VOLUMETRIC FLASK: CHARACTERISTICS, TYPES AND INDICATIONS FOR USE - CHEMISTRY - 2025

The volumetric flask, also known as a fiola , is a glass container used in chemistry laboratories to perform reactions, prepare solutions, and measure the volume of liquids.

The bottom of this instrument is a rounded-edged container, similar to a pear with a flat base, however, some lack this base. Hence a long and narrow neck.

From their base to the beginning of the neck, they have marks that are used to determine the volume of liquids.

There are two types. The first type is used to prepare titrated solutions, that is, those in which there are precise measurements of solute and solvent necessary to produce the correct mixture. The measurements obtained by this type of instrument are very precise.

The second type is used to prepare other solutions that are not titrated. In this case, the measurements obtained are estimated and not precise.

They come in various sizes: 100 ml, 200 ml, 500 ml, among others. They resemble Erlenmeyer flasks. However, they have a much longer neck.

Description of the volumetric flask

The volumetric flask is a pear-shaped container with a flattened base. It has a long and thin neck, with markings that allow determining the volume of liquids.

On the neck, there is a label with basic information about the instrument, such as the volumetric capacity, the temperature at which the instrument should be worked and the manufacturer's brand.

It is equipped with a stopper that can be made of plastic, cork or tempered glass. It is usually made of polypropylene. This stopper fits perfectly in the mouth of the flask and prevents spillage from occurring when preparing solutions.

It has a mark called the capacity, which establishes the limit of liquid that the flask accepts. There is a considerable distance between the capacity and the mouth of the flask that allows the contents to be shaken if necessary.

Applications

To measure volumes of liquids

The volumetric flask is used to measure the volume of liquids. It has a series of marks on the neck that serve that purpose.

When measuring the volume of a liquid in a flask, it will be observed that it curves up or down: the edges will be higher and the center will be lower or vice versa. The shape of the curvature will depend on the type of liquid being measured.

This phenomenon is known as "meniscus". The central point is the one that must be taken into account when making the measurement.

The fact that the neck of the flask is so narrow makes measurement easier: any change in the volume of the liquid will be observed in the height of the meniscus.

It is necessary to bear in mind that when a liquid is to be measured, the eye must be at the level of the gauging, neither higher nor lower.

For the measurement to be correct, the capacity must be perceived by the eye as a straight line and not as an ellipse.

To prepare solutions

Volumetric flasks are commonly used in the preparation of standard solutions. That is, solutions in which the precise amounts of solute and solvent to be mixed are known.

For this, the volume of the solvent in the volumetric flask is measured, while the weight of the solute is determined with a precision balance or with an analytical balance.

Subsequently, the stopper is placed on the flask. In this way, the flask can be shaken to integrate the components of the solution without fear of spilling.

Types of flasks

According to the precision of the instrument

According to the precision of the instrument, there are two types of flasks. To begin with, there are those that are used to prepare standardized or titrated solutions. This type of flask is very accurate and is used in analytical chemistry laboratories.

The second type is less precise and is used for the preparation of other less demanding solutions. This is the kind of flask found in school labs.

According to the volumetric capacity

Moreover, the flasks can be classified according to their capacity. Thus, there are flasks from 1 ml to 2 l.

The most common measurements for these instruments are 25 ml, 50 ml, 100 ml, 200 ml, and 500 ml.

According to color

Most of the flasks are made of clear borosilicate glass. However, you can also find amber colors, which are used to make solutions that are susceptible to light, such as silver nitrate.

Indications of use

The first thing to do before using the flask is to thoroughly clean it and dry it. Any residue or drop of water on the instrument could alter the volume of the substance, generating measurement errors.

Any experiment with a volumetric flask should be carried out at a minimum of 20 ° C and a maximum of 25 ° C, since these instruments were created to work under these conditions.

It begins by adding the solute (which was previously weighed). If any of the solute adheres to the neck of the instrument, it must be carefully peeled off with the solvent. However, it is better to make the solute go directly to the bottom.

When half of the solvent has been added, shake the flask to dissolve the solute. Be careful not to shake it too vigorously, or to make the mixture splatter to capacity.

Subsequently, the rest of the solvent is added until reaching the indicated mark. The cap is placed on it and now it is shaken with greater force to make a homogeneous mixture.

Care and correct use

The volumetric flask is a precision instrument that can be affected by various conditions. If heated to very high temperatures, the glass in the flask could be altered, making the flask no longer as accurate in measuring volumes. Therefore, overheating should be avoided.

Like other pipettes and burettes, the volumetric flask should not be heat dried. When preparing aqueous solutions, the container can be used while still wet without drying it, as long as it has been washed with distilled water.

No volumetric flask should be washed with brushes because the interior could be affected, ruining its ability to accurately measure volumetric. The best way to wash them is by rinsing with solvents and plenty of distilled water.

The volumetric flask provides accurate volumetric figures. However, it is necessary to use it in the correct way in order to obtain results that are as close to reality as possible.

For example, when a standard solution is prepared from a solid sample, it does not dissolve in the flask but in a separate container and then move to the volumetric flask.

No sample should be poured or diluted directly to the marked line without stopping. The volume could change when mixing a sample and a solvent, so it is necessary to do it little by little and observe each time.

When it is last diluted, the solution should be mixed well, for which the flask needs to be inverted and shaken. Doing it any other way will not pay off.

Uses of the volumetric flask in research

Test Sara

In the hydrocarbon industry, the flask is a key instrument and one of the examples of this is the SARA test, an acronym for Saturates, Aromatics, Resins and Aslphatenes.

As its name implies, it is used to separate a petroleum sample into these 4 parts in order to analyze the solubility of each part and to know the behavior of the hydrocarbon before different solvents.

Acid-Base Titration

Also known as Acid-Base Volumetry. It is a quantitative analysis used to analyze the extent to which a substance can act as an acid, neutralizing it with another base substance.

It is called volumetry because it seeks to measure the volume of the substances used to calculate the concentration sought. In addition to calculating concentrations, this study is done to know the purity of certain substances.

Distillation

When you want to separate the different components present in a solution, distillation is the most commonly used method. The flask is heated to take advantage of the different boiling points of each element in the mixture.

The less volatile ones, thanks to their higher boiling point, remain at the bottom in their original state, while the shape of the neck of the flask allows the collection of the most volatile elements in the gaseous state as a result of evaporation, to then pass through a condensation process that allows it to return to its original state.

Crystallization

It is a process by which a gas or liquid solidifies. This technique is what allows to obtain the salt: the water is evaporated and the sodium chloride crystals are obtained.

But the flask plays an important role mainly in the purification of other crystals, where the crystallized material dissolves and it is necessary to know the volume of the solvent to obtain a new, purer crystal.

For example, a crystal of benzoic acid mixed with acetone can be separated by adding water.

References

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