Theme "Balance"

Usually, problems on this topic turn out to be difficult, because specific knowledge of chemistry in itself does not help to solve them; but the applicant is required to have a "mathematical vision" of the problem and the conversion of chemical quantities (mol) into fairly simple algebraic expressions. Not everyone is ready for the fact that in the exam in chemistry they will not have to remember what they have learned by heart, but think "in mathematical terms."

The tasks below are taken from the collection: Kuzmenko N.E., Eremin V.V., Churanov S.S., Collection of competitive tasks in chemistry - M .: Exam, 2001 - 576 p. ; in [square brackets] are the pages where the conditions and solutions (answers) are located.

Tasks

1. (Khimfak-97, version of software-97-1 [p. 290])
One mole of ammonia was placed in a 20-liter vessel and heated to 600 0 C. The pressure in the vessel was 435 kPa. Calculate the degree of decomposition of ammonia.

2. (Khimfak-spring-98; VKNM-98; Chemfak-correspondence-99, variant SO-98-1 [p. 93])
Three moles of substances A, B, C were mixed. After the equilibrium A + B = 2C was established, 5 moles of substance C were found in the system. Calculate the equilibrium constant. Determine the equilibrium composition of the mixture (in mole%) obtained by mixing substances A, B, C in a molar ratio of 3:2:1 at the same temperature.

3. (Chemistry-Spring-93; Chemistry Faculty-correspondence-94; Chemistry Faculty-Spring-94; VKNM-96, version 171-94-2 [p. 55]. This is one of the most difficult competitive tasks of the Chemistry Faculty of Moscow State University)
There is a mixture of nitrogen and hydrogen, which is 5% lighter than helium. After passing the mixture over the heated catalyst, ammonia was formed, as a result of which the mixture became heavier than helium under the same conditions. Calculate the tolerance range for the reaction output.

Theme "Balance"

1 . [Collection, p. 560]
Amount (mol) of gases after the reaction: PV / RT \u003d 435 * 20 / (8.31 * 873) \u003d 1.20 mol
If x mole of ammonia decomposed, then the decomposition scheme: NH 3 (1-x) N 2 (x / 2) + H 2 (3x / 2)
From the equation: 1.20 mol = (1-x) + x/2 + 3x/2 = 1+x
we get x = 0.2 mol.
Answer: The degree of decomposition of ammonia 20%

2 . [Collection, p. 412]

K \u003d (1 + 2x) 2 / ((3-x) (2-x)) \u003d 6.25
x = 1.115

Answer: Mole fractions of substances in an equilibrium mixture:
(A) \u003d (3-1.115) / 6 \u003d 0,314 ;
(B) \u003d (2-1.115) / 6 \u003d 0,148 ;
(C)= 0,538

3 . [Collection, p. 371]
Let there be X mol N 2 and Y mol H 2 in the initial mixture.
The average molar mass of the mixture is 5% lighter than helium or 0.95 * 4:
M cf. \u003d (28X + 2Y) / (X + Y) \u003d 0.95 * 4 \u003d 3.8;
Then Y = 13.44X
Reaction: N 2 + 3 H 2 = 2 NH 3
If a mol N 2 and 3a mol H 2 reacted, we get after the reaction:
(X - a) + (Y - 3a) + 2a = 14.44X - 2a (mol)
The mass of the mixture after the reaction (we express in X, since Y = 13.44X):
28X + 2Y = 54.9 X g
The average molar mass of the mixture after the reaction is > 4 g/mol (according to the condition):
M cf. = 54.9X/(14.44X - 2a) > 4;
then: a > 0.3575X
The reaction yield is the proportion of reacted nitrogen (coefficient in reaction 1): a/X;
The mixture will become heavier than helium (Mavg > 4) at a/X > 35.75%
Answer: ammonia yield is more than 35.75%

Topic "Equilibrium in solutions"
Tasks

The topic "equilibrium in solutions" is considered difficult, because it uses concepts that are only included in the curriculum for schools and classes with in-depth study of chemistry - the product of solubility and pH. But the main difficulty is not in the fairly simple formulas themselves, but in the ability to use them in a wide range of problem conditions.

