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Number of items Chemical dictionary or chemistry reference book

In everyday life, we very rarely come across the question of finding a number substances, except in the case of jointly solving chemistry problems with a schoolchild.

Instructions

1. As we know from the original chemistry course, the number substances(n) is measured in moles and determines the number of structural units substances(electrons, protons, atoms, molecules, etc.) contained in a given mass (or volume).

2. This physical quantity is convenient to use when describing chemical reactions, since molecules interact in multiples of an integer, regardless of their mass (indicators in chemical equations reflect the ratio between the numbers of substances that reacted).

3. Considering that in real skills the number of molecules (atoms) substances too large, it is inconvenient to use in calculations. Instead, it is customary to express the number of molecules in moles.

4. That. number substances in one mole is numerically equal to Avogadro’s continuous (NA = 6.022 141 79(30)?1023 mol?1). By rounding we get NA = 6.02.1023

5. The uniqueness of this continuous line is that if the number of molecules is N = NA, then their weight in amu. (nuclear mass units) is numerically equal to their weight in grams. In other words, in order to translate a.u.m. into grams, you need to simply multiply them by NA.6.02.1023 *a.m.u. = 1 g

6. Such fractions of molecules (atoms) substances called a mole substances. So, mole is a measure of number substances. 1 mole is equal to 6.02.1023 structural particles of this substances .

7. Mass of one mole substances called molar mass (M). Molar mass is determined by multiplying the molecular mass substances to continuous Avogadro (NA).

8. Molecular mass is found by adding the nuclear mass of all the atoms that make up the molecule of a given substances. Let's say, for water molecules (H2O) it will be: 1*2+16=18 gmol.

9. It turns out the number substances calculated by the formula: n = mM, where m is mass substances.The number of molecules is determined: N = NA*n, and for gases: V = Vm *n, where Vm is the molar volume of the gas, equal to 22.4 lmol (under typical conditions).

10. We obtain the general relation:n = mM = NNA = VVm

Video on the topic

Let's talk about what is the amount of a substance, how this term is used in natural science subjects. Since quantitative relationships in chemistry and physics are given serious attention, it is important to know the physical meaning of all quantities, their units of measurement, and areas of application.

Designation, definition, units of measurement

In chemistry, quantitative relationships are of particular importance. To carry out calculations using equations, special quantities are used. In order to understand what an amount of substance is in chemistry, let’s give the term a definition. which characterizes the number of similar structural units (atoms, ions, molecules, electrons) present in a substance. To understand what the amount of a substance is, we note that this quantity has its own designation. When carrying out calculations that involve the use of this value, use the letter n. Units of measurement - mole, kmol, mmol.

Value value

Eighth-graders who do not yet know how to write chemical equations do not know what an amount of a substance is or how to use this quantity in calculations. After becoming acquainted with the law of constancy of the mass of substances, the meaning of this quantity becomes clear. For example, in the combustion reaction of hydrogen in oxygen, the ratio of reactants is two to one. If the mass of hydrogen that entered the process is known, it is possible to determine the amount of oxygen that took part in the chemical reaction.

The use of formulas for the amount of a substance allows you to reduce the ratio between the initial reagents and simplify calculations. What is the amount of a substance in chemistry? In mathematical terms, these are the stereochemical coefficients put into the equation. They are used to carry out certain calculations. Since it is inconvenient to count the number of molecules, they use Mole. Using, you can calculate that 1 mol of any reagent includes 6 1023 mol −1.

Computations

Do you want to understand what the amount of a substance is? This quantity is also used in physics. It is needed where calculations of pressure and volume of gaseous substances are carried out according to the Mendeleev-Clapeyron equation. To perform any quantitative calculations, the concept is used

By it we mean the mass that corresponds to one mole of a specific chemical substance. The molar mass can be determined through (their sum, taking into account the number of atoms in the molecule) or determined through the known mass of the substance, its quantity (mol).

Not a single problem in a school chemistry course related to calculations using an equation is complete without the use of such a term as “amount of substance.” Having mastered the algorithm, you can cope not only with ordinary software calculations, but also with complex Olympiad tasks. In addition to calculations through the mass of a substance, it is also possible, using this concept, to carry out calculations through the molar volume. This is relevant in cases where gaseous substances take part in the interaction.

