Mole (Russian designation: mole ; international: mol ; outdated name gram molecule(relative to the number of molecules) ; from lat. moles - quantity, mass, countable set) - a unit of measurement for the amount of matter in the International System of Units (SI), one of the seven basic SI units.

The mole was adopted as the SI base unit by the XIV General Conference on Weights and Measures (CGPM) in 1971.

While the definition of mole is related to mass. However, the XXVI General Conference on Weights and Measures (November 13-16, 2018) approved a new definition of the mole, based on the fixation numerical value Avogadro's constant. The decision will come into force on World Metrology Day on May 20, 2019.

Definition

The exact definition of a mole is formulated as follows:

Mole is the amount of substance in a system containing the same amount structural elements, how many atoms are there 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.

From the definition of a mole it follows directly that the molar mass of carbon-12 is 12 g/mol exactly.

The number of specified structural elements in one mole of a substance is called Avogadro's constant (Avogadro's number), usually denoted as N A. Thus, carbon-12 weighing 0.012 kg contains N A atoms. The value of Avogadro's constant recommended by the Committee on Data for Science and Technology (CODATA) in 2014 is 6.022140857(74)⋅10 23 mol −1. Hence, 1 carbon-12 atom has a mass of 0.012/ N A kg = 12/ N A g. 1/12 of the mass of a carbon-12 atom is called an atomic mass unit (symbol a.m.u.), and therefore 1 a.m. e.m. = 0.001/ N A kg =1/ N A g. Thus, the mass of one mole of a substance ( molar mass) is equal to the mass of one particle of a substance, atom or molecule, expressed in a. e.m. and multiplied by N A.
For example, the mass of 1 mole lithium, having an atomic crystal lattice, will be equal
7 a. e.m.x N A =7 x 1/ N A g x N A mol −1 = 7 g/mol,
and the mass is 1 mole oxygen, consisting of diatomic molecules
2 x 16 a. e.m.x N A =2 x 16 x 1/ N A g x N A mol −1 =32 g/mol.
That is, from definition a. e.m. it follows that the molar mass of a substance, expressed in grams per mole, numerically equal to mass the smallest particle(atom or molecule) of this substance, expressed in atomic units masses.

The mole will remain a unit of quantity of a substance; but its magnitude will be set by fixing the numerical value of Avogadro's constant to exactly 6.02214X⋅10 23 when expressed in the SI unit mol −1.

Here X stands for one or more significant figures, which will be determined further based on the most accurate CODATA recommendations.

The XXV CGPM, held in 2014, decided to continue work on preparing a new revision of the SI, including a redefinition of the mole, and planned to complete this work by 2018 in order to replace the existing SI with an updated version at the XXVI CGPM in the same year.

Multiples and submultiples

Decimal multiples and submultiples formed using standard SI prefixes. Moreover, the unit of measurement “ioctomole” can only be used formally, since such small quantities of a substance must be measured individual particles(1 imole is formally equal to 0.602 particles).

Holiday "Day of Prayer"

see also

Notes

1. Term gram-atom in relation to a mole of atoms is also little used at present.
2. Mole (unit of amount of substance) // Moesia - Morshansk. - M.: Soviet Encyclopedia, 1974. - (Great Soviet Encyclopedia: [in 30 volumes] / chief ed.

The concept mole is used to measure chemical substances. Let us find out the features of this quantity, give examples of calculation tasks with its participation, and determine the importance this term.

Definition

The mole in chemistry is a unit of calculation. It represents the quantity a certain substance, which contains so much structural units(atoms, molecules), how many are contained in 12 grams of a carbon atom.

Avogadro's number

The amount of substance is related to Avogadro's number, which is 6*10^23 1/mol. For substances molecular structure It is believed that one mole includes precisely Avogadro's number. If you need to count the number of molecules contained in 2 moles of water, then you need to multiply 6*10^23 by 2, we get 12*10^23 pieces. Let's look at the role moths play in chemistry.

Quantity of substance

A substance that consists of atoms contains Avogadro's number. For example, for a sodium atom it is 6*10*23 1/mol. What is its designation? Mole in chemistry means Greek letter"nude" or Latin "n". For mathematical calculations associated with the amount of substance, use the mathematical formula:

n=N/N(A), where n is the amount of substance, N(A) is Avogadro’s number, N is the number of structural particles of the substance.

