Acid-base titration with a burette is one of the most widely used volumetric techniques for determining the concentration of an acidic or basic solution. Its principle consists of reacting a known or measurable amount of sample with a solution of known concentration, called the titrant, until a point close to chemical equivalence is reached.
Although the basic principle is straightforward, obtaining a reliable result requires control of several factors: the condition of the burette, correct meniscus reading, sample preparation, indicator selection, titrant addition rate and the final stoichiometric calculation.
In this article, we explain how to perform an acid-base titration with a burette step by step, which laboratory equipment is needed, the different types of burettes that may be used and the most common errors to avoid.
What is an acid-base titration?
An acid-base titration is a quantitative analytical technique based on a neutralisation reaction between an acid and a base.
In general terms:
acid + base → neutralisation products
In simple aqueous systems, neutralisation involves the reaction between acidic and basic species until a defined stoichiometric relationship is reached.
During the analysis, one of the solutions has a known concentration. This solution is normally placed in the burette and added in a controlled manner to a measured amount of the unknown sample.
The objective is to determine how much titrant is required to react stoichiometrically with the analyte.
Equivalence point and endpoint
Two concepts should be distinguished.
The equivalence point is the theoretical moment at which the quantities of acid and base have reacted according to the stoichiometric relationship of the chemical reaction.
The endpoint, by contrast, is the experimental signal used to stop the titration. When an acid-base indicator is used, it is usually identified through a visible colour change.
A good procedure therefore aims to make the observed endpoint as close as possible to the equivalence point.
Equipment required for an acid-base titration with a burette
The setup may vary depending on the method, but it normally includes:
- A burette suitable for the required volume and accuracy.
- Laboratory stand.
- Burette clamp.
- Volumetric pipette or another suitable device for measuring the aliquot.
- Erlenmeyer flask.
- Titrant of known concentration.
- Sample containing the acid or base to be determined.
- Suitable acid-base indicator when visual endpoint detection is used.
- Water of appropriate quality for the procedure.
- Auxiliary containers for preparation and rinsing.
At Pobel, the relevant laboratory equipment families include burettes, pipettes, Erlenmeyer flasks, stands and burette clamps.
The conical shape of an Erlenmeyer flask is particularly convenient for titration because the solution can be swirled while reducing the risk of splashing.
Types of burettes for acid-base titrations
The burette is the central component of the procedure. It allows the titrant to be added gradually and the delivered volume to be determined from the initial and final readings.
Straight burettes
Straight burettes are the traditional configuration for manual titrations.
The range described in the Pobel catalogue includes class A and class B straight burettes, with different capacities, graduations and stopcock configurations.
For quantitative work where volume accuracy is especially important, the volumetric class should be selected according to the requirements of the analytical method.
Burettes with different stopcock types
Depending on the model, the catalogue includes configurations with:
- Glass stopcock.
- Conical PTFE stopcock.
- PTFE needle stopcock.
- Other closing systems depending on the model.
The appropriate choice depends on the intended application, the reagents being handled and the laboratory's specific requirements.
Burettes with reservoirs
Reservoir burettes integrate a reservoir that facilitates titrant supply.
They may be particularly useful when several determinations are performed using the same solution, as they can reduce repetitive filling operations.
Schilling burettes
Schilling-type burettes incorporate automatic zero adjustment. According to the Pobel catalogue, these class A models use a closed system designed to reduce exposure to external contamination and allow the burette to be filled through the bottle system.
This configuration can be useful for repetitive work.
Automatic bench burettes
Another option is the bench burette with automatic zero adjustment and filling bottle.
Its main operational advantage is the ability to streamline repeated titration cycles when the same titrant is used many times.
How to select the right burette
There is no single burette that is ideal for every analysis. Several criteria should be considered.
Capacity
Burette capacity should be appropriate for the expected titrant consumption.
A very large burette used for an extremely small titration volume may reduce the practical resolution of the measurement. Conversely, a burette that is too small may need to be refilled during the analysis.
Different capacities are available across the burette families described in the Pobel catalogue.
Scale graduation
Smaller graduations allow finer volume readings, although the actual accuracy of the analysis depends on the complete procedure and the specifications of the volumetric equipment.
Volumetric glassware class
The Pobel catalogue distinguishes between class A and class B volumetric glassware. The class is related to the specified tolerances and degree of accuracy of the equipment.
For demanding quantitative procedures, the analytical method, standard operating procedure and tolerance of the selected equipment should always be checked.
Pobel also describes the option of requesting batch certificates or individual certificates for volumetric glassware under the conditions applicable to those products.
