How to spell nude in chemistry. Buy a higher education diploma inexpensively

Instructions

One of the formulas for the volume of a solution: V = m/p, where V is the volume of the solution (ml), m is the mass (g), p is the density (g/ml). If you need to additionally find the mass, this can be done by knowing the formula and amount of the required substance. Using the formula of a substance, we will find its molar mass by adding up the atomic masses of all the elements included in it. For example, M(AgNO3) = 108+14+16*3 = 170 g/mol. Next, we find the mass using the formula: m = n*M, where m is mass (g), n is the amount of substance (mol), M is the molar mass of the substance (g/mol). It is assumed that the quantity of the substance is given in the problem.

The following for finding the volume of a solution is derived from the molar formula: c = n/V, where c is the molar concentration of the solution (mol/l), n is the amount of substance (mol), V is the volume of the solution (l). We derive: V = n/c. The amount of a substance can additionally be found using the formula: n = m/M, where m is mass, M is molar mass.

The following are formulas for finding the volume of gas. V = n*Vm, where V is the volume of gas (l), n is the amount of substance (mol), Vm is the molar volume of gas (l/mol). Under normal conditions, i.e. pressure equal to 101 325 Pa 273 K, the molar volume of the gas is constant and equal to 22.4 l/mol.

For a gas system there is a formula: q(x) = V(x)/V, where q(x)(phi) is the volume fraction of the component, V(x) is the volume of the component (l), V is the volume of the system (l) . From this formula we can derive 2 others: V(x) = q*V, and also V = V(x)/q.

If the problem statement contains a reaction equation, the problem should be solved using it. From the equation you can find the amount of any substance; it is equal to the coefficient. For example, CuO + 2HCl = CuCl2 + H2O. From this we see that the interaction of 1 mole of copper oxide and 2 moles of hydrochloric acid produces 1 mole of copper chloride and 1 mole of water. Knowing from the conditions of the problem the amount of substance of just one component of the reaction, you can easily find the amounts of all substances. Let the amount of copper oxide substance be 0.3 mol, which means n(HCl) = 0.6 mol, n(CuCl2) = 0.3 mol, n(H2O) = 0.3 mol.

note

Don't forget about units of measurement!

Sources:

• "Collection of problems in chemistry", G.P. Khomchenko, I.G. Khomchenko, 2002.
• volume formula from mass

The mass of any substance or molecule is equal to the sum of the masses of the atoms that form it. If you use relative atomic masses in your calculations, you get the relative molecular mass of the substance. Relative molecular mass shows how many times the absolute mass of a molecule of a given substance is greater than 1/12 of the absolute mass of a carbon atom. Typically, approximate values ​​of relative atomic and molecular masses are used. These quantities are dimensionless.

Instructions

Calculate the value of each element in the molecule. To find out the relative mass of one atom, look at the periodic table of elements. The atomic number is the atomic mass. You can also calculate it using the formula Ar(element)=m(element)/1a.e.m. For ease of calculation, approximate values ​​are used.
Ar(H)=1?2=2;Ar(O)=16?1=16Ar(Fe)=56?2=112;Ar(S)=32?3=96;Ar(O)=16?12 =192

Add up the results obtained. This will be the molecular mass of the substance.
Mr(H2O)=2Ar(H)+Ar(O)=2+16=18
Mr(Fe2(SO4)3)=2Ar(Fe)+3Ar(S)+12Ar(O)=112+96+192=400

In addition to relative molecular mass, molar mass is often used in calculations. Its unit of measurement is g/mol. It is numerically equal to the relative molecular mass of the substance.
M(H2O)=18 g/mol
M(Fe2(SO4)3=400 g/mol

Video on the topic

During a chemical reaction, a variety of substances can be formed: gaseous, soluble, slightly soluble. In the latter case, they precipitate. It is often necessary to find out what the exact mass of the sediment formed is. How can this be calculated?

You will need

• - glass funnel;
• - paper filter;
• - laboratory scales.

Instructions

You can act experimentally. That is, carry out a chemical test, carefully separate the formed precipitate from the filtrate using an ordinary glass funnel and a paper filter, for example. More complete separation is achieved using vacuum filtration (on a Buchner funnel).

After this, dry the sediment - naturally or under vacuum, and weigh it as accurately as possible. Best of all, on a sensitive laboratory scale. This is how the task will be solved. This method is used when the exact quantities of the starting substances that reacted are unknown.

