Determination of molecular weight. Molecular mass. See what "Molecular weight" is in other dictionaries

Many experiments show that molecule size very small. The linear size of a molecule or atom can be found in various ways. For example, with the help of an electron microscope, photographs of some large molecules were taken, and with the help of an ion projector (ion microscope), one can not only study the structure of crystals, but also determine the distance between individual atoms in a molecule.

Using the achievements of modern experimental technology, it was possible to determine the linear dimensions of simple atoms and molecules, which are about 10-8 cm. The linear dimensions of complex atoms and molecules are much larger. For example, the size of a protein molecule is 43*10 -8 cm.

To characterize atoms, the concept of atomic radii is used, which makes it possible to approximately estimate the interatomic distances in molecules, liquids or solids, since atoms do not have clear boundaries in their size. I.e atomic radius- this is a sphere in which the main part of the electron density of an atom is enclosed (at least 90 ... 95%).

The size of a molecule is so small that it can only be represented by comparisons. For example, a water molecule is many times smaller than a large apple, how many times an apple is smaller than the globe.

mole of substance

The masses of individual molecules and atoms are very small, so it is more convenient to use relative rather than absolute mass values ​​in calculations.

Relative molecular weight(or relative atomic mass) substances M r is the ratio of the mass of a molecule (or atom) of a given substance to 1/12 of the mass of a carbon atom.

M r \u003d (m 0) : (m 0C / 12)

where m 0 is the mass of a molecule (or atom) of a given substance, m 0C is the mass of a carbon atom.

The relative molecular (or atomic) mass of a substance shows how many times the mass of a substance molecule is greater than 1/12 of the mass of the C 12 carbon isotope. Relative molecular (atomic) mass is expressed in atomic mass units.

Atomic mass unit is 1/12 of the mass of the carbon isotope C 12. Precise measurements showed that the atomic mass unit is 1.660 * 10 -27 kg, that is

1 amu = 1.660 * 10 -27 kg

The relative molecular mass of a substance can be calculated by adding the relative atomic masses of the elements that make up the molecule of the substance. The relative atomic mass of chemical elements is indicated in the periodic system of chemical elements by D.I. Mendeleev.

In the periodic system D.I. Mendeleev for each element is indicated atomic mass, which is measured in atomic mass units (amu). For example, the atomic mass of magnesium is 24.305 amu, that is, magnesium is twice as heavy as carbon, since the atomic mass of carbon is 12 amu. (this follows from the fact that 1 amu = 1/12 of the mass of the carbon isotope that makes up the majority of the carbon atom).

Why measure the mass of molecules and atoms in amu, if there are grams and kilograms? Of course, you can use these units, but it will be very inconvenient for writing (too many numbers will have to be used in order to write down the mass). To find the mass of an element in kilograms, multiply the atomic mass of the element by 1 amu. The atomic mass is found according to the periodic table (written to the right of the letter designation of the element). For example, the weight of a magnesium atom in kilograms would be:

m 0Mg = 24.305 * 1 a.e.m. = 24.305 * 1.660 * 10 -27 = 40.3463 * 10 -27 kg

The mass of a molecule can be calculated by adding the masses of the elements that make up the molecule. For example, the mass of a water molecule (H 2 O) will be equal to:

m 0H2O \u003d 2 * m 0H + m 0O \u003d 2 * 1.00794 + 15.9994 \u003d 18.0153 a.e.m. = 29.905 * 10 -27 kg

mole is equal to the amount of substance of the system, which contains as many molecules as there are atoms in 0.012 kg of carbon C 12. That is, if we have a system with some substance, and in this system there are as many molecules of this substance as there are atoms in 0.012 kg of carbon, then we can say that in this system we have 1 mole of substance.

Avogadro constant

Amount of substanceν is equal to the ratio of the number of molecules in a given body to the number of atoms in 0.012 kg of carbon, that is, the number of molecules in 1 mole of a substance.

ν = N / N A

where N is the number of molecules in a given body, N A is the number of molecules in 1 mole of the substance that makes up the body.

N A is Avogadro's constant. The amount of a substance is measured in moles.

Avogadro constant is the number of molecules or atoms in 1 mole of a substance. This constant got its name in honor of the Italian chemist and physicist Amedeo Avogadro (1776 – 1856).

1 mole of any substance contains the same number of particles.

