November 2013

# Sharing chemistry with the community: The Ramp of Science

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Audrey Hagopian*, Duke University, Durham NC

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The Ramp of Science, so dubbed by Duke students a few years ago, is a versatile, engaging demonstration. Hexane vapor or carbon dioxide gas is poured down the ramp to a lighted candle situated at the bottom. The hexane ignites and produces flames that travel up the ramp, while the carbon dioxide extinguishes the candle flame. This demonstration has been used to illustrate the fluid nature of gases, to discuss gas density, and to introduce audiences to some of the physical and chemical properties of hexane and carbon dioxide. This demonstration is also relevant to our everyday lives — why one should be wary of nearby ignition sources when working with a volatile, flammable substance and why carbon dioxide is used in some fire extinguishers. At the tertiary level, this demonstration has been used to initiate discussion about gas diffusion, collision frequency of the gas particles, and the mean free path. The Ramp of Science continues to be one of our most popular demonstrations performed at chemistry outreach presentations.

## Concepts

- Gases, like liquids, are fluids; the molecules that make up a gas are not held in place by intermolecular attractions so they can easily move past one another.
- Hexane vapor and carbon dioxide gas (generated from dry ice) are both denser than the surrounding air; therefore, they will both tend to flow downwards.
- Hexane is flammable while carbon dioxide is not.

## Materials

- Specially constructed ramp
- Two 1-liter Erlenmeyer flasks fitted with rubber stoppers
- Hexane (liquid, 2-4 mL)
- Disposable pipet (to dispense hexane)
- Dry ice (1 grape sized piece)
- Tongs (to handle dry ice)
- Tea light candle and lighter (to light candle)

## Safety

- Wear safety glasses/goggles.
- Wear protective gloves while dispensing the hexane into the flask but do not wear them when performing the demonstration due to the presence of an open flame; gloves may melt and adhere to the skin.
- Avoid inhalation of the hexane vapor; perform demonstration in a well-ventilated area; keep stopper on flask containing the hexane when not performing the demonstration.
- Open flame present; fire hazard; be sure to remove all combustible materials from the area prior to performing the demonstration.
- When “pouring” the hexane vapor down the ramp, be sure NOT to allow any liquid hexane to exit the flask and flow down the ramp; fire hazard!
- When “pouring” the hexane, position the flask so that the vapor will pour out but not the liquid, keep your eyes focused on the bottom of the ramp; when the hexane ignites remove the flask to prevent it from catching on fire. If it does catch on fire, set it down and cover loosely with the rubber stopper to smother the fire.
- Do not handle the dry ice with your bare hands or allow any part of your body to come in contact with it; severe skin damage may result; handle only with tongs or gloves designed for handling cold materials.
- Be sure NOT to tightly stopper the flask containing the piece of dry ice; the pressure inside the flask will build up as the dry ice sublimes; if the stopper is on tight, the flask could potentially rupture.
- One should be thoroughly practiced performing this demonstration before doing it in front of an audience.

## Advanced preparation

### Construction of the ramp

Photos of various views of the constructed ramp are given on page 9 to assist you in building your own ramp.

- All materials can be obtained from a local hardware store; the most expensive part is the piece of right-angled aluminum ($10-15)
- One ~36-inch length of right-angled aluminum
- One 1” x 6” x 6’ wooden board — use good quality and check to be sure the board is flat (not warped). This will be used to make the base and the two vertical supports
- Eight 1” x 1” L-brackets with mounting screws
- Wood glue (optional)
- Two ~3” lengths of industrial strength Velcro® (super
  strong adhesive)
- Four self-adhesive circular furniture pads used to protect floors from damage due to sliding furniture
- Saw, screw driver and drill

### Preparing the chemicals

- Place a small piece of dry ice in a designated labelled 1-L Erlenmeyer flask, stopper loosely, and allow time for the dry ice to sublime and fill the flask with carbon dioxide.
- Place 2-4 mL of hexane in a designated labelled 1-L Erlenmeyer flask, stopper tightly, swirl, and allow time for the flask to be filled with hexane vapor; sometimes enough pressure builds up to pop off the stopper; merely put it back on if this happens. The Erlenmeyer flask should always be stoppered outside the fume hood. Always put back the stock bottle properly before performing demonstrations.
- Dispensing hexane should be done in a fume hood since it is a volatile liquid. Please review the MSDS information on hexane as you would any chemical before doing a demonstration.

## Procedure

- Place the ramp on the table so the audience can see along the V of the ramp.
- Place the candle at the base of the ramp and light; darken the room if desired.
- Pour the hexane vapor down the ramp by holding the flask in a horizontal position (to ensure that any liquid does not exit the flask); remove the flask from the ramp when the hexane first ignites at the bottom; repeat (stopper the flask and swirl for a moment after each use to fill the flask with hexane vapor)
- Repeat the process using the flask filled with carbon dioxide. The flame will go out.
- If you wish, alternate between the hexane and the carbon dioxide.