The algorithm for finding the amount of a substance is quite simple; it can be useful for simplifying the solution. Also become familiar with another concept that you will need to calculate the amount of a substance: molar mass, or the mass of one mole of an individual atom of an element. Already from the definition it is noticeable that it is measured in g/mol. Use a standard table that contains molar mass values for some elements.

What is the amount of a substance and how is it determined?

In this case, the mass of hydrogen participating in the reaction is approximately 8 times less than the mass of oxygen (since the atomic mass of hydrogen is approximately 16 times less than the atomic mass of oxygen). When the heat of reaction is written as it is in this equation, it is assumed that it is expressed in kilojoules per stoichiometric unit ("mole") of the reaction of the written equation. Heats of reactions are always tabulated per mole of compound formed.

In order to understand what an amount of substance is in chemistry, let’s give the term a definition. To understand what the amount of a substance is, we note that this quantity has its own designation. Eighth-graders who do not yet know how to write chemical equations do not know what an amount of a substance is or how to use this quantity in calculations. After becoming acquainted with the law of constancy of the mass of substances, the meaning of this quantity becomes clear. By it we mean the mass that corresponds to one mole of a specific chemical substance. Not a single problem in a school chemistry course related to calculations using an equation is complete without the use of such a term as “amount of substance.”

2.10.5. Establishing the formula
chemical compound by its elemental
composition

We get the true formula of the substance: C2H4 - ethylene. 2.5 mol hydrogen atoms.

Denoted as Mr. It is found according to the periodic table - it is simply the sum of the atomic masses of a substance. The law of conservation of mass - the mass of substances that enter into a chemical reaction is always equal to the mass of the formed substances. That is, if in the problem we are given normal conditions, then, knowing the number of moles (n), we can find the volume of the substance. Basic formulas for solving problems in chemistry These are formulas.

Where in the Periodic Table are the elements corresponding to simple substances and metals? From the sentences below, write down the numbers corresponding to metals in one column, and the numbers corresponding to non-metals in another column. To obtain a certain amount of a product (in a chemical laboratory or in a factory), it is necessary to take strictly defined quantities of starting substances. Chemists, conducting experiments, noticed that the composition of the products of some reactions depends on the proportions in which the reacting substances were taken. How many atoms will there be in this mass?

N is the number of structural links, and NA is Avogadro’s constant. Avogadro's constant is a proportionality coefficient that ensures the transition from molecular to molar relationships. V is the gas volume (l), and Vm is the molar volume (l/mol).

The unit of measurement for the quantity of a substance in the International System of Units (SI) is the mole. Definition. Write down the formula for calculating this energy and the names of the physical quantities included in the formula. This question belongs to the section “10-11″ grades.

Designation, definition, units of measurement

In chemistry, quantitative relationships are of particular importance. To carry out calculations using equations, special quantities are used. In order to understand what an amount of substance is in chemistry, let’s give the term a definition. This is a physical quantity that characterizes the number of similar structural units (atoms, ions, molecules, electrons) present in a substance. To understand what the amount of a substance is, we note that this quantity has its own designation. When carrying out calculations that involve the use of this value, use the letter n. Units of measurement – mole, kmol, mmol.

Value value

The use of formulas for the amount of a substance allows you to reduce the ratio between the initial reagents and simplify calculations. What is the amount of a substance in chemistry? In mathematical terms, these are the stereochemical coefficients put into the equation. They are used to carry out certain calculations. Since it is inconvenient to count the number of molecules, they use Mole. Using Avogadro's number, we can calculate that 1 mol of any reagent contains 6 1023 mol−1.

Computations

Do you want to understand what the amount of a substance is? This quantity is also used in physics. It is needed in molecular physics, where calculations of pressure and volume of gaseous substances are carried out using the Mendeleev-Clapeyron equation. To perform any quantitative calculations, the concept of molar mass is used.

By it we mean the mass that corresponds to one mole of a specific chemical substance. The molar mass can be determined through relative atomic masses (their sum taking into account the number of atoms in the molecule) or determined through the known mass of a substance, its quantity (mol).

