A burette is a volumetric laboratory instrument used to deliver liquids in controlled and accurately measured volumes. It is particularly important in titration, where the exact volume of solution delivered must be determined. Choosing the correct burette requires consideration of its capacity, type, accuracy class, graduation interval, stopcock and chemical compatibility.
Right Burette = Accurate Volume Control + Reliable Titration
What Is a Burette?
A burette is a long graduated tube equipped with a stopcock that controls liquid flow.
Common capacities include:
- 10 mL
- 25 mL
- 50 mL
- 100 mL
The 50 mL burette is one of the most commonly used sizes for general titration work.
Unlike a volumetric pipette, a burette allows the operator to deliver a variable amount of liquid, including dropwise addition near the endpoint.
Where Are Burettes Used?
Typical applications include:
- Acid-base titrations
- Redox titrations
- Complexometric titrations
- Precipitation titrations
- Volumetric analysis
- Controlled reagent dispensing
The delivered volume is calculated from the difference between the final and initial readings:
Volume Delivered = Final Reading − Initial Reading
Main Types of Burettes
1. Standard Stopcock Burette
The traditional laboratory burette uses a glass or PTFE stopcock to control liquid flow.
It is widely used for routine titration.
2. PTFE Stopcock Burette
PTFE stopcocks can provide low friction and broad chemical compatibility, and many designs can operate without stopcock grease.
Compatibility should still be verified for the specific chemicals being used.
3. Automatic Burette
An automatic burette can be refilled from a reservoir and is particularly useful when multiple titrations are performed with the same titrant.
4. Schilling Burette
Schilling-type burettes use a reservoir and filling arrangement that simplifies repeated filling, making them practical for routine titration work.
Class A vs. Class B
Class A
Provides tighter tolerances and is generally preferred for analytical applications requiring higher accuracy.
Class B
Typically has wider tolerances and may be suitable for routine laboratory work.
Exact tolerances depend on the nominal capacity, graduation interval and applicable standard.
What Is a Class AS Burette?
Some volumetric glassware is designated Class AS.
In addition to accuracy requirements, Class AS products may have defined delivery and waiting-time conditions. The applicable standard and manufacturer instructions should therefore be considered when performing high-accuracy analyses.
How Is a Burette Read?
Burette scales generally increase from top to bottom.
For example:
Initial reading: 2.30 mL
Final reading: 18.75 mL
Volume delivered:
18.75 − 2.30 = 16.45 mL
For water and many aqueous solutions, the bottom of the concave meniscus is read at eye level.
Why Are Air Bubbles Important?
Before titration, the burette tip and the area below the stopcock should be filled with titrant and free from air bubbles.
Otherwise, some of the apparent delivered volume may actually be used to fill the empty tip rather than entering the sample.
How to Choose the Right Burette
| Criterion | What to Consider |
|---|---|
| Capacity | Match the expected titration volume |
| Graduation | Match the required reading precision |
| Accuracy class | Class A, AS or B |
| Stopcock | Glass or PTFE |
| Material | Chemical compatibility |
| Type | Manual, automatic or Schilling |
| Standard | Check the applicable specification |
A larger burette is not automatically better. The capacity and graduation interval should be appropriate for the expected titration volume.
Common Burette Errors
Typical mistakes include:
- Reading the meniscus above or below eye level
- Leaving air bubbles in the tip
- Failing to record the initial reading
- Adding titrant too quickly near the endpoint
- Failing to condition the burette with the titrant
- Ignoring stopcock leakage
- Selecting an inappropriate accuracy class
Conclusion
A burette is an essential volumetric instrument for the controlled delivery and accurate determination of liquid volume during titration.
When selecting between standard, PTFE-stopcock, automatic and Schilling burettes, consider:
Capacity + Graduation + Accuracy Class + Stopcock + Chemical Compatibility
Selecting and using the correct burette helps improve the reliability and reproducibility of titration results.
