"Green Flame" experiment
How to make a green fire
This colorful experiment shows how not only chemical properties, but also physical ones, change in a chemical reaction.
Reagents and equipment:
- boric acid (5 g);
- ethyl alcohol (50 ml);
- concentrated sulfuric acid;
- porcelain cups (2);
- glass rod;
Pour ethyl alcohol into two porcelain cups and ignite it. We observe that the alcohol burns with a yellow flame. Now put out the fire. In one of the cups, add 5 g of boric acid and a few milliliters of concentrated sulfuric acid. Mix together well and wait for a while. Ignite the alcohol in the cups again. We see that the cup to which we added boric and sulfuric acid, the flame has turned green.
Boric acid can form complex esters with alcohol. Complex esters are a class of compounds which are the products of the interaction of acids with alcohols with the general formula of R(C=O)OR in the presence of a catalyst, for example sulfuric acid. In the interaction of acids and alcohols, the properties may change fundamentally. For example, in the interaction of isoamyl alcohol with acetic acid in the presence of sulfuric acid, the complex ester isoamyl acetate forms, which has the odor of pears, while the ester of formic acid and benzyl alcohol has the odor of jasmine. Boric acid is one of the few mineral acids which is capable of forming complex esters. Esters of boric acid burn with a green flame, and this property is used in analytical chemistry for detecting boric acid and its salts. Pure esters of boric acid burn at a temperature of around 30 °С, so you can safely put your hand in the flame.
The experiment uses concentrated alcohol and sulfuric acid. Wear gloves and work in a well-ventilated room. Observe fire safety rules.
Warning! Substances of this experiment are toxic and highly dangerous for your health. Do not try this at home. Only under professional supervision.