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 the amount of a substance that contains as many structural units of a given substance (molecules, atoms, ions, etc.) as there are carbon atoms contained in 0.012 kg (12 g) of a carbon isotope 12 WITH .
Considering that the value of the absolute atomic mass for carbon is equal to m(C) = 1.99 10 26 kg, the number of carbon atoms can be calculated 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 is 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 mole.
Molar mass is designated by the letter M and has the dimension [g/mol]. In physics they use the unit [kg/kmol].
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, relative molecular mass water is equal to:
Мr(Н 2 О) = 2Аr (Н) + Аr (O) = 2∙1 + 16 = 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. Water, with an amount of substance of 1 mole, contains 2 moles of hydrogen atoms and one 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 therefore the value of its molar mass, you can determine the amount of the substance and, conversely, knowing the amount of the substance, you can determine its mass. For such calculations you should use the formulas:
where ν is the amount of substance, [mol]; m– mass of the substance, [g] or [kg]; M – molar mass of the substance, [g/mol] or [kg/kmol].
For example, to find the mass of sodium sulfate (Na 2 SO 4) in an amount of 5 moles, we find:
1) the value of the relative molecular mass 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) a 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 quantity
Under normal conditions (n.s.), 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 different gases and vapors occupies the same volume equal to 22.4 l.
The volume occupied by 1 mole of gas or vapor at ground level is called molar volumegas and has the dimension 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 – volume of gaseous substance [l]; V mol = 22.4 l/mol.
And, conversely, knowing the volume ( V) of a gaseous substance under normal conditions, its quantity (ν) can be calculated :
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Chemical formula
Molar mass of H2O, water 18.01528 g/mol
1.00794 2+15.9994
Mass fractions of elements in the compound
Using the Molar Mass Calculator
- Chemical formulas must be entered case sensitive
- Subscripts are entered as regular numbers
- The dot on the midline (multiplication sign), used, for example, in the formulas of crystalline hydrates, is replaced by a regular dot.
- Example: instead of CuSO₄·5H₂O in the converter, for ease of entry, the spelling CuSO4.5H2O is used.
Molar mass calculator
Mole
All substances are made up of atoms and molecules. In chemistry, it is important to accurately measure the mass of substances that react and are produced as a result. By definition, the mole is the SI unit of quantity of a substance. One mole contains exactly 6.02214076×10²³ elementary particles. This value is numerically equal to Avogadro's constant N A when expressed in units of mol⁻¹ and is called Avogadro's number. Amount of substance (symbol n) of a system is a measure of the number of structural elements. A structural element can be an atom, molecule, ion, electron, or any particle or group of particles.
Avogadro's constant N A = 6.02214076×10²³ mol⁻¹. Avogadro's number is 6.02214076×10²³.
In other words, a mole is an amount of substance equal in mass to the sum of the atomic masses of atoms and molecules of the substance, multiplied by Avogadro's number. The unit of quantity of a substance, the mole, is one of the seven basic SI units and is symbolized by the mole. Since the name of the unit and its symbol are the same, it should be noted that the symbol is not declined, unlike the name of the unit, which can be declined according to the usual rules of the Russian language. One mole of pure carbon-12 is equal to exactly 12 g.
Molar mass
Molar mass - physical property of a substance, defined as the ratio of the mass of that substance to the amount of substance in moles. In other words, this is the mass of one mole of a substance. The SI unit of molar mass is kilogram/mol (kg/mol). However, chemists are accustomed to using the more convenient unit g/mol.
molar mass= g/mol
Molar mass of elements and compounds
Compounds are substances consisting of different atoms that are chemically bonded to each other. For example, the following substances, which can be found in any housewife’s kitchen, are chemical compounds:
- salt (sodium chloride) NaCl
- sugar (sucrose) C₁₂H₂₂O₁₁
- vinegar (solution acetic acid) CH₃COOH
The molar mass of a chemical element in grams per mole is numerically the same as the mass of the element's atoms expressed in atomic mass units (or daltons). The molar mass of compounds is equal to the sum of the molar masses of the elements that make up the compound, taking into account the number of atoms in the compound. For example, the molar mass of water (H₂O) is approximately 1 × 2 + 16 = 18 g/mol.