N A \u003d 6.02 * 10 23 mol -1

Molar mass is the mass of a substance taken in the amount of one mole:

μ = m 0 * N A

where m 0 is the mass of the molecule.

Molar mass is expressed in kilograms per mole (kg/mol = kg*mol -1).

Molar mass is related to relative molecular mass by the relationship:

μ \u003d 10 -3 * M r [kg * mol -1]

The mass of any amount of substance m is equal to the product of the mass of one molecule m 0 by the number of molecules:

m = m 0 N = m 0 N A ν = μν

The amount of a substance is equal to the ratio of the mass of the substance to its molar mass:

ν = m / μ

The mass of one molecule of a substance can be found if the molar mass and the Avogadro constant are known:

m 0 = m / N = m / νN A = μ / N A

A more accurate determination of the mass of atoms and molecules is achieved using a mass spectrometer - a device in which a beam of charged particles separates in space depending on their charge mass using electric and magnetic fields.

For example, let's find the molar mass of a magnesium atom. As we found out above, the mass of a magnesium atom is m0Mg = 40.3463 * 10 -27 kg. Then the molar mass will be:

μ \u003d m 0Mg * N A \u003d 40.3463 * 10 -27 * 6.02 * 10 23 \u003d 2.4288 * 10 -2 kg / mol

That is, 2.4288 * 10 -2 kg of magnesium “fits” in one mole. Well, or about 24.28 grams.

As you can see, the molar mass (in grams) is almost equal to the atomic mass indicated for the element in the periodic table. Therefore, when they indicate the atomic mass, they usually do this:

The atomic mass of magnesium is 24.305 amu. (g/mol).

In chemistry, the values ​​​​of the absolute masses of molecules are not used, but the value of the relative molecular mass is used. It shows how many times the mass of a molecule is greater than 1/12 of the mass of a carbon atom. This value is denoted by M r .

The relative molecular weight is equal to the sum of the relative atomic masses of its constituent atoms. Calculate the relative molecular weight of water.

You know that a water molecule contains two hydrogen atoms and one oxygen atom. Then its relative molecular mass will be equal to the sum of the products of the relative atomic mass of each chemical element and the number of its atoms in a water molecule:

Knowing the relative molecular weights of gaseous substances, one can compare their densities, i.e., calculate the relative density of one gas from another - D (A / B). The relative density of gas A for gas B is equal to the ratio of their relative molecular masses:

Calculate the relative density of carbon dioxide for hydrogen:

Now we calculate the relative density of carbon dioxide for hydrogen:

D(co.g./hydrogen.) = M r (co. g.) : M r (hydrogen.) = 44:2 = 22.

Thus, carbon dioxide is 22 times heavier than hydrogen.

As you know, Avogadro's law applies only to gaseous substances. But chemists need to have an idea about the number of molecules and in portions of liquid or solid substances. Therefore, to compare the number of molecules in substances, chemists introduced the value - molar mass .

Molar mass is denoted M, it is numerically equal to the relative molecular weight.

The ratio of the mass of a substance to its molar mass is called amount of matter .

The amount of a substance is denoted n. This is a quantitative characteristic of a portion of a substance, along with mass and volume. The amount of a substance is measured in moles.

The word "mole" comes from the word "molecule". The number of molecules in equal amounts of a substance is the same.

It has been experimentally established that 1 mol of a substance contains particles (for example, molecules). This number is called Avogadro's number. And if you add a unit of measurement to it - 1 / mol, then it will be a physical quantity - the Avogadro constant, which is denoted N A.

Molar mass is measured in g/mol. The physical meaning of the molar mass is that this mass is 1 mole of a substance.

According to Avogadro's law, 1 mole of any gas will occupy the same volume. The volume of one mole of gas is called the molar volume and is denoted by V n .

Under normal conditions (and this is 0 ° C and normal pressure - 1 atm. Or 760 mm Hg or 101.3 kPa), the molar volume is 22.4 l / mol.

Then the amount of gas substance at n.o. can be calculated as the ratio of gas volume to molar volume.

TASK 1. What amount of substance corresponds to 180 g of water?

TASK 2. Let us calculate the volume at n.o., which will be occupied by carbon dioxide in the amount of 6 mol.