If you know these quantities, then the problem can be solved much easier and faster. Suppose you need to calculate how much chloride was formed from 20 grams of chloride - table salt - and 17 grams of silver nitrate. First of all, write the equation: NaCl + AgNO3 = NaNO3 + AgCl.

During this reaction, a very slightly soluble compound is formed - silver chloride, which precipitates in the form of a white precipitate.

Calculate the molar masses of the starting substances. For sodium chloride it is approximately 58.5 g/mol, for silver nitrate – 170 g/mol. That is, initially, according to the conditions of the problem, you had 20/58.5 = 0.342 moles of sodium chloride and 17/170 = 0.1 moles of silver nitrate.

Thus, it turns out that sodium chloride was initially taken in excess, that is, the reaction with the second starting substance will proceed to completion (all 0.1 moles of silver nitrate will react, “binding” the same 0.1 moles of table salt). How much silver chloride is produced? To answer this question, find the molecular weight of the formed precipitate: 108 + 35.5 = 143.5. By multiplying the initial amount of silver nitrate (17 grams) by the ratio of the molecular masses of the product and the starting substance, you get the answer: 17 * 143.5/170 = 14.3 grams. This will be the exact mass of the precipitate formed during the reaction.

Helpful advice

Of course, the answer you received is not very accurate, since you used rounded values ​​of the atomic masses of the elements in your calculations. If greater accuracy is required, it is necessary to take into account that the atomic mass of silver, for example, is not 108, but 107.868. Accordingly, the atomic mass of chlorine is not 35.5, but 35, 453, etc.

Sources:

• calculate the mass of the sediment that formed during the interaction

In school chemistry problems, as a rule, you need to calculate the volume for the gaseous reaction product. You can do this if you know the number of moles of any participant in the chemical reaction. Or find this quantity from other problem data.

Lesson objectives:

• Introduce the concept of the amount of a substance and its units of measurement: mole, mmol, kmol.
• Give an idea of ​​Avogadro's constant.
• Show the relationship between mass, amount of matter and number of particles.

Lesson objectives:

• 1. Contribute to the formation of students’ worldview ideas about the relationship between different properties of phenomena in the surrounding world.
• 2. Develop students’ ability to establish cause-and-effect relationships, as well as observe, generalize and draw conclusions.

Key terms:

• Nonmetals – chemical elements that form in free form simple substances that do not have the physical properties of metals.
• A mole is a quantity of any substance that contains the same number of structural elements as atoms contained in 12g. carbon-12 nuclide

  DURING THE CLASSES

Quantity of substance

In chemistry (as well as in physics and other natural sciences) you have to deal with large quantities of tiny particles - the so-called structural elements of matter (molecules, atoms, ions, electrons, etc.).
In order to express the number of such particles, a unit of quantity was introduced - the mole. 1 mole is the amount of any substance that contains the same number of structural elements as there are atoms in 12g. carbon-12 nuclide. It was experimentally found that the number of structural elements corresponding to 1 mole is 6.02∙1023 (the constant 6.02∙1023 mol-1 is called Avogadro’s constant. Cylinders with substances of 1 mole).

Rice. 1. Avogadro's constant
Illustration of a corollary to Avogadro's law

Rice. 2. – unit of quantity of substance

Mole is a unit of quantity of a substance


Rice. 3. Quantity of substance
This portion of a substance has a mass called molar mass. It is denoted by M, which is found by the formula M = m/n. Guess in what units molar mass will be measured?
Molar mass coincides in value with relative atomic or molecular mass, but differs in units of measurement (M - g/mol; Mr, Ar - dimensionless quantities).


Rice. 4. Amount of substance in moles


Rice. 5. Molar mass

Control block

№1.
The mass of 3 mol H2O is ____ g
The mass of 20 mol H2O is ____ g
№2.
36 g of H2O equals ______ moles
180g H2O equals _______ moles

Homework

How many molecules are there in 180 g of water?
Find the mass of 24x1023 ozone molecules?

