Online molecular weight calculation. Calculation of molar mass

Instructions

The unit of molecular mass is 1/12 of the mass of an atom, which is conventionally taken to be 12. Molecular mass is the total relative atomic mass of all atoms in a molecule, and it is very easy to calculate.

And there is the simplest option if you know the substances. Take the periodic table, look at the molecular weight of each element included in. For example, for hydrogen it is equal to 1. – 16. And to find the molecular mass of the entire substance (take for example water, which consists of two hydrogen molecules and one), simply add up the masses of all the elements included in it. For water: M(H2O) = 2M(H)+M(O) = 2 1+16 = 18 a. e.m.

Useful advice

As you can see, finding the molecular weight is very simple. The main thing is not to confuse it with the molar mass of a substance - they are numerically equal to each other, but have different units of measurement and physical meaning.

Sources:

  • Determine the molecular formula of a hydrocarbon if

Video on the topic

Sources:

  • Experience as a teacher

In order to determine mass atom, find the molar mass of a monatomic substance using the periodic table. Then divide this mass by Avogadro's number (6.022 10^(23)). This will be the mass of the atom, in the units in which the molar mass was measured. The mass of a gas atom is found through its volume, which is easy to measure.

You will need

  • To determine the mass of an atom of a substance, take the periodic table, tape measure or ruler, pressure gauge, thermometer.

Instructions

Determination of atomic mass solid or To determine the mass of an atom of a substance, determine it (what it consists of). In the periodic table, find the cell that describes the corresponding element. Find the mass of one mole of this substance in grams per mole that is in this cell (this number corresponds to the mass of the atom in atomic mass units). Divide the molar mass of the substance by 6.022 10^(23) (Avogadro's number), the result will be the substance in grams. You can determine the mass of an atom in another way. To do this, multiply the atomic mass of the substance in atomic mass units taken from the periodic table by the number 1.66 10^(-24). Get the mass of one atom in grams.

Determining the mass of a gas atom If there is an unknown gas in the vessel, determine its mass in grams by weighing the empty vessel and the vessel with the gas, and find the difference in their masses. After this, measure the volume of the vessel using a ruler or tape measure, followed by calculations or other methods. Express the result in . Use a pressure gauge to measure the gas pressure inside the vessel, and measure its temperature with a thermometer. If the thermometer scale is graduated in Celsius, determine the temperature in Kelvin. To do this, add the number 273 to the temperature value on the thermometer scale.

Definition molar mass substances by molecular weight If the mass of one molecule in grams is known, multiply it by Avogadro's number 6.022 10^(23), which is equal to the number of molecules in one mole of the substance. The result will be substances in grams per mole. Having found it in the periodic table, if necessary, determine the substance itself, if it is simple (consists of a monatomic molecule).

Determining the molar mass of a gas Take a vessel of known volume and put a certain mass of gas into it. To do this, first pump the gas out of it and weigh it, and then pump the gas in and weigh it again. After this, measure the gas pressure in pascals using a thermometer and its temperature. To convert Celsius to , add 273 to them. In order to find the molar mass, transforming the Clapeyron-Mendeleev equation, take the value of the gas mass in grams, multiply it by the temperature and the number 8.31, which is universal. Sequentially divide the resulting number by the pressure in cubic meters (M=m 8.31 T/(P V)). The result will be the molar mass of the gas in grams per mole.

Video on the topic

Sources:

  • molar masses of substances table

In order to find the molar mass substances, determine its chemical formula and, using the periodic table of Mendeleev, calculate its molecular mass. It is numerically equal to the molar mass substances in grams per mole. If the mass of one molecule is known substances, convert it to grams and multiply by 6.022 10^23 (Avogadro's number). Molar mass gas can be found using the equation of state ideal gas.

You will need

  • Periodic table, pressure gauge, thermometer, scales.

Instructions

Determination of molar mass using a chemical formula. Find items in periodic table Mendeleev, which correspond to the atoms the molecule consists of substances. If a molecule substances monoatomic, then this will be his. If not, find the atomic mass of each element and add up these masses. The result will be molar mass substances, expressed in grams per mole.

