Special purpose dishes (). Volumetric flask - an indispensable laboratory tool

Volumetric flasks - traditional for various measurements, experiments, research. They were invented several centuries ago, but to this day they have not lost their relevance.

Design features, manufacturing principles

Volumetric flasks are presented in the form of glass or plastic vessels of a conical shape (flasks with a pear-shaped or spherical base, a long cylindrical neck and a flat bottom are also available). Glass flasks are made from light or dark glass raw materials with low expansion rates. The capacity of vessels of this type can vary from 1 ml to 5 liters.

The manufacture of the neck of the volumetric flask is carried out with a section for a ground glass stopper, or without a section. If the product is without a thin section, then it is closed with a cotton, polyethylene, silicone, rubber stopper (if the specialist works with strong-smelling or volatile substances). Flasks with a thin section are designed for long-term storage of solutions and substances in them.

Volumetric flasks have a flat bottom because the vessel must be as stable as possible on a horizontal surface or on a slightly inclined surface. An empty 25 ml flask should no longer roll off a surface with an inclination of 15 degrees or less. Small vessels should remain stable when tilted at 10 degrees.

Volume marks are usually applied to the neck.

• If the product has one label, then it is intended "for infusion".
• If the product has two labels, then it is used "for pouring".
• There are also volumetric flasks with a scale on the neck, with an extended upper part of the neck for a funnel and other types of vessels.

The production of volumetric flasks is carried out in accordance with the requirements of GOST and international standards. In the factory, each vessel is calibrated according to the required accuracy class, for which GOST defines the maximum error limits at a temperature of 20 degrees.

What are measuring flasks for?

Products of this type are used to prepare chemical solutions of a certain concentration directly in the vessel. Graduation occurs due to the circular mark on the flask, which indicates the nominal volume of the liquid in the vessel. When pouring the solution from the flask, it is necessary to take into account the remains of the liquid that linger on the walls of the vessel. That is why, as a result, the volume of the poured solution will become less than it was in the flask.

Volumetric flasks that work "for infusion" and "for pouring" have two marks: the lower mark is used if only the volume of the infused liquid needs to be measured; if measurement of the poured liquid is required, the upper mark is used.

Flasks with a measuring scale on the neck are used to work with solutions made from two constituent liquids. The presence of graduation allows you to determine the decrease or increase in volume when one substance is dissolved in another.

How to work with volumetric flasks?

All volumetric flasks are marked: there is information about the accuracy class of the vessel, the nominal volume, the manufacturer, the calibration temperature, the type of glass used, etc.

When conducting laboratory tests, products must not be heated (even during thermal sterilization). To increase the measurement accuracy, it is recommended to set the temperature in the room to the same temperature as when the vessel was calibrated by the manufacturer. For this, a specialized laboratory is used.

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A flask is a vessel with a wide base and a long cylindrical neck. However, over the centuries, many types of flasks have been developed for different tasks, which determined the shape of a particular vessel. Now in the arsenal of chemists there are flasks with a spherical, pear-shaped and conical base, with high and low, wide and narrow necks.

Distinctive features of a flat-bottomed flask

As the name implies, flat-bottom flasks are flasks with a flat bottom. Their main advantage is that the researcher does not need to worry about how to set up the vessel, because a flat-bottomed flask does not need a tripod or a special stand. It is tabletop stable, lab tile stable, easy to store and use in lab setups.

Classification of flat-bottomed flasks:

All flat-bottomed flasks can be classified according to different criteria:

By capacity: the capacity of the flasks varies from 5 ml to 50 l.

Heat resistant and non heat resistant.

According to the method of application:
reaction flasks;
measured;
receiver vessels.

By form:
round flasks;
conical flasks.

Flat bottom flasks, like round bottom flasks, can have multiple necks. But such vessels are rarely encountered and used and are usually made by special order.

Each type of flask has its own advantages. For example, quartz flasks are distinguished by increased heat resistance, and glass flasks, although they cannot compete with quartz flasks in this indicator, are usually cheaper and more practical for standard tasks. Round flat-bottomed flasks are more convenient as reaction vessels, while conical flasks are more suitable as receiver vessels. Volumetric flasks, as a rule, are round, small in volume, with a long narrow neck, which makes it possible to mark the amount of a substance with high accuracy.

