Burette — Definition, Use, and Diagram

If you look at a burette diagram, you will see three main parts:

1. The Graduated Tube: It is a long, narrow glass tube with volume markings (graduations) printed along its length. The markings start with 0 ml at the TOP and increase downwards (usually up to 50 ml).
2. The Stopcock: Located at the very bottom, this is a precision valve (usually made of glass or Teflon/PTFE). Turning the stopcock controls the flow of liquid out of the bottom tip, allowing you to release liquid drop by drop.
3. The Tip: The narrow opening at the bottom where the liquid exits.

Burettes are primarily used for Titration.

In a titration, a chemical solution of known concentration (the titrant) is placed inside the burette. It is then carefully dripped into a flask containing a solution of unknown concentration until a chemical reaction is perfectly completed (indicated by a color change). Because the burette is marked, the chemist can see exactly how many milliliters of liquid were dispensed from the tube.

Reading a burette can be tricky for beginners because the zero is at the top.

1. Fill the burette and note the starting level of the liquid (e.g., 2.0 ml).
2. Open the stopcock and let the liquid flow.
3. Close the stopcock and read the final level of the liquid (e.g., 24.5 ml).
4. Volume used = Final reading − Initial reading (24.5 - 2.0 = 22.5 ml dispensed).

Important: Always read the volume at the bottom of the curved surface of the liquid (the meniscus) at eye level.