Problems of 2002 are taken from the collection of problems of the past academic year published at the Faculty of Chemistry annually: "Written exam in chemistry of Moscow State University-2002" Khim. Faculty of Moscow State University, 2002.

Tasks

1) (Chemical department, 2002) 500 ml of a saturated solution of Zn 3 (PO 4) 2 contains 2.47 * 10 -7 mol of phosphate ions. Calculate the salt solubility in mol/l and the solubility product of Zn 3 (PO 4) 2
2) (VKNM-96, version YuM-96-1, [p. 240]) Determine the molar concentration of a saturated solution of iron (II) hydroxide at 25 0 С, if its solubility product at this temperature is 1 * 10 -15
3) (Khim. Ft., 1993, version 171-93-4 [p. 49]) Acetic acid weighing 25 g is dissolved in water, and the volume of the solution is adjusted to 1 liter. Determine the concentration of H + ions in the resulting solution if the dissociation constant of acetic acid is 1.8 * 10 -5. Disregard the change in acid concentration during dissociation.
4) (Fundamental Medicine Faculty - 2002) The dissociation constant of acetic acid is 1.75 * 10 -5. Calculate: a) the pH of a 0.1 M solution of this acid; b) pH of a solution containing 0.1 mol/l of this acid and 0.1 mol/l of sodium acetate

Solutions:

1) (collection 2002, p. 44)
1 liter contains phosphate ions: 2.47 * 10 -7 (1000/500) \u003d 4.94 * 10 -7 mol / l. The solution will contain 2 times less than phosphate ions, formula units of zinc phosphate Zn 3 (PO 4) 2: 4.94 * 10 -7 / 2 = 2.47 * 10 -7 mol / l
The solubility product is defined as a constant of heterogeneous equilibrium under the assumption that a poorly soluble substance goes into solution only in the form of ions.
Then for the process:

mistaking for With molar concentration of iron hydroxide, we get:

(s)(2s) 2 = 4s 3 = 1*10 –15
Then c \u003d (0.25. 10 -15) 1/3 \u003d (250. 10 -18) 1/3 \u003d 6.3. 10 –6 (mol/l)
Answer: c (Fe (OH) 2) \u003d 6.3 * 10 -6 mol / l

3. [Collection, p. 361]
Acetic acid is weak, and the concentration of H + ions in its solution is not equal to the concentration of the acid, as in the case of dilute solutions of strong acids.
The dissociation of acetic acid can be simply written as an equilibrium: CH 3 COOH H + + CH 3 COO -
The equilibrium constant, it is also the dissociation constant:
K d = () /
1 liter contains 25/60 = 0.417 mol to-you; let us denote the degree of its dissociation, which is equal to the ratio of the dissociated molecules to the total number of molecules in the solution. The concentration of H + ions (mol / l) is determined from the concentration of the acid and the degree of its dissociation: = With.Since the value is unknown to us, it must be expressed in terms of known quantities - the concentration of the acid c and its dissociation constant K d.
If the acid concentration c, then upon dissociation we get With mole of H + ions and the same number of CH 3 COO - ions. In the solution will remain (1-) With mol CH 3 COOH.
Then the dissociation constant:

K d =	(With)*(c) ;
	(1-)c

At a low degree of dissociation (<< 1) можно приближенно считать, что (1-)With is equal to With. Then K d 2 s; (K d / s) 1/2:
(K d / s) 1/2 \u003d 6.6. 10–3; = c = 6.6. 10–3. 0.417 \u003d 2.74 * 10 -3 mol / l
Answer: 2.74*10 -3 mol/l

4) (collection 2002, p. 59)
This is a typical task on the topic "Buffer solutions". But it is unlikely that applicants know (and are not required to know) ready-made formulas for calculating the pH of buffer solutions - there is no such topic either in the school curriculum or in the program for applicants to Moscow State University. Therefore, for calculations, only known expressions for the equilibrium constant of a weak acid, the value of the ionic product of water and the determination of pH should be used: pH = - lg, where the entry in square brackets means that the concentrations are expressed in mol / l.

a) Dissociation constant of acetic acid:

K d = /
Since = , we can write: 2 = K d . Since acetic acid is a weak electrolyte with a small dissociation constant, we can neglect the fact that part of the original acid has dissociated and equate the acid concentration in the expression for the equilibrium constant to the initial (total) concentration: С CH3COOH .