Determination of molar mass substances by mass of one molecule. If the mass of one molecule is known, convert it to , then multiply by the number of molecules in one mole of any substances, which is 6.022 10^23 (Avogadro's number). Get molar mass substances in grams per mole.

Determination of the molar mass of a gas. Take a cylinder that can be hermetically sealed with a predetermined volume, which is converted to . Using a pump, pump out the gas from it and weigh the empty cylinder on the scale. Then fill it with a gas whose molar mass is measured. Weigh the cylinder again. The difference in the masses of an empty and filled with gas cylinder will be the mass of gas, express it in grams.
Using a pressure gauge, measure the gas pressure inside the cylinder; to do this, attach it to the gas injection hole. You can immediately use a cylinder with a built-in pressure gauge to quickly monitor pressure readings. Measure pressure in pascals.

Wait a while for the gas inside the cylinder to reach the temperature environment, and measure it with a thermometer. Convert the indicator from degrees Celsius to kelvins by adding the number 273 to the measured value.
Multiply the gas mass by the temperature and the universal gas constant (8.31). Sequentially divide the resulting number into pressure and volume values ​​(M=m 8.31 T/(P V)). The result will be the molar mass of the gas in grams per mole.

Sources:

  • determination of molar mass

Molecular weight is the molecular weight, which can also be called the mass value of a molecule. Molecular mass is expressed in atomic mass units. If we analyze the value of the molecular mass in parts, it turns out that the sum of the masses of all the atoms that make up the molecule represents its molecular mass mass. If we talk about units of measurement of mass, then predominantly all measurements are made in grams.

Instructions

Molecular mass itself is associated with the concept of a molecule. But it cannot be said that this condition can only be applied to those where the molecule, for example, hydrogen, is located separately. For cases where the molecules are not separately from the rest, but in close interconnection, all of the above conditions and definitions are also valid.

To begin with, to determine mass hydrogen, you will need -, which contains hydrogen and from which it can be easily isolated. This can be some kind of alcohol solution or other mixture, some of the components of which, under certain conditions, change their state and easily free the solution from its presence. Find a solution from which you can evaporate necessary or unnecessary substances using heat. This is the most easy way. Now decide whether you will evaporate a substance that you do not need or whether it will be hydrogen, a molecular mass which you plan to measure. If an unnecessary substance evaporates, it’s okay, so long as it’s not toxic. in the case of evaporation of the desired substance, you need equipment so that all the evaporation is preserved in the flask.

After you have separated everything unnecessary from the composition, start measuring. For this purpose, Avogadro's number is suitable for you. It is with its help that you can calculate the relative atomic and molecular mass hydrogen. Find all the options you need hydrogen which are present in any table, determine the density of the resulting gas, as it will be useful for one of the formulas. Then substitute all the results obtained and, if necessary, change the unit of measurement to , as mentioned above.

The concept of molecular weight is most relevant when it comes to polymers. It is for them that it is more important to introduce the concept of average molecular weight, due to the heterogeneity of the molecules included in their composition. Also by average molecular weight can be used to judge how high the degree of polymerization of a substance is.

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Molecular mass is the mass of a molecule of a substance, expressed in atomic units. The task often arises is to determine the molecular weight. How can this be done?

Instructions

If you know, then the problem can be solved in an elementary way. All you need is the Periodic Table. For example, you need to find the molecular weight of chloride. Write the formula of the substance: CaCl2. Using the periodic table, determine the atomic mass of each element included in its composition. For calcium it is equal to (rounded) 40, for (also rounded) – 35.5. Taking into account index 2, find: 40 + 35.5*2 = 111 a.m.u. (atomic mass units).

But what about in cases where the exact substance is unknown? Here you can act in different ways. One of the most effective (and at the same time simple) is the so-called “osmotic pressure method”. It is based on osmosis, which consists in the fact that solvent molecules can penetrate through a semi-permeable membrane, while solute molecules cannot penetrate through it. The magnitude of osmotic pressure can be measured, and it is directly proportional to the concentration of molecules of the substance under study (that is, their number per unit volume of solution).