If necessary, you can calculate the number of atoms (molecules):

The actual mass of a mole is called the molar mass. If the amount of a substance is determined in moles, then the molar mass has units of g/mol. IN numerically it corresponds to the relative molecular mass value, which can be determined by summing the relative atomic masses of the individual elements.

For example, in order to determine the molar mass of a carbon dioxide molecule, it is necessary to carry out the following calculations:

M (CO2)=Ar(C)+2Ar(O)=12+2*16=44

When calculating the molar mass of sodium oxide we obtain:

M (Na2O)=2*Ar(Na)+Ar(O)=2*23+16=62

When determining the molar mass of sulfuric acid, we sum up the two relative atomic masses of hydrogen with one atomic mass sulfur and four relative atomic masses of oxygen. Their meanings can always be found in periodic table Mendeleev. As a result we get 98.

The mole in chemistry allows for a variety of calculations involving chemical equations. All typical calculation problems in inorganic and organic chemistry, which involve finding the mass and volume of substances, are solved precisely through moles.

Examples of calculation problems

The molecular formula of any substance indicates the number of moles of each element included in its composition. For example, one mole of phosphoric acid contains three moles of hydrogen atoms, one mole of phosphorus atoms and four moles of oxygen atoms. Everything is quite simple. The mole in chemistry is a transition from the microworld of molecules and atoms to the macrosystem with kilograms and grams.

Task 1. Determine the number of water molecules contained in 16.5 moles.

To solve, we use the relationship between Avogadro’s number (amount of substance). We get:

16.5*6.022*1023 = 9.9*1024 molecules.

Task 2. Calculate the number of molecules contained in 5 g of carbon dioxide.

First you need to calculate the molar mass of a given substance, using its relationship with the relative molecular weight. We get:

N=5/44*6.023*1023=6.8*1023 molecules.

Algorithm for chemical equation problems

When calculating the mass or reaction products using the equation, use specific algorithm actions. First, determine which starting materials in short supply. To do this, find their number in moles. Next, they compose an equation for the process, and be sure to set up the stereochemical coefficients. The initial data is written above the substances, below them the amount of the substance taken in moles (according to the coefficient) is indicated. If necessary, convert units of measurement using formulas. Next, they make up a proportion and solve it mathematically.

If more than difficult task, then the mass of the pure substance is first calculated, removing impurities, and then they begin to determine its quantity (in moles). Not a single problem in chemistry related to the reaction equation can be solved without such a quantity as the mole. In addition, using this term, you can easily determine the number of molecules or atoms, using for such calculations constant number Avogadro. Calculation tasks included in test questions in chemistry for graduates of basic and secondary schools.

Length and distance converter Mass converter Bulk and food volume converter Area converter Volume and units converter in culinary recipes Temperature converter Pressure, mechanical stress, Young's modulus converter Energy and work converter Power converter Force converter Time converter Converter linear speed Flat Angle Thermal Efficiency and Fuel Efficiency Converter Number Converter to various systems notations Converter of units of measurement of quantity of information Exchange rates Sizes of women's clothing and shoes Sizes men's clothing and Shoe Converter angular velocity and rotation speed Acceleration converter Converter angular acceleration Density Converter Specific Volume Converter Moment of Inertia Converter Moment of Force Converter Torque Converter Converter specific heat combustion (by mass) Energy density and specific heat of combustion converter (by volume) Temperature difference converter Coefficient converter thermal expansion Thermal Resistance Converter Converter thermal conductivity Converter specific heat capacity Energy Exposure and Thermal Radiation Power Converter Density Converter heat flow Heat Transfer Coefficient Converter Volume Flow Converter Mass Flow Converter Molar Flow Converter Mass Flow Density Converter Molar Concentration Converter mass concentration in solution Dynamic (absolute) viscosity converter Kinematic viscosity converter Converter surface tension Vapor permeability converter Vapor permeability and vapor transfer rate converter Sound level converter Microphone sensitivity converter Sound pressure level (SPL) converter Sound pressure level converter with selectable reference pressure Brightness converter Luminous intensity converter Illuminance converter Resolution converter computer graphics Frequency and wavelength converter Optical power in diopters and focal length Optical power in diopters and lens magnification (×) Converter electric charge Linear Charge Density Converter Converter surface density Charge Converter bulk density Charge Converter electric current Linear current density converter Surface current density converter Voltage converter electric field Converter electrostatic potential and voltage converter electrical resistance Electrical Resistivity Converter Converter electrical conductivity Electrical conductivity converter Electrical capacity Inductance Converter American Wire Gauge Converter Levels in dBm (dBm or dBmW), dBV (dBV), watts and other units Converter magnetomotive force Magnetic Field Strength Converter Converter magnetic flux Magnetic induction converter Radiation. Absorbed dose rate converter ionizing radiation Radioactivity. Converter radioactive decay Radiation. Exposure dose converter Radiation. Absorbed Dose Converter Decimal Prefix Converter Data Transfer Typography and Imaging Converter Timber Volume Unit Converter Molar Mass Calculation Periodic table chemical elements D. I. Mendeleev

