Source: Laboratory of Dr. Neal Abrams — SUNY College of Environmental Science and Forestry
Glassware is a regular appearance in the professional chemistry laboratory, because it has a relatively low cost, extreme durability, and specific levels of precision. While some labware is being supplemented with plastic or even everyday kitchen materials, glass is still the standard material by which laboratory work is done. While there are few rules about glassware, there are some best practices for use that set the groundwork for good techniques in the lab.
Glass is ubiquitous in the chemistry laboratory, but not all glass is the same. Standard consumer-grade glass is known as "soda-lime" or "float" glass. It is good for many applications, but cracks under rapid heating and cooling applications due to expansion/contraction. Borosilicate glass is used to solve this problem in the lab. Made with an introduction of small amounts of boron, borosilicate glass has a very low coefficient of expansion, which prevents internal stresses. The most common trade name for borosilicate glass is Pyrex, the same type of glass used in some kitchen bakeware.
While borosilicate glass is thermally robust, the impurities found in borosilicate and standard glass lead to a limited temperature range and optical quality. Fused silica, or quartz, is used in situations where glass needs to be heated above 450 °C or to be transparent to UV light. Fused silica is chemically-pure silicon dioxide with no impurities and a very high melting point above 1,600 °C. The easiest way to tell the difference between borosilicate glass and fused silica in the lab is to look down the long axis of a piece of glassware. A greenish color is indicative of borosilicate impurities, whereas fused silica is optically clear and colorless.
While there are few rules to how glassware must be used, each piece of glassware was designed for a general set of procedures. Unique situations create some flexibility on the application, and nearly all glassware can be further adapted and customized with the assistance of a professional glassblower.
Glassware has long been a core component of the chemistry laboratory.
Glass’s longstanding popularity has remained high because it is relatively inert, highly durable, easily customizable, and inexpensive.
Because of these desirable traits, glass has been used to create a wide assortment of apparatuses. Being unfamiliar with this equipment could lead to confusion, misuse and disaster. Therefore, a solid understanding of glassware is necessary to ensure safety and success in the lab.
This video will explore many of the common pieces of glassware found in the laboratory.
Laboratory glassware is manufactured with different compositions, each possessing unique properties that are useful in different experimental conditions.
Equipment made from consumer-grade, or “soda-lime”, glass is the least expensive, and is adequate for many applications. However, rapid temperature changes can cause this glass to crack.
Borosilicate glass, which exhibits little thermal expansion, is preferred in thermally stressful conditions. This glass is manufactured through the addition of small amounts of boron, and is often used in bakeware, such as Pyrex.
However, both borosilicate and standard glass contain impurities, resulting in reduced optical quality. Therefore, a glass composed of purely silicon and oxygen is utilized in situations that require the glass to be transparent to UV light. This is known as fused silica or fused quartz.
Now that you understand the different types of glass used in the laboratory, let’s look at common glassware, as well as related paraphernalia.
We will begin our survey with glassware used for qualitative analysis. Any measurements, or graduations, on this equipment are approximate, and they are best used for procedures that do not require high levels of accuracy. First, the beaker, one of the most common pieces of glassware, is available in a range of sizes. Beakers are often used to hold, mix, and heat reagents. Most have a small lip for pouring liquids.
Test tubes, which are relatively small cylindrical vessels, are also used to store, heat, and mix chemicals. Their design allows for multiple samples to be easily manipulated, stored, and observed at once.
Watch glasses are used when a large surface area is needed for a small volume of liquid. This is common for crystallizing and evaporating procedures. Watch glasses can also be used as covers for beakers.
The crystallization dish is similar to the watch glass, proving a large surface area for liquids. However, it is more commonly used as a container for bath processes. Lastly, the flask. Each type of flask is shaped for its purpose, but all are designed with wide bodies and narrow necks, allowing the contents to be mixed without spilling. They are also easily fitted with stoppers. The Erlenmeyer flask is the most common. The flat bottom allows it to be directly heated and used in simple boiling and condensation procedures.