Test on the topic “Basic chemical concepts”

(Several correct answers are possible)

1. The volume fractions of nitrogen and ethylene (C 2 H 4) in the mixture are the same. Mass fractions of gases in the same mixture:

a) are the same; b) more for nitrogen;

c) more for ethylene; d) depend on pressure.

2. Mass of 10 m3 of air at no. equal (in kg):

a) 20.15; b) 16.25; c) 14.50; d) 12.95.

3. 465 mg of calcium phosphate contains the following numbers of cations and anions, respectively:

a) 2.7 1021 and 1.8 1021; b) 4.5 1020 and 3.0 1020;

c) 2.7 1025 and 1.8 1025; d) 1.2 1025 and 1.1 1025.

4. The number of moles of water molecules contained in 18.06 1022 water molecules is equal to:

a) 0.667; b) 0.5; c) 0.3; d) 12.

5. Of the following substances, simple ones include:

a) sulfuric acid; b) sulfur;

c) hydrogen; d) bromine.

6. An atom with a mass of 2.66 10–26 kg corresponds to the element:

a) sulfur; b) magnesium;

c) oxygen; d) zinc.

7. A particle that is chemically divisible is:

a) proton; b) molecule;

c) positron; d) atom.

8. Carbon is described as a simple substance in the statement:

a) carbon is distributed in nature in the form of an isotope with a mass number of 12;

b) carbon during combustion, depending on conditions, can form two oxides;

c) carbon is part of carbonates;

d) carbon has several allotropic modifications.

9. The valency of an atom is:

a) the number of chemical bonds formed by a given atom in a compound;

b) oxidation state of the atom;

c) the number of electrons given or received;

d) the number of electrons missing to obtain the electron configuration of the nearest inert gas.

10. Which of the following is a chemical phenomenon?

a) Ice melting; b) electrolysis of water;

c) sublimation of iodine; d) photosynthesis.

Key to the test

Problems to determine the amount of a substance using basic formulas

(According to known mass, volume, number of structural units)

Level A

1. How many chromium atoms are contained in 2 g of potassium dichromate?

Answer. 8,19 1021.

2. Which atoms - iron or magnesium - are more numerous in the earth's crust and by how many times? The mass fraction of iron in the earth's crust is 5.1%, magnesium - 2.1%.

Answer. There are more iron atoms than magnesium atoms by 1.04 times.

3. What volume (in l) does:

a) 1.5 1022 fluorine molecules;

b) 38 g of fluorine;

c) 1 1023 oxygen molecules?

Answer. a) 0.558; b) 22.4; c) 3.72.

4. Find the mass (in g) of one molecule: a) water;

b) hydrofluoric acid; c) nitric acid.

Answer. a) 2.99 10–23; b) 3.32 10–23; c) 1.046 10–22.

5. How many moles of substance are contained in:

a) 3 g boron trifluoride;

b) 20 l of hydrogen chloride;

c) 47 mg phosphorus pentoxide;

d) 5 ml of water?

Answer. a) 0.044; b) 0.893; c) 0.33; d) 0.28.

6. A metal weighing 0.4 g contains 6.02 1021 atoms. Identify metal.

Given:

N= 6.02 1021 atoms, m(M) = 0.4 g.

Find:

metal.

Solution

The desired metal is Ca.

Answer. Calcium.

7. On one pan of the scale there is a certain amount of copper shavings, on the other pan of the scale there is a portion of magnesium containing 75.25 1023 magnesium atoms, while the scales are in a state of equilibrium. What is the mass of a portion of copper filings?

Answer. 300 g.

8. Calculate the amount of calcium contained in 62 kg of calcium phosphate.

Answer. 600 mol.

9. In a sample of a copper-silver alloy, the number of copper atoms is equal to the number of silver atoms. Calculate the mass fraction of silver in the alloy.

Answer. 62.8%.

10. Find the mass of one structural unit of table salt NaCl.

Answer. 9.72 10–23 G.

11. Find the molar mass of a substance if the mass of one molecule is 5.31 10–23 G.

Answer. 32 g/mol.