1 millimole per liter [mmol/l] = 0.001 mol per liter [mol/l]

Initial value

Converted value

moles per meter³ moles per liter moles per centimeter³ moles per millimeter³ kilomoles per meter³ kilomoles per liter kilomoles per centimeter³ kilomoles per millimeter³ millimoles per meter³ millimoles per liter millimoles per centimeter³ millimoles per millimeter³ moles per cubic. decimeter molar millimolar micromolar nanomolar Picomolar Femtomolar Attomolar zeptomolar yoctomolar

More about molar concentration

General information

The concentration of a 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, the substance is the soluble substance, and we measure the volume for the entire solution, even if other substances are dissolved in it. Quantity of substance is the number of elementary components, such as atoms or molecules of a substance. Since even in small amounts of a substance it is usually big number elementary components, then special units, moles, are used to measure the amount of a substance. One mole equal to the number atoms in 12 g of carbon-12, that is, approximately 6 x 10²³ atoms.

It is convenient to use moles if we are working with an amount of a substance so small that its amount can easily be measured with home or industrial instruments. Otherwise you would have to work with very large numbers, which is inconvenient, or with very small weight or volume, which is difficult to find without specialized laboratory equipment. The most common particles used when working with moles are atoms, although it is possible to use other particles, such as molecules or electrons. It should be remembered that if non-atoms are used, 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, rather than to the mass of the entire solution. When the solvent is water and the amount of solute compared to the amount of water is small, then molarity and molality are similar in meaning, but otherwise they are usually different.

Factors affecting molar concentration

Molar concentration depends on temperature, although this dependence is stronger for some solutions and weaker for other solutions, depending on what substances are dissolved in them. Some solvents expand when the temperature increases. 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, but the amount of 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 the solute dissolves. For example, some or all of the solute stops dissolving 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 unit volume. 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 the 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 solution in moles, we find out from the periodic table the atomic mass of each atom in the solution, and then divide total weight substances by the total atomic mass of atoms in a molecule. Before adding atomic masses together, we should make sure that we multiply the mass of each atom by the number of atoms in the molecule we are considering.

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

Examples

Let's find the molarity of a solution of 20 liters of water and 3 tablespoons of soda. One tablespoon contains approximately 17 grams, and three tablespoons contain 51 grams. Soda is sodium bicarbonate, the formula of which 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 let's add up the masses of all the atoms and get 84.006609. 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 equal to 84.006609 grams. In our problem - 51 grams of soda. Let's 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. Let's divide this amount of soda by the total volume of the solution, that is, 0.6 mol / 20 l = 0.03 mol/l. Since the solution was used a large number of solvent and a small amount of soluble substance, then its concentration is low.

Let's look at another example. Let's find the molar concentration of one piece of sugar in a cup of tea. Table sugar consists of sucrose. First, let's find the weight of one mole of sucrose, the formula of which is C₁₂H₂₂O₁₁. Using the periodic table, we will 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 the sugar concentration 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 involving chemical reactions. The branch of chemistry in which the relationships between substances in chemical reactions are calculated and often work with moles is called stoichiometry. The molar concentration can be found from 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 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 equation of a chemical reaction, 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, you can perform calculations in reverse order, using information about the molar concentration of the substance.

Let's look at a simple example. This time we'll mix baking soda and vinegar to see what's interesting. chemical reaction. Both vinegar and baking soda are easy to find - you probably have them in your kitchen. As mentioned above, the formula of soda is NaHCO₃. Vinegar is not pure substance, and a 5% solution of acetic acid in water. The formula of acetic acid is CH₃COOH. The concentration of acetic acid in vinegar may 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 varies. In this experiment, you don't have to worry about chemical reactions between water and other substances, since water doesn't react with baking soda. We only care about the volume of water when we later 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, due to its low stability, again enters into a chemical reaction.

