A burette is a specialized laboratory instrument designed for dispensing precise, variable volumes of liquid. It consists of a long, graduated glass tube with a stopcock at the bottom for controlled release. This tool is used in quantitative chemistry experiments, requiring exact volume control. It enables chemists to add specific, measured quantities of one solution to another.
Understanding Burette Capacities
Burettes are manufactured in various capacities, typically ranging from 10 milliliters (mL) to 100 mL, with the most commonly encountered sizes being 25 mL and 50 mL. A 50 mL burette, for instance, can hold a maximum of 50 milliliters of liquid. These standard capacities are prevalent in laboratory settings, well-suited for typical reaction volumes in analytical chemistry.
While a burette has a fixed total capacity, its primary function is to deliver variable amounts of liquid up to that maximum. A 50 mL burette can accurately dispense 10 mL, 25.5 mL, or any other volume within its range. The choice of burette capacity depends on the expected volume of reagent needed for a particular reaction.
Accurate Measurement Techniques
Achieving precise measurements with a burette relies on careful techniques, beginning with proper filling and initial reading. Before use, the burette is rinsed with the solution it will contain to ensure concentration consistency. After filling slightly above the zero mark, the liquid level is adjusted to zero or a convenient starting point, ensuring no air bubbles remain in the tip.
When reading the volume, position the eye at the same level as the meniscus. For aqueous solutions, the reading is taken at the bottom of the meniscus curve to avoid parallax error, a distortion that occurs when viewing an object from an angle. Burettes are graduated to 0.1 mL, allowing for readings to be estimated to the nearest 0.01 mL. The final volume delivered is determined by subtracting the initial reading from the final reading.
Key Applications of Burettes
The precise measurement capabilities of burettes are used in numerous chemical applications, most notably in titration. Titration is a quantitative analytical method used to determine the unknown concentration of a substance by reacting it with a solution of known concentration. During a titration, the burette adds a titrant (solution of known concentration) to an analyte (solution of unknown concentration) until the reaction reaches its equivalence point.
The accuracy of the burette ensures the exact volume of titrant required to react completely with the analyte can be determined, which is used for calculating the unknown concentration. Beyond titration, burettes are also employed in other laboratory procedures requiring precise liquid dispensing. These include preparing solutions of specific concentrations or performing gravimetric analyses where the exact volume of a liquid added directly impacts the experimental outcome.