritating to eyes, skin and respiratory tract. Perform The Blues of Winter Battle the Sunshine of Spring demonstration in well-ventilated room. Avoid all body tissue contact with all chemicals. Dilute hydrochloric acid solution is a skin and eye irritant. Dilute sodium hydroxide solution, although dilute, is corrosive; skin burns are possible; very dangerous to eyes. The indicator solutions contain ethyl alcohol, which is a flammable liquid and a fire risk; keep away from heat and open flame. Indigo carmine indicator solution is moderately toxic by ingestion and is a body tissue irritant. Sodium hydroxide solution is a corrosive liquid and skin burns are possible. It is very dangerous to eyes. 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. Hydrochloric acid solutions are highly toxic by ingestion or inhalation; severely corrosive to skin and eyes. The sulfur produced in this reaction has low toxicity and may be a skin irritant. Sulfur dioxide is an irritant to eyes and other tissues. 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.

Supplemental Demonstrations
Hydrogen peroxide solution, 30%, is severely corrosive to the skin, eyes and respiratory tract; a very strong oxidant; a dangerous fire and explosion risk. Do not heat this substance. Sodium iodide is slightly toxic by ingestion. Do not stand over the reaction; steam and oxygen are produced quickly. Potassium hydroxide is strongly corrosive as a solid and as a solution; skin contact causes severe blisters; extremely dangerous to eyes; very harmful if swallowed. Methylene blue is moderately toxic. Wear protective eyewear and insulated gloves for the Easter Egg in a Flash demonstration. 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. Dispose of the reaction mixture from The Blues of Winter Battle the Sunshine of Spring according to Flinn Suggested Disposal Method #12a. The final solutions from Spring Colors Arrive and Bright Sun, Warmth and Leaves may be flushed down the drain with excess water according to Flinn Suggested Disposal Method #26b. Indicators from the Spring Blooms demonstration can be disposed by using Flinn Suggested Disposal Method #18b. The flowers from Weather-or-Not Flowers may be disposed of according to Flinn Suggested Disposal Method #26a, and the cobalt(II) chloride solution may be disposed of according to Flinn Suggested Disposal Method #27f. The final reaction mixture from Fun in the Sun can be filtered and the solid disposed of according to Flinn Suggested Disposal Method #26a. The remaining filtrate can be disposed of by diluting with water and then neutralizing it according to Flinn Suggested Disposal Method #24b.

Supplemental Demonstrations
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. The foam and solution left in the beaker and on the Easter rabbit in the Easter Explosion demonstration may be washed down the drain with plenty of excess water according to Flinn Suggested Disposal Method #26b. Neutralize the resulting solution from the Feeling Blue demonstration according to Flinn Suggested Disposal Method #10. In the Easter Egg in a Flask demonstration, the egg can be disposed of in a waste can.

Prelab Preparation

Spring Colors Arrive

1. Set up six 250-mL beakers on an overhead projector or light box, or in front of the class.
2. Add three drops of “violet” indicator solution to the first beaker. Add three drops of “blue” indicator solution to the second beaker. Continue adding three drops of each of the other indicator solutions to the appropriate beakers.
3. Allow time for the solvent in the indicator solutions to evaporate.
4. To a 1000-mL beaker, add approximately 100 mL of 0.1 M sodium hydroxide solution. Dilute to 1 L with distilled or deionized water to make a 0.01 M NaOH solution. Transfer this solution to a 1-L bottle. Cap the bottle and label 0.01 M NaOH.
5. Repeat step 4 using 100 mL of the 0.1 M hydrochloric acid solution to prepare 1 L of 0.01 M HCl.

Spring Blooms

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).
   {13938_Preparation_Figure_1}
3. Cut in half along the seam. This gives you four rectangular pieces, one on top of another. (see Figure 2).
   {13938_Preparation_Figure_2}
4. Accordion pleat in ¼-inch pleats. Fold the small ¼-inch portion over, and take this portion and fold under until you have used the entire facial tissue. This alternates the over and under pattern. (see Figure 3)
   {13938_Preparation_Figure_3}
   .
5. Fasten the pleated tissues together in the middle with a green pipe cleaner. (see Figure 4).
   {13938_Preparation_Figure_4}
6. Separate each of the four pieces on each side of the pipe cleaner by gently pulling each ply away from the others. This will give a ruffled look.
7. Repeat steps 1–6 for additional flowers.
8. Fill three spray bottles with a separate indicator solution.
9. Spray each flower with an indicator using a spray bottle. Alternate between indicators (allow to 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 spray bottle.

