The Bunsen burner is a typical device used in laboratories, typically as an open gas flame for heating, sterilization, and combustion.
Its name is due to the German chemist Robert Bunsen, who was responsible, together with the technician Peter Desaga, for its implementation and improvement based on a model already designed by Michael Faraday. This lighter is small and light, so it can be moved practically anywhere where there is a gas cylinder and optimal connections.
Above is the Bunsen burner in action. Note that the setting is not even that of a laboratory. The blue flame heats the contents of the flask to develop a chemical reaction, or simply to dissolve a solid more quickly. The main use of this instrument is thus simply to heat a surface, sample or material.
The origins of this iconic lighter date back to 1854, in one of the laboratories of the University of Heidelberg, where Robert Bunsen worked. By then, the university facilities already had a system of more rudimentary gas pipes and lighters with which to carry out experiments.
However, these lighters, designed by Michael Faraday, generated very bright and “dirty” flames, which means that they deposited charcoal stains on the surface that they touched. These flames, in addition to camouflaging the colors that certain substances released when heated, were not hot enough.
It was thus that Robert Bunsen, together with the German technician, Peter Desaga, decided to implement improvements in the Faraday lighters. To achieve this, they sought to make the gas burn with a greater flow of air, higher than that freely roaming the laboratory. In this way, the Bunsen-Desaga burner was born.
Since then, laboratories have had a lighter on hand that allows a much hotter and “cleaner” flame to be obtained. Likewise, thanks to this lighter the foundations or origins of spectroscopy were established.
Features and parts of the Bunsen burner
In the image above there is an illustration of the Bunsen burner. The respective inlets for both air and gas are indicated.
Air, on the other hand, enters the lighter through the circular (or rectangular) holes in its collar. As the collar is rotated, more air will flow into the holes and mix with the gas. This air-gas mixture will rise along the barrel or column, to finally exit through the burner nozzle.
The entire lighter is made from a lightweight metal, such as aluminum, and is small enough to fit on any shelf or drawer.
By placing a heat source just at the height of the lighter nozzle, either using a lit match or a spark, the air-gas mixture will ignite and combustion will begin. So the flame will appear. However, the visual and chemical characteristics of this flame depend on the air-gas ratio.
If the collar is closed, preventing air from entering through its holes, there will be a mixture rich in gas, which will barely burn with the oxygen in the surrounding air. This flame corresponds to 1 (upper image), and is known as the “safe” and “dirty” flame, as it is the least hot and also produces the most soot. Note how bright it is and also its yellow-orange colors.
The luminosity of this flame is due to the fact that the soot particles, made up practically of carbon atoms, absorb heat and give off light and color. The more open the gas inlet, the larger this flame will be.
This flame is also known to be reducing, because it contributes carbon as soot particles, which are capable of reducing some substances.
As the collar rotates, the holes through which the air passes open, thus increasing the amount of air in the resulting gaseous mixture. As a result, the yellow flame will become increasingly bluish (from 2 to 4), to a point where it can appear transparent if the background and purity of the mixture allow it.
Flame 4 is the most desired and useful in the laboratory, as it is the hottest and can also perfectly oxidize the sample that is placed in contact with it. For this reason, this flame is known to be oxidizing, since the combustion products (essentially carbon dioxide and water vapor) do not interfere with the surrounding oxygen and the substances to be oxidized.
Functions / uses
From the previous section it can be concluded that the flame is the most important element or characteristic of the Bunsen burner. It is in fact this that defines the respective functions or uses of this instrument, which in short are nothing more than heating a surface, material or sample.
However, this does not mean that it can be used to heat everything in the laboratory. To begin with, the melting point of the material must be above 1500 ºC, the maximum temperature at which the flame can reach. Otherwise, it will melt and cause a disaster on the workbench.
Second, the flame temperature is so high that it is capable of igniting the vapors of any organic solvent, which would increase the risk of fire. Therefore, only liquids with high boiling points and low volatility should be heated .
It is for this reason that water is an example of an ideal liquid to be heated through the use of the Bunsen burner. For example, it is common to heat distillation flasks, beakers, flasks, or pots, which contain aqueous solutions.
One of the main uses of the Bunsen burner is to burn a sample; that is, to oxidize it quickly and exothermically. For this, the oxidizing flame (blue in color and almost transparent) is used and the sample is placed inside a container such as a crucible.
However, most samples are subsequently transferred to a flask, where it can continue to heat for hours (even a whole day).
As with combustion, using the Bunsen burner the thermal decomposition of certain substances, such as chlorate and nitrate salts, can be carried out. However, this method absolutely does not allow you to track the progress of decomposition over time.
Metal ions can be qualitatively detected by flame testing. To do this, a wire previously heated and immersed in hydrochloric acid, is put in contact with the sample and brought into the flame.
The released colors help to identify the presence of metals such as copper (blue-green), potassium (violet), sodium (deep yellow), calcium (orange-red), etc.
Sterilization of materials
The heat of a flame is such that it can be used for another ingenious use: that of destroying microorganisms on the surface of materials. This is especially useful when dealing with glass or metals that are intended for purposes closely linked to health (needles, pipettes, scalpels, etc.).
It was previously said that water is one of the liquids that is preferably heated with the Bunsen burner. Because of this, it is used to heat distillation bottles, and thus boil the water so that its vapors carry some essences or fragrances of the vegetable matter (orange peels, cinnamon powder, etc.).
On the other hand, it can also be used to distill other types of mixtures, as long as the intensity of the flame is moderated and too many vapors are not generated in the process.
Determination of boiling points
With the help of the Thiele tube, oil, a support and a capillary, the boiling points of certain liquids are determined using the Bunsen burner to heat the handle of the tube or its side arm. This experiment is quite common in general chemistry and organic chemistry teaching labs.