Oxygen is the most common chemical element in the earth's crust. Oxygen is part of almost all substances around us. For example, water, sand, many rocks and minerals that make up the earth's crust contain oxygen. Oxygen is also an important part of many organic compounds, such as proteins, fats and carbohydrates, which are of exceptional importance in the life of plants, animals and humans.
In 1772, the Swedish chemist K.V. Scheele established that air consists of oxygen and nitrogen. In 1774, D. Priestley obtained oxygen by decomposition of mercury oxide (2). Oxygen is a colorless gas, tasteless and odorless, relatively slightly soluble in water, slightly heavier than air: 1 liter of oxygen under normal conditions weighs 1.43 g, and 1 liter of air weighs 1.29 g. (Normal conditions - abbreviated as: n.u. . – temperature 0 ° C and pressure 760 mm Hg, or 1 atm). At a pressure of 760 mm Hg. Art. and a temperature of – 183 °C, oxygen liquefies, and when the temperature drops to – 218.8 °C, it solidifies.
The chemical element oxygen O, in addition to ordinary oxygen O2, exists in the form of another simple substance - ozone O3. Oxygen O2 is converted into ozone in a device called an ozonizer.
This is a gas with a sharp characteristic odor (the name “ozone” is translated from Greek as “smelling”). You've probably smelled ozone more than once during a thunderstorm. Ozone is made up of three atoms of the element oxygen. Pure ozone is a blue gas, one and a half times heavier than oxygen, and is more soluble in water.
In the air atmosphere above the Earth at an altitude of 25 km there is an ozone layer. There, ozone is formed from oxygen under the influence of ultraviolet radiation from the Sun. In turn, the ozone layer traps this radiation, which is dangerous for all living beings, which ensures normal life on Earth.
Ozone is used to disinfect drinking water, since ozone oxidizes harmful impurities in natural water. In medicine, ozone is used as a disinfectant.

Bibliography

1. Lesson on the topic “Amount of Substance”, teacher of biology and chemistry Larisa Aleksandrovna Yakovleva, Kurgan region, Petukhovsky district, Municipal Educational Institution “Novogeorgievskaya Secondary School”
2. F. A. Derkach “Chemistry” - scientific and methodological manual. – Kyiv, 2008.
3. L. B. Tsvetkova “Inorganic chemistry” - 2nd edition, corrected and expanded. – Lvov, 2006.
4. V. V. Malinovsky, P. G. Nagorny “Inorganic chemistry” - Kyiv, 2009.
4. Glinka N.L. General chemistry. – 27th ed./Under. ed. V.A. Rabinovich. – L.: Chemistry, 2008. – 704 pp.

Edited and sent by Borisenko I.N.

Amount of substance in chemistry (moles):

Formulas in chemistry determine what a substance is made of. Now we will learn to determine in what quantities these substances are present in compounds.

Quantity of substance is essentially the number of smallest particles (or structural units) of which matter is composed. The smallest particles are either atoms (Fe) (they have only one element) or molecules (H 2 O) (from different elements).

Quantity of substance in chemistry expressed through (this is the Greek letter "nu", which is similar to the English "v", only with rounded tops).

Even in a grain of matter there are billions of molecules, so they don’t count them all, but use special units of measurement - moths.

1 mole is an amount of substance equal to 6.02 * 10 23 structural units of the substance. That is exactly how many (6.02*10 23) molecules there are, for example, in one mole of water or sugar or anything else.

As you can see, this is very, very much - a billion multiplied by a billion, by another 100,000 and by 6!!! If you take that many one-kopeck coins and cover the entire surface of the Earth with them (as well as all the seas and oceans), you will get a layer 1 km thick!

Chemical formula is an image using symbols.

Chemical element signs

Chemical sign or chemical element symbol– this is the first or two first letters of the Latin name of this element.

For example: FerrumFe , Cuprum –Cu , OxygeniumO etc.

Table 1: Information provided by a chemical symbol

Intelligence	Using the example of Cl
Item name	Chlorine
	Non-metal, halogen
One element	1 chlorine atom
(Ar) of this element	Ar(Cl) = 35.5
Absolute atomic mass of a chemical element m = Ar 1.66 10 -24 g = Ar 1.66 10 -27 kg	M (Cl) = 35.5 1.66 10 -24 = 58.9 10 -24 g

The name of a chemical symbol in most cases is read as the name of a chemical element. For example, K – potassium, Ca – calcium, Mg – magnesium, Mn – manganese.

