Definitions

Burette

Burette

[byoo-ret]

A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. It is used to dispense known amounts of a liquid reagent in experiments for which such precision is necessary, such as a titration experiment. Burettes are extremely accurate: class A burettes are accurate to ± 0.05 cm3.

Using a burette

The precision of a burette makes careful measurement with a burette very important to avoid systematic error. When reading a burette, the viewer's eyes must be at the level of the graduation to avoid parallax error. Even the thickness of the lines printed on the burette matters; the bottom of the meniscus of the liquid should be touching the top of the line you wish to measure from. A common rule of thumb is to add 0.02 mL if the bottom of the meniscus is touching the bottom of the line. Due to the precision of the burette, even a single drop of liquid hanging from the bottom of a burette should be transferred to the receiving flask, usually by touching the drop to the side of the receiving flask and washing into the solution with the experimental solvent (usually water). Through careful control of the stopcock and rinsing, even partial drops of liquid can be added to the receiving flask.

History

The history of the burette parallels the history of volumetric analysis. Francois Antoine Henri Descroizilles developed the first burette (which looked more like a graduated cylinder) in 1791. Joseph Louis Gay-Lussac developed an improved version of the burette that included a side arm, and coined the terms "pipette" and "burette" in an 1824 paper on the standarization of indigo solutions. A major breakthrough in the methodology and popularization of volumetric analysis was achieved by Karl Friedrich Mohr, who redesigned the burette by placing a clamp and a tip at the bottom.

References

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