Flasks with polished necks are very convenient. They can store prepared solutions and substances obtained as a result of synthesis. A conical flask with a thin section is good because you can insert an adapter or another device into it, say, a refrigerator, so that the connection is both hermetic and easily disassembled (assembled).

Personalized flat-bottomed flasks

The most famous flat-bottomed flasks are the Bunsen flask. and an Erlenmeyer flask. The Erlenmeyer flask is conical, with a wide base and a low neck. Several divisions of the approximate volume scale are applied to its walls, as well as a white matte rectangle for pencil marks. The flask is very stable, suitable for the use of mechanical and magnetic stirrers. The wide base and narrow neck make the vessel extremely practical - liquids do not spill during transportation and mixing. The wide bottom is convenient for laboratory tiles. Erlenmeyer flasks are used for analytical work, titration, gas production, as a reaction or receiving vessel, washing.

The Bunsen flask is also conical, designed for vacuum filtration. It is made of thick glass, on the side, in the upper part it is supplied with a side outlet for connecting to a vacuum pump or vacuum line. A funnel is inserted into the neck through a rubber stopper.

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Round-bottom flasks (Fig. 55) are made from ordinary and special (for example, Jena) glass. Everything that has been said about the handling of flat-bottom flasks applies to round-bottom flasks; they are used in many jobs. Some round bottom flasks have a short but wide neck.

To heat round-bottom flasks on a naked flame, asbestos nets with a hemispherical recess are used.

Round-bottomed flasks, as well as flat-bottomed flasks, come in a wide variety of capacities.; with and without a throat cut.

Round-bottom flasks are conveniently placed in wooden stands with a recess (Fig. 56). Stands are also used in the form of rings of different diameters, made of various materials, for example, rubber, rubber tubes, etc.

Kjeldahl flasks are pear-shaped and have an elongated neck (Fig. 57), they are used to determine nitrogen according to Kjeldahl; their capacity is usually from 300 to 800 ml. Such flasks are made of refractory and heat-resistant pyrex glass.

Flasks for distillation. For the distillation of liquids, special flasks are used, for example, flasks of Wurtz, Claisen, Arbuzov and others.

The most common are Wurtz flasks (Fig. 58) with a capacity of 50 ml to 1-2 l; they are round-bottomed flasks with a long neck, from which a long narrow outlet tube extends at an angle.

Fig.55 Round-bottom flasks.

Fig.56 Stand for round-bottom flasks.

Rice. 57. Kjeldahl flask and a facility for heating such flasks.

This tube can be located at various distances from the ball of the flask. Wurtz flasks, which have a vapor tube located close to the ball, are designed for the distillation of substances with a low boiling point. Flasks with a vapor tube located in the middle of the neck are used for the distillation of substances with an average boiling point. High-boiling liquids are distilled in Wurtz flasks, the vapor tube of which is located closer to the open end of the throat.

When working, a cork or rubber stopper with a thermometer is tightly inserted into the neck of the Wurtz flask, and the side tube is attached to the refrigerator on the stopper or thin section. The thermometer is set up so that it

Rice. 58. Wurtz flasks.

so that the tank does not touch the walls of the neck and is in the middle of it against the opening of the outlet tube. Plugs are put on the side tube so that the end of the tube, which will be inserted into the refrigerator, enters it by at least 4-5 cm.

When the flask is prepared, it is fixed in a foot on a tripod, placed in a bath or on an asbestos grid, and then a refrigerator is attached to it. Before starting work, the cork with the thermometer is removed, a funnel is inserted into the throat with an end of such a length that it is below the level of the outlet tube, and the liquid to be distilled is poured into the flask. When the liquid fills the ball of the flask to a maximum of 3/4, the latter is closed with a stopper with a thermometer, the entire device is checked again and distillation is started.

Flasks with saber outlet tube(Fig. 59) is used for distillation or sublimation of substances with a high solidification point. They have a wide saber-shaped outlet tube, which serves as an air. ny refrigerator and at the same time as a receiver. The most common flasks are 50, 100, or 250 ml.