Some people are familiar with the universal Mendeleev-Clapeyron equation, which describes the state of the so-called “ideal gas”. It looks like this: PVm = MRT. Van't Hoff's formula is very similar: P = CRT, where P is the osmotic pressure, C is the molar concentration of the solute, R is the universal gas constant, T is the temperature in Kelvin. This similarity is not accidental. It was as a result of Van't Hoff's work that it became clear that molecules (or ions) behave as if they were in a gas (with the same volume).

By measuring the osmotic pressure, you can simply calculate the molar concentration: C=P/RT. And then, knowing also the mass of the substance in the solution, find its molecular mass. Suppose it was experimentally established that the molar concentration of the already mentioned substance is 0.2. Moreover, the solution contains 22.2 grams of this substance. What is its molecular weight? 22.2/0.2 = 111 amu - exactly the same as the previously mentioned calcium chloride.

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Molecular weight substances is the mass of a molecule, expressed in atomic units and numerically equal to the molar mass. In calculations in chemistry, physics and engineering, the calculation of molar mass values ​​is often used various substances.

You will need

  • - periodic table;
  • - table of molecular weights;
  • - table of cryoscopic constant values.

Instructions

Find required element in the periodic table. Pay attention to the fractional numbers under its sign. For example, O has a numerical value in the cell equal to 15.9994. This is the atomic mass of the element. Atomic mass must be multiplied by the index of the element. The index shows how much of an element is contained in a substance.

If given complex, then multiply the atomic mass each element by its index (if there is one atom of a particular element and there is no index, then multiply by one) and add the resulting atomic masses. For example, water is calculated as follows - MH2O = 2 MH + MO ≈ 2·1+16 = 18 a. e.m.

Calculate molar mass using suitable formulas and equate it to molecular. Change the units of measurement from g/mol to amu. If pressure, volume, temperature are given according to absolute scale Kelvin and mass, calculate molar mass gas according to the Mendeleev-Cliperon equation M=(m∙R∙T)/(P∙V), in which M is the molecular () in amu, R is the universal gas constant.

Calculate molar mass according to the formula M=m/n, where m is the mass of any given substances, n - chemical quantity substances. Express the quantity substances through Avogadro's number n=N/NA or using volume n=V/VM. Substitute into the formula above.

Find the molecular mass gas, if only the value of its volume is given. To do this, take a sealed cylinder of known volume and pump out

In chemistry, they do not use the absolute masses of molecules, but use the relative molecular mass. It shows how many times the mass of a molecule is greater than 1/12 the mass of a carbon atom. This quantity is denoted by Mr.

The relative molecular weight is equal to the sum of the relative atomic masses atoms included in it. Let's calculate the relative molecular mass 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 by the number of its atoms in a water molecule:

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

Let's calculate the relative density carbon dioxide for hydrogen:

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

D(arc/hydr) = Mr(arc) : Mr(hydr) = 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 of ​​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 substance .

The amount of substance is indicated n. This quantitative characteristic portions 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 mole of a substance contains particles (for example, molecules). This number is called Avogadro's number. And if we add a unit of measurement to it - 1/mol, then it will be a physical quantity - Avogadro's constant, which is denoted N A.

Molar mass is measured in g/mol. The physical meaning of 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 molar volume and is denoted Vn.

At normal conditions(which is 0 °C and normal pressure- 1 atm. or 760 mm Hg. Art. or 101.3 kPa) molar volume is 22.4 l/mol.

Then the amount of gas substance at ground level is 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 zero level that will be occupied by carbon dioxide in an amount of 6 mol.

References

  1. Collection of problems and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry, 8th grade” / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M.: AST: Astrel, 2006. (p. 29-34)
  2. Ushakova O.V. Workbook in chemistry: 8th grade: to the textbook P.A. Orzhekovsky and others. “Chemistry. 8th grade” / 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 education institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005. (§§ 12, 13)
  4. Chemistry: inorg. chemistry: textbook. for 8th grade. general education institution / G.E. Rudzitis, F.G. Feldman. - M.: Education, OJSC “Moscow Textbooks”, 2009. (§§ 10, 17)
  5. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed.V.A. Volodin, Ved. scientific ed. I. Leenson. - M.: Avanta+, 2003.
  1. 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 No. 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 problems and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry, 8th grade” / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M.: AST: Astrel, 2006.