Weather–or–Not Flowers
Prepare each flower as follows (see Figure 5):

1. Flatten out one sheet of filter paper.
2. Fold the filter paper into a small wedge shape (three folds).
3. Fold the wedge about 4 cm from the tip. Fold the wedge in half, placing the pointed end on the inside of the fold. Set the filter paper aside.
4. Cut out a rectangle, about 10 cm by 15 cm, from the green tissue sheet. Fold the sheet in half twice.
5. Cut the folded tissue into the shape of a leaf, leaving the fold edge uncut.
6. Unfold the tissue. There should be four connected leaves.
7. Cut the tissue in half, producing two sets of two leaves.
8. Bend the center of a green pipe cleaner over the bottom of the folded filter (step 3) and twist the pipe cleaner tightly for three twists.
9. Place one set of the leaves around the folded filter, then tightly twist the pipe cleaner around both.
10. Repeat step 9 for the other set of leaves.
11. 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.
12. Repeat steps 1–11 for additional flowers.

Procedure

The Blues of Winter Battle the Sunshine of Spring

1. Using a clean 50-mL graduated cylinder, measure out 40 mL of 8.6% hydrogen peroxide solution and transfer it to a 250-mL beaker.
2. Using a second clean 50-mL graduated cylinder, measure out 40 mL of the acidified 0.2 M potassium iodate solution and add it to the beaker. Stir using a stirring rod or magnetic stirrer.
3. Using the third 50-mL graduated cylinder, measure out 40 mL of the starch–malonic acid–manganous sulfate solution. Add this solution to the beaker and stir.
4. Bubbles will begin to appear. In a short time, the solution will turn yellow, then blue, and finally colorless. The entire process repeats itself over and over again. The yellow to blue to colorless oscillations will continue for about 10 minutes.

Spring Colors Arrive

1. Add approximately 50 mL of the 0.01 M hydrochloric acid solution to each of the 250-mL beakers. All six resulting solutions should be colorless. (Some of the solutions may appear slightly cloudy.)
2. Add approximately 75 mL of 0.01 M sodium hydroxide solution to each beaker. Each of the six solutions should turn a different color of the rainbow! The solution may require a slight stir to become uniform.
3. Add approximately 100 mL of 0.01 M hydrochloric acid solution to each beaker. The solutions will once again turn colorless.

Precise amounts of acid and base solutions are not important. Each addition of acid or base solution should neutralize the solution in the beaker and drive the pH in the opposite direction. Stirring the solution helps the mixing but is not necessary. All solutions can be poured into one large two-liter beaker at the end of the demonstration. The final solution will be acidic and colorless.

Bright Sun, Warmth and Leaves

1. To prepare a 1% indigo carmine solution, carefully add 100 mL of distilled or deionized water to the bottle containing the indigo carmine powder included in the kit. Replace the bottle cap and shake vigorously. This solution has a poor shelf life and will deteriorate over a period of months; try to prepare it fresh.
2. Place 100 mL of the dextrose solution and 100 mL of the sodium hydroxide solution into a 500-mL Erlenmeyer flask.
3. Add 10 mL of the indigo carmine indicator solution to the flask. Firmly insert the stopper.
4. Allow the solution to sit and become fully reduced (amber).
5. Show the amber solution to the class and then place it behind your back and shake it gently. Show the students that it is now red. Again place it behind your back and let it change back to the amber color. Shake it vigorously, and show the students the green color.

Spring Blooms

1. Explain to students that the magic flowers need watering.
2. Spray the flowers with the aqueous ammonia solution. Watch as the “treated” flowers change to their appropriate indicator colors.
3. Blowing on the flowers will cause the color to slowly disappear.