Cases when the name of a chemical symbol is read differently are given in Table 2:

Chemical element name	Chemical sign	Chemical symbol name (pronunciation)
Nitrogen	N	En
Hydrogen	H	Ash
Iron	Fe	Ferrum
Gold	Au	Aurum
Oxygen	O	ABOUT
Silicon	Si	Silicium
Copper	Cu	Cuprum
Tin	Sn	Stanum
Mercury	Hg	Hydrargium
Lead	Pb	Plumbum
Sulfur	S	Es
Silver	Ag	Argentum
Carbon	C	Tse
Phosphorus	P	Pe

Chemical formulas of simple substances

The chemical formulas of most simple substances (all metals and many non-metals) are the signs of the corresponding chemical elements.

So iron substance And chemical element iron are designated the same - Fe .

If it has a molecular structure (exists in the form , then its formula is the chemical sign of the element with index bottom right indicating number of atoms in a molecule: H 2, O2, O 3, N 2, F 2, Cl2, BR 2, P 4, S 8.

Table 3: Information provided by a chemical sign

Intelligence	Using C as an example
Substance name	Carbon (diamond, graphite, graphene, carbyne)
Belonging of an element to a given class of chemical elements	Non-metal
One atom of an element	1 carbon atom
Relative atomic mass (Ar) element that forms a substance	Ar(C) = 12
Absolute atomic mass	M(C) = 12 1.66 10-24 = 19.93 10 -24 g
One substance	1 mole of carbon, i.e. 6.02 10 23 carbon atoms
	M (C) = Ar (C) = 12 g/mol

Chemical formulas of complex substances

The formula of a complex substance is prepared by writing down the signs of the chemical elements of which the substance is composed, indicating the number of atoms of each element in the molecule. In this case, as a rule, chemical elements are written in order of increasing electronegativity in accordance with the following practical series:

Me, Si, B, Te, H, P, As, I, Se, C, S, Br, Cl, N, O, F

For example, H2O , CaSO4 , Al2O3 , CS 2 , OF 2 , NaH.

The exceptions are:

• some compounds of nitrogen with hydrogen (for example, ammonia NH 3 , hydrazine N 2H 4 );
• salts of organic acids (for example, sodium formate HCOONa , calcium acetate (CH 3COO) 2Ca) ;
• hydrocarbons ( CH 4 , C2H4 , C2H2 ).

Chemical formulas of substances existing in the form dimers (NO 2 , P2O 3 , P2O5, salts of monovalent mercury, for example: HgCl , HgNO3 etc.), written in the form N 2 O4,P 4 O6,P 4 O 10Hg 2 Cl2,Hg 2 ( NO 3) 2 .

The number of atoms of a chemical element in a molecule and a complex ion is determined based on the concept valency or oxidation states and is recorded index lower right from the sign of each element (index 1 is omitted). In this case, they proceed from the rule:

the algebraic sum of the oxidation states of all atoms in a molecule must be equal to zero (the molecules are electrically neutral), and in a complex ion - the charge of the ion.

For example:

2Al 3 + +3SO 4 2- =Al 2 (SO 4) 3

The same rule is used when determining the oxidation state of a chemical element using the formula of a substance or complex. It is usually an element that has several oxidation states. The oxidation states of the remaining elements forming the molecule or ion must be known.

The charge of a complex ion is the algebraic sum of the oxidation states of all the atoms that form the ion. Therefore, when determining the oxidation state of a chemical element in a complex ion, the ion itself is placed in brackets, and its charge is taken out of brackets.

When compiling formulas for valency a substance is represented as a compound consisting of two particles of different types, the valencies of which are known. Next they use rule:

in a molecule, the product of valence by the number of particles of one type must be equal to the product of valence by the number of particles of another type.

For example:

The number before the formula in a reaction equation is called coefficient. She indicates either number of molecules, or number of moles of substance.

The coefficient before the chemical symbol, indicates number of atoms of a given chemical element, and in the case when the sign is the formula of a simple substance, the coefficient indicates either number of atoms, or the number of moles of this substance.

For example:

• 3 Fe– three iron atoms, 3 moles of iron atoms,
• 2 H– two hydrogen atoms, 2 moles of hydrogen atoms,
• H 2– one molecule of hydrogen, 1 mole of hydrogen.

The chemical formulas of many substances have been determined experimentally, which is why they are called "empirical".