Molecular mass
Molecular mass (the old name is molecular weight) is the mass of a molecule, calculated as the sum of the masses of each atom that makes up the molecule, multiplied by the number of atoms in this molecule. Molecular weight is dimensionless a physical quantity numerically equal to molar mass. That is, molecular mass differs from molar mass in dimension. Even though molecular mass is a dimensionless quantity, it still has a value called the atomic mass unit (amu) or dalton (Da), and approximately equal to mass one proton or neutron. The atomic mass unit is also numerically equal to 1 g/mol.
Calculation of molar mass
Molar mass is calculated as follows:
- determine atomic masses elements according to the periodic table;
- determine the number of atoms of each element in the compound formula;
- determine the molar mass by adding the atomic masses of the elements included in the compound, multiplied by their number.
For example, let's calculate the molar mass of acetic acid
It consists of:
- two carbon atoms
- four hydrogen atoms
- two oxygen atoms
- carbon C = 2 × 12.0107 g/mol = 24.0214 g/mol
- hydrogen H = 4 × 1.00794 g/mol = 4.03176 g/mol
- oxygen O = 2 × 15.9994 g/mol = 31.9988 g/mol
- molar mass = 24.0214 + 4.03176 + 31.9988 = 60.05196 g/mol
Our calculator performs exactly this calculation. You can enter the acetic acid formula into it and check what happens.
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.
Water is the most abundant substance in nature. It is a thermodynamically stable compound that can be in three states of aggregation at once: liquid, solid (ice) and gaseous (water vapor), each of which is determined by temperature and pressure (Fig. 1).
Rice. 1. Diagram of the state of water.
The AO curve corresponds to equilibrium in the ice-steam system, DO to equilibrium in the supercooled water-steam system, the OC curve to equilibrium in the water-steam system, and the OB curve to equilibrium in the ice-water system. At point O all curves intersect. This point is called the triple point and corresponds to equilibrium in the ice-water-steam system.
The gross formula of water is H 2 O. As is known, the molecular weight of a molecule is equal to the sum of the relative atomic masses of the atoms that make up the molecule (the values of the relative atomic masses taken from D.I. Mendeleev’s Periodic Table are rounded to whole numbers).
Mr(H 2 O) = 2×Ar(H) + Ar(O);
Mr(H 2 O) = 2×1 + 16 = 2 + 16 = 18.
DEFINITION
Molar mass (M) is the mass of 1 mole of a substance.
It is easy to show that the numerical values of the molar mass M and the relative molecular mass M r are equal, however, the first quantity has the dimension [M] = g/mol, and the second is dimensionless:
M = N A × m (1 molecule) = N A × M r × 1 amu = (N A ×1 amu) × M r = × M r .
It means that molar mass of water is 18 g/mol.