Bibliography

1. Collection of tasks and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. "Chemistry, Grade 8" / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M.: AST: Astrel, 2006. (p. 29-34)
2. Ushakova O.V. Chemistry workbook: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. Grade 8” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006. (p. 27-32)
3. Chemistry: 8th grade: textbook. for general institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005. (§§ 12, 13)
4. Chemistry: inorg. chemistry: textbook. for 8 cells. general institution / G.E. Rudzitis, F.G. Feldman. - M .: Education, JSC "Moscow textbooks", 2009. (§§ 10, 17)
5. Encyclopedia for children. Volume 17. Chemistry / Chapter. edited by V.A. Volodin, leading. scientific ed. I. Leenson. - M.: Avanta +, 2003.

1. A single collection of digital educational resources ().
2. Electronic version of the journal "Chemistry and Life" ().
3. Chemistry tests (online) ().

Homework

1.p.69 No. 3; p.73 Nos. 1, 2, 4 from the textbook "Chemistry: 8th grade" (P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M .: AST: Astrel, 2005).

2. №№ 65, 66, 71, 72 from the Collection of tasks and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. "Chemistry, Grade 8" / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M.: AST: Astrel, 2006.

The composition of substances is complex, although they are formed by tiny particles - atoms, molecules, ions. many liquids and gases, as well as some solids. Metals and many salts are composed of atoms and charged ions. All particles have a mass, even the smallest if expressed in kilograms, gets a very small value. For example, m (H 2 O) \u003d 30. 10 -27 kg. Such important characteristics of a substance as the mass and size of microparticles have long been studied by physicists and chemists. The foundations were laid in the works of Mikhail Lomonosov and let's consider how the views on the microworld have changed since then.

Lomonosov's ideas about "corpuscles"

The assumption about the discrete was expressed by the scientists of ancient Greece. At the same time, the name "atom" was given to the smallest indivisible particle of bodies, the "brick" of the universe. The great Russian researcher M. V. Lomonosov wrote about an insignificantly small particle of the structure of matter, indivisible by physical means - a corpuscle. Later, in the works of other scientists, it was called the "molecule".

The mass of a molecule, as well as its dimensions, are determined by the properties of its constituent atoms. For a long time, scientists were unable to look deep into the microworld, which hampered the development of chemistry and physics. Lomonosov repeatedly urged his colleagues to study and in their work rely on precise quantitative data - "measure and weight." Thanks to the work of the Russian chemist and physicist, the foundations of the doctrine of the structure of matter were laid, which became an integral part of a harmonious atomic-molecular theory.

Atoms and molecules are the building blocks of the universe

Even microscopically small bodies are complex and have different properties. Particles such as atoms, formed by the nucleus and electron layers, differ in the number of positive and negative charges, radius, and mass. Atoms and molecules do not exist in the composition of substances in isolation, they are attracted with different strengths. The action of attractive forces is more noticeable in solids, weaker - in liquids, almost not felt in gaseous substances.

Chemical reactions are not accompanied by the destruction of atoms. Most often, their rearrangement occurs, another molecule appears. The mass of a molecule depends on what atoms it is formed from. But with all the changes, the atoms remain chemically indivisible. But they can be part of different molecules. At the same time, atoms retain the properties of the element to which they belong. A molecule, before its disintegration into atoms, retains all the attributes of a substance.

A microparticle of the structure of bodies is a molecule. Molecule mass

Instruments are used to measure the mass of macro-objects, the oldest of which is scales. The measurement result is conveniently obtained in kilograms, because this is the main unit of the international system of physical quantities (SI). To determine the mass of a molecule in kilograms, it is necessary to add the atomic masses, taking into account the number of particles. For convenience, a special unit of mass, the atomic, was introduced. You can write it as a letter abbreviation (a.m.u.). This unit corresponds to one twelfth of the mass of the carbon nuclide 12 C.

If we express the found value in standard units, then we get 1.66. 10 -27 kg. Physicists mainly operate with such small indicators for the mass of bodies. The article contains a table from which you can find out what the masses of atoms of some chemical elements are equal to. To find out what the mass of one in kilograms is, we multiply the atomic mass of this chemical element given in the table by two. As a result, we obtain the value of the mass of a molecule consisting of two atoms.

Relative molecular weight

It is difficult to operate in calculations with very small values, this is inconvenient, leads to time-consuming, errors. As for the mass of microparticles, the way out of the difficult situation was the use of the term familiar to chemists consists of two words - "atomic mass", its designation is Ar. An identical concept was introduced for molecular weight (the same as the mass of a molecule). The formula connecting the two quantities: Mr = m (in-va) / 1/12 m (12 C).