Most secondary school students consider chemistry to be one of the most difficult and unpleasant subjects for them. In fact, chemistry is no more complicated than physics or mathematics, and in some cases it is much more interesting than them. Many students, having not yet started studying chemistry, are already subconsciously afraid of it, having heard plenty of reviews from high school students about all the “horrors” of this subject and the “tyranny” of its teacher.

Another reason why chemistry is difficult is that it uses some specific key concepts and terms that the student has never encountered before and for which it is difficult to find an analogy in everyday life. Without an appropriate explanation from the teacher, these terms remain misunderstood by students, which complicates the entire subsequent process of studying chemistry.

One of these terms is the concept of the molar mass of a substance and the task of finding it. This is the basis of the fundamentals of the entire subject of chemistry.

What is the molar mass of a substance
The classic definition is that molar mass is the mass of one mole of a substance. Everything seems simple, but it remains unclear what “one moth” is and whether it has any connection with insects.

Mole- this is the amount of a substance that contains a certain number of molecules, to be precise, 6.02 ∙ 10 23. This number is called a constant or Avogadro's number.

All chemicals have different compositions and molecular sizes. Therefore, if you take one portion consisting of 6.02 ∙ 10 23 molecules, then different substances will have their own volume and mass of this portion. The mass of this portion will be the molar mass of a particular substance. Molar mass is traditionally denoted in chemistry by the letter M and has the dimensions g/mol and kg/mol.

How to find the molar mass of a substance
Before you begin calculating the molar mass of a substance, you need to clearly understand the key concepts associated with it.

  1. Molar mass of a substance is numerically equal to the relative molecular mass if the structural units of the substance are molecules. The molar mass of a substance can also be equal to the relative atomic mass if the structural units of the substance are atoms.
  2. Relative atomic mass shows how many times the mass of an atom of a particular chemical element is greater than a predetermined constant value for which the mass of 1/12 of a carbon atom is taken. The concept of relative atomic mass is introduced for convenience, since it is difficult for a person to operate with such small numbers as the mass of one atom.
  3. If a substance consists of ions, then in this case we talk about its relative formula mass. For example, the substance calcium carbonate CaCO 3 consists of ions.
  4. The relative atomic mass of a substance of a particular chemical element can be found in the periodic table. For example, for the chemical element carbon, the relative atomic mass is 12.011. Relative atomic mass has no units of measurement. The molar mass of carbon will be equal, as mentioned above, to the relative atomic mass, but at the same time it will have units of measurement. That is, the molar mass of carbon will be 12 g/mol. This means that 6.02 ∙ 10 23 carbon atoms will weigh 12 grams.
  5. Relative molecular mass can be found as the sum of the atomic masses of all chemical elements that form a molecule of a substance. Let's consider this using the example of carbon dioxide, or as everyone else calls it carbon dioxide, which has the formula CO 2.

    A carbon dioxide molecule contains one carbon atom and two oxygen atoms. Using the periodic table, we find that the relative molecular mass of carbon dioxide will be equal to 12 + 16 ∙ 2 = 44 g/mol. This is exactly the mass that a portion of carbon dioxide will have, consisting of 6.02 ∙ 10 23 molecules.

  6. The classic formula for finding the molar mass of a substance in chemistry is as follows:

    M = m/n



    where, m is the mass of the substance, g;
    n is the number of moles of a substance, that is, how many portions of 6.02 ∙ 10 23 molecules, atoms or ions it contains, moles.

    Accordingly, the number of moles of a substance can be determined by the formula:

    n = N/Na



    where, N – total number atoms or molecules;
    N a is Avogadro’s number or constant, equal to 6.02 ∙ 10 23.

    Most problems in finding the molar mass of a substance in chemistry are based on these two formulas. Using two related relationships is unlikely to be an insurmountable difficulty for most people. The main thing is to understand the essence of basic concepts such as mole, molar mass and relative atomic mass, and then solving problems in chemistry will not cause you any difficulties.

