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1 mol per liter [mol / l] = 1000 mol per meter³ [mol / m³]

Initial value

Converted value

mol per meter³ mol per liter mol per centimeter³ mol per millimeter³ kilomole per meter³ kilomole per liter kilomole per centimeter³ kilomole per millimeter³ millimole per meter³ millimol per liter millimole per centimeter³ millimole per millimeter³ mol per cubic meter. decimeter molar millimolar micromolar nanomolar picomolar femtomolar attomolar zeptomolar yoctomolar

More on molar concentration

General information

The concentration of the solution can be measured different ways, for example, as the ratio of the mass of the solute to the total volume of the solution. In this article, we will look at molar concentration, which is measured as the ratio between the amount of substance in moles to the total volume of the solution. In our case, a substance is a soluble substance, and we measure the volume for the entire solution, even if other substances are dissolved in it. Amount of substance is the number of elementary constituents, such as atoms or molecules of a substance. Since even in a small amount of a substance there is usually a large number of elementary components, special units, moles, are used to measure the amount of a substance. One mole equal to the number atoms in 12 grams of carbon-12, which is approximately 6 × 10²³ atoms.

It is convenient to use moths if we work with an amount of a substance so small that its amount can be easily measured with household or industrial devices. Otherwise, one would have to work with very large numbers, which is inconvenient, or with very low weight or volume, which are difficult to find without specialized laboratory equipment. Atoms are most commonly used when working with moles, although other particles such as molecules or electrons can be used. It should be remembered that if you are not using atoms, then you must indicate this. Sometimes molar concentration is also called molarity.

Molarity should not be confused with molality... Unlike molarity, molality is the ratio of the amount of soluble substance to the mass of the solvent, not to the mass of the entire solution. When the solvent is water, and the amount of soluble substance is small compared to the amount of water, then molarity and molality are similar in meaning, but in other cases they usually differ.

Factors affecting molar concentration

The molar concentration depends on temperature, although this dependence is stronger for some and weaker for other solutions, depending on what substances are dissolved in them. Some solvents expand with increasing temperature. In this case, if the substances dissolved in these solvents do not expand with the solvent, then the molar concentration of the entire solution decreases. On the other hand, in some cases, as the temperature rises, the solvent evaporates, and the amount of the soluble substance does not change - in this case, the concentration of the solution will increase. Sometimes the opposite happens. Sometimes a change in temperature affects how a soluble substance dissolves. For example, part or all of the soluble substance stops dissolving, and the concentration of the solution decreases.

Units

Molar concentration is measured in moles per unit volume, for example moles per liter or moles per cubic meter... Moles per cubic meter is the SI unit. Molarity can also be measured using other units of volume.

How to find molar concentration

To find the molar concentration, you need to know the amount and volume of the substance. The amount of a substance can be calculated using the chemical formula of this substance and information about the total mass of this substance in solution. That is, to find out the amount of solution in moles, we learn from the periodic table the atomic mass of each atom in the solution, and then divide the total mass of the substance by the total atomic mass of atoms in the molecule. Before adding the atomic mass together, make sure we multiply the mass of each atom by the number of atoms in the molecule we are looking at.

You can perform calculations in reverse order... If you know the molar concentration of the solution and the formula of the soluble substance, then you can find out the amount of solvent in the solution, in moles and grams.

Examples of

Find the molarity of a solution of 20 liters of water and 3 tablespoons of soda. In one tablespoon - about 17 grams, and in three - 51 grams. Soda is sodium bicarbonate, whose formula is NaHCO₃. In this example, we will use atoms to calculate molarity, so we will find the atomic mass of the constituents sodium (Na), hydrogen (H), carbon (C), and oxygen (O).

Na: 22.989769
H: 1.00794
C: 12.0107
O: 15.9994

Since oxygen in the formula is O₃, it is necessary to multiply the atomic mass of oxygen by 3. We get 47.9982. Now we add the masses of all atoms and get 84.006609. The atomic mass is indicated in the periodic table in atomic mass units, or a. e. m. Our calculations are also in these units. One A. e. m. is equal to the mass of one mole of a substance in grams. That is, in our example, the mass of one mole of NaHCO₃ is 84.006609 grams. In our task - 51 grams of soda. Find molar mass, dividing 51 grams by the mass of one mole, that is, by 84 grams, and we get 0.6 mole.

