Buret
Definition and meaning of Buret in chemistry.
A buret is a long, highly accurate graduated glass tube used in analytical chemistry laboratories. It features a precision control valve called a stopcock located at the very bottom. Chemists use a buret to carefully deliver precise and variable volumes of a liquid reagent.
In more detail
The adjustable stopcock lets the analyst release liquid slowly drop by drop into a flask. Meanwhile, a printed column of graduated volume markings shows exactly how much liquid was dispensed. The total volume delivered is calculated by subtracting the initial reading from the final reading.
Therefore, the buret does not need to be filled to an exact zero starting mark. You must always take these volume readings with your eyes perfectly level with the liquid. The liquid surface forms a curved shape inside the glass tube called a meniscus.
You should read the measurement at the lowest point of this curved meniscus. For very dark or opaque solutions, you read from the top of the liquid instead. Analysts estimate readings to one decimal place past the printed marks, usually to 0.01 milliliters.
This exceptional volumetric precision makes the buret an absolutely essential tool for quantitative chemical analysis. It is used extensively for determining unknown sample concentrations during acid-base and redox titration experiments. Proper cleaning and preparation are necessary to prevent contamination and ensure perfectly accurate volume measurements.
Chemists must rinse the buret with the titrant solution before using it to remove water. Any leftover water would dilute the titrant and completely ruin the final concentration calculation.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Typical capacity | 50 mL (also common 10 mL or 25 mL) |
| Readability | Marked in 0.1 mL increments |
| Precision | Read and estimated to the nearest 0.01 mL |
| Primary use | Delivering variable volumes of titrant in titrations |
| Key component | Adjustable stopcock valve for drop control |
An analyst performs a classic acid-base titration using a standard 50-milliliter glass buret. They fill the buret with a standardized sodium hydroxide solution of known molar concentration. They carefully drip this basic solution into a flask containing unknown hydrochloric acid and an indicator. The analyst closes the stopcock the exact moment the liquid turns a permanent faint pink. They record the final buret volume reading to calculate the original concentration of the acid.
Frequently asked questions
How do you read a buret correctly?
Position your eye exactly level with the liquid surface to prevent a parallax error. Read the bottom of the curved meniscus and estimate one digit beyond the printed markings.
How is a buret fundamentally different from a chemical pipette?
A buret dispenses a variable volume through a stopcock and is read before and after. A volumetric pipette is designed to deliver one specific fixed volume in a single transfer.
Why do you read the buret twice during a titration?
You must read the starting volume and the final volume after the titration is complete. The exact difference between these two readings tells you how much liquid was actually dispensed.