12. Find the molar mass of the gaseous substance, if 112 ml of it at ambient conditions. have a mass of 0.14 g.

Answer. 28 g/mol.

13. Find the molar mass of the gaseous substance if at no. 5 g of this substance occupy a volume of 56 liters.

Answer. 2 g/mol.

14. Which contains more hydrogen atoms: 6 g of water or 6 g of ethyl alcohol?

Answer. In 6 g of ethyl alcohol.

15. How many grams of calcium are contained in 1 kg of gypsum?

Answer. 232.5 g.

16. Calculate in Mohr's salt, which has the formula Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O, mass fractions (%):

a) nitrogen; b) water; c) sulfate ions.

Answer. a) 7.14; b) 27.55; c) 48.98.

Level B

1. To 100 g of a 20% hydrochloric acid solution, add 100 g of a 20% sodium hydroxide solution. How many structural units of NaCl salt and water molecules does the resulting solution contain?

Answer. 5.65 1024 water molecules and 3.01 1023 structural units of NaCl salt.

2. Determine the mass of 8.2 liters of a gas mixture of helium, argon and neon (n.u.), if for one helium atom in this mixture there are two neon atoms and three argon atoms.

Answer. 10 g.

3. In what ratio by mass should 2% solutions of potassium chloride and sodium sulfate be mixed so that the final solution contains four times more sodium ions by mass than potassium ions?

Answer. 6.46:1.

4. The density of liquid oxygen at a temperature of –183 °C is 1.14 g/cm3 . How many times will the volume of oxygen increase when it passes from a liquid state to a gaseous state at zero conditions?

Answer. 798 times.

5. What is the mass fraction of sulfuric acid in a solution in which the numbers of hydrogen and oxygen atoms are equal?

Solution

Solution H 2 SO 4 consists of H 2 SO 4 and H 2 O. Let (H 2 SO 4 ) = x mol, then (H in H 2 SO 4 ) = 2xmol;

(H 2 O) = y mol, then (H in H 2 O) = 2y mol.

Amount (H in solution) = (2x + 2y) mol.

Let us determine the amount of atomic oxygen substance:

(O to H 2 SO 4 ) = 4x mol, (O in H 2 O) = y mol.

Amount (O in solution) = (4x + y) mol.

Since the numbers of O and H atoms are equal, then 2x + 2y = 4x + y.

Solving the equation, we get: 2x = y. If

Determination of the equivalent amount of matter from a secondary cloud

Determination of the equivalent amount of matter from the primary cloud

Determination of quantitative characteristics of the release

Forecasting the depths of SDYAV infection zones

Initial data for predicting the scale of SDYAV infection

1. The total number of chemically active substances at the facility and data on the placement of their reserves in tanks and process pipelines.

2. The amount of explosive substances released into the atmosphere and the nature of their spill on the underlying surface (“free”, “into a pan” or “embankment”).

3. The height of the pallet or bund of storage tanks.

4. Meteorological conditions: air temperature, wind speed (at the height of the weather vane), degree of vertical air stability.

When predicting in advance the scale of contamination in the event of industrial accidents, it is recommended to take as initial data: the value of the release of toxic substances ( Q about ) – its content in the maximum volume capacity (technological, storage, transport, etc.), meteorological conditions – the degree of vertical stability of the air, wind speed and temperature. To predict the scale of contamination immediately after an accident, specific data must be taken on the amount of ejected (spilled) SDYAS, the time that has passed since the accident, and the nature of the spill on the underlying surface. The external boundaries of the SDYV infection zone are calculated based on the threshold toxodose during inhalation exposure to the human body.

Calculation of the depth of the SDYAV contamination zone is carried out using the data given in Tables 11-13; the value of the depth of the contamination zone during an emergency release (spill) of SDYAV is determined according to Table 8 depending on the quantitative characteristics of the release and wind speed.

Quantitative characteristics of the release of SDYAV for calculating the scale of infection are determined by their equivalent values.

For compressed gases, the equivalent amount of substance is determined only from the primary cloud.

For liquefied SDYAS, the boiling point of which is higher than the ambient temperature, the equivalent amount of the substance is determined only by the secondary cloud. For SDYAS, the boiling point of which is lower than the ambient temperature, the equivalent amount of the substance is determined by the primary and secondary cloud.

