- Round-bottom flask
Round-bottom flasks (also called round-bottomed flasks and Erlenmeyer Bulbs) are types of
flask s having spherical bottoms used aslaboratory glassware , mostly for chemical or biochemical work. They are typically made ofglass for chemicalinertness ; and in modern days, they are usually made of heat-resistant glass calledPyrex . There is at least one tubular section known as the "neck" with an opening at the tip. Two or three-necked flasks are common as well. Round bottom flasks come in many sizes, from 5 mL to 5 L, with the sizes usually inscribed on the glass. In pilot plants even larger flasks are encountered.The ends of the necks are usually conical (female)
ground glass joint s. These are standardized, and can accept any similarly-sized tapered (male) fittings. Standard Taper 24/40 is common for 250 mL or larger flasks, while smaller sizes such as 14 or 19 are used for smaller flasks.Because of the round bottom, cork rings are needed to keep the round bottom flasks upright. When in use, round-bottom flasks are commonly held at the neck by clamps on a stand.
Applications
The round bottoms on these types of flasks allow more uniform heating and/or boiling of liquid. Thus, round-bottom flasks are used in a variety of applications where the contents are heated or boiled. Round-bottom flasks are usually used in
distillation by chemists as distilling flasks and receiving flasks for the distillate (see distillation diagram). One-neck round-bottom flasks are used as the distilling flasks inrotary evaporator s.Round-bottom flasks are often used to contain
chemical reaction s run by chemists, especially forreflux set-ups andlaboratory -scalesynthesis .Boiling chip s are often added in distilling flasks for distillations or boiling chemical reactions to allow a nucleation site for gradual boiling. This nucleation avoids a sudden boiling surge where the contents may overflow from the boiling flask. Stirring bars or other stirring devices suited for round-bottom flasks are sometimes used. For a reflux set-up, a condenser is typically attached to the middle or only neck of the flask being used. Additional necks on a flask could allow athermometer or a mechanical stirrer to be inserted into the flask contents. The additional necks can also allow adropping funnel to be attached to letreactant s slowly drip in.Special electrically powered heating mantles are available in various sizes into which the bottoms of round-bottom flasks can fit so that the contents of a flask can be heated for distillation, chemical reactions, boiling, etc. Heating can also be accomplished by submerging the bottom of the flask into a
heat bath ,water bath , orsand bath . Similarly cooling can be accomplished by partial submerging into acooling bath , filled with e.g. coldwater ,ice ,eutectic ice/salt mixtures,dry ice /solvent mixtures, orliquid nitrogen Related glassware
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Flat-bottomed flask A flask with similar uses as the round-bottom flask, but the flat bottom allows it to stand on a level surface.
*Florence flask s are similar flasks that have round bodies and either a round bottom or a flat bottom so that one can stand the flask on a level surface. Florence flasks typically have one neck which is longer and may be somewhat wider than the usual neck of a round bottom flask. The necks of traditional Florence flasks often don't have a ground glass joint like modern round bottom flasks do. Round-bottom flasks are used more commonly by professionalchemist s than Florence flasks.
*Retort a spherical vessel with a long downward-pointing neck, specially used for distillation ordry distillation of substances.
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