Canned Heat - Colorful Flaming Gel
Publication information:
Abstract
Calcium acetate and ethanol form a flammable gel that gives off enough heat to keep food hot! Additional chemicals can be added to color the flame.
What it Shows
When ethanol is poured into a saturated solution of calcium acetate, a gel immediately forms. Spoonfuls of the gel are scooped out and placed on watch glasses. Lithium chloride, sodium chloride, and boric acid are sprinkled over the gel, then the gel is set on fire. As the flame burns, different colors are emitted. Iron filings can also be sprinkled over the flame to see "firework-like" gold sparks.
This demo touches on several aspects of chemistry:
Thermochemistry/Chemical reactions: Lighting the gel on fire combusts the ethanol, releasing heat. This gel is similar to the commercial Sterno gel found in metal cans, which is used to keep food in chafing dishes hot.
Atomic spectra/flame tests: Various salts added to the gel show the characteristic flame test colors of different elements.
Colloids: The calcium acetate and ethanol form a gel, which is a colloidal dispersion of a solid in a liquid. This can be compared to other gels like Jello and hair gel.
How it Works
When the ethanol is mixed with the calcium acetate solution, the calcium acetate precipitates out as a solid forming a colloidal dispersion with the liquid ethanol. The calcium acetate and ethanol form a network with ion-dipole forces between the calcium ions and ethanol, as well as hydrogen bonds between the acetate and ethanol molecules. The exact structure of the network is not known. Ethanol is used as the same base in the commercial product Sterno with some small amount of proprietary salt and t-butyl alcohol (STL/Sterno, 2023).
When the gel is set on fire, the ethanol evaporates and combusts releasing heat. The following reaction takes place:
C2H5OH (g) + 3O2 (g) --> 2CO2 (g) + 3H2O (l)
The heat of combustion is 1367 kJ/mol (NIST Chemistry WebBook, SRD 69). A tablespoon of the gel, containing approximately 12 g of ethanol, releases enough heat to bring 1 liter of water from 25°C to boiling.
The salts sprinkled on the gel give off their characteristic flame colors: bright yellow-orange for sodium, hot pink red for lithium, and green for boric acid. The iron filings give off a sparkly gold color when they are sprinkled on.
Setting it Up
Safety: Wear safety glasses or goggles when preparing. Gloves are optional. Make sure to keep flammable objects away from the flame. The flame will keep burning for quite a while, so if you want to extinguish the flame, blow it out or place a metal bowl over it. The evaporating dishes will be hot so handle carefully.
Materials: calcium acetate, distilled water, ethanol (denatured is fine to use, but pure is best), sodium chloride, 250 mL beaker, 150 mL beaker, 3 evaporating dishes, spoon or scoopula. Optional chemicals for colored flames: sodium chloride, lithium chloride, boric acid, iron filings.
Measure out approximately 50 mL of ethanol in the 150 mL beaker. To make the gel, mix 3 g of calcium acetate in 10 mL of distilled water in a 250 mL beaker. Add the ethanol all at once to the beaker with the calcium acetate. The gel will instantly solidify. Use a spoon to put one scoop of gel onto each watch glass.
If you want to connect this to atomic spectra and fireworks, sprinkle a small amount of the three salts onto the gel. Using a match or lighter, light the gel on fire. To add sparks, shake a small amount of iron filings onto the flame from above. Make sure to keep your hand high above the flame to avoid being burned.
Cleanup and Disposal: The gel, along with any solid residues, may be thrown in the trash.
Comments
You may color the gel by placing one drop of food coloring to the ethanol. Alternatively, instead of sprinkling the salts on the gel, you can place a pinch of the salt in the calcium acetate before adding the ethanol. We have only tried this with sodium chloride, so you may need to experiment if trying out a different salt.
The amount of ethanol is adjustable - try experimenting with the amount to see if you can change the firmness of the gel. In Summerlin and Ealy, they use 5 mL of safurated calcium acetate solution with 30 mL of ethanol. They also mention that other alcohols can be substituted. It may be worth experimenting with 91% isopropanol, which is readily available in drugstores.
Roasting a marshmallow over the flame is a nice touch. Students can also use a known mass of gel to estimate the heat of combustion of ethanol using a calorimetry setup such as a metal cup filled with a known mass of water and a thermometer.
The calcium acetate also decomposes into calcium oxides, calcium carbonate, carbon dioxide, and water. But the ethanol combustion is what supplies the heat.
References
Canned heat: (2017). The preparation of Sterno. Flinn Scientific ChemFax. https://www.flinnsci.com/api/library/Download/2e576e551fd54164aff207a22efbc271
Summerlin, Lee R. and James L. Ealy, Jr., Chemical Demonstrations: A Sourcebook for Teachers, American Chemical Society, 1985.
P.J. Linstrom and W.G. Mallard, Eds., NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg MD, 20899, https://doi.org/10.18434/T4D303, (retrieved May 28, 2024).
SCL/Sterno Corporation (2023, June 26) Safety Data Sheet for Sterno Ethanol Gel/Sterno Green/Sterno Canned Heat. https://www.sterno.com/media//sterno/sds/pdf/s/t/sterno_ethanol_gel_sds_06_26_2023.pdf
Full text
Calcium acetate and ethanol form a flammable gel that gives off enough heat to keep food hot! Additional chemicals can be added to color the flame.
