Green is probably the coolest color to turn flames. But there is only one chemical, that will give you real, vibrant green. Here is which one:
- This experiment uses dangerous chemicals. Please review the safety
- The green color is generated from a chemical called trimethyl borate
- Methanol is used because, on its own, it has a very weak, blue flame
How to make real green flames
- Gradually add the boric acid to the methanol. Stir to speed up the dissolving process.
- Take some of the solution and spread it on a non-flammable surface.
- When ready, ignite the solution. Immediately a vibrant green colour will appear.
How does fire turn green?
Boric acid can form complex esters with several alcohols. Esters are a class of compounds which are the products of the interaction of alcohols with acids. Their general formula is R(C=O)OR. Usually, carboxylic acids are used in the formation of esters. For example, in the interaction of isoamyl alcohol with acetic acid in the presence of sulfuric acid (catalyst), isoamyl acetate is formed, an ester which has the odour of pears.
Boric acid is one of the few mineral acids capable of forming complex esters. Esters of boric acid burn with a green flame. Trimethyl borate, the ester we have just made, has the strongest colour. That’s why boric acid is used in analytical chemistry to identify methanol (and visa versa).
Safety & Disposal
Boric acid is a danger to the environment. The solution can not be poured down the drain and has to be disposed of in a labelled container. The disposal requirements may differ in your country.
Methanol is a highly flammable, toxic liquid. Boric acid may cause harm to the unborn child. Wear skin and eye protection at all times. Only perform this experiment outside or in a fume hood.
GHS H&P: H(225, 301+311+331, 360FD, 370) – P(201, 210, 280, 308+313, 302+352+312, 370+378, 403+235)
The use of this instruction and the information provided therein takes place at the user’s own risk.