Differences in Lab Glassware
If you’re working in a lab or taking a lab class, you’ll encounter many different kinds of glassware, each of which has features that make it especially well-suited to certain applications. Lab glassware you’re almost guaranteed to encounter includes flasks, beakers, pipette and graduated cylinders. Most serve as tools to measure out quantities of liquids; some are roughly accurate, others have great accuracy. Knowing the differences between the kinds of glassware available to you will help you design and carry out experiments more efficiently.
Types of Glassware
Erlenmeyer flasks have a narrow neck over a conical base, while beakers are basically large open-mouthed glass jars with a lip and spout for pouring. Graduated cylinders are tall cylinders with a spout to pour liquids; they have hash marks on the side to measure the volume of their contents. Volumetric flasks have a flat-bottomed bulb and a long, narrow neck with a hash mark along the side to indicate the point at which the flask is full. Burets are long, tall cylinders–generally much narrower and taller than graduated cylinders–with hash marks to measure volume and a stopcock at the bottom; the stopcock can be turned to allow the contents to drip out. Pipets are long narrow glass tubes with a bulb in the center, a hash mark to indicate when they are full, and a narrow tip. Sucking air from the pipet using a rubber bulb (like a turkey baster) draws liquid up through the tip into the pipet, and a precisely measured volume can then be transferred to another container.
Graduated cylinders, beakers, volumetric pipets, burette and volumetric flasks are five kinds of glassware often used to measure out specific volumes. Volumetric pipets, flasks and burets are the most accurate; the glassware makers calibrate these to a high level of accuracy. The accuracy is usually measured in terms of the tolerance, which is the uncertainty in a measurement made with the glassware. Class A volumetric glassware has a lower tolerance than Class B; for class A, the tolerance can be as low as 0.08 ml for a 100 ml flask or pipette. Generally, measurements with class A volumetric glassware can be considered reliable to two places after the decimal point.