The equivalent amount of matter in the primary cloud (in tons) is determined by the formula

Where K 1 - coefficient depending on the storage conditions of SDYAV, table 12;

K 3- coefficient equal to the ratio of the threshold toxodose of chlorine to the threshold toxodose of another SDYAV, table 12;

K 5- coefficient taking into account the degree of vertical air stability (assumed equal for inversion - 1; for isotherm - 0.23; for convection - 0.08), table 11;

K 7- coefficient taking into account the influence of air temperature, table 12;

Qo- the amount of substance released (spilled) during an accident, i.e.

The equivalent amount of matter in the secondary cloud is calculated using the formula

Where K 2 – coefficient depending on the physicochemical properties of SDYAV, table 12;

K 4– coefficient taking into account wind speed, table 13;

K 6– coefficient depending on the time elapsed after the start of the accident; N , K 6 determined after calculating the duration t And the time of evaporation of the substance, at N = t I;

h– thickness of the SDYAV layer, m;

d– SDYAV density, t/m3, table 12.

The height of the spilled liquid during a free spill is assumed to be 0.05 m. If there is a pallet or the container is diked, then

where H is the height of the pallet or embankment.

The evaporation time of SDYAV is calculated by the formula

, (h). (4)

Table 11

Determining the degree of vertical air stability based on the weather forecast

NOTE:

1. Designation: in – inversion; from– isothermia; To– convection, letters in brackets - with snow cover.

2. Under the term "morning" refers to the period of time within two hours after sunrise; under the term "evening"- within two hours after sunset.

The period from sunrise to sunset minus two morning hours - day, and the period from sunset to sunrise minus two evening hours - night.

3. Wind speed and the degree of vertical air stability are taken into account in calculations at the time of accidents.

Table 9

Table 13

The value of coefficient K4 depending on wind speed

Wind speed, m/s
K 4	1,0	1,33	1,67	2,0	2,34	2,67	3,0	3,34	3,67	4,0	5,68

Formula for finding the amount of a substance?

Irina Ruderfer

The quantity of a substance is a physical quantity that characterizes the number of similar structural units contained in a substance. Structural units refer to any particles that make up a substance (atoms, molecules, ions, electrons or any other particles). The SI unit for measuring the amount of a substance is the mole.

[edit] Application
This physical quantity is used to measure macroscopic quantities of substances in cases where, for a numerical description of the processes being studied, it is necessary to take into account the microscopic structure of the substance, for example, in chemistry, when studying electrolysis processes, or in thermodynamics, when describing the equations of state of an ideal gas.

When describing chemical reactions, the amount of a substance is a more convenient quantity than mass, since molecules interact regardless of their mass in quantities that are multiples of whole numbers.

For example, the combustion reaction of hydrogen (2H2 + O2 → 2H2O) requires twice as much hydrogen as oxygen. In this case, the mass of hydrogen participating in the reaction is approximately 8 times less than the mass of oxygen (since the atomic mass of hydrogen is approximately 16 times less than the atomic mass of oxygen). Thus, using the quantity of a substance makes it easier to interpret reaction equations: the relationship between the quantities of reacting substances is directly reflected by the coefficients in the equations.

Since it is inconvenient to use the number of molecules directly in calculations, because this number in real experiments is too large, instead of measuring the number of molecules “in pieces,” they are measured in moles. The actual number of units of a substance in 1 mole is called Avogadro's number (NA = 6.022 141 79(30) × 1023 mol-1 (more correctly, Avogadro's constant, since, unlike a number, this quantity has units of measurement).

The amount of a substance is denoted by the Greek letter ν (nu) or, simplified, by the Latin letter n (en). To calculate the amount of a substance based on its mass, the concept of molar mass is used: ν = m / M where m is the mass of the substance, M is the molar mass of the substance. Molar mass is the total mass of one mole of molecules of a given substance. The molar mass of a substance can be obtained by multiplying the molecular mass of this substance by the number of molecules in 1 mole - by Avogadro's number.