Examples of problem solving
EXAMPLE 1
| Exercise | Calculate the mass fraction of elements in the following molecules: a) water (H 2 O); b) sulfuric acid (H 2 SO 4). |
| Answer |
Let us calculate the mass fractions of each of the elements that make up the indicated compounds. a) Find the molecular mass of water: Mr (H 2 O) = 2×Ar(H) + Ar(O); Mr (H 2 O) = 2x1.00794 + 15.9994 = 2.01588 + 15.9994 = 18.0159. It is known that M = Mr, which means M(H 2 O) = 32.2529 g/mol. Then the mass fractions of oxygen and hydrogen will be equal: ω (H) = 2 × Ar (H) / M (H 2 O) × 100%; ω(H) = 2 × 1.00794 / 18.0159 × 100%; ω(H) = 2.01588 / 18.0159× 100% = 11.19%. ω (O) = Ar (O) / M (H 2 O) × 100%; ω(O) = 15.9994 / 18.0159× 100% = 88.81%. b) Find the molecular sulfuric acid: Mr (H 2 SO 4) = 2×Ar(H) + Ar(S) + 4×Ar(O); Mr (H 2 SO 4) = 2 × 1.00794 + 32.066 + 4 × 15.9994 = 2.01588 + + 32.066 + 63.9976; Mr (H 2 SO 4) = 98.079. It is known that M = Mr, which means M(H 2 SO 4) = 98.079 g/mol. Then the mass fractions of oxygen, sulfur and hydrogen will be equal: ω (H) = 2 × Ar (H) / M (H 2 SO 4) × 100%; ω(H) = 2 × 1.00794 / 98.079 × 100%; ω(H) = 2.01588 / 98.079× 100% = 2.06%. ω (S) = Ar (S) / M (H 2 SO 4) × 100%; ω(S) = 32.066 / 98.079 × 100% = 32.69%. ω (O) = 4×Ar (O) / M (H 2 SO 4) × 100%; ω (O) = 4 × 15.9994 / 98.079 × 100% = 63.9976 / 98.079 × 100% = 65.25% |
EXAMPLE 2
| Exercise | Calculate where in which of the compounds the mass fraction (in %) of the element hydrogen is greater: in methane (CH 4) or hydrogen sulfide (H 2 S)? |
| Solution | The mass fraction of element X in a molecule of the composition NX is calculated using the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let's calculate the mass fraction of each element of hydrogen in each of the proposed compounds (we will round the values of relative atomic masses taken from D.I. Mendeleev's Periodic Table to whole numbers). Let's find the molecular weight of methane: Mr (CH 4) = 4×Ar(H) + Ar(C); Mr (CH 4) = 4×1+ 12 = 4 + 12 = 16. It is known that M = Mr, which means M(CH 4) = 16 g/mol. Then the mass fraction of hydrogen in methane will be equal to: ω (H) = 4 × Ar (H) / M (CH 4) × 100%; ω(H) = 4 × 1 / 16 × 100%; ω(H) = 4/ 16 × 100% = 25%. Let's find the molecular weight of hydrogen sulfide: Mr (H 2 S) = 2×Ar(H) + Ar(S); Mr (H 2 S) = 2×1+ 32 = 2 + 32 = 34. It is known that M = Mr, which means M(H 2 S) = 34 g/mol. Then the mass fraction of hydrogen in hydrogen sulfide will be equal to: ω (H) = 2 × Ar (H) / M (H 2 S) × 100%; ω(H) = 2 × 1 / 34 × 100%; ω (H) =2/ 34 × 100% = 5.88%. Thus, the mass fraction of hydrogen is greater in methane, since 25 > 5.88. |
| Answer | The mass fraction of hydrogen is higher in methane (25%) |
8.31. Gas temperature T = 500K. What is the molar mass of the gas?
From me: k=1.38*10^-23
Na=6.022*10^23
I solved and solved and got lost) somewhere in the calculations I made a mistake and the answer came out wrong.
The root mean square speed of the molecules of some ideal gas having a density ρ=1.8 kg/m3 is 500 m/s. What is the gas pressure:1) increases
2) decreases
3) increases or decreases depending on changes in volume
4) does not change
What is the compression pressure of air weighing 12 kg in a cylinder with a volume of 20 l at 17°C?
What is the pressure of nitrogen with a density of 2.8 kg/m3 if its temperature in the vessel is 400 K?
What is the molar mass of a gas weighing 0.017 g located in a vessel with a volume of 10 liters under a pressure of 2.105 Pa and a temperature of 400 K?
1) 0.028 KG/MOL
2) 0.136 KG/MOL
3) 2.4 KG/MOL
4) 40 KG/MOL
What amount of gas is contained in a vessel with a volume of 8.31 m3 at a pressure of 105 Pa and a temperature of 100 K?
