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What is the molar mass of water. Molar mass of water Molar mass of water kg mol

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 FROM .

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 BUT 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 BUT ).

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) :

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Chemical formula

Molar mass of H 2 O, 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
Indexes 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, the converter uses the spelling CuSO4.5H2O for ease of entry.

Ferrofluids

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 entering into a reaction and resulting from it. By definition, the mole is the SI unit for the amount of a substance. One mole contains exactly 6.02214076×10²³ elementary particles. This value is numerically equal to the Avogadro constant N A when expressed in units of moles⁻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, a molecule, an ion, an 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 the amount of a substance equal in mass to the sum of the atomic masses of the atoms and molecules of the substance, multiplied by the Avogadro number. The mole is one of the seven basic units of the SI system and is denoted by the mole. Since the name of the unit and its symbol are the same, it should be noted that the symbol is not inflected, 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 equals exactly 12 grams.

Molar mass

Molar mass is a physical property of a substance, defined as the ratio of the mass of that substance to the amount of the substance in moles. In other words, it is the mass of one mole of a substance. In the SI system, the 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 made up of different atoms that are chemically bonded to each other. For example, the following substances, which can be found in the kitchen of any housewife, are chemical compounds:

salt (sodium chloride) NaCl
sugar (sucrose) C₁₂H₂₂O₁₁
vinegar (acetic acid solution) CH₃COOH

The molar mass of chemical elements 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 weight (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. The molecular weight is dimensionless a physical quantity numerically equal to the molar mass. That is, the molecular weight differs from the molar mass in dimension. Although the molecular mass is a dimensionless quantity, it still has a value called the atomic mass unit (amu) or dalton (Da), and is approximately equal to the mass of one proton or neutron. The atomic mass unit is also numerically equal to 1 g/mol.

Molar mass calculation

The molar mass is calculated as follows:

determine the atomic masses of the 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 does just that. You can enter the formula of acetic acid 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 to TCTerms and within a few minutes you will receive an answer.

In a sealed vessel with a volume of V \u003d 62.3 l at a pressure of p \u003d 4 * 10 ^ 5 Pa, there is some gas with a mass of m \u003d 12 g. The molar gas constant is R \u003d

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, solved and got lost) somewhere in the calculations I made a mistake and the answer came out wrong.

The root-mean-square velocity of the molecules of some ideal gas with a density ρ=1.8 kg/m3 is 500 m/s. What is the pressure of the gas:

1) increases

2) decreases

3) increases or decreases depending on the change in volume

4) does not change

What is the compression pressure of 12 kg air in a 20 l cylinder 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 of mass 0.017 g, located in a vessel with a volume of 10 liters at a pressure of 2.105 Pa and a temperature of 400 K?

1) 0.028 KG/MOLE

2) 0.136 KG/MOLE

3) 2.4 KG/MOLE

4) 40 KG/MOLE

What amount of gas is contained in a vessel with a volume of 8.31 m3 at a pressure of 105Pa and a temperature of 100K?

1) 1000 mol

Find the average kinetic energy of the 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 the root-mean-square velocity of 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 the mass of a neon atom. Based on these data, determine what the molar mass is

1) 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. Diffusion rate does not depend on temperature
C. The arrangement of liquid molecules is characterized by close order
D. You can’t talk about the pressure of one gas molecule
D. The SI unit of molar mass is kilogram
E. Solids retain their shape but retain their volume.

2. Mark one correct, in your opinion, answer.
What is the molar mass of hydrochloric acid?
A. 18 kg/mol
B. 36 kg/mol
B. 18 x 10 (in minus third) kg / mol
D. 36 x 10 (minus third) kg / mol

3. The pressure of an ideal gas is doubled isochorically and then doubled isothermally. Draw graphs of the described processes. (see Attachment)

4. Solve the problem.

A solution was poured into a sprayer bottle with a capacity of 12 liters and air was pumped up with a volume of 7 liters to a pressure of 3 x 10 (to the fifth degree) Pa. What will the air in the balloon look like after all the solution has been used up?

Chemical formula

Molar mass of H 2 O, 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
Indexes 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, the converter uses the spelling CuSO4.5H2O for ease of entry.

Molar mass calculator

mole

Avogadro's constant N A = 6.02214076×10²³ mol⁻¹. Avogadro's number is 6.02214076×10²³.

Molar mass

molar mass = g/mol

Molar mass of elements and compounds

salt (sodium chloride) NaCl
sugar (sucrose) C₁₂H₂₂O₁₁
vinegar (acetic acid solution) CH₃COOH

Molecular mass

Molar mass calculation

The molar mass is calculated as follows:

determine the atomic masses of the elements according to the periodic table;

Post a question to TCTerms

Water is the most common substance in nature. It is a thermodynamically stable compound capable of being 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 the equilibrium in the supercooled water-steam system, the OC curve - to the equilibrium in the water-steam system, and the OB curve - to the equilibrium in the ice-water system. At point O, all curves intersect. This point is called the triple point and corresponds to the equilibrium in the ice-water-steam system.

The gross formula of water is H 2 O. As you know, 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 the Periodic Table of D.I. Mendeleev are rounded to integers).

Mr(H 2 O) = 2×Ar(H) + Ar(O);

Mr(H 2 O) \u003d 2 × 1 + 16 \u003d 2 + 16 \u003d 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 value has the dimension [M] = g/mol, and the second is dimensionless:

M = N A × m (1 molecules) = N A × M r × 1 a.m.u. = (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

The task

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 weight of water:

Mr(H 2 O) = 2×Ar(H) + Ar(O);

Mr(H 2 O) = 2 x 1.00794 + 15.9994 = 2.01588 + 15.9994 = 18.0159.

It is known that M \u003d Mr, which means M (H 2 O) \u003d 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) \u003d 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) = 2x1.00794 + 32.066 + 4x15.9994 = 2.01588 + + 32.066 + 63.9976;

Mr (H 2 SO 4) = 98.079.

It is known that M \u003d Mr, which means M (H 2 SO 4) \u003d 98.079 g / mol. Then the mass fractions of oxygen, sulfur and hydrogen will be equal:

ω (H) \u003d 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) \u003d Ar (S) / M (H 2 SO 4) × 100%;

ω(S) = 32.066 / 98.079×100% = 32.69%.

ω (O) \u003d 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

The task

Calculate where in which of the compounds the mass fraction (in%) of the hydrogen element is greater: in methane (CH 4) or hydrogen sulfide (H 2 S)?

Solution

The mass fraction of the element X in the molecule of the HX composition is calculated by the following formula:

ω (X) = n × Ar (X) / M (HX) × 100%.

Let us calculate the mass fraction of each element of hydrogen in each of the proposed compounds (the values of the relative atomic masses taken from the Periodic Table of D.I. Mendeleev will be rounded to integers).

Find the molecular weight of methane:

Mr (CH 4) = 4×Ar(H) + Ar(C);

Mr (CH 4) \u003d 4 × 1 + 12 \u003d 4 + 12 \u003d 16.

It is known that M \u003d Mr, which means M (CH 4) \u003d 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%.

Find the molecular weight of hydrogen sulfide:

Mr(H 2 S) = 2×Ar(H) + Ar(S);

Mr (H 2 S) \u003d 2 × 1 + 32 \u003d 2 + 32 \u003d 34.

It is known that M \u003d Mr, which means M (H 2 S) \u003d 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) \u003d 2 / 34 × 100% \u003d 5.88%.

Thus, the mass fraction of hydrogen is greater in methane, since 25 > 5.88.

Answer

The mass fraction of hydrogen is greater in methane (25%)