Borate Flame

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Required Training	Required PPE
UC Lab Safety Fundamentals	Flame-resistant lab coat, safety glasses/goggles, nitrile gloves
Performers Required: 1
Equipment	Chemicals
1 L Erlenmeyer flask with solid rubber stopper	Boric acid (B(OH)₃)
40-60mm Ceramic Buchner funnel with rubber stopper	Methanol (CH₃OH)
Watch glass (slightly larger than Buchner funnel)	Sulfuric acid (H₂SO₄), 18 M
Hotplate with clamp for flask
Boiling chips
BBQ-style butane lighter (≥ 6” long)

Procedure:

Add 2-3 mL of H₂SO₄ to 150 mL of CH₃OH in the 1-L Erlenmeyer flask.
Add 30 g of B(OH)₃ to the mixture and stir until all solids have dissolved.
Add the boiling chips to the flask and secure it in the clamp on the hotplate. Place the ceramic Buchner funnel (with tight-fitting rubber stopper) in the neck of the flask and heat the mixture to a vigorous boil. This may take 5-10 minutes, and should be started slightly before the demo is to be performed.
Ignite the vapor in the Buchner funnel with the lighter. If the vapor does not ignite, increase the heat from the hotplate. Ensure the mixture is boiling rapidly enough to maintain a flame, which will be the same diameter as the Buchner funnel and up to 12” in height. Do not heat the flask so rapidly that it boils over.
When finished turn off the hot plate. To extinguish the flame either place a watch glass on top of the Buchner funnel or simply wait until the mixture has cooled sufficiently, as the flame will diminish and then self-extinguish as the boiling subsides.

Clean-up: The flask should remain clamped to the hotplate to minimize the chance of spilling methanol around any ignition sources. Once everything has cooled to room temperature, the mixture should be saved for future use by replacing the Buchner funnel with a solid rubber stopper.

Hazards: Sulfuric acid is strongly oxidizing and corrosive, and will cause immediate chemical burns on contact. Methanol is toxic and highly flammable. Keep all solutions away from ignition sources until the demo is performed.

Principle: B(OH)₃ will react with CH₃OH in the presence of a dehydrating agent (H₂SO₄) to form trimethyl borate (B(OCH₃)₃) and H₂O. This borate ester is volatile (b.p. = 68 °C) and burns with the green flame characteristic of all boron compounds. The color is due to broadband emissions in the green region of the spectrum from various molecular species as they relax from excited electronic states back to their ground states.

Notes: A freshly-prepared solution may be added to the flask whenever the volume of the solution becomes too low to perform the demonstration (<50 mL). Do not heat the flask with an open flame, as this may cause the mixture to bump and boil out of the flask, creating a fast-spreading methanol fire.