Next, we will review glassware used for accurately measuring liquids. The graduated cylinder is used to measure semi-precise volumes, and deliver to another container. The surface of most liquids forms a concave meniscus in narrow glassware. Volume should be read at the bottom for accuracy.
While the graduated cylinder is versatile, volumetric glassware is used when a higher level of accuracy is required. Volumetric glassware can be an order of magnitude more precise than a graduated cylinder. Each piece is marked with either “TD” or “TC”. If the equipment is calibrated to transport the measured volume, it is marked “TD” for “To deliver”. Conversely, other pieces of volumetric glassware are only calibrated to be accurate while holding the measured volume, and are marked “TC” for “To Contain”.
The volumetric flask is used to make and contain solutions of precise volumes. This is done by first dissolving the solute, and then adding solvent to the graduation to dilute to the intended volume.
Unlike the apparatuses that are accurate only to contain, the volumetric pipette is used to deliver a specific volume with a high degree of accuracy. A bulb is used to draw the liquid, never by mouth.
The burette is used to deliver variable, but precise, volumes of liquid, controlled with the stopcock. It’s often used in titration experiments.
Next, our survey will cover glassware that has more specific procedural uses.
First, the round-bottom, or boiling flask, is designed to allow for even heating and stirring, to drive chemical reactions. To prevent spills, it should never be filled to more than 50% of its total volume.
While traditional funnels have a familiar shape, there can be variations depending on their intended use. For example, funnels used for gravity filtration are fitted with folded filter paper. Powder funnels have wider stems designed for dispensing solids and viscous liquids.
The separatory funnel is used in liquid-liquid extractions to separate immiscible liquids of different densities. It has a specialized shape, with a wide top for mixing, and a narrow bottom leading to a stopcock for the separation. The Büchner flask and funnel are used for vacuum filtration. The funnel is typically ceramic, with pin-sized holes in its flat bottom. It is fitted into the flask with a rubber collar to provide an airtight seal. The flask resembles an Erlenmeyer in shape, but has a barbed side arm for the vacuum hose.
In some chemical processes, laboratory glassware may need to be sealed, connected, or supported. Sealing glassware is typically done with a stopper. Rubber and neoprene are used in pieces with standard necks. They can be manufactured with holes to allow for the insertion of tubes, thermometers, or stirrers, while still providing an airtight seal.
Glass stoppers are used to seal equipment with ground glass fittings. These provide a strong seal, but the possibility of glass to glass seizing necessitates the use of joint grease. Joint grease must also be used when connecting two pieces of glassware together. However, because these joints are not mechanically strong, plastic connector clips are used to prevent them from separating.
When additional structural support is needed, glassware is often clamped in place. Clamps provide this support by connecting to a piece’s neck on one end, and a retort stand on the other. While some glassware should always be secured, clamping can also be used to ensure that components stay upright during a procedure.
Now that we’ve surveyed many of the pieces of glassware found in professional laboratories, we’ll discuss some of their many uses.
Observation of naturally occurring, spontaneous reactions can be performed in the lab by replicating their original conditions. Glassware is vital to these investigations because of its inert and durable nature.
In the Miller-Urey experiment, the environment of early earth was simulated in a round-bottomed flask to investigate the abiotic synthesis of organic compounds. A large manifold of interlocking glassware helped to provide the necessary atmospheric gasses, which was then sparked, simulating lighting. The product was pipetted out of the flask to avoid contamination, and stored for further investigation.
When synthesizing organic molecules, it is often necessary to apply heat for long periods of time. In this example, a carbon-carbon cross-coupling reaction was performed using an apparatus made from three pieces of glassware. The apparatus – made from a round-bottomed flask, a reflux condenser, and an oil bubbler – allows for the solution to be boiled indefinitely, without losing volume or changing pressure.
You’ve just watched JoVE’s introduction to Common Glass Laboratory Equipment and Their Uses. You should now be familiar with the glassware used for qualitative, measuring, and procedural applications.
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