Then we get: 2 \u003d K d C CH3COOH;
\u003d (K d C CH3COOH) 1/2 \u003d (1.75. 10 -5. 10 -1) 1/2 \u003d 1.32. 10–3; pH = - lg = 2.88

b) Sodium acetate (salt), unlike acetic acid, dissociates completely. Therefore, in the formula for the dissociation constant describing the equilibrium, we get: K d = / ;
With CH3COOH ; = CCH3COONa = 0.1 mol/l.
Then: = K d. C CH3COOH / C CH3COONa = 1.75. 10–5 . 10 -1 / 10 -1 \u003d 1.75. 10–5;
pH = 4.76
Answer: a) pH = 2.88; b) pH = 4.76

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

Initial value

Converted value

moles per meter³ moles per liter moles per centimeter³ moles per millimeters decimeter molar millimolar micromolar nanomolar picomolar femtomolar attomolar zeptomolar yoctomolar

More about molar concentration

General information

The concentration of a solution can be measured in many ways, such 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 a small amount of a substance usually contains a large number of elementary components, special units, moles, are used to measure the amount of a substance. One mole is equal to the number of atoms in 12 g of carbon-12, that is, it is approximately 6 × 10²³ atoms.

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

Molarity should not be confused with molality. Unlike molarity, molality is the ratio of the amount of solute to the mass of the solvent, and not to the mass of the entire solution. When the solvent is water and the amount of solute is small compared to the amount of water, then molarity and molality are similar in meaning, but otherwise 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, with increasing temperature, the solvent evaporates, and the amount of the solute 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 solute dissolves. For example, some or all of the solute ceases to dissolve and the concentration of the solution decreases.

Units

Molar concentration is measured in moles per unit volume, such as moles per liter or moles per cubic meter. Moles per cubic meter is an 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 a substance. The amount of a substance can be calculated using the chemical formula of that substance and information about the total mass of that substance in solution. That is, to find out the amount of the solution in moles, we find out from the periodic table the atomic mass of each atom in the solution, and then we divide the total mass of the substance by the total atomic mass of the atoms in the molecule. Before adding together the atomic mass, make sure that we multiply the mass of each atom by the number of atoms in the molecule we are considering.

You can also do the calculations in reverse order. If the molar concentration of the solution and the formula of the solute are known, then you can find out the amount of solvent in the solution, in moles and grams.

Examples

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. Baking soda is sodium bicarbonate whose formula is NaHCO₃. In this example, we'll use atoms to calculate molarity, so we'll find the atomic masses of the sodium (Na), hydrogen (H), carbon (C), and oxygen (O) constituents.

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

Since the oxygen in the formula is O₃, it is necessary to multiply the atomic mass of oxygen by 3. We get 47.9982. Now 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. We find the molar mass by dividing 51 grams by the mass of one mole, that is, by 84 grams, and we get 0.6 moles.

It turns out that our solution is 0.6 moles 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 \u003d 0.03 mol / l. Since a large amount of solvent and a small amount of solute were used in the solution, its concentration is low.

Let's consider another example. Find the molar concentration of one sugar cube in a cup of tea. Table sugar is made up of sucrose. First, let's 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 of sugar, which gives us 4/342 = 0.01 moles. There are about 237 milliliters of tea in one cup, so the concentration of sugar in one cup of tea is 0.01 moles / 237 milliliters × 1000 (to convert milliliters to liters) = 0.049 moles per liter.

Application

Molar concentration is widely used in calculations related to chemical reactions. The branch of chemistry that calculates the ratios between substances in chemical reactions and often works with moles is called stoichiometry. The molar concentration can be found from the chemical formula of the final product, which then becomes a soluble substance, as in the soda solution example, but you can also first find this substance from the formulas of the 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 chemical reaction equation, we find out the formula of the molecule of the solute, and then we find the mass of the molecule and the molar concentration using the periodic table, as in the examples above. Of course, it is possible to perform calculations in reverse order, using information about the molar concentration of a substance.

Let's consider a simple example. This time we mix baking soda with vinegar to see an interesting chemical reaction. Both vinegar and baking soda are easy to find - you probably have them in your kitchen. As mentioned above, the formula for baking 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 the concentration of vinegar varies from country to country. 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 we later calculate the concentration of the solution.