It turns out that our solution is 0.6 mol of soda dissolved in 20 liters of water. We divide this amount of soda by the total volume of the solution, that is, 0.6 mol / 20 l = 0.03 mol / l. Since a large amount of solvent and a small amount of a soluble substance were used in the solution, its concentration is low.

Let's look at another example. Find the molar concentration of one sugar cube in a cup of tea. Table sugar is composed of sucrose. First, we find the weight of one mole of sucrose, the formula of which is C₁₂H₂₂O₁₁. Using the periodic table, we find the atomic masses and determine the mass of one mole of sucrose: 12 × 12 + 22 × 1 + 11 × 16 = 342 grams. There are 4 grams of sugar in one cube, which gives us 4/342 = 0.01 moles. There are about 237 milliliters of tea in one cup, which means that the concentration of sugar in one cup of tea is 0.01 mol / 237 milliliters × 1000 (to convert milliliters to liters) = 0.049 mol per liter.

Application

Molar concentration is widely used in calculations related to chemical reactions. The section of chemistry, in which the ratios between substances in chemical reactions are calculated and often work with moles, is called stoichiometry... The molar concentration can be found by chemical formula the final product, which then becomes a soluble substance, as in the example with a soda solution, but you can also first find this substance by the formulas chemical reaction during which it is formed. To do this, you need to know the formulas of the substances involved in this chemical reaction. Having solved the equation of the chemical reaction, we find out the formula of the molecule of the dissolved substance, and then we find the mass of the molecule and the molar concentration using the periodic table, as in the examples above. Of course, calculations can also be made in reverse order using information on the molar concentration of a substance.

Let's take a look at a simple example. This time we'll mix baking soda and vinegar to see an interesting chemical reaction. Both vinegar and soda are easy to find - you probably have them in your kitchen. As mentioned above, the formula for soda is NaHCO₃. Vinegar is not a pure substance, but a 5% solution of acetic acid in water. The formula for acetic acid is CH₃COOH. The concentration of acetic acid in vinegar can be more or less than 5%, depending on the manufacturer and the country in which it is made, as in different countries the concentration of vinegar is different. In this experiment, you do not have to worry about the chemical reactions of water with other substances, since water does not react with soda. We only care about the volume of water, when later we will calculate the concentration of the solution.

First, let's solve the equation for the chemical reaction between soda and acetic acid:

NaHCO₃ + CH₃COOH → NaC₂H₃O₂ + H₂CO₃

The reaction product is H₂CO₃, a substance that reacts chemically again due to its low stability.

H₂CO₃ → H₂O + CO₂

The reaction produces water (H₂O), carbon dioxide (CO₂) and sodium acetate (NaC₂H₃O₂). We mix the resulting sodium acetate with water and find the molar concentration of this solution, just as before we found the concentration of sugar in tea and the concentration of soda in water. When calculating the volume of water, it is necessary to take into account the water in which the acetic acid is dissolved. Sodium acetate is an interesting substance. It is used in chemical warmers such as hand warmers.

Using stoichiometry to calculate the amount of substances that enter into a chemical reaction, or reaction products, for which we will later find the molar concentration, it should be noted that only a limited amount of a substance can react with other substances. It also affects the amount of the final product. If the molar concentration is known, then, on the contrary, it is possible to determine the amount of the starting products by the method of reverse calculation. This method is often used in practice, in calculations related to chemical reactions.

When using recipes, whether in cooking, making medicines, or creating the ideal environment for your aquarium fish, you need to know the concentration. In everyday life, it is most often more convenient to use grams, but in pharmaceuticals and chemistry, molar concentration is more often used.

