Burettes

What is a burette?

If you are a chemical scientist or happen to know one, it’s likely that you have heard the term ‘burette’ being used. If you have ever wondered, what is a burette and what is a burette used for, let’s help you solve this mystery. For one who has ever performed a quantitative analysis in a chemistry lab, you would most likely have come across a burette. The word ‘burette’ has French origins and was coined by the chemist, Joseph Louis Gay-Lussac.

A burette is a laboratory apparatus, which consists of a long, graduated glass tube, with a stopcock on its lower end. It is used in quantitative chemical analysis to measure the volume of a liquid or gas. It is used to dispense and measure a variable amount of a chemical solution. The stopcock valve controls the flow of the fluid from the burette, either in a steady stream or drops by drop.

A burette (sometimes also spelt as buret) is often used in the process of titration. Titration is a process of chemical analysis in which the quantity of some constituent of a sample is determined by adding to the measured sample an exactly known quantity of another substance with which the desired constituent reacts in a precise proportion.

Types of burettes

Burettes can be classified in different ways: As per the mechanism

1) Volumetric burette – The volume scale is printed on the burette wall

2) Piston burette – Syringe design with barrel and plunger arrangement

As per operation

1) Manual burette – Marked by graduations and operated manually

2) Digital burette – Operated manually or electronically with digital displays

3) Electronic burette – Motor-controlled operations with the elimination of human errors, and electronic display

As per fluid handled

1) Liquid burette – Dispenses liquids. The stopcock is at the bottom of the burette, and the flow of the fluid is enabled by gravity

2) Gas burette – Dispenses gases. The stopcock is at the top of the burette, and the gas is collected by displacing a liquid like water or mercury, through a fluid reservoir at the bottom

Uses of Burettes

Now that we have some information about burettes, let’s find out what is a burette used for. As we saw before, burettes are used in the process of chemical titration. These can include acid/base titrations, reduction/oxidation titrations, and precipitation titrations. 

A burette can hence be used in the below industries:

1) Pharmaceutical Industry: Verification of concentrations in medicines

2) Food Industry: Testing the acidity levels of food liquids

3) Cosmetic Industry: Verifying concentration of ingredients in a safe amount

4) Meteorology: Measuring the amount of gases in the air

5) Bio-fuel Manufacturing: Measurement of impurities in bio-fuel

6) Medical Diagnosis: Analysis of body fluids like urine and blood

How to use a burette?

Now that we know more about the uses of the burette, we give you step-by-step pointers and best practices to use a burette for titration:

Rinsing: Rinse the burette with the liquid you wish to use. Do this by adding a small amount of liquid into the buret, turning the pipette horizontally and rotating it so that the liquid contacts the entire inside surface of the burette. Let the liquid drain through the stopcock into a waste container.

Support: Place the burette in appropriate support. This can be done by using a burette clamp attached to a ring stand.

Filling: Fill the burette with the titrating solution to be used just above the zero mark (+/- 10mm). Fill the tip of the burette with the solution. If necessary, the funnel can be placed on the upper end of the nozzle to help fill.

Remove air bubbles: The burette should not have air bubbles in the tube after the liquid is filled. If there are bubbles, use rubber or other items that will not break the glass to tap the wall to allow the bubbles to float out of the surface. There may also be air in the channel of the stopcock switch. In this case, the plug should be twisted several times quickly, and the bubble can be discharged.

Initial Reading: Verify that the burette is sealing well. To make a reading of the liquid level in the burette, the reading must be made tangentially to the lower part of the meniscus. Keep your eyes to this level, to avoid parallax errors

Dripping: Open the stopcock and slowly allow the liquid to drain into the receiving vessel until it approaches the end point.

End Point: You may add the titration solution quickly until a few milliliters less than the endpoint. After that, one should be careful when adding the solution, to determine the endpoint accurately. When the appropriate amount of liquid has been delivered close the stopcock and touch the buret to the side of the vessel to remove any partial drops.

Final Reading: Read the volume of the remaining liquid.

Calculation: The volume of liquid delivered can now be calculated by subtracting the Final Reading from the Initial Reading.

Drain: Drain the buret of any excess liquid and rinse it with water to clean it.