First, we solve the equation for the chemical reaction between soda and acetic acid:

NaHCO₃ + CH₃COOH → NaC₂H₃O₂ + H₂CO₃

The reaction product is H₂CO₃, a substance that, due to low stability, enters into a chemical reaction again.

H₂CO₃ → H₂O + CO₂

As a result of the reaction, we get 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 acetic acid is dissolved. Sodium acetate is an interesting substance. It is used in chemical heating pads, 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. This 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 starting products by the reverse calculation method. This method is often used in practice, in calculations related to chemical reactions.

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

In pharmaceuticals

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

It is worth noting that in some cases the molar and osmotic concentrations are equal, but this is not always the case. It depends on whether the substance dissolved in water has broken down 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 are working with molecules, but the substance has decomposed into ions, then there will be less molecules than the total number of particles (including both molecules and ions), and hence the molar concentration will be lower than the osmotic one. To convert the molar concentration to osmotic concentration, you need to know the physical properties of the solution.

In the manufacture of medicines, pharmacists also take into account tonicity solution. Tonicity is a property of a solution that depends on concentration. Unlike osmotic concentration, tonicity is the concentration of substances that the membrane does not let through. The process of osmosis causes 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, then there is pressure on the membrane. Such pressure is usually problematic. If a drug is intended to enter the blood or other body fluid, then the tonicity of the drug must be balanced against the tonicity of the body fluid 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 at a concentration that balances the tonicity of the fluid in the body and the tonicity of the mixture of this solution and the drug. Usually isotonic solution is stored in sterile containers and infused intravenously. Sometimes it is used in its pure form, and sometimes - as a mixture with medicine.

Do you find it difficult to translate units of measurement from one language to another? Colleagues are ready to help you. Post a question to TCTerms and within a few minutes you will receive an answer.

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 a substance, the number of particles and the Avogadro constant, as well as the relationship between the molar mass, mass and amount of a substance. Learn to do calculations.

Lesson type: lesson of studying and primary consolidation of new knowledge.

During the classes

I. Organizational moment

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

III. Learning new material

1. Amount of substance - mole

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

2H 2 + O 2 \u003d 2H 2 O

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

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

It is impossible to determine the number of atoms, molecules and other particles in practice - they are too small and not visible to the naked eye. To determine the number of structural units (atoms, molecules) in chemistry, a special value is used - amount of matter ( v - nude). The unit of quantity 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 mol of hydrogen (H 2) contains 6 10 23 molecules.
• 1 mol of water (H 2 O) contains 6 10 23 molecules.
• 1 mole of iron (Fe) contains 6 10 23 molecules.

Exercise: Using the information you received, answer the following 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 is called Avogadro's constant in honor of the Italian scientist of the 19th century and is designated NA. Units of measurement are atoms/mol or molecules/mol.

2. Solving problems for finding the amount of substance

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

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

v= N / NA

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

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

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

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

Task 3. How many molecules are there in 5 moles of 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 \u003d 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 \u003d 0.1 mol.

Task 6. How much of a substance is 3 10 23 molecules of this substance?

v= 3 10 23 / 6 10 23 \u003d 0.5 mol.

3. Molar mass

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

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

For convenience in chemistry, molar mass is used.

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 the 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 I find relative atomic or relative molecular weights?

Mr(S) = 32; M (S) \u003d 32 g / mol - which corresponds to 1 mole of sulfur

Mr (H 2 O) = 18; M (H 2 O) \u003d 18 g / mol - which corresponds to 1 mole of water.

4. Solving problems on finding the mass of matter

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

Task 8. Determine the mass of 0.25 mol of copper

Task 9. Determine the mass of 2 moles of carbon dioxide (CO 2)

Task 10. How many moles of copper oxide - CuO make up 160 g of copper oxide?

v= 160 / 80 = 8 mol

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

v= 30/18 = 1.66 mol

Task 12. How many moles of magnesium corresponds to its 40 grams?

v= 40/24 = 1.66 mol

IV. Anchoring

Front poll:

1. What is the amount of substance?
2. What is 1 mole of any substance equal to?
3. What is molar mass?
4. Is there a difference between the terms "mole of molecules" and "mole of atoms"?
5. Explain using the example of the ammonia molecule NH3.
6. Why is it important to know formulas when solving problems?