1) 1000 mol
Find the average kinetic energy of translational motion of ideal gas molecules under normal conditions.
1) 6.2 .10-21J
2) 12.4 .10-21J
3) 3.5 .10-21J
4) 5.65 .10-21J
What is rms speed molecules weighing 3.10-26 kg each, if they create a pressure of 105 Pa and their concentration is 10 25 m-3?
1) 10-3 m/s
2) 6.102m/s
3) 103m/s
4) 106 m/s
What is the molar gas constant R if the density of saturated water vapor at 100°C and normal pressure is 0.59 kg/m3?
1) 8.31 J/mol.K
2) 8.21 J/mol.K
3) 8.41 J/mol.K
4) 8.51 J/mol.K
What is the temperature of the gas in Celsius if it is 273K in Kelvin?
The molar mass of neon is 0.02 kg/mol, the mass of an argon atom is 2 times greater than the mass of a neon atom. Based on these data, determine what the molar mass is1) cannot be calculated
2) 0.01 kg/mol
3) 0.04 kg/mol
4) 0.12*10^23 kg/mol
1. Mark all correct answers. Which statements are true?A. Liquid evaporates at any temperature
B. The rate of diffusion does not depend on temperature
B. The arrangement of liquid molecules is characterized by close order
D. You cannot talk about the pressure of one gas molecule
D. The SI unit of molar mass is kilogram
E. Solids retain shape but retain volume.
2. Mark one correct answer, in your opinion.
What is the molar mass of hydrochloric acid?
A. 18 kg/mol
B. 36 kg/mol
B. 18 x 10(minus third) kg/mol
G. 36 x 10(minus third) kg/mol
3. The pressure of an ideal gas was isochorically doubled and then isothermally decreased by a factor of two. Draw graphs of the processes described. (see Attachment)
4. Solve the problem.
A solution was poured into a sprayer cylinder with a capacity of 12 liters and air with a volume of 7 liters was pumped to a pressure of 3 x 10 (to the fifth power) Pa. What will the air in the cylinder be like after all the solution has been used up?
Length and distance converter Mass converter Converter of volume measures of bulk products and food products Area converter Converter of volume and units of measurement in culinary recipes Temperature converter Converter of pressure, mechanical stress, Young's modulus Converter of energy and work Converter of power Converter of force Converter of time Linear speed converter Flat angle Converter thermal efficiency and fuel efficiency Converter of numbers in various number systems Converter of units of measurement of quantity of information Currency rates Women's clothing and shoe sizes Men's clothing and shoe sizes Angular velocity and rotation frequency converter Acceleration converter Angular acceleration converter Density converter Specific volume converter Moment of inertia converter Moment of force converter Torque converter Specific heat of combustion converter (by mass) Energy density and specific heat of combustion converter (by volume) Temperature difference converter Coefficient of thermal expansion converter Thermal resistance converter Thermal conductivity converter Specific heat capacity converter Energy exposure and thermal radiation power converter Heat flux density converter Heat transfer coefficient converter Volume flow rate converter Mass flow rate converter Molar flow rate converter Mass flow density converter Molar concentration converter Mass concentration in solution converter Dynamic (absolute) viscosity converter Kinematic viscosity converter Surface tension converter Vapor permeability converter Water vapor flow density converter Sound level converter Microphone sensitivity converter Converter Sound Pressure Level (SPL) Sound Pressure Level Converter with Selectable Reference Pressure Luminance Converter Luminous Intensity Converter Illuminance Converter Computer Graphics Resolution Converter Frequency and Wavelength Converter Diopter Power and Focal Length Diopter Power and Lens Magnification (×) Converter electric charge Linear charge density converter Surface charge density converter Volume charge density converter Electric current converter Linear current density converter Surface current density converter Electric field strength converter Electrostatic potential and voltage converter Electrical resistance converter Electrical resistivity converter Electrical conductivity converter Electrical conductivity converter Electrical capacitance Inductance Converter American Wire Gauge Converter Levels in dBm (dBm or dBm), dBV (dBV), watts, etc. units Magnetomotive force converter Magnetic field strength converter Magnetic flux converter Magnetic induction converter Radiation. Ionizing radiation absorbed dose rate converter Radioactivity. Radioactive decay converter Radiation. Exposure dose converter Radiation. Absorbed dose converter Decimal prefix converter Data transfer Typography and image processing unit converter Timber volume unit converter Calculation of molar mass Periodic table of chemical elements by D. I. Mendeleev
Chemical formula
Molar mass of H2O, water 18.01528 g/mol
1.00794 2+15.9994
Mass fractions of elements in the compound
Using the Molar Mass Calculator
- Chemical formulas must be entered case sensitive
- Subscripts are entered as regular numbers
- The dot on the midline (multiplication sign), used, for example, in the formulas of crystalline hydrates, is replaced by a regular dot.
