The burette is part of the laboratory equipment used for the quantitative analysis of chemical substances, it is used to measure chemical solutions, also the volume of liquids, and gases.
In addition to measuring, it is an important dispenser, it serves to add small and large amounts of bases or substances to the preparation of a chemical solution. It also collects gas as the liquid travels, the amount of gas being measured by the volume of fluid displaced. In this sense, this instrument is used to carry out very exact volumetric measurements.
What is the burette and what is it for?
The burette is a glass instrument used in laboratories, which is used to dose precise amounts of liquid, it is used in various research areas and in general in any space where it is necessary to work with liquid solutions and compounds.
It consists of an elongated and graduated tube, generally made of glass, which is open at the upper end, while its lower end ends at a point, it has a key that is used to control the exit of the liquid.
What is the main function of the burette?
This instrument, generally have a capacity of 25 or 50 milliliters, subdivided into tenths of milliliters. There are other smaller measures that allow a higher level of precision, according to their size and capacity, their use can be:
- The main use of the burette is to accurately measure and dispense different amounts of liquid of varied nature, in volumetric work.
- Burettes are used more frequently in methods such as titrations, since they allow us to know the concentration of a solution.
- Through this instrument we can assess solutions, these chemical mixtures can be acidic or basic in nature. A burette allows us to know the precise amount of base that is needed to neutralize an acid and thus calculate its concentration.
- In the same way, the opposite operation can be carried out. Using the burette, we can know the end point of the titration or titration, since we can add drop by drop to the test sample, another compound known as an indicator, this will be a visual indicator in the reaction, as it will allow the color change at this point.
General characteristics of the burette
Burettes, along with other glass instruments, constitute the basic volumetric material within laboratories. There are also graduated volumetric pipettes, volumetric flasks, among others.
The burettes have a series of divisions, that is why it is said that they are graduated, this characteristic allows us to measure volumes of liquids very precisely, almost exactly.
Parts of the burette
The most commonly used burette is made up of:
- A fairly fragile, thin, graduated glass tube with a constant internal diameter.
- A stopcock, which is also known as a Mohr clamp. There are other types of keys, intended to be used in burettes when we work with basic, acidic or neutral solutions.
- Base that serves as a support that provides stability and greater ease of handling. The material of this base is highly resistant and is tied with Teflon.
All burette keys are made of inert materials, such as glass and Teflon.
- Frosted glass faucet, which is particularly used in acidic or neutral solutions.
- Mohr’s key is used in burettes when working with basic solutions.
- The multipurpose keys, are used more frequently, they are made of ground glass, necessary for some liquids, such as organic and iodine solutions.
Caring for the burette
The burette is a delicate instrument, so it must be treated with great care. When working with a burette, as with any other laboratory equipment or instrument, there are certain considerations that we must always keep in mind:
- It should be cleaned with water and detergent, using a suitable brush, then rinsed with distilled water, this should be done immediately after use.
- At the time of use, it must be rinsed with the titrant solution.
- The buret must be filled, avoiding the formation of bubbles, as this will interfere with the interpretation of the results, which may be erroneous.
- The lower end or peak of the burette cannot be expired or damaged, since if so, the measurement that will be thrown at us will not be precise at all.
- In the event that indicator solutions are used, that is, they change color, a white paper should be placed under the Erlenmeyer flask to better demonstrate this color change.
- The solutions to be titrated cannot be hot, as the burette could burst as its material is not capable of withstanding high temperatures. The temperature range is from 10 to 40 ° C.
- During the experiment or titration, special care must be taken when handling the buret tap.
- In order for this instrument to maintain its accuracy and be most useful, it must be completely clean and degreased.
- To maintain the precision of the work with the burette, it is advisable to grease the stopcock, so that it is easy to manipulate and fits well.
In this maintenance process, petroleum jelly or lanolin is often used when aqueous solutions are titrated, while paraffin-based lubricants are used for fat-dissolving solutions.
How to use the burettes
- The burette is placed on the stand, which is known as the universal stand. The burette is held with a clamp.
- On the support and under the burette, we put filter paper.
- Before filling the burette we must rinse its walls three times, for this we use the solution with which we will work.
- To fill the burette, the first thing we must do is verify that the tap is closed, then we can pour the solution, for this we use a funnel. It must be filled until we exceed the zero line.
- The tap is opened and the liquid is dropped until it is level, (to have the necessary liquid volume), exactly with zero to avoid the formation of bubbles inside the burette.
- The tap is opened gently with one hand, until the solution begins to fall drop by drop. The final volume and the volume of the liquid that was transferred are then noted.
- The other hand is used to gently move the Erlenmeyer flask, beaker or container containing the solution to be titrated. In this way we will achieve that its content is homogenized and the end of the reaction can be detected.
- The end of the reaction can be determined because we can generally observe that there is a color change.
- Finally , the burette can be refilled or simply use the final volume as the new starting volume and continue with the study.
It is important to note that the instrument’s zero is usually at the top of the burette, so the measurement increases from top to bottom. In turn, the reading must be done correctly, observing the meniscus at eye level.
Types of Burettes
At present and with the advancement of technology there are mainly two types of burettes:
The analog burette is the traditional glass burette, which has a constant diameter throughout its entire length, it also has a stopcock at the lower end and presents its graduation scale. This type of burette includes a sub-classification, due to the variety of parts and accessories added:
- Mohr’s burette : the key is replaced by a rubber tube, which contains inside a glass ball whose function is to act as a valve.
- Amber Burette : It is similar to the previous one, but amber in color, specially designed for endothermic substances, which are those that can absorb energy that manifests as heat. These substances can react with the presence of light, either artificial or solar.
- Geissler burette : The key is made of ground glass, which is very useful when we use certain liquids. We must mention that in this case the liquid to be measured cannot remain in the burette for a long time, since it can clog or immobilize the faucet.
The digital burette is the easiest to use, it is the most up-to-date so it provides greater and better precision. However, its use is more common in large laboratories. It has a digital display, which is used to measure large figures, its calibration is much easier than in the case of the analog burette. This type of burette completely prevents the formation of bubbles. They can be electric or they can also be manipulated manually.
Conclusion of the burettes
To conclude, it is important to emphasize the great utility of this instrument in laboratories, in the areas of measurements and chemical procedures, as well as in volumetry, as it allows us to accurately measure quantities of liquid materials.
Working with this type of instrument can carry out a large number of scientific studies, where chemistry, its principles and concepts are of vital importance for new discoveries in various areas of science.
Laboratory work also requires care and attention with the materials to be used, it merits certain personal safety regulations, the use of implements for our protection, such as gowns, glasses, gloves and face masks.
Dr. Samantha Robson ( CRN: 0510146-5) is a nutritionist and website content reviewer related to her area of expertise. With a postgraduate degree in Nutrition from The University of Arizona, she is a specialist in Sports Nutrition from Oxford University and is also a member of the International Society of Sports Nutrition.