What it Shows
When ethanol is poured into a saturated solution of calcium acetate, a gel immediately forms. Spoonfuls of the gel are scooped out and placed on watch glasses. Lithium chloride, sodium chloride, and boric acid are sprinkled over the gel, then the gel is set on fire. As the flame burns, different colors are emitted. Iron filings can also be sprinkled over the flame to see "firework-like" gold sparks.
This demo touches on several aspects of chemistry:
Thermochemistry/Chemical reactions: Lighting the gel on fire combusts the ethanol, releasing heat. This gel is similar to the commercial Sterno gel found in metal cans, which is used to keep food in chafing dishes hot.
Atomic spectra/flame tests: Various salts added to the gel show the characteristic flame test colors of different elements.
Colloids: The calcium acetate and ethanol form a gel, which is a colloidal dispersion of a solid in a liquid. This can be compared to other gels like Jello and hair gel.
How it Works
When the ethanol is mixed with the calcium acetate solution, the calcium acetate precipitates out as a solid forming a colloidal dispersion with the liquid ethanol. The calcium acetate and ethanol form a network with ion-dipole forces between the calcium ions and ethanol, as well as hydrogen bonds between the acetate and ethanol molecules. The exact structure of the network is not known. Ethanol is used as the same base in the commercial product Sterno with some small amount of proprietary salt and t-butyl alcohol (STL/Sterno, 2023).
When the gel is set on fire, the ethanol evaporates and combusts releasing heat. The following reaction takes place:
C2H5OH (g) + 3O2 (g) --> 2CO2 (g) + 3H2O (l)
The heat of combustion is 1367 kJ/mol (NIST Chemistry WebBook, SRD 69). A tablespoon of the gel, containing approximately 12 g of ethanol, releases enough heat to bring 1 liter of water from 25°C to boiling.
The salts sprinkled on the gel give off their characteristic flame colors: bright yellow-orange for sodium, hot pink red for lithium, and green for boric acid. The iron filings give off a sparkly gold color when they are sprinkled on.
Setting it Up
Safety: Wear safety glasses or goggles when preparing. Gloves are optional. Make sure to keep flammable objects away from the flame. The flame will keep burning for quite a while, so if you want to extinguish the flame, blow it out or place a metal bowl over it. The evaporating dishes will be hot so handle carefully.
Materials: calcium acetate, distilled water, ethanol (denatured is fine to use, but pure is best), sodium chloride, 250 mL beaker, 150 mL beaker, 3 evaporating dishes, spoon or scoopula. Optional chemicals for colored flames: sodium chloride, lithium chloride, boric acid, iron filings.
Measure out approximately 50 mL of ethanol in the 150 mL beaker. To make the gel, mix 3 g of calcium acetate in 10 mL of distilled water in a 250 mL beaker. Add the ethanol all at once to the beaker with the calcium acetate. The gel will instantly solidify. Use a spoon to put one scoop of gel onto each watch glass.
If you want to connect this to atomic spectra and fireworks, sprinkle a small amount of the three salts onto the gel. Using a match or lighter, light the gel on fire. To add sparks, shake a small amount of iron filings onto the flame from above. Make sure to keep your hand high above the flame to avoid being burned.
Cleanup and Disposal: The gel, along with any solid residues, may be thrown in the trash.
Comments
You may color the gel by placing one drop of food coloring to the ethanol. Alternatively, instead of sprinkling the salts on the gel, you can place a pinch of the salt in the calcium acetate before adding the ethanol. We have only tried this with sodium chloride, so you may need to experiment if trying out a different salt.
The amount of ethanol is adjustable - try experimenting with the amount to see if you can change the firmness of the gel. In Summerlin and Ealy, they use 5 mL of safurated calcium acetate solution with 30 mL of ethanol. They also mention that other alcohols can be substituted. It may be worth experimenting with 91% isopropanol, which is readily available in drugstores.
Roasting a marshmallow over the flame is a nice touch. Students can also use a known mass of gel to estimate the heat of combustion of ethanol using a calorimetry setup such as a metal cup filled with a known mass of water and a thermometer.
The calcium acetate also decomposes into calcium oxides, calcium carbonate, carbon dioxide, and water. But the ethanol combustion is what supplies the heat.
References
Canned heat: (2017). The preparation of Sterno. Flinn Scientific ChemFax. https://www.flinnsci.com/api/library/Download/2e576e551fd54164aff207a22efbc271
Summerlin, Lee R. and James L. Ealy, Jr., Chemical Demonstrations: A Sourcebook for Teachers, American Chemical Society, 1985.
P.J. Linstrom and W.G. Mallard, Eds., NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg MD, 20899, https://doi.org/10.18434/T4D303, (retrieved May 28, 2024).
SCL/Sterno Corporation (2023, June 26) Safety Data Sheet for Sterno Ethanol Gel/Sterno Green/Sterno Canned Heat. https://www.sterno.com/media//sterno/sds/pdf/s/t/sterno_ethanol_gel_sds_06_26_2023.pdf