Tasks:

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

V. Homework

Study the text of the paragraph, make 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 Teacher's Guide. _ M.: Enlightenment, 2009.
2. Rudzites G.E., Feldman F.G. Chemistry. Grade 8: Textbook for general educational institutions - M .: Education, 2009.

Dahl's Explanatory Dictionary

Female aphid (from small) tiny twilight (butterfly), broomstick; his caterpillar, which sharpens furs and woolen clothes, Tinca. There is a fur coat moth, clothes moth, cheese moth, bread moth, vegetable moth. Moth disappears from hops, camphor. | Moth vegetable, aphid, moth, ... ... Dahl's Explanatory Dictionary

1. MOL, and; well. A small butterfly whose caterpillar is a pest of woolen things, grains and plants. 2. MOL, and; f.; MOLE, I; m. Spec. Timber rafted down the river with logs not bound into a raft. The m was floating along the river. Wandering in a boat ... ... encyclopedic Dictionary

MOL- a unit of the amount of a substance in SI, defined as the amount of a substance containing as many formula (structural) units of this substance (atoms, molecules, ions, electrons, etc.) as there are atoms in 12 g of the carbon isotope 12 (12C); ... ... Great Polytechnic Encyclopedia

Exhausted by a moth .. Dictionary of Russian synonyms and expressions similar in meaning. under. ed. N. Abramova, M .: Russian dictionaries, 1999. moth aphid, moth Dictionary of Russian synonyms ... Synonym dictionary

1) the name of the beer in Nimwegen. 2) woolen fabric. 3) in beekeepers: plexus at the top of the hive. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. mol 1 it. molle soft) music. the same as minor 1 (opposite dur). 2… … Dictionary of foreign words of the Russian language

mole- Unit. number of items, i.e. values, estimating. number of contents in physical the system is identical. structures, elements (atoms, molecules, ions, and other particles or their specific groups), m. is equal to the number of things of the system, containing. so many structural elements ... ... Technical Translator's Handbook

MOL (Mohl) Hugo von (1805-1872), German botanist, pioneer in the study of the anatomy and physiology of plant cells. He formulated the hypothesis that the cell nucleus is surrounded by a granular colloidal substance, which in 1846 he called ... ... Scientific and technical encyclopedic dictionary

MOL, and, wives. A small butterfly, a caterpillar to a swarm, is a pest of fur, wool, cereal grains, and plants. Moth eaten away (also translated: about what N. is clearly outdated, obsolete; neod.). | adj. prayer, oh, oh. II. MOLE, me, husband. (specialist.). The alloy of the forest ... ... Explanatory dictionary of Ozhegov

- (mol, mol), unit SI count in va. 1 M. contains as many molecules (atoms, ions, or c.l. of other structural elements in va) as there are atoms in 0.012 kg of 12C (a carbon nuclide with an atomic mass of 12) (see AVOGADRO CONSTANT). Physical… … Physical Encyclopedia

MOL, in meaning. unchangeable adj. (music). The same as the mole. Sonata a mole. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov

Books

• Moth for Mr. L Cupid, Lydia Scriabin. This is a psychological novel about love, about money and about the love of money. About how the previously forbidden and condemned languidly sweet ideas of "personal enrichment" broke into the life of modern ...

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

mole – this is such an 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 a carbon isotope 12 WITH .

Given that the value of the absolute atomic mass for carbon is m(C) \u003d 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 with an 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 denoted by the letter M and has the unit [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:

Mr (H 2 O) \u003d 2Ar (H) + Ar (O) \u003d 2 ∙ 1 + 16 \u003d 18 a.m.u.

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. 1 mole of water contains 2 moles of hydrogen atoms and 1 mole of oxygen atoms.

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

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

where ν is the amount of substance, [mol]; m is the mass of the 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:

Mr (Na 2 SO 4) \u003d 2Ar (Na) + Ar (S) + 4Ar (O) \u003d 142,

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

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

3) and, finally, a 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 quantity

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

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

V mol \u003d 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 \u003d 22.4 l / mol.

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