Claisen flask(Fig. 60) differs from the Wurtz flask in that its neck has two necks, one of which is equipped with an elbow-shaped outlet tube. Sometimes necks come with one or more spherical extensions. Claisen flasks are used to distill liquids under reduced pressure.

The upper part of both necks of the Claisen flask is somewhat pulled back, and place a thermometer on the stopper into it, as. in a Wurtz flask, it is impossible. The thermometer in the neck of the Claisen flask is fixed with a piece of elastic rubber tube about 3 cm long. less than the diameter of the neck of the flask. The position of the thermometer reservoir should be the same as in the Wurtz flask.

Rice. 59. Flask with a saber outlet tube.

Rice. 60. Claisen flask.

In the other neck, in exactly the same way, a glass tube is inserted, the end of which, located inside the flask, is extended into the capillary. The capillary should be at a distance of 2-3 mm from the bottom of the flask. A rubber tube fitted with a screw clamp is put on the outer part of this tube. It is recommended to insert a piece of thin wire into the rubber tube so that the rubber does not stick together at the place where the tube is squeezed by the clamp. Such a device makes it possible to create a channel with a very small cross section to control the flow of air into the flask.

The introduction of air into the flask during vacuum distillation is necessary in order to prevent or mitigate the shocks and shocks that are observed during the distillation of liquids under vacuum. However, it should be remembered that when passing a jet of air, the boiling point will be lower than the true one. This is easy to verify if you start to let the air through very intensively. Therefore, to maintain the boiling point close to the true air jet should not be strong. It is enough if the air passes in small bubbles, one bubble per second.

The outlet tube is connected to the refrigerator with a rubber stopper.

Arbuzov's flask (Fig. 61) is an improved Claisen flask. Such flasks have a large

Rice. 61. Flask Arbuzov. Rice. 62. Allonge.

refluxing ability. When working with the Arbuzov flask, the possibility of liquid getting from the flask into the receiver is excluded, since both necks of the flask are interconnected and in the event of sudden boiling, the liquid enters the expanded part and flows back into the flask. Arbuzov flasks usually come in capacities from 20 to 1000 ml.

Allonge- glass curved tubes (Fig. 62). Allonges are used in distillation for connection, a refrigerator with a receiver, and in other works.

To the wide end of the allonge, a cork is first selected, in which a hole is drilled for the refrigerator fore-stash; The forshtos of the refrigerator should enter the allonge by 3-4 cm. The narrow end of the allonge is lowered into the receiver.

Desiccators - devices used for slow drying and for the preservation of substances that easily absorb moisture from the air. Desiccators are closed with glass lids, the edges of which are ground to the top of the cylinder. There are two main types of desiccators: ordinary (Fig. 63) and vacuum desiccators (Fig. 64). The latter have a hole into which a tube with a tap is inserted on a rubber stopper, or in the lid there is a tube with a ground stopper, to which a glass tube with a tap is soldered; this makes it possible to connect the desiccator to a vacuum pump and, creating a reduced pressure inside the desiccator, carry out drying under vacuum (Fig. 65). A manometer 2 and a safety bottle 3 are usually placed between the vacuum desiccator / and the vacuum pump.

Some vacuum desiccators (see Fig. 64) have a device for heating with electricity. In such a desiccator, it is possible to dry in a vacuum when heated. It is necessary to let air into the vacuum desiccator very carefully (but, since the jet of rushing air can scatter the substance to be dried. Therefore, the inlet cock must be turned very slowly and the lid must be lifted only after a few minutes after the inlet cock is ajar.

Inside the desiccator, on the bottom of the cylinder, above the cone-shaped part, a porcelain insert is usually placed (Fig. 66). Instead of tabs, you can use the usual

Rice. 63. Desiccator.

Rice. 64, Vacuum desiccators.

glass (except when hot crucibles are placed in the desiccator). Place the glass on corks so as not to isolate the cylindrical part of the desiccator from the cone. Desiccators very often have to be moved from place to place, and it is not uncommon for the lid to slip and break. Therefore, when carrying the desiccator, be sure to hold the lid (Fig. 67).