Table 4: Information provided by the chemical formula of a complex substance

Intelligence	For example C aCO3
Substance name	Calcium carbonate
Belonging of an element to a certain class of substances	Medium (normal) salt
One molecule of substance	1 molecule calcium carbonate
One mole of substance	6.02 10 23 molecules CaCO3
Relative molecular mass of the substance (Mr)	Мr (CaCO3) = Ar (Ca) +Ar (C) +3Ar (O) =100
Molar mass of the substance (M)	M (CaCO3) = 100 g/mol
Absolute molecular mass of the substance (m)	M (CaCO3) = Mr (CaCO3) 1.66 10 -24 g = 1.66 10 -22 g
Qualitative composition (what chemical elements form the substance)	calcium, carbon, oxygen
Quantitative composition of the substance:
The number of atoms of each element in one molecule of a substance:	a calcium carbonate molecule is made up of 1 atom calcium, 1 atom carbon and 3 atoms oxygen.
The number of moles of each element in 1 mole of the substance:	In 1 mole CaCO 3(6.02 · 10 23 molecules) contained 1 mole(6.02 · 10 23 atoms) calcium, 1 mole(6.02 10 23 atoms) of carbon and 3 mol(3 6.02 10 23 atoms) of the chemical element oxygen)
Mass composition of the substance:
Mass of each element in 1 mole of substance:	1 mole of calcium carbonate (100g) contains the following chemical elements: 40g calcium, 12g carbon, 48g oxygen.
Mass fractions of chemical elements in the substance (composition of the substance as a percentage by weight):	Composition of calcium carbonate by weight: W (Ca) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (1·40)/100= 0.4 (40%) W (C) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (1 12)/100 = 0.12 (12%) W (O) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (3 16)/100 = 0.48 (48%)
For a substance with an ionic structure (salt, acid, base), the formula of the substance provides information about the number of ions of each type in the molecule, their quantity and the mass of ions per 1 mole of the substance:	Molecule CaCO 3 consists of an ion Ca 2+ and ion CO 3 2- 1 mol ( 6.02 10 23 molecules) CaCO 3 contains 1 mol Ca 2+ ions And 1 mole of ions CO 3 2-; 1 mole (100g) of calcium carbonate contains 40g ions Ca 2+ And 60g ions CO 3 2-
Molar volume of a substance at standard conditions (for gases only)

Graphic formulas

To obtain more complete information about a substance, use graphic formulas , which indicate order of connection of atoms in a molecule And valence of each element.

Graphic formulas of substances consisting of molecules sometimes, to one degree or another, reflect the structure (structure) of these molecules; in these cases they can be called structural .

To compile a graphical (structural) formula of a substance, you must:

• Determine the valence of all chemical elements that form the substance.
• Write down the signs of all chemical elements that form the substance, each in an amount equal to the number of atoms of a given element in the molecule.
• Connect the signs of chemical elements with dashes. Each dash denotes a pair that communicates between chemical elements and therefore belongs equally to both elements.
• The number of lines surrounding the sign of a chemical element must correspond to the valence of this chemical element.
• When formulating oxygen-containing acids and their salts, hydrogen atoms and metal atoms are bonded to the acid-forming element through an oxygen atom.
• Oxygen atoms are combined with each other only when formulating peroxides.

Examples of graphic formulas:

Instructions

To find a mole of a substance, you need to remember a very simple rule: the mass of one mole of any substance is numerically equal to its molecular mass, only expressed in other quantities. How is it determined? Using the periodic table, you will find out the atomic mass of each element included in the molecules of a substance. Next, you need to add the atomic masses, taking into account the index of each element, and you will get the answer.

Calculate its molecular weight taking into account the index of each element: 12*2 + 1*4 + 16*3 = 76 amu. (atomic mass units). Therefore, its molar mass (that is, the mass of one mole) is also 76, only its dimension is grams/mol. Answer: one mole of ammonium nitrate weighs 76 grams.

Suppose you are given such a task. It is known that the mass of 179.2 liters of some gas is 352 grams. It is necessary to determine how much one mole of this gas weighs. It is known that under normal conditions one mole of any gas or mixture of gases occupies a volume approximately equal to 22.4 liters. And you have 179.2 liters. Do the calculation: 179.2/22.4 = 8. Therefore, this volume contains 8 moles of gas.

Dividing the mass known according to the conditions of the problem by the number of moles, you get: 352/8 = 44. Therefore, one mole of this gas weighs 44 grams - this is carbon dioxide, CO2.

