Round-bottom flasks (also called round-bottomed flasks or RB flasks) are types of

flask Flask may refer to: Container * Hip flask, a small container used to carry a small amount of liquid * Laboratory flask, laboratory glassware for holding larger volumes than simple test tubes ** Erlenmeyer flask, a common laboratory flask with a ...

s having spherical bottoms used as

laboratory glassware Laboratory glassware refers to a variety of equipment used in scientific work, and traditionally made of glass. Glass can be blown, bent, cut, molded, and formed into many sizes and shapes, and is therefore common in chemistry, biology, and anal ...

, mostly for

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...

biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology an ...

work. They are typically made of

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...

for chemical inertness; and in modern days, they are usually made of heat-resistant

borosilicate Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...

glass. 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 20 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

ground glass joint Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may ...

s. These are

standardized Standardization or standardisation is the process of implementing and developing technical standards based on the consensus of different parties that include firms, users, interest groups, standards organizations and governments. Standardization ...

, and can accept any similarly-sized tapered (male) fittings. 24/20 is common for 250 mL or larger flasks, while smaller sizes such as 14/20 or 19/22 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. A round-bottom flask is featured prominently on the logo of the

OPCW The Organisation for the Prohibition of Chemical Weapons (OPCW) is an intergovernmental organisation and the implementing body for the Chemical Weapons Convention (CWC), which entered into force on 29 April 1997. The OPCW, with its 193 member ...

, the implementing body for the

Chemical Weapons Convention The Chemical Weapons Convention (CWC), officially the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction, is an arms control treaty administered by the Organisation for ...

Uses

* Heating and/or boiling of liquid. *

Distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

. * Contain chemical reactions. * Distilling flask in

Rotary evaporators A rotary evaporator (rotovap) is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the use of this technique and ...

. * Storage of the culture media. * Preparation of gas-phase standards for flasks fitted with septa (requires volumetric calibration) 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 used in

distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

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 in

rotary evaporator A rotary evaporator (rotovap) is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the use of this technique and ...

s. This flask shape is also more resistant to fracturing under vacuum, as a sphere more evenly distributes stress across its surface. Round-bottom flasks are often used to contain

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

s run by chemists, especially for

reflux Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions ...

set-ups and

laboratory A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physicia ...

-scale

synthesis Synthesis or synthesize may refer to: Science Chemistry and biochemistry *Chemical synthesis, the execution of chemical reactions to form a more complex molecule from chemical precursors ** Organic synthesis, the chemical synthesis of organ ...

Boiling chip A boiling chip, boiling stone, porous bit anti-bumping granule is a tiny, unevenly shaped piece of substance added to liquids to make them boil more calmly. Boiling chips are frequently employed in distillation and heating. When a liquid becomes ...

s are 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. Round bottom flasks suffer from poor stirring when compared with

Erlenmeyer flask An Erlenmeyer flask, also known as a conical flask (British English) or a titration flask, is a type of laboratory flask which features a flat bottom, a conical body, and a cylindrical neck. It is named after the German chemist Emil Erlenmeyer ...

s, as they can't accept large stir bars and material can become trapped at the base. 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 a

thermometer A thermometer is a device that temperature measurement, measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a merc ...

or a mechanical stirrer to be inserted into the flask contents. The additional necks can also allow a

dropping funnel A dropping funnel is a type of laboratory glassware used to transfer fluids. They are fitted with a stopcock which allows the flow to be controlled. Dropping funnels are useful for adding reagents slowly, i.e. drop-wise. This may be desirable wh ...

to be attached to let

reactant In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

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 In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

, water bath, or

sand bath A sand bath is a common piece of laboratory equipment made from a container filled with heated sand. It is used to evenly heat another container, most often during a chemical reaction. A sand bath is most commonly used in conjunction with a hot ...

. Similarly cooling can be accomplished by partial submerging into a

cooling bath A cooling bath or ice bath, in laboratory chemistry practice, is a liquid mixture which is used to maintain low temperatures, typically between 13 °C and −196 °C. These low temperatures are used to collect liquids after distillation ...

, filled with e.g. cold

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...

, eutectic mixtures,

dry ice Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily a ...

/solvent mixtures, or

liquid nitrogen Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wide ...

. For gas preparation where heating is required. Since the flask is round bottomed heat is uniformly distributed throughout on heating.

Related glassware

Flat-bottomed flask Laboratory flasks are vessels or containers that fall into the category of laboratory equipment known as glassware. In laboratory and other scientific settings, they are usually referred to simply as flasks. Flasks come in a number of shapes and ...

: A flask with similar uses as the round-bottom flask, but with a flat bottom that allows it to stand on a level surface. *

Florence flask A Florence flask/boiling flask is a type of flask used as an item of laboratory glassware and is named after the city Florence. It is used as a container to hold liquids. A Florence flask has a round body, a long neck, and often a flat bottom. ...

: A flask similar to the flat-bottomed flask that has 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 do not have a ground glass joint like modern round bottom flasks do. Round-bottom flasks are used more commonly by professional

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

s than Florence flasks. *

Retort In a chemistry laboratory, a retort is a device used for distillation or dry distillation of substances. It consists of a spherical vessel with a long downward-pointing neck. The liquid to be distilled is placed in the vessel and heated. The n ...

: A spherical vessel with a long downward-pointing neck, specially used for distillation or

dry distillation Dry distillation is the heating of solid materials to produce gaseous products (which may condense into liquids or solids). The method may involve pyrolysis or thermolysis, or it may not (for instance, a simple mixture of ice and glass could be se ...

of substances. *

Schlenk flask A Schlenk flask, or Schlenk tube, is a reaction vessel typically used in air-sensitive chemistry, invented by Wilhelm Schlenk. It has a side arm fitted with a PTFE or ground glass stopcock, which allows the vessel to be evacuated or filled with g ...

: A round-bottom flask with a built-in plug valve or

stopcock A stopcock is a form of valve used to control the flow of a liquid or gas. The term is not precise and is applied to many different types of valve. The only consistent attribute is that the valve is designed to completely stop the flow when clo ...

Legality

In the United States, it is illegal for an individual to possess, manufacture, buy, or sell a three neck round bottom flask while knowing, suspecting or intending the flask's purpose to be the manufacture of illegal or controlled substances. It is ''not'' illegal, however to possess, manufacture, buy or sell a three neck round bottom flask for legal activities.

Gallery

References

{{DEFAULTSORT:Round-Bottom Flask Laboratory glassware