Glassware in the laboratory comes in a range of different shapes and sizes, and is used for a number of purposes. Don’t know your round-bottomed flask from your Florence flask, or your pipettes from your burettes? This graphic has you covered. Below there’s also a little detail on the usage of each.
These items should be familiar to anyone who’s been in a chemistry practical lesson in school. Test tubes are the archetypal image of chemistry, whilst beakers also make frequent appearances in school practicals. Boiling tubes aren’t that different from test tubes in appearance, but are used when heating is required – they tend to be made of thicker glass, and are slightly larger and wider.
Of all the flasks used in chemistry, the most iconic is the conical (Erlenmeyer) flask. Named after the German chemist Emil Erlenmeyer, who created the flask in 1860, it’s designed so that its contents can be swirled easily without spilling out. This also makes them useful for boiling liquids, and additionally their necks can support filter funnels.
Volumetric flasks are used primarily in the preparation of standard solutions. To create a solution of a specific concentration, we need to know the volume of the solution; the narrow neck of the volumetric flask will have a thin graduation to show where a specific volume is reached.
Round-bottomed flasks and Florence flasks look very similar, but there is a slight difference between the two. Both have round bottoms, designed to spread out heat evenly when they are heated. They are frequently used by chemists for reactions and in rotary evaporators. Whereas round-bottomed flasks will usually have a ground glass joint on their neck, to allow connection to other apparatus, Florence flasks, supposedly named after Florence in Italy, tend to merely have a lip. They can also come with either a flat bottom so they are free-standing, or a rounded bottom, and have longer necks.
The Kjeldahl flask has an even longer neck, and was developed for use in the Kjeldahl method, which is used to determine the nitrogen content in a substance.
Pear-shaped flasks are usually rather small flasks, used for small-scale distillations. Their shape allows recovery of more material than the round-bottomed flasks.
The rather odd-looking retort flasks are used in distillations, though their use was primarily before the advent of condensers. Today, they are very rarely used.
The Schlenk flask and the Straus flask are another two that look fairly similar. Schlenk flasks are commonly used in air-sensitive chemistry, as the side arm allows an inert gas such as nitrogen to be pumped into the vessel. The Straus flask, on the other hand, is used to store dried solvents. The main neck is actually filled in halfway up, and connected to a plugged smaller neck; this main neck can be connected to other apparatus, and allows the solvent to be extracted when the plug is slightly withdrawn or removed entirely.
Finally, the Claisen flask, designed by chemist Ludwig Claisen, is designed for vacuum distillation; distillation under vacuum produces problematic amounts of bubbles when solutions are boiled. Claisen’s flask includes a capillary tube that inserts small bubbles into the liquid, easing the ferocity of boiling, whilst the branched portion of the flask hosts a thermometer. Today, Claisen’s flask is less commonly used.
Funnels, Analysis & Separation
A variety of different apparatus can be used for filtration. The most obvious is the filter funnel, into which filter paper can be placed, and a mixture can then be poured through. The smaller thistle funnel is not used for filtering at all, but to add liquids into apparatus.
The Buchner flask can be used in conjunction with a Buchner funnel in vacuum filtration, and is a much quicker process than the gravity filtration used with normal filter funnels. A vacuum tube can be affixed to the flask’s sidearm, which rapidly sucks through the solvent, leaving any solid in the Buchner funnel.
For separating solutions or liquids of different densities, separating funnels can be used. Liquids of a lower density will float to the top, then the mixtures can be tapped off separately. The similar-looking dropping funnel is used to add liquids or solutions to a reaction.
Another method of separating mixtures of compounds is column chromatography, which can be carried out using a chromatography column. The mixture is passed through a column of silicon dioxide or aluminium oxide, with different components of the mixture taking differing amounts of time to pass through the column.
Finally, the Thiele tube is a piece of apparatus used to determine the melting point of a solid compound. It contains and heats an oil bath, into which a sample can be placed along with a thermometer. Heating then allows melting point to be determined. The design of the flask allows the oil to circulate, ensuring even heating.
A range of different condensers can be utilised in laboratories as important components of distillation apparatus. The most commonly seen condenser in schools is the Liebig condenser, which has an inner tube through which vapour flows, surrounded by a ‘jacket’ through which cool water passes and condenses the vapour. The Graham condenser is similar to this, but has a coiled path for the vapour to flow through and condense. Meanwhile, the Friedrichs condenser inverts the arrangement, having a spiral coil through which the coolant flows, with the vapour surrounding it. Other varieties of condenser are also available, though are not shown here.
Another piece of glassware that falls loosely into this category is the fractionating column. This helps separate a mixture during distillation, as vapours collect and distill on the small glass ‘trays’ ascending the column. Only the most volatile gases will ascend all the way to the top of the column to be distilled off.
A number of pieces of chemistry glassware are used to accurately measure volumes; the most obvious being the graduated cylinder, or measuring cylinder, which can come in a variety of sizes.
For measuring volumes of solutions more precisely, a volumetric pipette can be used. These come in a variety of sizes, each measuring a fixed volume of solution. Graduated pipettes can also be used, which allow various small volumes to be measured out. For measurement of volumes during titrations (the addition of one solution to another to determine an unknown concentration) burettes are used. These are long, narrow tubes, with incremental volume markings, which allow precise volumes of solutions to be dropped into another solution.
For measuring the volume of gas produced in a reaction, a gas syringe can be used. This piece of apparatus can be attached to the top of a flask via a piece of tubing, and the gas produced pushes the plunger out of the syringe, allowing the gas volume to be measured.
The only piece of glassware we haven’t mentioned is the Soxhlet extractor. This is used to extract chemicals from a solid sample into a liquid. You can see it in action in this video which details the extraction of caffeine from coffee.
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References & Further Reading
- Classic kit – Chemistry World