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Non-burning Towel

Last updated

Aug 15, 2020
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- new BZ
- Nylon

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Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves

Equipment	Chemicals
Cloth towel, money, or other absorbent material	50 mL isopropyl alcohol
Candle and matches	50 mL distilled water
Tongs	1 liter or other large beaker
Metal ice pans

Procedure:

Pour the alcohol and water into the beaker.
Immerse the dry towel in the mixture and thoroughly wet it.
Squeeze the towel to remove excess liquid.
Light the candle.
Hold the towel at the center with the crucible tongs.
Move the towel into the flame of the candle at arms length and allow the wet towel to catch fire.
As the flame subsides, prevent the towel from actually burning by snuffing it out.

Discussion:

After an ordinary cotton towel or paper money is immersed in a solution of alcohol and water and then held over a lighted burner, a blue flame surrounds the towel without burning it as the alcohol burns off. The combustion reaction is as follows:

2 C₃H₇OH (l) + 9 O₂ (g) → 6 CO₂ (g) + 8 H₂O (g)

The heat of reaction for this equation is -1987 kJ/mol. This is enough to set the towel on fire as can be demonstrated by soaking the towel in pure alcohol instead of the water mixture. The water absorbs a good deal of heat as its temperature raises to 100 C and it boils. Heating 50 g water from room temperature to boiling requires 17 kJ and boiling it requires 130 kJ. As combustion of 50 mL (0.833 mols) isopropanol produces 1659kJ, it is clear that most of the heat produced is lost to the surrounding air and through the vaporization of the alcohol. This vaporization is visible in the form of a blue flame. Lower proportions of water result in charring of the towel and show that a 50-50% ratio is barely sufficient. Ethanol and methanol can be used in place of isopropanol.

Hazards:

Be cautious to not set the towel on fire. To avoid burns the flaming towel must be handled with care. Combustible materials should be removed from the vicinity, and a fire extinguisher should be available. Isopropyl alcohol can damage the eyes severely.

SOP:

N/A

Disposal (by Storeroom)

The excess solution can be saved for a future demonstration or flushed down the drain.

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