- Example: instead of CuSO₄·5H₂O in the converter, for ease of entry, the spelling CuSO4.5H2O is used.
Molar mass calculator
Mole
All substances are made up of atoms and molecules. In chemistry, it is important to accurately measure the mass of substances that react and are produced as a result. By definition, the mole is the SI unit of quantity of a substance. One mole contains exactly 6.02214076×10²³ elementary particles. This value is numerically equal to Avogadro's constant N A when expressed in units of mol⁻¹ and is called Avogadro's number. Amount of substance (symbol n) of a system is a measure of the number of structural elements. A structural element can be an atom, molecule, ion, electron, or any particle or group of particles.
Avogadro's constant N A = 6.02214076×10²³ mol⁻¹. Avogadro's number is 6.02214076×10²³.
In other words, a mole is an amount of substance equal in mass to the sum of the atomic masses of atoms and molecules of the substance, multiplied by Avogadro's number. The unit of quantity of a substance, the mole, is one of the seven basic SI units and is symbolized by the mole. Since the name of the unit and its symbol are the same, it should be noted that the symbol is not declined, unlike the name of the unit, which can be declined according to the usual rules of the Russian language. One mole of pure carbon-12 is equal to exactly 12 g.
Molar mass
Molar mass is a physical property of a substance, defined as the ratio of the mass of this substance to the amount of substance in moles. In other words, this is the mass of one mole of a substance. The SI unit of molar mass is kilogram/mol (kg/mol). However, chemists are accustomed to using the more convenient unit g/mol.
molar mass = g/mol
Molar mass of elements and compounds
Compounds are substances consisting of different atoms that are chemically bonded to each other. For example, the following substances, which can be found in any housewife’s kitchen, are chemical compounds:
- salt (sodium chloride) NaCl
- sugar (sucrose) C₁₂H₂₂O₁₁
- vinegar (acetic acid solution) CH₃COOH
The molar mass of a chemical element in grams per mole is numerically the same as the mass of the element's atoms expressed in atomic mass units (or daltons). The molar mass of compounds is equal to the sum of the molar masses of the elements that make up the compound, taking into account the number of atoms in the compound. For example, the molar mass of water (H₂O) is approximately 1 × 2 + 16 = 18 g/mol.
Molecular mass
Molecular mass (the old name is molecular weight) is the mass of a molecule, calculated as the sum of the masses of each atom that makes up the molecule, multiplied by the number of atoms in this molecule. Molecular weight is dimensionless a physical quantity numerically equal to molar mass. That is, molecular mass differs from molar mass in dimension. Although molecular mass is dimensionless, it still has a value called the atomic mass unit (amu) or dalton (Da), which is approximately equal to the mass of one proton or neutron. The atomic mass unit is also numerically equal to 1 g/mol.
Calculation of molar mass
Molar mass is calculated as follows:
- determine the atomic masses of elements according to the periodic table; Post a question in TCTerms and within a few minutes you will receive an answer.