Bunsen burner: flame test
Two fiery experiments with Bunsen burners!
Attention! All experiments are performed by professionals. Do not attempt.
The burner flame consists of a heating zone, an intensive combustion zone, and a luminous zone. In the heating zone, hydrocarbon gases and oxygen are heated by the surrounding blue flame, but do not react with one another. Therefore, this part of the flame is colorless and is located at the bottom, and its temperature reaches about 350 °C (660 °F). Passing into the intense combustion zone, the gases react, releasing a blue glow and a lot of heat. This is the hottest part of the flame, with a temperature of approximately 1500 °C (2730 °F). The blue color is due to the formation of radicals such as OH and CH. These radicals are highly unstable and do not exist under normal conditions; they appear at high temperatures. In the flame, these radicals are in an excited state, that is, they have an excess of energy. In an effort to move to a more stable, ground state, these particles release energy in the form of blue light. Some gas molecules do not burn completely, forming small particles of soot. These particles rise higher and are oxidized by oxygen, heating up to about 1000 °C (1830 °F) and emitting yellow light. The flame of the burner can be used to detect metal ions: they absorb the thermal energy of the flame, which is then emitted in the form of light with a characteristic color. For example, copper(II) ions emit green light, sodium ions emit yellow light, and calcium or strontium create shades of red. In addition, the flame’s temperature is high enough to melt glass, causing it to bend and stretch. This time, the flame turns yellow-orange due to the sodium and calcium oxides presence in the glass.
Safer (but just as cool) experiments await you in the MEL Chemistry subscription!