Rice. 65. Connection diagram of a vacuum desiccator with a vacuum pump:

1 - vacuum desiccator; 2 - manometer; 3 - safety bottle.

*Rice. 66. Porcelain inserts for desiccators.

If hot crucibles are placed in the desiccator, the lid sometimes rises due to the heating of the air, and it may slip off and break. Therefore, having placed a hot crucible in a desiccator and covered it with a lid, they grind it for a while, i.e., move it to the right and left. As the crucible cools, a small vacuum is created inside the desiccator and the lid is held very tightly. To open the desiccator, you must not lift the lid, but first slide it to the side, after which it can be easily removed (Fig. - 68).

Laboratory glassware is distinguished by its diversity. It is used in the process of conducting analyzes in various fields. A huge number of variations of the containers presented allows you to use the most suitable variety in each case.

Existing types of flasks can be classified according to some criteria. This allows you to delve deeper into their application and significance for analysis. Varieties of laboratory glassware deserve special attention.

general characteristics

Most commonly used in laboratory studies glass flasks. They allow you to perform many different operations and chemical reactions. A rather large expense item for any laboratory is precisely the container.

Since most flasks are made of glass, they can break. Today there are many different types of flasks. They may be exposed to temperatures or chemicals. Therefore, the material from which laboratory glassware is made must withstand such loads.

Flask configuration can be very unusual. This is necessary in order to conduct a full as well as analysis of the required substances. Most often, these containers have a wide base and a narrow neck. Some of them may be equipped with a cork.

Varieties of form

In laboratory studies, flat-bottomed and round bottom flask. These are the most commonly used types of containers. Flat-bottomed varieties can be placed on a flat surface. Their purpose is very varied.

The round-bottom flasks are held in a rack. This is very convenient if the container needs to be heated. For some reactions, this speeds up the process. Therefore, the round-bottom flask is most often made from heat-resistant glass due to this application feature.

Also, both presented varieties of laboratory glassware are used to store various substances. Sometimes, in very rare cases, sharp-bottomed varieties of containers are used in the course of laboratory analysis.

The use of flasks and their configuration

Very varied. They depend on the application. The Kjeldahl flask is pear-shaped. It is most often used in the device of the same name for the determination of nitrogen. This flask may have a glass stopper.

A Wurtz flask is used to distill various substances. In its design there is a discharge tube.

The Claisen flask has two necks, the diameter of which is the same along the entire length. A tube is connected to one of them, designed to remove steam. The other end communicates the dishes with the refrigerator. This variety is used for distillation and distillation at normal pressure.

The Bunsen flask is used in filtration processes. Its walls are very strong and thick. At the top there is a special process. It approaches the vacuum line. For experiments under reduced pressure conditions, this variety is ideal.

Erlenmeyer flask

Considering the existing types of flasks, it is impossible not to pay attention to another form of laboratory glassware. The name of this container is given in honor of its creator - the German chemist Erlenmeyer. This is a conical container that has a flat bottom. Its neck is characterized by a cylindrical shape.

This flask has divisions that allow you to determine the volume of liquid inside. A unique feature of this type of container is an insert made of special glass. This is a kind of notebook. On it, the chemist can make the necessary notes.

The neck, if necessary, can be closed with a stopper. The conical shape promotes high-quality hashing of contents. The narrow neck prevents spillage. The evaporation process in such a container is slower.

The flask of the presented type is used when carrying out titration, cultivation of pure cultures or heating. If the flask has divisions on the body, they are not heated. Such dishes allow you to measure the amount of the content of the substance.

A few more features

The types of flasks used can also be divided into groups depending on the type of neck. They are simple (for a rubber stopper), as well as with a cylindrical or conical section.

Depending on the type of material from which the cookware is made, it can be heat-resistant or plain. By purpose, the flasks can be divided into volumetric containers, receivers and reactors.

The volume of laboratory glassware is also quite diverse. Their capacity can be from 100 ml to 10 liters. There are flasks of even larger volume. When working with such containers, it is imperative to follow safety rules. Each type of equipment presented must be used strictly for its intended purpose. Otherwise, you can break the flask or harm your body.