What Lab Equipment Is Used to Measure Volume?
In any well-equipped lab, you’ll find a wide assortment of glassware designed to measure, pour, and hold liquids. This glassware comes in all shapes and sizes, from slender pipettes used to deliver small amounts of liquid to beakers that contain a much larger liquid volume.
Each device serves a specific purpose. Lab glassware, made from borosilicate glass, is strong and hard to break. It is suitable for containing chemical reactions and heating liquids to high temperatures.
The accuracy of the markings on laboratory glassware varies. Larger containers, like beakers and flasks, are typically ±5% of the total volume. They are generally used only when the volume measurement does not need to be precise. For graduated cylinders, the margin of error, or tolerance, is about 1%.
Volumetric labware is for measuring liquids with precision. Volumetric flasks, burettes, and pipettes made for measuring small amounts of liquid are the most accurate, with tolerances of less than ±0.02. Research and testing require precise measurements, and many lab vessels are even designed to account for the liquid residue that clings inside a flask. Therefore, scientists can be confident that the measurements poured out of volumetric glassware are precise and accurate.
Instruments for Measuring Volume
Glassware used in lab settings come in a wide variety of sizes and shapes. Here are some of the most common pieces of glassware used to measure liquid.
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.
- Serological pipettes are used to transfer liquid amounts from less than 1 mL to up to 50 mL. They may be plastic, disposable pipettes, or reusable glass. Serological pipettes are often used to mix chemical solutions or cell suspensions, transfer liquids from one container to another, or layer reagents of different densities.
- Volumetric pipettes have a single gradation intended for only one accurate measurement. They come in a variety of sizes, typically ranging from 1 mL to 100 mL. They are marked with a line indicating a full liquid level, plus a temperature and accuracy estimation.
Steps to Measure Volume
- Ensure the device you’re using to transfer liquid is clean and dry.
- Check the temperature. In most cases, your lab area should be at 20.0°C (68°F).
- Fill the measuring device to the exact line. The lowest curve of the meniscus should hit the line when viewed at eye-level.
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.
Sources of Error When Measuring Volume
Dirty 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.
Meniscus Miscalculation – 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.
Wrong Temperature – 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.
To ensure accuracy, it’s important to meet the conditions marked on the side of the volumetric device.
Equipping Your Lab
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.
To cut your expenses and save money for all the small and not-so-small costs of setting up and running a lab, we offer a cost-effective solution to some of your biggest headaches.
Learn more about leasing lab equipment and help keep your lab under budget and within reason.