H₂CO₃ → H₂O + CO₂

As a result of the reaction we obtain water (H₂O), carbon dioxide(CO₂) and sodium acetate (NaC₂H₃O₂). Let's 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 it is dissolved. acetic acid. Sodium acetate is an interesting substance. It is used in chemical warmers, such as hand warmers.

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

When using recipes, whether in cooking, making medicine, or creating the perfect environment for aquarium fish, you need to know the concentration. IN Everyday life It is often more convenient to use grams, but in pharmaceuticals and chemistry molar concentrations are more often used.

In pharmaceuticals

When creating drugs, molar concentration is very important because 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, the drug is ineffective. In addition, concentration is important when exchanging fluids through cell membranes in organism. When determining the concentration of a liquid that must either pass or, conversely, not pass through 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 compared to the concentration 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 through the membrane is often problematic. For example, if fluid moves into a cell, such as into a blood cell, it is possible that the membrane will become damaged and rupture due to this fluid overflow. Leakage of fluid from the cell is also problematic, since this will impair the functioning of the cell. It is desirable to prevent any drug-induced flow of fluid across the membrane out of or into the cell, and to achieve 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 is worth noting that in some cases the molar and osmotic concentrations are equal, but this is not always the case. This depends on whether the substance dissolved in water has broken down into ions during the process electrolytic dissociation . When calculating osmotic concentration, particles in general are taken into account, while when calculating 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 broken up into ions, then there will be fewer molecules total number particles (including molecules and ions), and therefore the molar concentration will be lower than the osmotic one. To convert molar concentration to osmotic concentration, you need to know physical properties 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 allow through. The process of osmosis causes solutions of higher concentration to move into solutions of lower concentration, but if the membrane prevents this movement by not allowing the solution to pass through, then pressure occurs on the membrane. This kind of pressure is usually problematic. If a drug is intended to enter the blood or other body fluid, the tonicity of the drug must be balanced with the tonicity of the body fluid to avoid osmotic pressure on membranes in the body.

To balance the tonicity, medications 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. Typically, 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 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 in TCTerms and within a few minutes you will receive an answer.

The number of particles in one mole of any substance is constant and is called Avogadro's number ( N A).

Multiples and submultiples

Decimal multiples and submultiples are formed using standard SI prefixes.

Note: unit yoctomole can only be used formally, since such small amounts of a substance must be measured in individual particles (1 imole is formally equal to 0.602 particles).

Wikimedia Foundation.

2010.

See what “Mole (unit)” is in other dictionaries: Mole, a unit of quantity of a substance, i.e., a quantity estimated by the amount contained in physical system identical structural elements (atoms, molecules, ions and other particles or their specific groups). M. is equal to the amount of substance... ... Big

Soviet encyclopedia

1. MOL, and; and. A small butterfly whose caterpillar is a pest of woolen items, grains and plants. 2. MOL, and; and.; MOL, I; m. Special Forest floated down the river with logs not tied into a raft. The m floated along the river. Making your way by boat... ... encyclopedic Dictionary

Mole ambiguous word: Mole is a unit of measurement of the amount of a substance, Mole is a representative of moles (under the name “moths” they are combined into a non-taxonomic group of small insects from the order Lepidoptera). Settlements Moth......Wikipedia

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

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, SI unit of amount of substance. Designation mole. 1 mole contains as many molecules (atoms, ions or any other structural elements of a substance) as there are atoms in 0.012 kg of 12C (carbon with atomic mass 12). number… … Modern encyclopedia

The SI unit of quantity of a substance is denoted by the mole. 1 mole contains as many molecules (atoms, ions or any other structural elements of a substance) as there are atoms in 0.012 kg of 12C (carbon with atomic mass 12), i.e. 6.022.1023... ... Big Encyclopedic Dictionary

Mole- MOL, SI unit of amount of substance. Designation mole. 1 mole contains as many molecules (atoms, ions or any other structural elements of a substance) as there are atoms in 0.012 kg of 12C (carbon with atomic mass 12). Number… … Illustrated Encyclopedic Dictionary

This article is about the unit of measurement. The word "Mole" has other meanings: see Mole (meanings). Mole (Russian designation: mol; international: mol) unit of measurement of the amount of substance in International system units (SI), one of seven ... Wikipedia