In pharmaceuticals

When creating drugs, molar concentration is very important, since it determines how the drug affects the body. If the concentration is too high, the drugs can even be fatal. On the other hand, if the concentration is too low, then the medicine is ineffective. In addition, concentration is important when exchanging fluids through cell membranes in organism. When determining the concentration of a liquid, which must either pass or, conversely, not pass through the membranes, either the molar concentration is used, or with its help one finds osmotic concentration... Osmotic concentration is used more often than molar concentration. If the concentration of a substance, for example a drug, is higher on one side of the membrane, compared to the concentration on the other side of the membrane, for example, inside the eye, then the more concentrated solution will move across the membrane to where the concentration is lower. This flow of solution through the membrane is often problematic. For example, if fluid moves into a cell, such as a blood cell, it is possible that this fluid overflow will damage the membrane and rupture. Leakage of fluid from the cell is also problematic, as this will disrupt the cell's performance. Any drug-induced flow of fluid through the membrane from the cell or into the cell is desirable to prevent, and for this, the concentration of the drug is tried to be similar to the concentration of fluid in the body, for example, in the blood.

It should be noted that in some cases the molar and osmotic concentration are equal, but this is not always the case. It depends on whether the substance dissolved in water has disintegrated into ions in the process electrolytic dissociation ... When calculating the osmotic concentration, particles in general are taken into account, while when calculating the molar concentration, only certain particles, such as molecules, are taken into account. Therefore, if, for example, we work with molecules, but the substance has disintegrated into ions, then there will be fewer molecules the total particles (including molecules and ions), and hence the molar concentration will be lower than the osmotic. To convert molar concentration to osmotic concentration, you need to know physical properties solution.

In the manufacture of pharmaceuticals, pharmacists also take into account tonicity solution. Tonicity is a property of a solution that depends on its concentration. Unlike osmotic concentration, tonicity is the concentration of substances that the membrane does not pass. The osmosis process forces solutions with a higher concentration to move into solutions with a lower concentration, but if the membrane prevents this movement by not allowing the solution to pass through it, then there is pressure on the membrane. Such pressure is usually problematic. If a drug is intended to penetrate the blood or other fluid in the body, then it is necessary to balance the tonicity of this drug with the tonicity of the body fluid in order to avoid osmotic pressure on the membranes in the body.

To balance tonicity, drugs are often dissolved in isotonic solution... An isotonic solution is a solution of table salt (NaCL) in water with a concentration that allows you to balance the tonicity of the fluid in the body and the tonicity of the mixture of this solution and the drug. Usually, the isotonic solution is stored in sterile containers and infused intravenously. Sometimes it is used in its pure form, and sometimes as a mixture with a medicine.

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Class: 8

Target: To acquaint students with the concepts of "amount of substance", "molar mass" to give an idea of ​​the Avogadro constant. Show the relationship between the amount of matter, the number of particles and Avogadro's constant, as well as the relationship between molar mass, mass and amount of matter. To teach how to make calculations.

Lesson type: a lesson in the study and primary consolidation of new knowledge.

During the classes

I. Organizational moment

II. Checking d / s on the topic: "Types of chemical reactions"

III. Learning new material

1. Amount of substance - mol

Substances react in strictly defined proportions. For example, to get the substance water, you need to take so much hydrogen and oxygen so that for every two hydrogen molecules there is one oxygen molecule:

2H 2 + O 2 = 2H 2 O

To obtain the substance iron sulfide, you need to take so much iron and sulfur that there is one sulfur atom for each iron atom.

To obtain the substance phosphorus oxide, you need to take so many molecules of phosphorus and oxygen so that there are five molecules of oxygen for four phosphorus molecules.

In practice, it is impossible to determine the number of atoms, molecules and other particles - they are too small and not visible naked eye... To determine the number of structural units (atoms, molecules) in chemistry, a special value is used - amount of substance ( v - nude). The unit of the amount of a substance is mole.

• A mole is the amount of a substance that contains as many structural particles (atoms, molecules) as there are atoms in 12 g of carbon.

It has been experimentally established that 12 g of carbon contains 6 · 10 23 atoms. This means that one mole of any substance, regardless of its state of aggregation, contains the same number of particles - 6 · 10 23.

