May 2015

# Sharing chemistry with the community: Bubble-ology part 2

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Carolyn Peterseim*, Duke University, Durham NC

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In Part 1 — the April issue — we described four of our successful bubble activities. Part 2 will incorporate dry ice into our demonstrations and have reflections on these activities.

These demos are very popular with all audiences.

## Dry ice information

Safety considerations are required due to handling dry ice. Use gloves or tongs because dry ice can cause damage to one’s skin. We get our dry ice from Air-Gas. In some places dry ice may be available in grocery stores. Transport the dry ice in a simple ice chest such as one made of polystyrene.

- Do not put the dry ice in a sealed container. The pressure will build up due to sublimation of the dry ice to the point where the container could explode.
- Do not store the dry ice in a poorly ventilated area, including one’s automobile, overnight. Carbon dioxide will displace the oxygen making it difficult to breathe.
- Watch the participants closely in case anyone attempts to touch the dry ice.

### Clean up

Using tongs or gloves, return the dry ice to its storage container. To dispose of the dry ice, place the container in a well-ventilated area where no one will have access and allow it to completely sublime. Attempting to store it in a freezer will not work.

## Activity #5: Floating bubbles

The unique item for this is a large plastic storage container or large aquarium.

- In advance, place several pieces of dry ice around the bottom of the large container or aquarium. Dry ice often comes in blocks. It can be broken into smaller pieces using gloves and a hammer.
- Allow a few minutes for some of the dry ice to sublime in order to fill the container or aquarium.
- Blow soap bubbles using bubble wands. It is best to blow bubbles horizontally and allow them to fall into the tub. Blowing downward pushes the carbon dioxide out of the tub.
- Observe the bubbles as they float on the denser layer of carbon dioxide. Over time, they will become larger and slowly sink due carbon dioxide entering the bubble.

## Activity #6: Witch’s cauldron

One can often find a black plastic cauldron at Halloween time. Prepare a strip of cloth approximately 2 inches x 36 inches — the length depends on the size of the opening of the cauldron or round bucket with a smooth lip. Be sure the cauldron does not have a hole in bottom.

### Procedure

- Place strip of cloth completely into the soap solution. The cloth must be longer than the opening of the cauldron.
- Fill the witch’s cauldron with water — about ½ full, warm water if available.
- Soap the entire rim of the cauldron using the soapy strip of cloth.
- Starting at the edge farthest away, horizontally draw the soapy cloth strip towards you. Practice drawing a soap film across the circumference of the opening of the cauldron. In time you will find you can do this easily and quickly. Re-soak the cloth in the soap solution from time to time. If the cloth is long enough, fold it over itself so it is doubled.
- Once you are able to draw a soap film successfully, drop a golf-ball sized piece of dry ice into the cauldron and then draw a soap film. Watch the film grow in size. Note the fog forming inside and the rainbow of colors on the film itself.
- If one dips his/her fingers/hands in the soap solution, he/she can pass the fingers through the soap film. Be sure he/she does not try to grab the piece of dry ice. The soapy piece of cloth can also be passed through the bubble. Some have been able to make a double bubble with the aid of the cloth.
- Periodically, you will need to change the water because it will become very cold — near its freezing point. Be sure to not allow any dry ice to go down the drain.

## Activity #7: CO2 leaky faucet

The leaky faucet is a large plastic jar with a removable lid and a hose attached. When warm water and solid carbon dioxide are added, a thin fog streams out of the hose. The end of the hose is dipped in bubble solution, and the leaky faucet becomes an instant bubble-making machine. We use a commercial leaky faucet apparatus from Steve Spangler Science; “Boo Bubbles — Dry Ice Smoke Bubbles” $24.99).

If the tube is wrapped with a piece of paper towel, we have noted improvement to the delivery of bubbles from the apparatus. Wrap a strip of paper towel about 1 inch wide around the end of the tube 3-4 times; do not cover the opening. Cut off any excess towel. Secure the paper towel to the tube with a rubber band.

- Fill the container with water to about 2 inches below the opening. If available use warm water. It works best.
- Fill a small plastic cup with the soap solution — about half-full.
- Fill the plastic tub with enough water for the participants.

### Presenting

- Place approximately a golf-ball sized piece of dry ice in the container and close the lid. Don’t use a lot of dry ice because the pressure of the gas coming out of the tube will be too high, causing the bubbles formed to burst quickly.
- Dip the open end of the tube into the cup of soap solution then remove it and hold it over the plastic tub with water. Bubbles filled with carbon dioxide and condensed water will form at the end of the tube. The bubbles will periodically drop from the tube. If one gets his/her hand thoroughly wet, he/she can catch the bubbles.
- You can insert the tube into the bubble caught in one’s hand. The bubble will grow in size.
- Carefully observe the bubbles caught in one’s hand. They will shrink over time as the CO2 passes through the bubble film.
- You can quickly teach the kids how to generate the bubbles for themselves and then turn the operation over to them. Be sure to warn them to not open the container to touch the dry ice inside.

Three presenters recently participated in an outreach event at a local middle school. Each presenter supervised one of the bubble-ology activities. The following are brief summaries of their experiences overseeing the activities.

> When students and their families started blowing bubbles into the tub with dry ice, I watched the wonder in their eyes as they watched the bubbles float calmly above the dry ice." Carolyn Rath

> Would you like to hold a bubble?” In the context of bubble-ology, the leaky faucet activity is a fun-filled, hands-on method of demonstrating dry ice, its sublimation, and the condensation of water. While this activity is appropriate for ages 2 - 92, the middle school students especially loved it. By getting their hands slightly damp, students could “hold bubbles” that were filled with fog. Their faces lit up when they held their first bubble, and then put a bubble in their friends’ hands. I enjoyed working with these inquisitive students, teaching them about H2O and CO2, and sparking their interest in chemistry.”

> – Carolyn Peterseim

> “The witch’s cauldron is a personal favorite. Here, children marveled at the rising bubble and squabbled with friends over who would be next to pull the soapy fabric across the circumference of the cauldron. Children even invented unique ‘experiments’ to perform with the witch’s cauldron supplies. This involved sticking their entire soapy hands into the cauldron and creating a ‘double bubble’ with use of two strips of fabric.”

> – Erica Weinberg

*Carolyn Peterseim, a junior, is majoring in cultural anthropology with minors in chemistry and music. She plans to pursue medical anthropology abroad for one to two years upon graduation, and then enter medical school.

**Carolyn Rath, a junior, is majoring in biology with minors in chemistry and global health. She plans to pursue a degree in pharmacy, eventually working as a pediatric pharmacist.

***Erica Weinberg, a junior, is majoring in evolutionary anthropology with minors in chemistry and psychology. After graduation she plans to go to dental school, eventually working as a pediatric dentist.

****Dr. Kenneth Lyle is a Lecturing Fellow in the Department of Chemistry at Duke University and serves as the lecture-demonstrator and chemistry outreach coordinator.

The Powell Family Trust, Duke-Durham Partnership, and Biogen Idec Research Triangle Park, fund the Duke Chemistry Outreach program.

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