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It's a Chemoween Celebration!

Felicia Cherry
Product Manager for Physical Science, Physics, and Earth Science

Treat your ghosts and ghouls to some spirited demos and hands-on activities. Celebrate Chemoween as the finale to your October chemistry celebrations. Discuss topics such as acid-base chemistry, density, indicators, polymers, properties of matter, and phase changes. This is a celebration that students will not forget.

Safety

Perform all activities in accordance with established laboratory safety practices, including appropriate personal protective equipment (PPE). Ensure that students understand and adhere to these practices. Know and follow all school district guidelines for the disposal of laboratory wastes. Read the activity-specific cautions below before performing the activities.

Foaming Rainbow and Dry Ice Explosion

Dry ice is very cold, –78.4° C (–109° F). Do not allow it to contact bare skin. Store dry ice in a polystyrene foam cooler with a loose-fitting lid to prevent the pressure inside the cooler from increasing to unsafe levels. Never store dry ice in a sealed cooler, refrigerator, or freezer. Carbon dioxide gas is odorless and colorless. Use, store, and transport dry ice only in well-ventilated areas.

Puking Pumpkin

Hydrogen peroxide, 30%, is an extremely strong oxidizer that can cause burns. Do not allow it to contact bare skin.

Do not stand directly over or in front of the jack-o’-lantern during the demo. The reaction quickly generates heat and foam that contains iodine and food coloring, which may stain skin, clothing, and surfaces. Handle with care. Recommended PPE for clean up: eye protection, gloves, and a lab apron or coat. If you or a student is iodine sensitive, an alternate method for this demo is provided in the teacher prep section.

Preparation for Foaming Rainbow and Dry Ice Explosion (the 2 dry ice activities)

Materials

  • Foam Cooler with Loose-Fitting Lid
  • Pillowcase or Large Cloth
  • Hammer
  • Thermal Gloves
  • Safety Glasses
  • 1½-gal Terrarium

If possible, purchase the dry ice on the same day you perform the demonstrations. It is available at many grocery stores. You will need approximately 1 lb of dry ice. Use a foam cooler to transport it to your classroom. Caution: Do not store dry ice in a sealed container, refrigerator, or freezer.

Just before the demonstration and while wearing thermal gloves and eye protection, place approximately 1 lb of dry ice inside a pillowcase or wrap it in cloth. With a hammer, strike the dry ice and break it into fragments ½" or smaller. Place the fragments and powder in a 1½-gal terrarium. This will be your source of dry ice for both demonstrations.

Foaming Rainbow
Topic: Acid-base chemistry

Commercially, dry ice is used as a refrigerant in the food industry. Your students may be familiar with seeing a piece of dry ice, the solid form of carbon dioxide (CO2), bubble in water to create an eerie fog. Carbon dioxide dissolves in water to form a weak solution of carbonic acid:

CO2(g) + H2O(l) → H2CO3(aq) ↔ 2H+(aq) + CO32–(aq)

Adding dry ice to a basic solution of dish detergent and universal indicator causes the solution’s pH to decrease and the universal indicator to change colors. As carbon dioxide is released from the solution, it forms bubbles with the dish detergent, producing a mass of foam. Note: Bogen universal indicator is blue at a pH above 10.0, green at a pH of 8.0, yellow at a pH of 6.0, orange at a pH of 5.0, and cherry red at a pH of 1.0 or lower.

Safety

Dry ice is very cold, –78.4° C (–109° F). Do not allow it to contact bare skin. Store dry ice in a polystyrene foam cooler with a loose-fitting lid to prevent the pressure inside the cooler from increasing to unsafe levels. Never store dry ice in a sealed cooler, refrigerator, or freezer. Carbon dioxide gas is odorless and colorless. Use, store, and transport dry ice only in well-ventilated areas.

Make sure that the soapy foam does not create a slipping hazard.