According to Avogadro's law, the amount of a gaseous substance can also be determined based on its volume: ν = V / Vm - where V is the volume of gas (under normal conditions), Vm is the molar volume of gas at N.U., equal to 22.4 l/ mole.

Thus, a valid formula combines basic calculations with the amount of substance:

Diana Tangatova

designation: mole, international: mol - a unit of measurement of the amount of a substance. Corresponds to the amount of a substance that contains NA particles (molecules, atoms, ions). Therefore, a universal value was introduced - the number of moles. A frequently encountered phrase in problems is “… a mole of substance was obtained”

NA = 6.02 1023

NA is Avogadro's number. Also “a number by agreement.” How many atoms are there in the tip of a pencil? About a thousand. It is not convenient to operate with such quantities. Therefore, chemists and physicists around the world agreed - let’s designate 6.02 × 1023 particles (atoms, molecules, ions) as 1 mole of a substance.

1 mole = 6.02 1023 particles

This was the first of the basic formulas for solving problems.

Molar mass of a substance

The molar mass of a substance is the mass of one mole of the substance.

Denoted as Mr. It is found according to the periodic table - it is simply the sum of the atomic masses of a substance.

For example, we are given sulfuric acid - H2SO4. Let's calculate the molar mass of a substance: atomic mass H = 1, S-32, O-16.
Mr(H2SO4)=1 2+32+16 4=98 g\mol.

The second necessary formula for solving problems is

Substance mass formula:

That is, to find the mass of a substance, you need to know the number of moles (n), and we find the molar mass from the Periodic Table.

The law of conservation of mass - the mass of substances that enter into a chemical reaction is always equal to the mass of the formed substances.

If we know the mass(es) of the substances that reacted, we can find the mass(es) of the products of that reaction. And vice versa.

The third formula for solving problems in chemistry is

Volume of substance:

Basic formulas for solving chemistry problems

Where did the number 22.4 come from? From Avogadro's law:

Equal volumes of different gases taken at the same temperature and pressure contain the same number of molecules.
According to Avogadro's law, 1 mole of an ideal gas under normal conditions (n.s.) has the same volume Vm = 22.413 996(39) l

That is, if in the problem we are given normal conditions, then, knowing the number of moles (n), we can find the volume of the substance.

So, the basic formulas for solving problems in chemistry

NotationFormulaAvogadro's numberNA
6.02 1023 particles
Amount of substance n (mol)
n=m\Mr
n=V\22.4 (l\mol)
Mass of substancem (g)
m=n Mr
Substance volumeM (l)
V=n 22.4 (l\mol)

Or here’s another handy sign:

Basic formulas for solving chemistry problems
These are formulas. Often, to solve problems, you first need to write the reaction equation and (required!) arrange the coefficients - their ratio determines the ratio of moles in the process.

Formula to find the number of moles using mass and molar mass. Please give me the formula for the exam tomorrow!!!

Ekaterina of Kurgan

Mole, molar mass

Chemical processes involve the smallest particles - molecules, atoms, ions, electrons. The number of such particles even in a small portion of a substance is very large. Therefore, in order to avoid mathematical operations with large numbers, a special unit, the mole, is used to characterize the amount of a substance participating in a chemical reaction.

A mole is a quantity of a substance that contains a certain number of particles (molecules, atoms, ions) equal to Avogadro’s constant
Avogadro's constant NA is defined as the number of atoms contained in 12 g of the 12C isotope:
Thus, 1 mole of a substance contains 6.02 1023 particles of this substance.

Based on this, any amount of a substance can be expressed by a certain number of moles ν (nu). For example, a sample of a substance contains 12.04 1023 molecules. Therefore, the amount of substance in this sample is:
In general:

Where N is the number of particles of a given substance;
NA is the number of particles that contains 1 mole of a substance (Avogadro’s constant).
Molar mass of a substance (M) is the mass that 1 mole of a given substance has.
This quantity, equal to the ratio of the mass m of a substance to the amount of substance ν, has the dimension kg/mol or g/mol. The molar mass, expressed in g/mol, is numerically equal to the relative relative molecular mass Mr (for substances of atomic structure - the relative atomic mass Ar).
For example, the molar mass of methane CH4 is determined as follows:

Мr(CH4) = Ar(C) + 4 Ar(H) = 12+4 =16
M(CH4) = 16 g/mol, i.e. 16 g of CH4 contain 6.02 1023 molecules.
The molar mass of a substance can be calculated if its mass m and quantity (number of moles) ν are known, using the formula:
Accordingly, knowing the mass and molar mass of a substance, you can calculate the number of its moles:

Or find the mass of a substance by the number of moles and molar mass:
m = ν M
It should be noted that the value of the molar mass of a substance is determined by its qualitative and quantitative composition, i.e., it depends on Mr and Ar. Therefore, different substances with the same number of moles have different masses m.

