What is a Burette and what is it used for?
A burette is essentially a long, cylindrical piece of glassware marked with volume graduations, designed for dispensing known amounts of a liquid with high precision. Burettes are primarily of two types: glass and digital, with the former being the traditional choice for manual titrations.
Each part of a burette, from the stopcock at the bottom to the filling funnel at the top, plays a critical role in its operation. Accuracy and precision in using a burette are not just about the correct measurements; they're about repeatability and reliability in your chemical testing outcomes.
Different Types of Burettes and Their Applications
There are different kinds of burettes, each designed for specific titrations or chemical analyses. The choice of burette can affect the precision, ease of use, and suitability for your particular experiment. Here's an overview of the main types of burettes used in the laboratory:
- Class A Glass Burettes: These are high-precision burettes made from the highest quality of borosilicate glass, designed to deliver a known volume of a liquid with high accuracy.
Class A burettes are often used in analytical chemistry where precision is critical. They come with a certification of accuracy and are calibrated to deliver their contents with a precise tolerance limit.
- Class B Glass Burettes: These are similar to Class A burettes but with a slightly lower accuracy and precision. Class B burettes are suitable for general laboratory work where the highest precision is not required. They are also made from borosilicate glass and are less expensive than Class A burettes.
These are modern alternatives to traditional glass burettes, designed to offer precision and ease of use with a digital display that shows the volume dispensed. Digital burettes are particularly useful for repetitive titrations, reducing the risk of parallax error and improving accuracy. They can be calibrated easily and are ideal for applications requiring precise volume adjustments.
These burettes are designed for continuous titration. They are equipped with a reservoir bottle that automatically refills the burette. Automatic burettes are particularly useful for long titrations or when a large number of titrations need to be performed consecutively. They help in reducing the manual effort and time involved in refilling.
- Micro Burettes: Used for very precise titrations where small volumes are involved. Micro burettes have a smaller capacity and are calibrated for very fine volume adjustments.
- Teflon (PTFE) Stopcock Burettes: These burettes feature a Teflon stopcock, which is highly resistant to chemical attack and provides a smooth, precise flow control. They are particularly useful when working with aggressive chemicals that might damage glass stopcocks.
Each type of burette has its advantages and specific use cases. The choice of burette depends on the requirements of the experiment, including the level of accuracy needed, the volume of liquid to be dispensed, and the chemical nature of the solutions involved.
Setting Up the Burette
Setting up your burette requires a few steps before it is ready to be used. While what we wrote here primarily applies to traditional glass burettes with a stopcock, with slight modifications, these steps can be adapted to other types of burettes as well.
In any case, it’s best to consult your manual or message us if you brought one from our catalogue.
- Secure the Burette: Place the burette in a burette clamp attached to a stand. Ensure it is perfectly vertical to avoid any parallax errors during volume readings.
- Check for Cleanliness: Inspect the burette for cleanliness. Any residue can affect the accuracy of your measurements. If it's not clean, rinse it with distilled water followed by the solution you will be using.
- Rinse with the Solution: To prevent contamination and ensure consistency, rinse the inside of the burette with a small amount of the solution you will be measuring. Allow the solution to run through the tip to rinse it as well.
- Fill the Burette: Carefully fill the burette with your solution, using a funnel if necessary, to just above the 0.00 mL mark. Avoid overfilling.
- Remove Air Bubbles: After filling, check for air bubbles in the burette and its tip. If present, tap the sides of the burette gently or open the stopcock to release them. This step is crucial for accuracy.
- Adjust the Starting Level: With the stopcock closed, adjust the solution level to exactly at the 0.00 mL mark by slowly opening the stopcock and letting excess solution drain into a waste container. Use a dropper for fine adjustments if needed.
- Remove the Funnel: If you used a funnel to fill the burette, remove it before starting your experiment to prevent additional solution from dripping into the burette, which could lead to inaccurate measurements.
- Record the Initial Reading: Carefully record the initial volume of the solution in the burette. Ensure you are at eye level with the volume markings on the burette to avoid parallax errors.
- Perform a Blank Test: Before proceeding with your experiment, it might be helpful to perform a blank test by running a small amount of the solution through the burette and into a beaker to ensure there are no leaks and the stopcock is functioning correctly.
Performing a Titration
Titration is a technique where a solution of known concentration (in the burette) is used to determine the concentration of an unknown solution. If you’re a student or curious about how a burette is used for titration, here’s how it works:
- Titrate the Analyte: Slowly add the titrant from the burette to the analyte while constantly swirling the flask. Proceed slowly, especially as you approach the expected endpoint, to ensure that you do not overshoot the titration.
- Watch for the Endpoint: The endpoint is reached when the indicator changes color. This color change should be permanent for at least 30 seconds. Note that the endpoint and the equivalence point (the point at which the quantities of titrant and analyte are exactly stoichiometrically equivalent) may not be exactly the same, but for many purposes, they are close enough.
- Record the Final Volume: Note the final volume reading on the burette immediately after the endpoint is reached.
Calculating the Results
- Calculate the Volume of Titrant Used: Subtract the initial volume of titrant from the final volume to find out how much titrant was used.
- Calculate the Concentration of the Analyte: Using the volume of titrant used, its concentration, and the stoichiometry of the reaction, calculate the concentration of the analyte.
The basic formula is:
- CaCa is the concentration of the analyte,
- VaVa is the volume of the analyte,
- CbCb is the concentration of the titrant, and
- VbVb is the volume of the titrant used.
Depending on the reaction, you might need to adjust the formula to account for the stoichiometry.
Cleaning and Maintenance
After completing your experiments, cleaning and properly storing your burette is essential to preserve its accuracy. Rinse the burette with distilled water and a burette brush several times, followed by a final rinse with the solution it will next contain or storage solution if it's being put away. Ensuring the burette is dry and free from contaminants before storage will prolong its life and maintain its precision.
Key Takeaways on Using a Burette
Mastering the use of a burette is a fundamental skill in the chemistry lab. We have journeyed through the meticulous process of using a burette for simple chemical tests, with a focus on performing titrations. To summarise our discussion, let’s go over the key takeaways:
- Burette Selection: Choose the right type of burette (glass or digital, Class A or B) based on the experiment's accuracy needs.
- Setup Accuracy: Proper setup, including a clean, vertical burette free of air bubbles, is crucial for precise measurements.
- Performing Titration: Follow meticulous steps in titration, from filling the burette to recognising the endpoint indicated by the colour change of the indicator.
- Practice and Precision: Mastery in titration requires practice, emphasising careful addition of the titrant and accurate volume readings.
- Maintenance: Clean and maintain the burette after use to ensure its accuracy for future experiments.
- Safety and Accuracy: Always prioritise safety and follow steps accurately to ensure reliable titration results.