Materials

1½-gal Terrarium (empty)
500-mL Graduated Cylinder (use a clear plastic one for best results)
Bogen Universal Indicator
Sodium Hydroxide, 0.1 M
Dish Detergent
Dry Ice Chunks
Thermal Gloves
Stir Plate
Stir Bar (appropriate size for the graduated cylinder)
Pipet or Dropper
Water

Teacher prep

  1. Put on PPE.
  2. Place the stir bar inside the graduated cylinder and fill the cylinder about half-full of water.
  3. Place the cylinder on a stir plate. Turn on the stir plate.
  4. Add 5 drops of dish detergent and 1 mL of indicator.
  5. Add sodium hydroxide drop by drop until the solution is a deep shade of blue.
  6. Remove the cylinder from the stir plate. Set aside until ready to use.

Procedure

  1. Put on PPE.
  2. Place the graduated cylinder containing the solution inside the terrarium.
  3. Drop a piece of dry ice in the graduated cylinder.
  4. Continue adding pieces of dry ice until the solution in the graduated cylinder turns red.

Dry Ice Explosion
Topics: Phase changes, properties of matter

At standard pressure, dry ice transforms directly from a solid to a gas, a process called sublimation. To illustrate this, small pieces of dry ice are sealed in a plastic pipet and submerged in water. The dry ice continues to sublime in the sealed pipet bulb. When the pressure inside surpasses that of the triple point (5.1 atm), at which all 3 phases are in equilibrium, the carbon dioxide begins to melt and then to boil. For a moment, the 3 states of carbon dioxide exist in the bulb. After the bulb bursts, the pressure quickly drops and any remaining liquid or gaseous carbon dioxide in the bulb solidifies. You can see a free video of this activity here.

Safety

Dry ice is very cold, –78.4° C (–109° F). Do not allow it to contact bare skin. Store dry ice in a polystyrene foam cooler with a loose-fitting lid to prevent the pressure inside the cooler from increasing to unsafe levels. Never store dry ice in a sealed cooler, refrigerator, or freezer. Carbon dioxide gas is odorless and colorless. Use, store, and transport dry ice only in well-ventilated areas.

Materials

1½-gal Terrarium (¾ full of water)
10 to 15 Disposable Pipets
Pliers
Scissors
Thermal Gloves
Safety Goggles
Dry Ice (crushed)

Teacher prep

  1. Cut the tapered end off several disposable pipets at the 1-mL mark. To make filling the pipets easier, cut at an angle.
  2. Put on PPE and practice the demo a few times to get a feel for folding the pipet closed and creating a tight seal with the pliers. If no more than a very few bubbles are coming out of the submerged pipet, you have a good seal.

Procedure

  1. Put on PPE and have students do the same.
  2. Clear the area of any water-sensitive items (e.g., electronics, textbooks, and papers).
  3. Scoop crushed dry ice into the open stem of the trimmed pipet.
  4. Tap the pipet on its bulb end to move the dry ice into the bulb. Point out to students that the dry ice is in its solid form.
  5. Repeat the scooping and tapping steps until the bulb is half-full of dry ice.
  6. Fold the pipet stem over itself toward the bulb.
  7. Hold the folded pipet stem firmly with pliers. Make a good seal. Do not let go. Continue squeezing the pliers. Do not touch the pipet.
  8. Immerse the pipet bulb in the water-filled terrarium. Caution: Keep the pipet bulb submerged in the water until the explosion occurs.
  9. Have students come up to the tank to observe the following phase changes:
    • Sealed pipet—solid, gas
    • Melting then boiling—solid, liquid, gas
    • Bulging pipet—solid, liquid, gas
    • Burst pipet—solid
  10. Tap any excess dry ice particles into the terrarium.
  11. Discard the burst pipet.

Exploding pipets and splashing water are sure to generate excitement. If your students are capable of maintaining the required grip on the pliers, you may want them to experience this as a hands-on activity. Repeat steps 3 to 7 and then pass the pliers gripping the pipet to a student who immediately does step 8.