It is not uncommon to hear people say "molecular weight". This obsolete term is still used in relation to the mass of the molecule, but less and less often. The fact is that weight is another physical quantity - a force that depends on the body. On the contrary, mass serves as a constant characteristic of particles that participate in chemical processes and move at normal speed.

How to determine the mass of a molecule

The exact determination of the weight of the molecule is carried out using a device - a mass spectrometer. To solve problems, you can use information from the periodic system. For example, the mass of an oxygen molecule is 16. 2 \u003d 32. Let's perform simple calculations and find the value of Mr (H 2 O) - the relative molecular weight of water. According to the periodic table, we determine that the mass of an oxygen atom is 16, hydrogen is 1. Let's carry out simple calculations: M r (H 2 O) \u003d 1. 2 + 16 = 18, where M r is the molecular weight, H 2 O is the water molecule, H is the symbol of the element hydrogen, O is the chemical sign of oxygen.

Masses of isotopes

Chemical elements in nature and technology exist in the form of several varieties of atoms - isotopes. Each of them has an individual mass, its value cannot have a fractional value. But the atomic mass of a chemical element is most often a number with several decimal places. The calculations take into account the prevalence of each species in the earth's crust. Therefore, the masses of atoms in the periodic system are not always integers. Using such quantities for calculations, we get the masses of molecules, which are also not integers. In some cases rounding of values ​​is allowed.

Molecular weight of substances of non-molecular structure

Dimensions and mass of molecules

In electron micrographs of large molecules, individual atoms can be seen, but they are so small that they are not visible with a conventional microscope. The linear size of a particle of any substance, like mass, is a constant characteristic. The diameter of a molecule depends on the radii of its constituent atoms, their mutual attraction. Particle sizes change with an increase in the number of protons and energy levels. The hydrogen atom is the smallest in size, its radius is only 0.5. 10 -8 cm. A uranium atom is three times larger than a hydrogen atom. The real "giants" of the microcosm are the molecules of organic substances. So, the linear size of one of the protein particles is 44 . 10 -8 cm.

To summarize: the mass of molecules is the sum of the masses of the atoms that make up them. The absolute value in kilograms can be obtained by multiplying the molecular weight value found in the periodic table by 1.66. 10 -27 kg.

Molecules are negligible compared to macrobodies. For example, in terms of size, a water molecule H 2 O is inferior to an apple as many times as many times this fruit is smaller than our planet.

However, one should clearly understand the difference between molar mass and molecular weight, understanding that they are only numerically equal and differ in dimension.

The molecular weights of complex molecules can be determined by simply adding up the relative atomic masses of their constituent elements. For example, the molecular weight of water (H 2 O) is

see also

Wikimedia Foundation. 2010 .

• Brachauchenius
• Elbe-Lübeck Canal

See what "Molecular weight" is in other dictionaries:

MOLECULAR MASS- the value of the mass of the molecule, expressed in atomic mass units. In practice, molecular mass is equal to the sum of the masses of its constituent atoms (see ATOMIC MASS). Physical Encyclopedic Dictionary. Moscow: Soviet Encyclopedia. Editor-in-Chief A. M. Prokhorov. 1983... Physical Encyclopedia

MOLECULAR MASS- (molecular weight) the mass of a molecule, expressed in atomic mass units. Almost equal to the sum of the masses of all the atoms that make up the molecule. Molecular weight values ​​are used in chemical, physical and chemical engineering calculations… Big Encyclopedic Dictionary

MOLECULAR MASS- (mole mass), the term was previously used to refer to the RELATIVE MOLECULAR WEIGHT ... Scientific and technical encyclopedic dictionary

Molecular weight M m- Molecular weight, M. m. * molecular weight, M. m. * molecular mass or M. m. the mass of a molecule that does not have its own units of measurement, therefore, the term “molecular weight” is usually used in this sense (see) ... Genetics. encyclopedic Dictionary

molecular mass- — Biotechnology topics EN molecular mass … Technical Translator's Handbook

Molecular mass- - relative value, the ratio of the mass of a molecule of a given substance to 1/12 of the mass of an atom of the carbon isotope C12. [Usherov Marshak A. V. Concrete science: lexicon. Moscow: RIF Building Materials. 2009. - 112 p.] Term heading: General terms ... ... Encyclopedia of terms, definitions and explanations of building materials

