“Green flame” experiment
How to color flame green
This colorful experiment not only shows how chemical properties change in a chemical reaction, but also physical properties.
The experiment uses concentrated alcohol and sulfuric acid. Wear gloves and protective glasses, and work in a well-ventilated room. Observe fire safety rules.
Reagents and equipment:
- boric acid (1 g);
- 5 ml of ethyl alcohol;
- concentrated sulfuric acid;
- test tube;
- spirit burner;
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 (non-organic) 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.