How to Use a Burette

Burettes are glass volumetric instruments calibrated to deliver (TD, Ex) and are used for titration in volumetric analysis.

Calibration

Class AS: 'Ex + 30 s'

Class B: 'Ex'

Note on waiting time

Compared to pipettes, the handling of burettes is different during practical use and calibration. Typically, the volume used in a titration is less than the nominal volume, and the standard solution is added dropwise when close to the color change to avoid overtitration.

In practice, the time required for this dropwise addition is the same or longer than the established waiting time. As a result, it is not necessary to observe the established waiting time of 30 s with class AS burettes during practical use.

Types of burettes

Types of burettesTypes of burettes

Types of burettes

Handling

1. Rinse the burette with the standard solution to be used, and align burette tube vertically.

2. Fill the burette slightly above the zero mark. To prime the stopcock, drain the burette no further than the nominal capacity.

3. Refill the burette with titrant free of air bubbles to approx. 5 mm above the zero mark.

4. Drain liquid to set the zero point accurately. Important: Meniscus must be read at eye level (parallax-free level). Automatic burettes: Fill to approximately 5 mm above the zero mark This is adjusted automatically after air release.

5. Wipe off any drops adhering to the discharge tip.

6. Open the stopcock and slowly add titrant to the sample (containing the indicator). The discharge tip must not touch the wall of the vessel. Keep swirling the sample vessel lightly while adding titrant, or place it on a magnetic stirrer.

7. Read the discharged volume at eye level.

8. Any drops remaining on the tip of the stopcock should be wiped against the vessel wall and rinsed down. It is part of the titrated volume.

Notes on titration:

  • In addition to burettes, volumetric flasks, bulb pipettes and Erlenmeyer flasks are required for titrating.
  • For easiest recognition of the color change, place the sample vessel on a white surface.
  • Make sure that the solution is completely homogenous.
  • There must be no cloudiness, flocculation or precipitation present.
  • The titration is finished, when the color change is reached.
  • Before each new titration, reset the zero point and start the titration from there.

Materials