As aid to find the molar mass of a substance and solve the majority typical tasks in chemistry related to it, we suggest using our calculator. It's very easy to use. Below the line chemical formula of the compound in the drop-down list, select the first chemical element included in the formula of the chemical substance. In the box next to the list, enter the number of atoms of the chemical substance. If the number of atoms is one, leave the field blank. If you need to add a second and subsequent elements, then press the green plus and repeat the above action until you get full formula substances. Check the correctness of the input using the updated chemical formula of the compound. Click the button Calculate to obtain the molar mass of the desired substance.

To solve most typical chemistry problems, you can also add one of the known conditions: the number of molecules, the number of moles, or the mass of the substance. Below the button Calculate after clicking it, a complete solution to the problem will be given based on the entered initial data.

If there are brackets in the chemical formula of a substance, then expand them by adding the corresponding index to each element. For example, instead of the classic formula for calcium hydroxide Ca(OH) 2, use the following formula for the chemical substance CaO 2 H 2 in the calculator.

EPIGRAPH
And I will be like a moth for Ephraim...
Hosea 5:12

Knowing the molecular mass of the substance and the molarity of the solution, you can calculate the amount of dissolved substance and mass fraction dissolved substance.

You can calculate the molecular mass using the “Molecular Mass Calculator” (opens in a new tab), or by taking the data yourself (atomic mass is the number under the symbol of an element on the periodic table)

In practical cases, the molarity of a solution is given in multiples - milli, nano, etc. Below is a table of submultiple units recommended in the SI system

Terminology

A mole is a unit of measurement for the amount of a substance; the outdated name is a gram molecule. The mole is one of the seven base units in the SI system. The exact formulation of the concept “mole” is as follows:
Explanatory dictionary of medicine

MOLARITY- (molarity) the concentration of a solution, expressed in terms of the mass (in grams) of the dissolved substance contained in a liter of solution, in relation to its molecular weight (in other words, molarity is the number of moles contained in one liter of solution)

MOLALITY- (molality) the number of moles of dissolved substance in 1000 g of solvent. Measured in moles per kg, the expression "molality" is also common. Thus, a solution with a concentration of 0.5 mol/kg is called 0.5-mol.
Despite the similarity of names, molar concentration and molality are different quantities. Unlike molar concentration, when expressing concentration in molality, the calculation is based on the mass of the solvent, and not on the volume of the solution. As a result, molality does not depend on temperature. A mole is the amount of substance in a system containing the same number of structural elements as there are atoms in carbon-12 weighing 0.012 kg. When using a mole, the structural elements must be specified and can be atoms, molecules, ions, electrons and other particles or specified groups of particles.
The number of specified structural elements in one mole of a substance is called Avogadro's number. Avogadro's number is approximately 6.022×10 23 mol -1

From the above it follows that the molar mass of carbon-12 is 12 g/mol. To determine the molar mass of a substance, you should calculate its molecular mass, which is equal to the sum of the masses of the atoms that make up the molecule. For example, the NaCl salt has a sodium atom mass of approximately 23, a chlorine atom mass of slightly more than 35, for a total molecular mass of approximately 23+35=58, and a molar mass of 58 g/mol, respectively. Molar mass is necessary to calculate the content of substances in solutions, the concentration of which is given in the form molarity of solution. The definition of molarity is given in the box.

For example, according to the definition, a one-molar solution of sodium chloride NaCl is a solution whose 1 liter contains 1 mole (which, as we have already calculated, is 58 grams) of NaCl. Accordingly, a 0.1-molar solution will contain 5.8 g of NaCl per liter. Often molarity is denoted as M - 1M - 1-molar solution, 0.1M - 0.1-molar solution, etc.

