In a well-equipped laboratory, a diverse range of specialized glassware stands ready to gauge, transfer, and retain various liquids. From slender pipettes handling minuscule quantities to capacious beakers accommodating larger volumes, each vessel fulfills a distinct purpose. Crafted from robust borosilicate glass, this labware proves highly resilient, engineered to endure both chemical reactions and high-temperature conditions.
The precision of markings on laboratory glassware varies according to the type of container. Beakers and flasks, designed for tasks where exact measurements matter less, typically feature a margin of error of approximately ±5% relative to their total volume. Graduated cylinders, conversely, maintain a narrower tolerance of about 1%.
For achieving the utmost precision in liquid measurements, volumetric labware takes center stage. Volumetric flasks, burettes, and pipettes, engineered for the precise quantification of small quantities, deliver unparalleled accuracy, boasting tolerances of less than ±0.02. In research and testing environments where precision reigns supreme, these instruments shine.
Furthermore, many lab vessels are ingeniously designed to account for any residual liquid clinging to their interiors. This design feature ensures that scientists can confidently rely on the measurements obtained from volumetric glassware to be both exact and trustworthy. In this post, we'll review the various instruments used to measure different volumes in the lab.
These flasks have a narrow, cylindrical neck and a conical base with a flat bottom. They are named after Emil Erlenmeyer, the German organic chemist who designed the glassware in 1861. Erlenmeyer flasks are often used for mixing and heating solutions. They are typically made of borosilicate glass, which can be heated to high temperatures without breaking.
With a long neck over a round bulb with a flat bottom, Florence flasks are also usually made of borosilicate glass to withstand heating.
Beakers are cylindrical, glass containers with a rolled lip and spout for pouring. They can be found in almost every lab. Beakers are a piece of laboratory equipment used for a variety of purposes, including creating chemical reactions and heating solutions over a bunsen burner. Measurements are marked on the side of the beaker.
Similar to beakers, graduated cylinders are tall, cylindrical containers with a spout for pouring. They have hash marks (gradations) on the side to measure the volume of a liquid. Most labs have graduated cylinders in a variety of sizes. Typical volume measurements (marked in milliliters) are 10 mL, 25 mL, 50 mL,100 mL, 500 mL and 1,000 mL.
Also called Dewar flasks after Scottish chemist and physicist Sir James Dewar, volumetric flasks have a long, narrow neck and a round bulb with a flat bottom. A hash mark is printed on the side for precise measurement at a specific temperature. They’re calibrated to contain a precise volume at a certain temperature. Volumetric flasks are typically used for precise dilutions to prepare known solutions.
Burettes are long, narrow glass tubes with hash marks for measurement along the side. They have one tapered end to deliver precise liquid measurements and a stopcock (rubber stopper) used to control the flow of liquid in titrations. The stopcock can be turned to allow small amounts of liquid to flow out of the tube. Burettes are commonly used to measure precise, variable volumes of solution, primarily for titration, and mixing a known measurement of one reactant until the precise reaction is achieved.
Pipettes are measuring devices used to deliver liquids in tiny amounts. They are long, narrow glass tubes with tapered ends and a bulb in the center. They have a hash mark to indicate when they are full. Scientists use a small rubber bulb to draw liquid into the tube and transfer it to another container or mixture.
These steps should help produce a precise measurement. If you are using volumetric glassware, the expected deviation will be indicated on the side of the glassware.
In order for a measurement to be precise, laboratory glassware must be clean and dry. Dirt, film, residual liquid, grease, or other contaminants prevent liquid from draining properly. This can result in a measurement that is either more or less than intended or is a contaminated sample. Before using, make sure your labware is clean, residue-free, and dry. One good way to ensure the removal of fluid residue is to rinse the glassware several times with a suitable solvent.
When filling a pipette or volumetric flask to a specific volume, the level of the liquid must be exactly at the fill-level hash mark. Liquid is not flat, it has a slightly curved surface, called a meniscus. This can deceive the eye. It’s important to check the calibration mark with the flask on a flat surface at eye-level for accuracy and measure the bottom of the meniscus at the lowest part of the curve.
Volumetric flasks are marked with volume, temperature, and accuracy readings. The T.D. mark means “to deliver” and indicates precisely how much will be poured out after accounting for liquid that clings to the inside. This is followed by a temperature in celsius, and finally, the accuracy you can expect from the measurement. This might look like:
10 mL T. D.
20.0°C
±0.02 mL
To ensure accuracy, it’s important to meet the conditions marked on the side of the volumetric device.
There are plenty of necessary things to consider when equipping a lab. You’ll need everything from costly specialty equipment that may run up to tens of thousands of dollars to a large number of pipettes. While pipettes may not seem like much on the outset, even these small expenses can add up to a big bite out of your budget.
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