Weather–or–Not Flowers

1. Pour some of the 10% cobalt chloride solution into the shallow container or into a spray bottle.
2. Hold the flower upside-down and dip it briefly into the solution or apply the cobalt chloride solution from the spray bottle.
3. 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 form.
4. Open the blossom, spray the flower with water using the mist sprayer, and the flower color changes.
5. Dry the flower again.

Fun in the Sun

1. Cut out inner circle of Cutout 1 and place it on the overhead.
2. Cut out the figure in Cutout 2 and place it inside the hole in Cutout 1.
3. Place the Petri dish inside the hole in Cutout 1, on top of Cutout 2 (see Figure 6).
   {13938_Procedure_Figure_6}
4. Turn on the overhead projector. Focus the image on a projector screen or wall.
5. Measure out 14 mL of 0.2 M Na₂S₂O₃ solution; pour into the Petri dish.
6. Measure out 8 mL of 1 M HCl solution; pour into the Petri dish.
7. If desired, a CD of Hawaiian or Jimmy Buffet music, for example, can be played.
8. Observe the color of the projected light on the screen or wall.

Supplemental Demonstrations 

Easter Explosion

1. Cut holes in the eyes and mouth of the plastic bunny. Make sure the bunny fits over the 150-mL beaker.
2. Place the plastic Easter bunny and the 150-mL beaker in a large plastic demonstration tray that is several inches deep.
3. Measure 70 mL of the 30% hydrogen peroxide into the 150-mL beaker. Caution: Wear chemical-resistant gloves, chemicalresistant apron, and chemical splash goggles when handling 30% hydrogen peroxide. Contact with skin will cause burns.
4. Measure 10 mL of dishwashing liquid into a 10-mL graduated cylinder and add it to the beaker containing the hydrogen peroxide. Add a few drops of green food coloring and stir. Place the Easter bunny over the beaker.
5. Measure 5 mL of 2 M sodium iodide solution into a clean 10-mL graduated cylinder.
6. Tell students you will now call forth the spirit of the “Easter Bunny.”
7. Add the sodium iodide to the contents of the 150-mL beaker and quickly, but carefully, place the rabbit over the beaker.
8. Watch as the “spirit” erupts from the eyes and mouth.

Feeling Blue

1. Using a 100-mL graduated cylinder, measure out 100 mL of potassium hydroxide solution and transfer it to a 500-mL flask.
2. Using the graduated cylinder, measure out 100 mL of dextrose solution and transfer it to the flask. Swirl the flask to mix the solutions.
3. Add 3–4 drops of 1% methylene blue solution to the flask. Stopper the flask and swirl to mix the solutions.
4. Allow the solution to stand undisturbed until it turns colorless. This may take a few minutes.
5. Shake the flask gently to obtain the blue color again.
6. Repeat steps 4 and 5. The process of shaking to obtain the blue color can be repeated about ten times.

Easter Egg in a Flask

1. Place stopcock grease around the inner lip of the 1000-mL Erlenmeyer flask.
2. Place the ice-water mixture in the water bath or container.
3. Clamp the flask to the ring stand. Heat the flask for a minute or so with either a Bunsen burner with a low yellow flame or a hairdryer.
4. Place the shelled hard-boiled egg, pointed end down, in the neck of the flask.
5. Wearing insulated gloves, unclamp the flask and place it in the ice-bath. The egg will pop into the flask.
6. Wearing insulated gloves, invert the flask so that the narrow end of the egg points out of the neck of the flask.
7. Heat the flask with the Bunsen burner with the same luminous flame or with a hairdryer. Rotate the flask as it is heated. Within a minute, the egg should pop out of the flask.