Lava Lamp
Topics: Density, chemical reactions

Everyone knows the saying “Oil and water don’t mix.” Here is a dramatic demonstration of it. An effervescent tablet reacts with colored-water blobs in a bottle of oil to make tiny bubbles of carbon dioxide gas. These bubbles attach themselves to the water blobs and cause them to float to the surface because carbon dioxide gas is less dense than water and oil. When the water-gas blobs reach the surface, the bubbles expand and pop, allowing the denser water blob to sink back to the bottom, emulating a lava lamp.

Materials

  • Clean 16-oz Plastic Bottles with Caps
  • Vegetable Oil (16 oz for demo; 1 gal for 8 lamps)
  • Food Coloring
  • Effervescent Tablet
  • Water

Teacher prep (individual lava lamps)

A few weeks before the activity, ask each student to bring in a clean, empty, clear 16-oz plastic bottle (such as a water bottle) with the label removed and a cap.

Procedure

  1. Add water to the bottle until it is about an inch deep.
  2. Add 10 drops of food coloring. If that doesn’t achieve a deep, dark color, add more.
  3. Fill the bottle with vegetable oil almost to the top, but not overflowing.
  4. Divide the effervescent tablet into 4 to 6 pieces.
  5. Drop a piece of the tablet into the oil-water mixture. Watch what happens. When the bubbling stops, add another piece and observe. Repeat until you have used all the pieces.
  6. Wait until the bubbling has completely stopped. Screw on the cap. Tip the bottle back and forth and watch the wave appear. The tiny droplets of liquid have joined together to make a big blob.

Oozing Slime
Topics: Polymers, properties of matter

No Chemoween is complete without slime, a non-Newtonian fluid with interesting characteristics:

  • Under stress it dilates or expands.
  • Pull on it gently (low stress) and it flows and stretches, sometimes even forming a thin film.
  • Pull on it sharply (high stress) and it breaks.
  • Hit it with your hand and it doesn’t splash or splatter.
  • Stuff it through a tube and it appears to swell as it exits the other end.

The molecular bonding of PVA (polyvinyl alcohol) with borate ions explains the slime-forming process.

PVA
H4BO4
 
Slime

Cross-linking occurs when PVA is added to sodium borate; the electronegative oxygen on borate forms weak hydrogen bonds with the hydroxyl groups of PVA. The unique properties of PVA slime are a result of this cross-linking.

Materials

  • 1.6 g Sodium Borate Decahydrate
  • 8 g PVA, Powder
  • 240 mL Water
  • Stirring Rod
  • Glass Container (larger than 40 mL)
  • Heatproof Container (larger than 240 mL)
  • Hot Plate
  • Food Coloring

Additional materials for individual student batches:

  • Small Graduated Cups (e.g., medicine cups)
  • Larger Graduated Cups (30 to 60-mL capacity)
  • Stir Sticks
  • Plastic Bags

Teacher prep

  1. Dissolve 1.6 g sodium borate decahydrate in 40 mL water. Stir until completely dissolved. This takes approximately 15 min with frequent stirring. Add food coloring to color the slime.
  2. Dissolve 8 g PVA into 200 mL water. Use a hot plate to dissolve the PVA into solution. This may take several minutes. If time or lack of a hot plate is an issue, a ready-to-use 4% PVA solution is also available. If you alter the batch size, keep the sodium borate solution and PVA solution in a 1:5 volume ratio.

Procedure

One small batch: Pour the sodium borate decahydrate solution into the 200 mL PVA solution while slowly mixing.

Individual student batches: Provide each student with a cup containing 4 mL sodium borate solution and another cup containing 20 mL PVA solution. Have them pour the sodium borate into the PVA and then mix, using the stir sticks.

Tip: Prepare an individual batch before class to determine if you like the consistency. If you find it too slimy, add slightly more sodium borate solution. If you find it too thick, use less sodium borate.

Students will want to take slime home to disgust unsuspecting parents or siblings. Have them put it in plastic bags for transport. PVA slime is nontoxic.