Another case. You need to prepare 40 g of 0.1 mol NaCl solution. From the definition of molality it follows that 1 kg of solvent will require 5.844 NaCl. Let’s say that 40 g of solution requires X grams of NaCl. Then you will need (40-X) grams of solvent. Let's make a proportion and resolve it relative to the unknown X. We get X=40*0.1*58.44/1000 = 0.2324. Therefore, to obtain 40 g of 0.1-mol NaCl, 0.2324 g of salt should be dissolved in 40-0.2324 = 39.7676 g of solvent.
You can carry out this calculation in the Android application on the "Molality" tab

In practical and theoretical chemistry there are and have practical significance two concepts such as molecular (it is often replaced by the concept of molecular weight, which is not correct) and molar mass. Both of these quantities depend on the composition of a simple or complex substance.

How to determine or molecular? Both of these physical quantities cannot (or almost cannot) be found by direct measurement, for example, by weighing a substance on a scale. They are calculated based on chemical formula compounds and atomic masses of all elements. These quantities are numerically equal, but differ in dimension. expressed in atomic mass units, which are a conventional quantity and are designated a. e.m., as well as another name - “dalton”. The units of molar mass are expressed in g/mol.

The molecular masses of simple substances, the molecules of which consist of one atom, are equal to their atomic masses, which are indicated in the periodic table of Mendeleev. For example, for:

  • sodium (Na) - 22.99 a. e.m.;
  • iron (Fe) - 55.85 a. e.m.;
  • sulfur (S) - 32.064 a. e.m.;
  • argon (Ar) - 39.948 a. e.m.;
  • potassium (K) - 39.102 a. e.m.

Also, the molecular weights of simple substances, the molecules of which consist of several atoms of a chemical element, are calculated as the product of the atomic mass of the element by the number of atoms in the molecule. For example, for:

  • oxygen (O2) - 16. 2 = 32 a. e.m.;
  • nitrogen (N2) - 14.2 = 28 a. e.m.;
  • chlorine (Cl2) - 35. 2 = 70 a. e.m.;
  • ozone (O3) - 16. 3 = 48 a. e.m.

Molecular masses are calculated by summing the product of the atomic mass and the number of atoms for each element included in the molecule. For example, for:

  • (HCl) - 2 + 35 = 37 a. e.m.;
  • (CO) - 12 + 16 = 28 a. e.m.;
  • carbon dioxide (CO2) - 12 + 16. 2 = 44 a. e.m.

But how to find the molar mass of substances?

This is not difficult to do, since it is the mass of a unit amount of a particular substance, expressed in moles. That is, if the calculated molecular mass of each substance is multiplied by a constant value equal to 1 g/mol, then its molar mass will be obtained. For example, how do you find the molar mass (CO2)? It follows (12 + 16.2).1 g/mol = 44 g/mol, that is, MCO2 = 44 g/mol. For simple substances, molecules that contain only one atom of the element, this indicator, expressed in g/mol, numerically coincides with the atomic mass of the element. For example, for sulfur MS = 32.064 g/mol. How to find molar mass simple substance, the molecule of which consists of several atoms, can be considered using oxygen as an example: MO2 = 16. 2 = 32 g/mol.

Examples have been given here for specific simple or complex substances. But is it possible and how to find the molar mass of a product consisting of several components? Like the molecular mass, the molar mass of a multicomponent mixture is an additive quantity. It is the sum of the products of the molar mass of the component and its share in the mixture: M = ∑Mi. Xi, that is, both the average molecular and average molar mass can be calculated.

Using the example of air, which contains approximately 75.5% nitrogen, 23.15% oxygen, 1.29% argon and 0.046% carbon dioxide (the remaining impurities, which are contained in smaller quantities, can be neglected): Mair = 28. 0.755 + 32. 0.2315 + 40 . 0.129 + 44 . 0.00046 = 29.08424 g/mol ≈ 29 g/mol.

How to find the molar mass of a substance if the accuracy of determining the atomic masses indicated in the periodic table is different? For some elements it is indicated with an accuracy of tenths, for others with an accuracy of hundredths, for others to thousandths, and for such elements as radon - to whole ones, for manganese to ten-thousandths.

When calculating the molar mass, it makes no sense to carry out calculations with greater accuracy than to tenths, since they have practical application when the purity of the chemicals or reagents themselves will introduce a large error. All these calculations are approximate. But where chemists require greater accuracy, appropriate corrections are made using certain procedures: the titer of the solution is established, calibrations are made using standard samples, etc.



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