Complete acid-base titration procedure using a burette
A good titration begins before the burette stopcock is opened. Correct preparation of the equipment is essential.
1. Inspect the burette
Before use, visually inspect the burette.
It should be clean and free of visible damage that could compromise its operation. The stopcock should control the flow correctly and the delivery tip should be unobstructed.
If the laboratory method requires additional checks, they should be performed before the analysis begins.
2. Condition the burette
When appropriate for the procedure, the burette may first be rinsed with suitable water and then conditioned with small portions of the titrant itself.
Conditioning with titrant helps prevent residual water on the inner walls from causing significant dilution of the solution used for the titration.
The conditioning solution should not be returned to the original reagent container.
3. Fill the burette
Close the stopcock and add the titrant.
If a funnel is used for filling, remove it before taking the reading and beginning the titration. This prevents drops retained in the funnel from entering the burette later and changing the measured volume.
Fill the burette sufficiently to complete the expected determination.
4. Remove air from the delivery tip
Briefly open the stopcock to fill the delivery tip completely.
Check carefully for air bubbles, particularly around the lower section and tip.
If an air bubble disappears during titration, an error may occur because part of the recorded volume has been used to fill that space rather than being delivered to the flask.
5. Record the initial reading
A conventional burette does not have to start exactly at 0.00 mL. The important point is to record the initial reading accurately and subtract it from the final reading.
For transparent liquids producing a concave meniscus, the reading is generally taken at the lowest point of the meniscus.
Pobel's technical information also highlights a fundamental principle: the observer's eye should be at the same level as the meniscus. Looking from above or below introduces parallax error.
A dark strip placed behind the burette just below the meniscus can make the reading easier.
6. Prepare the sample
Measure the amount of sample specified by the analytical method.
When an accurately defined aliquot is required, a suitable volumetric pipette is commonly used.
Transfer the sample into an Erlenmeyer flask.
If the procedure allows it, sufficient water may be added to facilitate swirling. Adding water changes the total volume but does not change the initial amount of analyte in the measured aliquot. The specific requirements of the method must nevertheless always be followed.
7. Add the indicator
If visual detection is used, add the acid-base indicator specified in the method.
The indicator should be selected according to the pH range over which it changes colour and the characteristics of the titration.
It should not be chosen simply because its colour change is easy to see. Its transition range should allow the visual endpoint to occur close to the equivalence region of the system being analysed.
Instrumental methods may instead use a pH electrode or another endpoint detection system.
8. Start the titration
Place the Erlenmeyer flask under the burette and begin adding titrant while continuously mixing the solution.
At the beginning, when the system is far from the endpoint and the method permits it, the titrant may be added at a moderate rate.
The solution should become homogeneous after each addition.
9. Reduce the addition rate near the endpoint
As the indicator colour produced by each addition takes longer to disappear, the titration is approaching its endpoint.
At this stage, substantially reduce the rate of addition.
Close to the endpoint, the titrant should be added drop by drop while maintaining continuous mixing.
The inner wall of the Erlenmeyer flask may be carefully rinsed with a small amount of appropriate water to bring down any reagent droplets adhering to the glass. This water changes the overall volume but does not change the amount of analyte originally measured.
10. Identify the endpoint
Stop adding titrant when the change defined by the procedure appears and remains for the period specified by the analytical method.
There is no single endpoint criterion suitable for every indicator and every titration. The requirements of the specific laboratory method should always be followed.
A common mistake is to continue adding titrant in an attempt to obtain a more intense colour. The objective is generally to identify the first persistent change that satisfies the method, not to maximise colour intensity.
11. Record the final reading
Allow the appropriate time for liquid remaining on the inner walls of the burette to drain according to the conditions specified for the volumetric equipment and procedure.
Then read the meniscus again at eye level.
The volume delivered is calculated as:
Volume used = final reading − initial reading
For example, if the initial reading is 0.35 mL and the final reading is 24.80 mL:
V = 24.80 − 0.35 = 24.45 mL
How to calculate the result of an acid-base titration
The calculation depends on the chemical equation.
For a general reaction:
a A + b B → products
at the equivalence point:
n(A) / a = n(B) / b
Because the amount of substance in a solution can be expressed as concentration multiplied by volume:
C(A) × V(A) / a = C(B) × V(B) / b
For a simplified 1:1 reaction, the expression becomes:
C₁V₁ = C₂V₂
However, this simplified equation should only be used when the reaction stoichiometry is actually 1:1.
Volumes should be expressed in consistent units, and the final concentration should be reported in the units required by the analytical method.