MOLECULAR MASS- the sum of the masses of atoms that make up this molecule; expressed in atomic mass units (a.m.u.). Since 1 a. e.m. (sometimes called dalton, D) is equal to 1/12 of the mass of the 12 C nuclide atom and in SI mass units is 1.66057.10 27 kg, then ... ... Chemical Encyclopedia

molecular mass- santykinė molekulinė masė statusas T sritis Standartizacija ir metrologija apibrėžtis Molekulės vidutinės masės arba tiksliai apibrėžto medžiagos darinio masės ir nuklido ¹²C atomo masės 1/12 dalies dalmuo. atitikmenys: engl. molecular mass;… …

molecular mass- santykinė molekulinė masė statusas T sritis Standartizacija ir metrologija apibrėžtis Molekulę sudarančių atomų santykinių atominių masių suma, skaitine verte lygi medžiagos molio masei. atitikmenys: engl. molecular weight; molecular weight;… … Penkiakalbis aiskinamasis metrologijos terminų žodynas

molecular mass- santykinė molekulinė masė statusas T sritis chemija apibrėžtis Molekulę sudarančių atomų santykinių atominių masių suma, skaitine verte lygi vieno medžiagos molio masei. atitikmenys: engl. molecular weight; molecular weight; relative molecular mass … Chemijos terminų aiskinamasis žodynas

molecular mass- (molecular weight), the mass of a molecule expressed in atomic mass units. Almost equal to the sum of the masses of all the atoms that make up the molecule. Molecular weight values ​​are used in chemical, physical and chemical engineering calculations. * … encyclopedic Dictionary

Books

• Characteristics of hydrocarbons. Analysis of numerical data and their recommended values. Reference book , Yu. A. Lebedev , A. N. Kizin , T. S. Papina , I. Sh. Saifullin , Yu. E. Moshkin , This book presents the most important numerical characteristics of a number of hydrocarbons, among which the following physicochemical constants: molecular weight, temperature… Category: Chemistry Publisher: LENAND, Manufacturer: LENAND, Buy for 3578 UAH (Ukraine only)
• Hyaluronic acid in injection cosmetology, Khabarov Vladimir Nikolaevich, The book contains numerous literature data and the results of the author's own scientific research in the field of medical use of hyaluronic acid. Issues covered in detail... Category: Skin and venereal diseases Publisher:

Molecular weight is one of the basic concepts in modern chemistry. Its introduction became possible after the scientific substantiation of Avogadro's statement that many substances consist of the smallest particles - molecules, each of which, in turn, consists of atoms. Science owes much of this judgment to the Italian chemist Amadeo Avogadro, who scientifically substantiated the molecular structure of substances and gave chemistry many of the most important concepts and laws.

Mass units of elements

Initially, the hydrogen atom was taken as the basic unit of atomic and molecular mass as the lightest of the elements in the universe. But atomic masses were mostly calculated on the basis of their oxygen compounds, so it was decided to choose a new standard for determining atomic masses. The atomic mass of oxygen was taken equal to 15, the atomic mass of the lightest substance on Earth, hydrogen, - 1. In 1961, the oxygen system for determining the weight was generally accepted, but created certain inconveniences.

In 1961, a new scale of relative atomic masses was adopted, the standard for which was the carbon isotope 12 C. The atomic mass unit (abbreviated a.m.u.) is 1/12 of the mass of this standard. At present, atomic mass refers to the mass of an atom, which must be expressed in a.m.u.

Mass of molecules

The mass of a molecule of any substance is equal to the sum of the masses of all the atoms that form this molecule. Hydrogen has the lightest molecular weight of a gas, its compound is written as H 2 and has a value close to two. The water molecule consists of an oxygen atom and two hydrogen atoms. Hence, its molecular weight is 15.994 + 2*1.0079=18.0152 a.m.u. Complex organic compounds - proteins and amino acids - have the largest molecular weights. The molecular weight of a protein structural unit ranges from 600 to 10 6 and more, depending on the number of peptide chains in this macromolecular structure.

mole

Simultaneously with the standard units of mass and volume in chemistry, a very special system unit is used - the mole.

A mole is the amount of a substance that contains as many structural units (ions, atoms, molecules, electrons) as there are in 12 grams of the 12 C isotope.

When applying the measure of the amount of a substance, it is necessary to indicate which structural units are meant. As follows from the concept of "mole", in each individual case it should be indicated exactly what structural units are in question - for example, a mole of H + ions, a mole of H 2 molecules, and so on.

