Essential Glassware: Beakers, Flasks, and Tubes

Essential laboratory glassware includes beakers for holding and mixing, Erlenmeyer flasks for swirling and heating liquids, round-bottom flasks for heating and distillation, and test tubes for small-scale reactions. In brief: most lab glass is borosilicate glass, which resists heat and sudden temperature changes; the markings on beakers and flasks are only approximate, so use a graduated cylinder or volumetric glassware for accurate volumes.

Choosing the right container makes an experiment easier and safer. Each piece of glassware has a shape that suits a particular job. This article describes the most common pieces, what they are used for, how to handle and clean them, compares them in a table, explains why borosilicate glass is used, works through a selection exercise and gives the history of laboratory glass.

What are beakers used for?

A beaker is a cylindrical glass container with a flat bottom and a spout for pouring. It is used to hold, mix, heat and transfer liquids, and to collect filtrate. Its volume markings are approximate, usually within about 5% or worse, so it should not be used when an accurate volume is needed. Common sizes range from 25 mL to 2,000 mL or more. When heating a liquid in a beaker, fill it to no more than about half.

What types of flasks are there?

• Erlenmeyer (conical) flask: has a flat bottom, sloping sides and a narrow neck. The shape lets you swirl a liquid without spilling, so it is the usual flask for titrations. The neck can be closed with a stopper or covered with a watch glass or foil.
• Round-bottom flask: a spherical flask with a long neck, used for heating liquids evenly in a heating mantle and for distillation and reflux. It needs a ring support or a cork ring to stand upright, because it has no flat base.
• Florence (boiling) flask: a flat-bottomed flask with a round body and a long neck, used for heating liquids in simple setups.
• Filter (Büchner) flask: a thick-walled conical flask with a side arm to attach vacuum tubing, used in vacuum filtration.
• Volumetric flask: a flat-bottomed flask with a long thin neck and a single mark, used to prepare solutions of exact volume (see the article on precision glassware).

What are test tubes and other tubes used for?

Test tubes are small tubes that are closed at one end and are used for small-scale reactions and observations, usually holding about 10 to 20 mL. A boiling tube is a larger test tube made of heat-resistant glass for heating liquids. When heating a liquid in a test tube, fill it to less than one third, hold it with a holder at an angle of about 45° and point the opening away from yourself and others. Other tubes include culture tubes, centrifuge tubes (which resist spinning) and ignition tubes for strongly heating small samples.

What other common glassware is there?

• Watch glass: a shallow concave disc used to cover beakers, to hold small samples or to evaporate small amounts of liquid.
• Evaporating dish: usually made of porcelain, used for evaporating solutions by heating.
• Funnel: directs liquids into narrow openings, and holds filter paper.
• Separatory funnel: a conical funnel with a tap, used to separate immiscible liquids.
• Glass rod: for stirring and for guiding liquid when pouring.
• Condenser: a tube with a cooling jacket for condensing vapors in distillation.
• Dropper (Pasteur) pipette: for transferring small amounts of liquid by drops.

Glassware comparison

Why is borosilicate glass used?

Ordinary soda-lime glass expands considerably when heated and can crack when heated or cooled unevenly. Borosilicate glass contains boron oxide, which gives it a low coefficient of thermal expansion, about 3.3 × 10⁻⁶ per kelvin compared with about 9 × 10⁻⁶ per kelvin for soda-lime glass. It therefore withstands rapid temperature changes better. It is also more resistant to most chemicals, with the main exceptions of hydrofluoric acid and hot concentrated alkalis, which attack it. Brands such as Pyrex and Duran are borosilicate glass.

Worked example: choosing glassware

Choose a suitable container for each task and give a reason.

1. Titrating 25 mL of acid with sodium hydroxide. A 250 mL Erlenmeyer flask, because the narrow neck and the shape allow swirling without spilling.
2. Heating 80 mL of water to boiling. A 250 mL beaker. Fill it to about one third to one half, so the volume of the beaker is at least twice the volume of the liquid. 80 mL × 2 = 160 mL, so 250 mL is a good size.
3. Distilling 200 mL of a mixture. A 500 mL round-bottom flask. It should be half full or less, so 200 mL ÷ 500 mL = 40% is acceptable.
4. Measuring 37 mL of a liquid for a reaction. A 50 mL graduated cylinder, not a beaker. It has better accuracy, and a 100 mL cylinder would give a less accurate reading.
5. Making 100.0 mL of a standard solution. A 100 mL volumetric flask, because it contains the exact volume at the mark.

How do you handle and clean glassware?

• Inspect glassware for chips, cracks or star fractures before use, and discard damaged items, as they can break when heated or under pressure.
• Do not heat thick-walled vessels such as filter flasks, or heat closed containers.
• Let hot glass cool slowly. Do not place hot glass on a cold surface or run cold water over it.
• Clean with water and a brush, using detergent and rinsing with distilled water. Glass is clean when water forms a continuous film and does not form droplets.
• Dry volumetric glassware at room temperature, not in a hot oven.
• Place broken glass in a designated container.

How did laboratory glass develop?

Glassware has been used in alchemy and chemistry since antiquity, and the alembic and retort were common in medieval laboratories. The invention of borosilicate glass in the 1880s is credited to Otto Schott in Germany, and in 1915 Corning Glass Works in the United States introduced Pyrex. This type of glass made modern laboratory work and ovenware possible. The shape of the conical flask is named after the German chemist Emil Erlenmeyer, who introduced it in 1860.

Which mistakes are common?

Mistake 1: Using beaker markings for accurate measurements

The markings are only approximate. Use graduated cylinders or pipettes.

Mistake 2: Heating a sealed container

The pressure can break the glass. Leave the container open or fit a vent.

Mistake 3: Filling vessels too full when heating

Boiling liquids can bump and spill. Fill vessels to no more than half.

Mistake 4: Using a cracked piece of glassware

Small cracks can spread suddenly and cut hands. Replace it.