Good practices for improving accuracy
A consistent working routine is essential for reproducible results.
Important good practices include:
- Use volumetric equipment suitable for the required accuracy.
- Check that no bubbles remain in the burette tip.
- Always read the meniscus at eye level.
- Keep the burette correctly vertical.
- Remove the filling funnel before titration.
- Maintain homogeneous mixing during titration.
- Reduce the flow rate when approaching the endpoint.
- Record readings immediately.
- Respect applicable delivery and waiting times.
- Perform replicate determinations according to the laboratory procedure.
Where metrological traceability is particularly important, calibration or certification of volumetric equipment may also need to be considered.
Common errors when titrating with a burette
Incorrect meniscus reading
If the eye is not at the same level as the liquid surface, parallax error occurs.
This is one of the easiest manual errors to avoid and, at the same time, one of the most common.
Leaving an air bubble in the tip
This creates a difference between the volume shown by the burette and the volume actually delivered to the sample.
Failing to condition the burette when required
If a significant amount of water remains inside the burette, the titrant may be diluted.
Overshooting the endpoint
Adding titrant too quickly near the endpoint can result in an excess volume being delivered.
The flow rate should therefore be progressively reduced, with dropwise addition in the final stage.
Using an unsuitable indicator
An indicator whose transition range is not compatible with the titration curve can produce an endpoint that differs significantly from the equivalence point.
Confusing capacity with accuracy
A higher-capacity burette is not automatically the better choice.
Capacity, graduation, tolerance, volumetric class and expected titration volume should all be considered together.
Ignoring the waiting time
After delivery, a small amount of liquid may continue to flow down the inner wall of the burette.
Pobel's technical appendix highlights the importance of considering delivery and waiting times when aiming for the best possible volume measurement with burettes and pipettes.
Safety during an acid-base titration
The risks depend on the specific reagents used.
Many acids and bases used in laboratories can be corrosive or irritating. Their safety data sheets and the laboratory's internal procedures should therefore always be consulted.
General precautions include:
- Wear the required personal protective equipment.
- Use appropriate eye protection.
- Avoid contact of reagents with skin and eyes.
- Handle volatile or particularly hazardous reagents under the specified ventilation conditions.
- Secure the burette correctly to prevent it from falling.
- Do not use damaged glassware.
- Dispose of waste according to the established procedure.
Safety should never be assessed simply on the basis that a solution is described as “acidic” or “basic”; the specific reagent and its concentration determine the actual hazard.
Frequently asked questions about acid-base titration with a burette
Why use a burette instead of a graduated cylinder?
Because titration requires the reagent to be delivered in a controlled manner while accurately measuring the volume dispensed. A burette is specifically designed for this type of volumetric delivery.
Does the burette have to start exactly at zero?
Not necessarily. It can begin at any suitable point on the scale provided both the initial and final readings are accurately recorded.
The delivered volume is calculated from their difference.
Why must air bubbles be removed from the tip?
If air remains in the tip, part of the volume indicated by the burette may be used to fill that space instead of reaching the flask.
What is the difference between a class A and a class B burette?
The classification relates to the tolerances and degree of accuracy assigned to the volumetric glassware. The Pobel catalogue includes both categories and specifies the applicable tolerances according to the model.
The selection should match the requirements of the analytical method.
What burette capacity should I use?
It depends on the expected titrant volume.
A suitable capacity should allow the titration to be completed conveniently while also providing appropriate resolution for the volume being measured.
What happens if I overshoot the endpoint?
The titration may no longer be valid for the intended calculation because an unknown excess of titrant has been added.
Depending on the procedure, the determination will normally need to be repeated.
How many times should a titration be repeated?
This depends on the method, the laboratory's internal criteria and the acceptable uncertainty.
Repeated determinations are common in quantitative analysis, but the acceptance criteria for agreement between results should be defined by the applicable procedure.
Conclusion
Correctly performing an acid-base titration with a burette involves much more than adding acid to a base until a colour change appears.
Reliable results depend on choosing the appropriate equipment, conditioning the burette correctly, removing air bubbles, reading the meniscus without parallax error, controlling the rate of titrant addition near the endpoint and applying the correct reaction stoichiometry.
At Pobel, we work with different solutions for liquid handling and volumetric analysis, including straight burettes, reservoir burettes, Schilling systems and automatic burettes, as well as pipettes, Erlenmeyer flasks, clamps and stands for complete laboratory setups.
Selecting suitable laboratory equipment and combining it with a well-defined procedure and consistent working technique helps achieve more reproducible and reliable titration results.