Molar and molecular weight

The mass of an amount of a substance in 1 mol is measured in g / mol and is called the molar mass. The relationship between molecular and molar mass can be written as an equation

ν = k × m/M, where k is the coefficient of proportionality.

It is easy to say that for any ratios the coefficient of proportionality will be equal to one. Indeed, the isotope of carbon has a relative molecular mass of 12 amu, and, according to the definition, the molar mass of this substance is 12 g/mol. The ratio of molecular weight to molar is 1. From this we can conclude that the molar and molecular weights have the same numerical values.

Gas volumes

As you know, all the substances around us can be in a solid, liquid or gaseous state of aggregation. For solids, the most common base measure is mass; for solids and liquids, volume. This is due to the fact that solids retain their shape and final dimensions, Liquid and gaseous substances do not have finite dimensions. The peculiarity of any gas is that between its structural units - molecules, atoms, ions - the distance is many times greater than the same distances in liquids or solids. For example, one mole of water under normal conditions occupies a volume of 18 ml - approximately the same amount fits in one tablespoon. The volume of one mole of finely crystalline table salt is 58.5 ml, and the volume of 1 mole of sugar is 20 times more than a mole of water. Even more space is required for gases. One mole of nitrogen under normal conditions occupies a volume 1240 times greater than one mole of water.

Thus, the volumes of gaseous substances differ significantly from the volumes of liquid and solid ones. This is due to the difference in distances between the molecules of substances in different aggregate states.

Normal conditions

The state of any gas is highly dependent on temperature and pressure. For example, nitrogen at a temperature of 20 ° C occupies a volume of 24 liters, and at 100 ° C at the same pressure - 30.6 liters. Chemists took into account this dependence, so it was decided to reduce all operations and measurements with gaseous substances to normal conditions. All over the world, the parameters of normal conditions are the same. For gaseous chemicals, these are:

• Temperature at 0°C.
• Pressure at 101.3 kPa.

For normal conditions, a special abbreviation is accepted - n.o. Sometimes this designation is not written in tasks, then you should carefully reread the conditions of the problem and bring the given gas parameters to normal conditions.

Calculation of the volume of 1 mol of gas

As an example, it is easy to calculate one mole of any gas, such as nitrogen. To do this, you first need to find the value of its relative molecular weight:

M r (N 2)= 2×14=28.

Since the relative molecular mass of a substance is numerically equal to the molar mass, then M(N 2) \u003d 28 g / mol.

Empirically, it was found that under normal conditions, the density of nitrogen is 1.25 g / liter.

Let's substitute this value into the standard formula known from the school physics course, where:

• V is the volume of gas;
• m is the mass of gas;
• ρ is the gas density.

We get that the molar volume of nitrogen under normal conditions

V (N 2) \u003d 25 g / mol: 1.25 g / liter \u003d 22.4 l / mol.

It turns out that one mole of nitrogen occupies 22.4 liters.

If you perform this operation with all existing gaseous substances, you can come to a surprising conclusion: the volume of any gas under normal conditions is 22.4 liters. Regardless of what kind of gas we are talking about, what is its structure and physico-chemical characteristics, one mole of this gas will occupy a volume of 22.4 liters.

The molar volume of a gas is one of the most important constants in chemistry. This constant makes it possible to solve many chemical problems associated with measuring the properties of gases under normal conditions.

Results

The molecular weight of gaseous substances is important for determining the amount of a substance. And if the researcher knows the amount of substance of a particular gas, he can determine the mass or volume of such a gas. For the same portion of a gaseous substance, the following conditions are simultaneously satisfied:

ν = m/ M ν= V/ V m.

If we remove the constant ν, we can equate these two expressions:

So you can calculate the mass of one portion of the substance and its volume, and the molecular weight of the substance under study becomes known. By applying this formula, the volume-mass ratio can be easily calculated. When reducing this formula to the form M = m V m / V, the molar mass of the desired compound will become known. In order to calculate this value, it is enough to know the mass and volume of the gas under study.

It should be remembered that a strict correspondence between the real molecular weight of a substance and that found by the formula is impossible. Any gas contains a lot of impurities and additives that make certain changes in its structure and affect the determination of its mass. But these fluctuations make changes to the third or fourth digit after the decimal point in the result found. Therefore, for school tasks and experiments, the results found are quite plausible.