Content Areas: Chemistry, Physical Science
Activity Type: Experiment, Data Analysis
NGSS: HS-PS1-3, MS-PS1-4
35% ethyl alcohol (lowest boiling point)
white vinegar (highest boiling point)
Which of these solutions demonstrate the Leidenfrost effect at the lowest surface temperature?
Which solution demonstrates the Leidenfrost effect at the highest surface temperature?
Safety goggles and lab apron
Non-Teflon, heavy-bottomed skillet
Heat source: A hot plate or electric stove work best. Avoid using open flame.
Avoid Teflon-coated (non-stick), greased, or ceramic pans for this experiment.
- Metal or silicon spatula, rated for high temperatures
Four small cups or beakers, containing the following solutions:
- 10ml tap water + 10ml 70% ethyl Alcohol (available in first-aid section of many pharmacy stores)
Mix well, and store remaining ethanol away from the work area.
- 20ml white vinegar
- 20 ml distilled water
- 20 ml tap water + 5g (or more) table salt
Mix well; some salt will not dissolve.
Food coloring – add 1 drop of a different color to each solution to help tell them apart
1/4 cup of talc baby powder
Do not use cornstarch baby powder, which can easily burn.
- Put on safety goggles and a lab apron.
- Fill a dropper with the first liquid that you would like to test, and practice using it to drop single drops into the cup one at a time (this might seem easy, but every dropper is different, so it is good to practice).
- Gently sprinkle talc baby powder over the surface of the pan, so that it completely covers the surface.
- Using your spatula, make four “wells” or craters in the talc baby powder about one or two inches apart. These will help keep your droplets of liquid separate from one another on the pan.
- Download and print out your observation sheet, and find a safe place to record your observations away from your heat source.
- Starting on low heat, carefully squeeze a single droplet of each solution into its own well in the talc baby powder. Record your observations.
- Repeat this drop-observe procedure as you very slowly turn up the temperature to Medium, and then Medium-High heat, adding droplets and recording observations every 3-5 minutes as the surface heats up. Pay close attention to differences in evaporation time, simmering, boiling, splattering, or droplet formation for each solution.
- When a solution produces quiet droplets that do not sizzle or evaporate, but instead float on steam, you’re seeing the Leidenfrost effect in action. You can turn off the heat to the pan once you have observed the Leidenfrost effect in each of the four solutions.
- When you are finished, let the pan cool. Do not use cold water to cool the pan, as it may bend the pan or cause dangerous amounts of steam to be produced. As the pan cools, review the observations you recorded and identify the solution that showed the Leidenfrost effect first and the one that showed the Leidenfrost effect last. Also pay attention to your cooling pan—some of the Leidenfrost droplets will revert to boiling and sputtering as they lose heat.
Does the boiling point of a solution appear to be related to the surface temperature needed to achieve the Leidenfrost effect?
What other differences did you observe between the solutions as the surface heated up?
After you observed the Leidenfrost effect, did you notice any of the Leidenfrost droplets shrinking or drying out? Which ones? How might boiling point be related to these phenomena?
The Leidenfrost point of a liquid can be found by observing how long it takes drops of a liquid to evaporate from a surface that is hotter than the boiling point of the liquid. The temperature at which evaporation time is the longest is the Leidenfrost point. It is easiest to identify the Leidenfrost point by graphing how long it takes droplets to evaporate at different temperatures above the boiling point. The graph below charts the temperature of the surface (x-axis) and the amount of time it took for a droplet of water (boiling point 100°C) to evaporate from that surface (y-axis). Try using the graph below to identify the Leidenfrost point of water:
Using an IR thermometer and a stopwatch, you can experimentally determine the Leidenfrost points of the solutions you used in the earlier experiment. Repeat steps #1-9 using a single solution in a single well while recording the temperature between droplets. At what temperature do droplets suddenly persist without evaporating? This is the Leidenfrost point for the solution!
MS-PS1-4 Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
HS-PS1-3 Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.