THE GRAND FINALE!  Puking Pumpkin
Topics: Catalysts, exothermic reactions, decomposition reactions

You may have seen the decomposition of hydrogen peroxide catalyzed by potassium iodide (or yeast) demonstrated as “Elephant’s Toothpaste.” Exchange the graduated cylinder for a jack-o’-lantern and delight students.

The 2-step decomposition reaction:

H2O2(aq) + I(aq) → H2Ol + OI(aq) → (rate-determining step)
H2O2(aq) + OI(aq) → H2O(l) + O2(g)  + I(aq)

The rapidly produced oxygen mixes with the dish detergent to form foam that overflows the beaker and shoots out of the jack-o’-lantern. Iodine gives the foam a brown tint. Food coloring may be added to produce any shade you like. The teacher prep section describes how to make iodine-free foam.

Safety

Hydrogen peroxide, 30%, is an extremely strong oxidizer that can cause burns. Do not allow it to contact bare skin.

Do not stand directly over or in front of the jack-o’-lantern during the demo. The reaction quickly generates heat and foam that contains iodine and food coloring that may stain skin, clothing, and surfaces. Handle with care. Recommended PPE for clean up: eye protection, gloves, and a lab apron or coat. If you or a student is iodine sensitive, an alternate method for this demo is provided in the teacher prep section.

Make sure that the soapy foam does not create a slipping hazard.

Materials

  • Newspaper or Plastic (to cover the tabletop and the floor below)
  • Jack-o’-Lantern (natural or artificial)
  • 50 mL Hydrogen Peroxide, 30%
  • 15 mL Potassium Iodide, Saturated Solution
  • 10 mL Dish Detergent
  • Small Glass Beaker (100 or 150 mL)
  • Food Coloring
  • Paper Towels
  • Gloves
  • Apron or Lab Coat

For iodine-free option:

  • Packet of Yeast
  • 3 Tablespoons Warm Water
  • Small Cup

Teacher prep

Wear eye protection, gloves, and an apron or lab coat during the demo and for clean up. The foam may stain skin, clothing, tabletops, and floors.

Pumpkin

This demo requires a jack-o’-lantern. If you do not have one on display in your classroom, carve one out of a small pumpkin and bring it in a few days before the demo. You can also use an artificial jack-o’-lantern; just make sure it has a top and no electrical components (indicated by cords, lights, wires, or batteries).

Potassium iodide, saturated solution

Dissolve 100 g of KI in 70 mL water. Some potassium may remain undissolved. This solution can be prepared ahead of time and stored in an amber bottle until use.

Iodine-free jack-o’-lantern

In a small cup, mix 1 packet of yeast with 3 tablespoons of warm water. After mixing, allow 5 min for the yeast to activate before use. Substitute the yeast solution for the saturated KI solution during the demo.

Procedure

  1. Put on PPE as for teacher prep. Keep students a safe distance away from the demo to avoid splashing them with “puke.”
  2. Cover the demo table with newspaper or plastic. Place the jack-o’-lantern on the table, making sure that there is about 3 ft between the jack-o’-lantern’s face and the edge of the table.
  3. Add 50 mL hydrogen peroxide, 30%; 10 mL dish detergent; and a few drops of food coloring to the beaker.
  4. Place the beaker inside the jack-o’-lantern. Be sure the beaker rests level and upright. Put the top back on the jack-o’-lantern. Note: Be sure all cameras are filming before you start the next step.
  5. Remove the jack-o’-lantern’s top and pour the potassium iodide solution (or yeast) into the beaker. Quickly replace the top and stand back. In a few seconds foam will spew from the jack-o’-lantern. Warning: The reaction generates foam and heat. Allow a few minutes for the jack-o’-lantern to cool before touching it. Do not allow students to touch either the jack-o’-lantern or the puke.
  6. Wipe up any spills from areas not protected by the newspaper or plastic.
  7. Take a bow! You have provided your students with an unforgettable chemistry and Chemoween experience.

To reuse the jack-o’-lantern for multiple classes, rinse it with water and pat the inside dry with paper towels. At the end of the day, discard the jack-o’-lantern if it is made from a real pumpkin or clean and return to storage if it is artificial.

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