A pipette is a tube that delivers one fixed, accurate volume of liquid, such as 25.0 cm³, used wherever an exact known volume is needed.
Malay: Pipet · Chinese: 移液管
A pipette is a piece of laboratory apparatus that delivers one fixed, accurate volume of liquid, most often 25.0 cm³ or 20.0 cm³. It is used wherever a precise, known volume must be measured out, such as transferring a fixed volume of a solution into a conical flask for titration. Because it is made to deliver a single volume, a pipette is more accurate than a measuring cylinder, and the SPM Chemistry syllabus (4541) expects you to choose it when accuracy matters.
In use, liquid is drawn up past the mark with a pipette filler (never by mouth), and the level is set so that the bottom of the meniscus rests on the graduation line at eye level. The pipette is then allowed to drain, leaving the small amount in the tip, which the design already allows for. Done correctly, it delivers exactly the stated volume every time. Rinsing the pipette first with a little of the solution it will measure prevents dilution and keeps that delivered volume trustworthy.
The confusion to avoid is between a pipette and a burette. A pipette gives one fixed volume; a burette delivers a variable volume that you read off, letting you add liquid gradually until a reaction is complete. A second slip is reaching for a measuring cylinder when accuracy is needed, a measuring cylinder gives only an approximate volume and should not be used where a pipette is required.
Within the apparatus section of this chapter, the pipette belongs with the burette as the pair of “accurate volume” instruments used in titration. Our teachers show you how to read the meniscus correctly so your measured volumes are exact.
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