Teacher Tips

• The kits contains enough chemicals to perform the The Blues of Winter Battle the Sunshine of Spring demonstration as written seven times.
• The reaction can also be done using 3% hydrogen peroxide, although the color changes will not be as sharp. Therefore an 8–9% solution is recommended for this demonstration.
• A magnetic stirrer can be used to stir the solution throughout the entire demonstration or used to simply mix the solutions once at the beginning of the demonstration. The solution does not have to be stirred for the oscillations to occur.
• The demonstration can be done in a Petri dish on an overhead projector. Pour equal amounts (about 5 mL) of each solution into the Petri dish and swirl to mix. The solution will oscillate between yellow and blue for numerous cycles.
• Use only distilled or deionized water. Chloride ions from tap water will contaminate the reaction and stop the oscillations.
• This demonstration is also called Yellow and Blue Switcheroo, and is available from Flinn Scientific, Catalog No. AP8660.
• The kit contains enough chemicals to perform the Spring Colors Arrive demonstration as written seven times.
• The indicators are dissolved in 95% ethyl alcohol. The alcohol will readily evaporate, leaving the indicator powder in the beaker—unseen to the observers of the demonstration.
• You may use drops of a more concentrated acid or base to change the solutions from colored to colorless, or a more concentrated base to change the solutions from colorless to colored.
• This demonstration is also called The Disappearing Rainbow and is available from Flinn Scientific, Inc., Catalog No. AP8979.
• The kit contains enough chemicals to perform the Bright Sun, Warmth and Leaves demonstration as written seven times.
• The solution will be green initially. Allow the solution to sit undisturbed until it becomes a bright amber (yellow). This may take as long as 10 minutes. If the solution is not bright amber, you may need to add more indigo carmine.
• A little practice will quickly determine how many shakes are needed for the red color and how many additional shakes for the green color.
• The solution will repeat this yellow to red to green cycle for 20 minutes or so depending on how often it is shaken and how much oxygen is reintroduced by opening the bottle.
• The colors will become less vivid with time. The indigo carmine solution has a limited shelf life (6 to 12 months) and should be royal blue in color. If it is not blue, the solution needs to be prepared fresh in order for the demonstration to work.
• This demonstration is also called Stop–’N–Go Light and is available from Flinn Scientific, Inc., Catalog No. AP2083.
• A clear plastic bottle, such as Flinn Scientific AP8435, also works well for this demonstration.
• The kit contains enough chemicals and materials to perform the Spring Blooms demonstration as written seven times.
• Silk flowers can be reused when doing a series of presentations. It is best to wash them between each use.
• Tissue flowers are easy to make and are useful when performing this demonstration for many participants.
• This is an exciting activity for young students at an elementary school or at a science center. The flower can also be sprayed with household ammonia or a window cleaning solution with ammonia to change the color.
• Nitrophenol, meta or para, can also be used to give a yellow color when reacted with ammonia. Phenolphthalein, thymolphthalein, and nitrophenol can also be combined to give a variety of colors.
• One spray bottle can be used for all the solutions if it is thoroughly rinsed with deionized water between each change of solution.
• Spray bottles of consumer products, such as window cleaners, can be used if thoroughly rinsed out.
• Weather–or–Not Flowers The flowers can be dried and stored in zipper-lock bags to be reused later.
• Place the flower in different locations (e.g., near heating vents, the ceiling, a window, a closet). Record your observations for one week.
• You can illustrate the same principle using strips of filter paper or blotter paper treated with the cobalt chloride solution instead of the paper flowers.
• Spray bottles of consumer products, such as window cleaner, can be used if thoroughly rinsed out.
• The kit contains enough chemicals and materials to perform the Easter Explosion demonstration as written seven times. The Easter bunny may be cleaned and reused over and over.
• You may want to do this demonstration in a large demonstration tray since there is a lot of foam produced. Cleanup, however, is easy due to the presence of extremely safe final products and the generous amount of detergent.
• The beaker will get hot, so let it cool before handling.
• The slight brown tinge of the foam at the beginning is due to free iodine produced by the extreme oxidizing ability of the 30% hydrogen peroxide.
• If the Easter bunny is a chocolate color, try the demonstration without the addition of green food dye.
• Another catalyst that will catalyze this reaction is manganese(IV) oxide, MnO₂.
• Place a glowing splint in the foam and it will relight, showing the presence of oxygen.
• A drop cloth may be necessary to prevent the foam from landing on carpeting or floors. The iodine may stain the material.
• The Feeling Blue demonstration can be used to develop your students’ observation and scientific skills. Allow them to make observations, suggestions and ask questions. Make sure your students have a chance to observe the blue interface between the gas in the flask and the solution.
• Campbell’s article in the Journal of Chemical Education, (1963, 40, 578) is a well written explanation of kinetics as well as the specific kinetics of this demonstration.
• The length of time the solution stays blue is directly proportional to the amount of shaking.
• This demonstration is available from Flinn Scientific, Inc., Catalog No. AP8653.