• 1 mole of oxygen (O 2) contains 6 · 10 23 molecules.
• 1 mole of hydrogen (H 2) contains 6 · 10 23 molecules.
• 1 mole of water (H 2 O) contains 6 · 10 23 molecules.
• 1 mol of iron (Fe) contains 6 · 10 23 molecules.

Exercise: Using the information received, answer the questions:

a) how many oxygen atoms are there in 1 mole of oxygen?

- 6 · 10 23 · 2 = 12 · 10 23 atoms.

b) how many hydrogen and oxygen atoms are there in 1 mole of water (H 2 O)?

- 6 · 10 23 · 2 = 12 · 10 23 hydrogen atoms and 6 · 10 23 oxygen atoms.

Number 6 10 23 called Avogadro constant in honor of the Italian scientist of the 19th century and is designated NA. The units are atoms / mol or molecules / mol.

2. Solving problems to find the amount of substance

You often need to know how many particles of a substance are contained in a certain amount of a substance. Or find the amount of a substance by a known number of molecules. These calculations can be done using the formula:

where N is the number of molecules, NA is Avogadro's constant, v- the amount of substance. From this formula, you can express the amount of substance.

Objective 1. How many atoms are there in 2 moles of sulfur?

N = 2 6 10 23 = 12 10 23 atoms.

Objective 2. How many atoms are there in 0.5 moles of iron?

N = 0.5 6 10 23 = 3 10 23 atoms.

Objective 3. How many molecules are there in 5 moles carbon dioxide?

N = 5 6 10 23 = 30 10 23 molecules.

Task 4. How much of a substance is 12 · 10 23 molecules of this substance?

v = 12 · 10 23/6 · 10 23 = 2 mol.

Task 5. What amount of a substance is 0.6 · 10 23 molecules of this substance?

v = 0.6 10 23/6 10 23 = 0.1 mol.

Task 6. What amount of a substance is 3 · 10 23 molecules of this substance?

v = 3 · 10 23/6 · 10 23 = 0.5 mol.

3. Molar mass

For chemical reactions, you need to take into account the amount of substance in moles.

Q: But how to measure 2, or 2.5 mol of a substance in practice? What is the best unit to measure the mass of substances?

For convenience, molar mass is used in chemistry.

Molar mass is the mass of one mole of a substance.

It is designated - M. It is measured in g / mol.

The molar mass is equal to the ratio of the mass of a substance to the corresponding amount of a substance.

Molar mass is a constant value. The numerical value of the molar mass corresponds to the value of the relative atomic or relative molecular weight.

Q: How can you find the relative atomic or relative molecular weight?

Mr (S) = 32; M (S) = 32 g / mol - which corresponds to 1 mole of sulfur

Mr (H 2 O) = 18; M (H 2 O) = 18 g / mol - which corresponds to 1 mol of water.

4. Solving problems to find the mass of matter

Task 7. Determine the mass of 0.5 mol of iron.

Problem 8. Determine the mass of 0.25 mol of copper

Problem 9. Determine the mass of 2 mol of carbon dioxide (CO 2)

Problem 10. How many moles of copper oxide - CuO are 160 g of copper oxide?

v = 160/80 = 8 mol

Problem 11. How many moles of water correspond to 30 g of water

v = 30/18 = 1.66 mol

Problem 12. How many moles of magnesium are 40 grams?

v = 40/24 = 1.66 mol

IV. Anchoring

Frontal poll:

1. What is the amount of a substance?
2. What is 1 mole of any substance?
3. What is molar mass?
4. Does the concept of "mole of molecules" and "mole of atoms" differ?
5. Explain using the example of the ammonia molecule NH3.
6. Why do you need to know formulas when solving problems?

Tasks:

1. How many molecules are there in 180 grams of water?
2. How many molecules are 80 g of carbon dioxide?

V. Homework

Study the text of the paragraph, make up two tasks: to find the amount of substance; to find the mass of a substance.

