Laboratory flasks are vessels with a narrow neck and wider body, designed for mixing, heating, measuring, storing, and containing chemical reactions. Unlike beakers (which have a wide open top), flasks use their narrow neck to reduce evaporation, control splashing, and allow stoppering or connection to other apparatus. Common types include Erlenmeyer flasks, boiling flasks, volumetric flasks, filtering flasks, and distillation flasks.

Flasks are available in borosilicate glass for heating and chemical resistance, and in polypropylene or polymethylpentene plastic for shatter resistance and fieldwork. The type of flask you need depends on the procedure — each design is optimized for a specific function.

Laboratory flasks include Erlenmeyer flasks (conical shape for mixing and titration), boiling flasks (round bottom for uniform heating and distillation), volumetric flasks (precision calibrated for preparing exact solution concentrations), filtering flasks (thick-walled with a side arm for vacuum filtration), distillation flasks (with a side arm for directing vapors to a condenser), Kjeldahl flasks (long-necked for nitrogen determination), evaporating flasks (for rotary evaporation), and iodine flasks (with a liquid-seal stopper for iodometric titrations).

Erlenmeyer and volumetric flasks are available in both glass and plastic. Boiling, distillation, Kjeldahl, evaporating, and iodine flasks are glass only due to their heating and chemical requirements.

An Erlenmeyer flask has a flat bottom, conical body, and narrow neck — designed for mixing, swirling, and titration. It can sit on a bench or hot plate without support. A boiling flask has a round or spherical bottom designed for uniform heat distribution during distillation and reflux. Round-bottom boiling flasks require a clamp, heating mantle, or ring for support since they cannot stand on their own.

Use Erlenmeyer flasks for mixing and reactions at the bench. Use boiling flasks when uniform heating is critical, particularly in distillation and reflux setups. Florence flasks (flat-bottom boiling flasks) offer a middle ground — they can stand independently while still providing better heat distribution than an Erlenmeyer.

Use glass flasks when you need to heat the vessel, when working with organic solvents, when optical clarity matters, or when you need the highest volumetric accuracy (Class A glass). Use plastic flasks when breakage is a safety concern, when working with hydrofluoric acid or strong alkalis that attack glass, when weight matters for transport or fieldwork, or when equipping a classroom with high breakage rates.

Borosilicate glass handles temperatures up to 500°C, resists thermal shock, and is compatible with virtually all lab chemicals except HF. Polypropylene plastic is autoclavable to 135°C, shatter-resistant, and suitable for most aqueous solutions — but it melts on hot plates and degrades in contact with many organic solvents. In most labs, glass and plastic flasks work side by side — glass for heating and reactions, plastic for storage, culturing, and student-handled tasks.

A volumetric flask is a precision vessel calibrated to contain one exact volume, marked by a single graduation line on its long narrow neck. It is used exclusively for preparing solutions of known, precise concentration — you dissolve a measured solute, then add solvent to exactly the calibration mark. Volumetric flasks should never be heated, used for mixing, or used for storage.

Choose Class A glass volumetric flasks for analytical chemistry and quantitative work where accuracy directly affects results. Class B glass flasks are suitable for general teaching and routine preparation. Plastic volumetric flasks work for fieldwork and settings where breakage risk outweighs precision requirements, though they have wider tolerances than glass.

A filtering flask (vacuum flask, side-arm flask) is a thick-walled Erlenmeyer-shaped vessel with a side arm that connects to a vacuum source. It is used in vacuum filtration — a Buchner funnel sits on top of the flask, and vacuum suction pulls liquid through the filter paper much faster than gravity alone. The thick walls withstand the pressure differential created by the vacuum.

A complete vacuum filtration setup requires the filtering flask, a Buchner funnel, a rubber adapter, filter paper, rubber tubing, and a vacuum source (water aspirator or vacuum pump). Filtering flasks should never be heated due to their uneven wall thickness. They are available in glass for most lab applications and in plastic for settings where breakage is a concern.

For simple distillation, use a distillation flask — a round-bottom flask with an angled side arm that directs vapors toward a condenser. For fractional distillation, use a standard round-bottom boiling flask connected to a fractionating column (such as a Vigreux column) and then to a condenser. In both cases, the flask should be no more than two-thirds full to allow room for vapor formation.

Choose a flask approximately twice the volume of the liquid being distilled. Common sizes for teaching labs are 100ml, 250ml, and 500ml. Pear-shaped distilling flasks concentrate small volumes at the bottom for efficient micro-scale distillation. All distillation flasks are borosilicate glass — plastic cannot withstand the temperatures involved.

These are specialty flasks designed for specific analytical procedures. Kjeldahl flasks are long-necked round-bottom flasks used in the Kjeldahl method for determining nitrogen (and protein) content in food, soil, and other organic materials — the long neck prevents sample loss during acid digestion. Evaporating flasks are round-bottom vessels used with rotary evaporators to remove solvents under reduced pressure — standard equipment in organic chemistry research. Iodine flasks have a ground glass stopper surrounded by a moat that holds a liquid seal, preventing volatile iodine from escaping during iodometric titrations.

These flasks serve narrow but important functions in analytical and organic chemistry labs. General teaching labs rarely need them, but university analytical and organic chemistry programs consider them standard equipment.

Laboratory flasks are available in sizes from 5ml to 10,000ml depending on the type. Erlenmeyer flasks range from 25ml to 5,000ml, with 125ml, 250ml, and 500ml being the most common for teaching. Boiling flasks range from 50ml to 5,000ml, with 250ml and 500ml standard for distillation. Volumetric flasks range from 5ml to 2,000ml in precise calibrated sizes. Filtering flasks range from 125ml to 2,000ml.

For classrooms, stocking Erlenmeyer flasks in 3–4 sizes (125ml, 250ml, 500ml) and volumetric flasks in the volumes your curriculum requires covers most needs. As a general rule, never fill any flask more than two-thirds full — the remaining headspace is needed for mixing, vapor expansion, and safe handling.

The Lab Stockroom carries the full range of laboratory flasks in borosilicate glass and laboratory-grade plastic — Erlenmeyer flasks, boiling flasks, volumetric flasks, filtering flasks, distillation flasks, Kjeldahl flasks, evaporating flasks, and iodine flasks — with detailed specifications, transparent pricing, and fast shipping from New York.

Individual flasks and class-set quantities are available. Educators, lab managers, and procurement teams can purchase online, request a formal quote, or submit a purchase order. If you need help determining which flask types and sizes fit your curriculum, contact the team for recommendations.