Example
Calculate the masses of methane CH4 and ethane C2H6, taken in an amount of ν = 2 mol each.

Solution
The molar mass of methane M(CH4) is 16 g/mol;
molar mass of ethane M(C2H6) = 2 12 + 6 = 30 g/mol.
From here:
m(CH4) = 2 mol 16 g/mol = 32 g;
m(C2H6) = 2 mol 30 g/mol = 60 g.
Thus, a mole is a portion of a substance containing the same number of particles, but having different masses for different substances, since the particles of a substance (atoms and molecules) are not the same in mass.
n(CH4) = n(C2H6), but m(CH4)< m(С2Н6)
The calculation of ν is used in almost every calculation problem.

Ivan Knyazev

mass is measured in grams, amount of substance in moles, molar mass in grams divided by mole. It is clear that in order to obtain the molar mass, the mass must be divided by the quantity, respectively, the quantity is the mass divided by the molar mass

Quantity of substance used to measure macroscopic quantities of substances in many natural sciences such as physics, chemistry, in the study of electrolysis, in thermodynamics, which describes the state of an ideal gas. Since molecules interact regardless of their mass in quantities that are multiples of integers, when describing chemical reactions, It is more convenient to use quantities of a substance than mass. In order to understand what quantities of a substance are in chemistry, we note that a quantity has its own unit of measurement.

Definition, units of measurement, designation

The number of similar structural units contained in a substance (atoms, electrons, molecules, ions and other particles) is physical quantity - amount of substance. The International System of Units (SI) measures the amount of a substance in [mol],[kmol],[mmol], when used in calculations, is denoted as (en).

Application, meaning

In chemistry, when writing chemical equations, after becoming familiar with the law of constancy of mass of substances, it becomes clear how to use the quantity of a substance and its meaning. For example, in the combustion reaction of hydrogen, it is required 2 to 1 the value of oxygen. Knowing the mass of hydrogen, it is possible to obtain the amount of oxygen involved in the combustion reaction.

In real experiments, instead of the quantity of a substance “in pieces”, a unit of measurement is used [mol]. This reduces the ratio of starting reagents and simplifies calculations. In fact, in 1 mole the number of units of substance contained is 6 1023 mol −1, which is called N A ].

To calculate the amount of a substance based on its mass, use the concept molar mass, i.e. the ratio of the mass of a substance to the number of moles of this substance:

n = m/M,

where m is the mass of the substance, M is the molar mass of the substance.

Molar mass measured in [g/mol].

Also molar mass can be found by work molecular weight of this substance per number of molecules in 1 mole -

Amount of gaseous substance determined based on its volume:

n = V / V m,

where where V is the volume of gas under normal conditions, and V m - molar volume gas under the same conditions, equal 22.4 l/mol according to Avogadro's law.

Summarizing all the calculations, we can deduce general formula for the amount of substance:

Computations

To more accurately understand what the amount of a substance is, let’s solve the simplest problems: what amount of substance is contained in an aluminum casting, weighing m = 5.4 kg?

When solving this problem, it should be remembered that the molar mass is numerically equal to the relative molecular mass, to find which you will need the periodic table, rounding the values: μ = 2.7 ⋅ 10-2 kg/mol.

Thus, we find the amount of substance by simple calculations:

n = m/μ = 5.4 kg/ 2.7 ⋅ 10-2 kg/mol = 2⋅ 10-2 mol.

This quantity is also used in physics. It is needed in molecular physics, where calculations of pressure and volume of gaseous substances are carried out using the Mendeleev-Clapeyron equation: