BUNSEN BURNER: FEATURES, FUNCTIONS, USAGE EXAMPLES - CHEMISTRY - 2025

The Bunsen burner is a laboratory instrument capable of supplying a heat source efficiently and safely through a flame, which is the product of the combustion of a gas that is usually methane, or a mixture of propane and butane. This instrument by itself is synonymous with science and chemistry.

Its name comes from 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 almost anywhere where there is a gas cylinder and optimal connections.

Bunsen burner heating the solution in a flask. Source: Sally V / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

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 therefore to simply heat a surface, sample or material.

However, the Bunsen burner is also used for a wide variety of methods and processes, such as flame testing, sterilization, distillation, combustion, and decomposition. Since middle school, it has been the cause of amazement and fear among students, to later become an instrument of routine use.

History

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 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

- instrument

Drawing of the parts of the Bunsen burner. Source: Pearson Scott Foresman / Public domain

The image above shows an illustration of the Bunsen burner. The respective inlets for both air and gas are indicated.

The gas runs through the interior of a rubber hose from the gas tap, located in the same laboratory counter, to the inlet of the lighter. In the lower area of ​​the lighter, just above the ring-shaped support, there is a valve or wheel that evens out the flow of gas that will come out of the lighter nozzle.

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 lighter nozzle.

The entire lighter is made of a lightweight metal, such as aluminum, and is small enough to fit on any shelf or drawer.

- Call

Reducing

The flame obtained by the Bunsen burner can vary in color depending on the amount of incoming air. Source: Arthur Jan Fijałkowski / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

By placing a source of heat 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 the one that also produces the greatest amount of soot. Note how bright it is and also its yellow-orange colors.

The luminosity of this flame is due to the soot particles, made up practically of carbon atoms, absorbing heat and giving 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 provides carbon as soot particles, which are capable of reducing some substances.

Oxidant

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 products of combustion (essentially carbon dioxide and water vapor) do not interfere with the surrounding oxygen and the substances to be oxidized.

Functions / uses

A Bunsen burner heating a flask. Source: Sally V / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

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 fire hazards. 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 by using a Bunsen burner. For example, it is common to heat distillation bottles, beakers, flasks, or pots, which contain aqueous solutions.

Usage examples

Combustion

One of the main uses of the Bunsen burner is to subject a sample to combustion; that is, to oxidize it in a rapid and exothermic way. For this, the oxidizing flame (blue in color and almost transparent) is used and the sample is placed in 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).

Thermal decomposition

As with combustion, using the Bunsen burner the thermal decomposition of certain substances can be carried out, such as chlorate and nitrate salts. However, this method absolutely does not allow you to track the progress of decomposition over time.

Flame test

Metal ions can be qualitatively detected by flame testing. To do this, a previously heated wire 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: to destroy 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.).

Distillation

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 much vapors are not generated in the process.

Determination of boiling points

With the aid 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.

References

1. Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
2. Wikipedia. (2020). Bunsen burner. Recovered from: en.wikipedia.org
3. Compound Interest. (2016, March 31). Chemistry History: Bunsen Burner Day. Recovered from: compoundchem.com
4. Nikki Wyman. (2015, August 31). Bunsen Burner: Parts, Function & Diagram. Recovered from: study.com
5. Nichols Lisa. (August 18, 2019). Bunsen Burners. Chemistry Libretexts. Recovered from: chem.libretexts.org
6. Wayne State University. (sf). Proper Use of a Bunsen Burner.. Recovered from: research.wayne.edu