Literature:

1. Gara N.N. Chemistry. Lessons in grade 8: a guide for the teacher. _ M .: Education, 2009.
2. Rudzites G.E., Feldman F.G. Chemistry. Grade 8 .: Textbook for educational institutions - M .: Education, 2009.

One of the basic units in the International System of Units (SI) is the unit of the amount of substance is the mole.

Moth – this is the amount of a substance that contains as many structural units of a given substance (molecules, atoms, ions, etc.) as there are carbon atoms in 0.012 kg (12 g) of the carbon isotope 12 WITH .

Considering that the value of the absolute atomic mass for carbon is m(C) = 1.99 10  26 kg, you can calculate the number of carbon atoms N A contained in 0.012 kg of carbon.

A mole of any substance contains the same number of particles of this substance (structural units). The number of structural units contained in a substance in the amount of one mole is 6.02 10 23 and called Avogadro's number (N A ).

For example, one mole of copper contains 6.02 · 10 23 copper atoms (Cu), and one mole of hydrogen (H 2) contains 6.02 · 10 23 hydrogen molecules.

Molar mass(M) is the mass of a substance taken in an amount of 1 mol.

The molar mass is designated by the letter M and has the dimension [g / mol]. In physics, the dimension [kg / kmol] is used.

In the general case, the numerical value of the molar mass of a substance numerically coincides with the value of its relative molecular (relative atomic) mass.

For example, the relative molecular weight of water is:

Мr (Н 2 О) = 2Аr (Н) + Аr (O) = 2 ∙ 1 + 16 = 18 amu

The molar mass of water has the same value, but is expressed in g / mol:

M (H 2 O) = 18 g / mol.

Thus, a mole of water containing 6.02 · 10 23 water molecules (respectively 2 · 6.02 · 10 23 hydrogen atoms and 6.02 · 10 23 oxygen atoms) has a mass of 18 grams. In water, the amount of substance is 1 mol, contains 2 mol of hydrogen atoms and one mol of oxygen atoms.

1.3.4. The relationship between the mass of a substance and its amount

Knowing the mass of a substance and its chemical formula, and hence the value of its molar mass, it is possible to determine the amount of a substance and, conversely, knowing the amount of a substance, it is possible to determine its mass. For such calculations, you should use the formulas:

where ν is the amount of substance, [mol]; m- mass of substance, [g] or [kg]; M is the molar mass of the substance, [g / mol] or [kg / kmol].

For example, to find the mass of sodium sulfate (Na 2 SO 4) in the amount of 5 mol, we find:

1) the value of the relative molecular weight of Na 2 SO 4, which is the sum of the rounded values ​​of the relative atomic masses:

Мr (Na 2 SO 4) = 2Аr (Na) + Аr (S) + 4Аr (O) = 142,

2) the numerically equal value of the molar mass of the substance:

M (Na 2 SO 4) = 142 g / mol,

3) and, finally, the mass of 5 mol of sodium sulfate:

m = ν M = 5 mol 142 g / mol = 710 g.

Answer: 710.

1.3.5. The relationship between the volume of a substance and its amount

Under normal conditions (n.o.), i.e. at pressure R equal to 101325 Pa (760 mm Hg), and a temperature T, equal to 273.15 K (0 С), one mole of different gases and vapors occupies the same volume, equal to 22.4 l.

The volume occupied by 1 mole of gas or vapor at normal conditions is called molar volumegas and has a dimension of liter per mole.

V mol = 22.4 l / mol.

Knowing the amount of gaseous substance (ν ) and molar volume value (V mol) you can calculate its volume (V) under normal conditions:

V = ν V mol,

where ν is the amount of substance [mol]; V is the volume of the gaseous substance [l]; V mol = 22.4 l / mol.

And, conversely, knowing the volume ( V) of a gaseous substance under normal conditions, you can calculate its amount (ν) :

... mole/ l, = 0.28 mole/ l, = 0.44 mole/ l. Find molar fractions of components in 5% (by mass) aqueous ... to obtain ammonium chloride (NH4Cl) mass 10.7 g. mole carbon in 4 g of carbon disulfide (CS2)? Using the reference ...