Discussion

The Blues of Winter Battle the Sunshine of Spring
This oscillating reaction is known as the Briggs-Rauscher (BR) Reaction and was developed by Thomas S. Briggs and Warren C. Rauscher of Galileo High School in San Francisco. The reaction mechanism is very complex. During the reaction, oscillations occur in the concentration of iodine (I₂) and iodide ions (I^–). The yellowish color is attributed to the rise in I₂ concentration; the blue-black color of the starch–iodine complex results from the rise in both I^– and I₂ concentrations. The colorless solution is caused by the decline in I₂ concentration and the continued rise in I^– concentration.

The blue-black starch iodine complex is amylose–iodine. Amylose is the linear starch fraction which is composed of chains of 1,4-linked α-glucose units as shown above. The color of the complex, blue-black, comes from the pentaiodide anion, I₅^–, formed when the I₂ and I^– concentrations are elevated. Though normally an unstable anion, I₅^– becomes stable as a part of the starch–iodine complex.

The overall BR reaction is:

IO₃^–(aq) + 2H₂O₂(aq) + CH₂(CO₂H)₂(aq) + H⁺(aq) → ICH(CO₂H)₂(aq) + 2O₂(aq) + 3H₂O(l)

This reaction consists of two component reactions that create an intermediate molecule, HOI. The two reactions are themselves very complex, consisting of ten steps. Iodine (I₂) and iodide ions (I^–) are produced as intermediates in various steps of these reactions.

In the proposed reaction mechanism, the concentration of HOI rises and falls, triggering oscillations in the I^– and I₂ concentrations in solution. When I₂ and I^– concentrations are high, the solution is blue; when I₂ is high and I^– is low, the solution is yellow; and when I₂ is low and I^– is high, the solution is colorless.

The oscillations continue until either malonic acid or iodate ions are consumed.

Spring Colors Arrive
The three indicators used in this lab are phenolphthalein, thymolphthalein, and p-nitrophenol. All are colorless in acidic solution. In basic solution, phenolphthalein is red, thymolphthalein is blue and p-nitrophenol is yellow. The rainbow of colors produced in the demonstration result from various combinations of these primary colors.

The pH range of color change for each of the three indicators is listed in Table 1. The pH values for the color changes of the mixed indicators are in the range 5.6–10.5. A neutral solution, pH 7, may have a slight tinge of yellow left in four of the beakers from p-nitrophenol, while a slightly basic solution, pH 7.6, may leave all the beakers clear. If these occur in the demonstration, simply add a few milliliters more of the acid or base until there is a complete color transition in each beaker.

Bright Sun, Warmth and Leaves
An alkaline dextrose solution is shaken in the presence of oxygen and indigo carmine. Indigo carmine can be reduced by the alkaline sugar and oxidized by the oxygen in the bottle. When the reduced form of indigo carmine (amber color) is agitated in the presence of dissolved oxygen gas, it becomes oxidized to the green color.

Shakashiri proposes the middle structure below as the red color intermediate. As the solution containing the oxidized form is allowed to sit, most of the available dissolved oxygen is used up and the indigo carmine is slowly reduced by the dextrose back to the reduced form (amber color).

After about 10 or 15 cycles, when all of the oxygen in the flask has been used up, the redox reaction will cease. Remove the stopper to introduce more air and repeat the process. An outline of the proposed reaction mechanism is as follows: Spring Blooms
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 one. 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 solution. When blowing on the flowers, carbon dioxide in the breath combines with water to form carbonic acid. This lowers the pH, turning both the phenolphthalein and thymolphthalein soaked flowers colorless or white. The universal indicator soaked flowers will change to either red, orange or yellow, depending on the final pH.