## Disposal

- Extinguish the candle flame and allow the melted wax to re-solidify.
- Place the flasks in a fume hood, un-stopper, and allow chemicals to evaporate or sublime.

## Notes

- Check the area where the demonstration will be performed for drafts. Do not perform demonstration in a drafty location.
- Move the candle a short distance away from the end of the ramp when pouring the carbon dioxide otherwise, the carbon dioxide has a tendency to flow over and beyond the candle without extinguishing it.
- The carbon dioxide tends to be used up faster than the hexane; have several flasks filled with carbon dioxide on hand if you desire to repeat several times.
- Take the opportunity to mention signs at gas stations warning people not to smoke, use cell phones or get back into the car. These are posted because the vapors of flammable volatile liquids such as gasoline can flow, spread out, and ignite away from the source of the vapors.
- When working with flammable volatile liquids around the home, be aware of potential ignition sources in the area such as a water heater.
- Carbon dioxide has been used in fire extinguishers because of its ability to smother fires being denser than the surrounding air and not being flammable itself.

The following are Audrey’s thoughts about learning and performing this demonstration in front of a group of second-grade students.

The visits from Dr. Lyle, the chemistry department’s lecture demonstrator, were the best part of general chemistry lectures. His demonstrations always brought chemistry to life and made the science applicable to everyday situations. During one memorable “properties of gases” demonstration, Dr. Lyle showed up with the Ramp of Science. It is well described by its name: it is a metal ramp supported by a wooden frame accompanied by a candle and a couple of flasks containing different gases. The goal of the experiment was to show that gases flow in a similar way to liquids. These gases may be flammable or can extinguish flames.

I was thrilled when I discovered that my first chemistry outreach presentation would be with the Ramp of Science. The outreach event involved sixty second-graders at Endeavor Charter School, Raleigh, NC. During my practice session, I learned not just the mechanics, but also the what, how, and when of the actual demonstration. This preparation proved crucial on the day of the event.

To show that liquids flow, I poured red-food colored water down the ramp into an empty cup. When I asked the children, “Does a liquid flow like a river?” they answered in unison “Yes!” Next I asked if they thought a gas would flow like a river down the ramp, and their responses were mixed. I told them that we could test this with the Ramp of Science. A small lit candle was placed at the ramp’s base. A seemingly empty flask was held up and the children were informed the flask contained a flammable gas, hexane. I also explained that if a gas is flammable it means that the gas can catch on fire. With the lights out, I un-corked the flask and poured the invisible hexane. To the children’s amazement, the ramp lit up with fire! When the lights came back on, 120 wide eyes stared at me, thrilled by the unexpected outcome of the experiment. I emphasized that when I held the flask at the top of the ramp that the gas flowed down the ramp. When the hexane reached the candle, it was ignited by the flame and burned up the ramp.

My partner Rachel held up a second flask and told the kids that it was filled with a different gas, carbon dioxide. The solid carbon dioxide had turned into a gas, so now the flask was full of carbon dioxide gas. I mentioned that, unlike hexane gas, carbon dioxide gas is not flammable and can be used to extinguish a fire. While the lights out, Rachel held the un-corked flask at the top of the ramp. We again heard screams of delight as the candle was extinguished! We explained that the gas flowed down the ramp and extinguished the flame, noting carbon dioxide was not flammable and denser than air.

The children were all delighted by the demonstration, shouting “Encore, encore!” so we repeated the demonstration a few more times. We continued to reinforce the key teaching points so the children could understand what was happening and why. Before holding up a flask I would remind them which gas was in it and then ask, “Is this gas flammable or not?” We also stressed that gases, like liquids, flowed and could be poured. We repeatedly asked, “What is the gas going to do? Is it going to flow down the ramp?” They vocally responded in unison, “Yes!”

This, my first chemistry outreach event, was incredible. It was very satisfying to see young children so excited about science. It reminded me of my own experience of awe and excitement for this demonstration. Children’s thank-you letters were the most gratifying part of the whole experience. Many of the letters included little drawings of the ramp of science; some of the children even drew a stick figure of me holding a flask up by the ramp. Knowing that I made an impression on the children, and that I taught them some science along the way, was a priceless experience.

*Audrey Hagopian is a senior at Duke University majoring in Environmental Science with minors in chemistry and religion. She plans to pursue a career in medicine upon graduation.

**Dr. Kenneth Lyle, a lecturing-fellow in the Department of Chemistry at Duke University, serves as the lecture-demonstrator, chemistry outreach coordinator, and instructor of CHEM 180 Chemistry Outreach Service Learning Course. All inquiries should be addressed to kenneth.lyle@duke.edu.

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

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