Weather–or–Not Flowers
Anhydrous cobalt(II) chloride (CoCl₂) is blue and cobalt chloride hexahydrate {CoCl₂•6H₂O} is pink. The colors that you observe in this activity are a result of the loss or addition of water. In the aqueous solution the pink hydrate form of cobalt chloride is present. When the treated paper is dried, the blue anhydrous form is present. The color changes illustrate Le Chatelier’s principle.

Fun in the Sun
The thiosulfate ion decomposes in acid solution, producing colloidal sulfur according to the reaction:

S₂O₃^2–(aq) + 2H⁺(aq) → S(s) + SO₂(aq) + H₂O(l)

As the colloidal sulfur particles grow, the light from the overhead projector is scattered. As the concentration of colloidal sulfur and its particle size increases, the shorter wavelengths of light are scattered while the longer wavelengths pass through, producing a red color in the projected beam. Eventually, the concentration and particle size of the colloid becomes so great that no light can be transmitted through the solution.

Supplemental Demonstrations

Easter Explosion
This demonstration evolves a good deal of heat as shown by the steam coming off the foam as it is produced. The reaction, therefore, is exothermic. The action of a catalyst is demonstrated. The catalyst is the I^–(aq) ion which speeds up the decomposition of the hydrogen peroxide. The decomposition of hydrogen peroxide produces steam and oxygen gas. The oxygen gas and water vapor cause the dishwashing liquid to foam. Feeling Blue
The blue solution becomes colorless upon standing due to the reduction of the methylene blue. By shaking the flask, oxygen dissolves in the colorless solution. The methylene blue is then oxidized to its blue form by reacting with this dissolved oxygen. The blue color initially develops at the interface between the gas (oxygen in the flask) and the solution, demonstrating that the gas is entering the solution and causing the blue color.

In a series of fast reactions, alkaline glucose is converted to glucoside, oxygen in the flask goes into solution, and dissolved oxygen oxidizes the reduced colorless methylene blue to the blue oxidized form of methylene blue. In a slow reaction, the blue oxidized form is reduced by the glucoside, and it is not until this occurs that a completely colorless solution is observed.

The reaction mechanism (Campbell, 1963) occurs in four steps: Easter Egg in a Flask
For an ideal gas, at constant volume and moles, the pressure of the gas is directly related to its temperature T in degrees Kelvin. As temperature decreases, so does the pressure.

P = kT

For the gas at two temperatures, T₁ and T₂:

P₁/P₂ = T₁/T₂

If the equation is rearranged, then the final pressure, P₂, is equal to the ratio of the final temperature to the initial temperature times the initial pressure.

P₂ = (T₂/T₁) P₁

The larger the temperature difference, the bigger the change in the final pressure.

The gas in the Erlenmeyer flask is first heated, and then sealed with the egg. The flask is placed in an ice-water bath. This causes a reduction in the temperature and pressure of the air inside the flask. When the pressure inside the flask has been sufficiently reduced, atmospheric pressure forces the egg into the flask. When the flask is inverted and heated, the process is reversed, and the pressure buildup of the air inside the flask forces the egg out of the flask.

References

Special thanks to Jim and Julie Ealy, The Peddie School, Hightstown NJ, for providing Flinn Scientific with the instructions for The Blues of Winter Battle the Sunshine of Spring, the Bright Sun, Warmth and Leaves and the Feeling Blue activities. Special thanks to Penney Sconzo, Westminster Schools, Atlanta, Georgia, for providing Flinn Scientific with the instruction for the Weather–or–Not Flowers activity. Special thanks also to Shirley Wehner, Flinn Scientific, for developing the instructions to create the flowers. Special thanks to David Katz of Cabrini College in Radnor, PA, for bringing the Fun in the Sun demonstration to our attention.

Abbott, G. E., J. Chem. Educ. 1947, 2, 45.

Abbott, G. E., J. Chem. Educ. 1948, 26, 100.

Briggs, T. S. and Rauscher, W. C. J. Chem. Ed., 1973, 50, 496.

Campbell, J. A., J. Chem. Educ. 1963, 40, 578.

Dutton, F. B., J. Chem. Educ. 1960, 37, A799. 

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