If there is a certain amount of gas of mass M, enclosed in a volume V at a given temperature T and pressure P. It is required to determine its molar mass (that is, find what its mole is equal to). The universal Mendeleev-Clapeyron equation will help you solve the problem: PV = MRT/m, where m is the very molar mass that we need to determine, and R is the universal gas constant equal to 8.31. Transforming the equation, you get: m = MRT/PV. By substituting known quantities into the formula, you will find what a mole of gas is equal to.

Helpful advice

Calculations usually use rounded values ​​for the atomic weights of elements. If higher precision is required, rounding is not acceptable.

A. Avogadro in 1811, at the very beginning of the development of atomic theory, made the assumption that an equal number of ideal gases at the same pressure and temperature contain the same number of molecules. Later this assumption was confirmed and became a necessary consequence for the kinetic theory. Now this theory is called Avogadro.

Instructions

Avogadro's constant shows the number of atoms or molecules that are contained in one mole of a substance.

The number of molecules, provided that the system is one-component and the molecules or atoms of the same type contained in it, can be found using a special formula

Video on the topic

First, determine the chemical composition and state of aggregation of the substance. If you are testing a gas, measure its temperature, volume, and pressure, or place it under normal conditions and measure only the volume. After this, calculate the number of molecules and atoms. To determine the number of atoms in a solid or liquid, find its mass and molar mass, and then the number of molecules and atoms.

You will need

• pressure gauge, thermometer, scales and periodic table, find out Avogadro's constant.

Instructions

Determining the mass of one mole from a known amount of a substance If the amount of a substance in moles is known, the molar mass of which needs to be found, use a scale to find its actual mass, expressing it in grams. To determine the mass of one mole, divide the mass of the substance by its amount M=m/υ.

Determining the mass of one mole of a substance by the mass of a molecule If the mass of one molecule of a substance, expressed in grams, is known, find the mass of one mole by multiplying the mass of this molecule by the number of molecules in one mole (Avogadro's number), which is equal to 6.022 10^23, M = m0 NA .

Determining the mass of one mole of gas Take a sealed vessel of known volume, expressed in cubic meters. Pump out the gas from it and weigh it on a scale. Pump gas into it and weigh it again, the difference between the empty and filled cylinders will be equal to the mass of the gas. Convert it to kilograms.
Measure the temperature of the gas in the cylinder; if you wait a little after pumping, it will become equal to the ambient air temperature, and convert it to kelvins by adding the number 273 to degrees Celsius. Measure the gas pressure with a pressure gauge, in pascals. Find the molar mass of a gas (mass of one mole) by multiplying the mass of the gas by its temperature and 8.31 (the universal gas constant), and dividing the result by the pressure and volume M=m R T/(P V).

Sometimes researchers are faced with the following problem: how to determine the number of atoms of a particular substance? Initially, it may seem extremely complex, because the number of atoms even in a tiny sample of any substance is simply enormous. How to count them?

Instructions

Suppose you need to count the number of atoms in a piece of pure copper, for example, or even gold. Yes, imagine yourself in the place of the great scientist Archimedes, to whom King Hiero gave a completely different assignment, saying: “You know, Archimedes, in vain I suspected my jeweler of fraud, the crown turned out to be made of pure gold! Our Royal Majesty now wants to know the atoms in it.”

The task, naturally, would have plunged the real Archimedes into a stupor, even though he was. Well, you could deal with it in no time. First you need to accurately weigh the crown. Suppose it weighed exactly 2 kg, that is, 2000 grams. Then, using the periodic table, set the molar mass of gold (approximately 197 grams/mol.) To simplify the calculations, round up a little - let it be 200 grams/mol. Therefore, there are exactly 10 moles of gold in the ill-fated crown. Well, then take Avogadro’s universal number (6.022x1023), multiply by 10 and triumphantly take the result to King Hieron.

And then use the well-known Mendeleev–Clapeyron equation: PV = MRT/m. Note that M/m is nothing more than the number of moles of a given gas, since M is its actual mass and m is its molar mass.

Substitute the values ​​you know into the fraction PV/RT, multiply the result found by Avogadro’s universal number (6.022*1023) and get the number of gas atoms at a given volume, pressure and temperature.

What if you need to count the number of atoms in a sample of a complex substance? And there is nothing particularly difficult here. Weigh the sample, then write its exact chemical formula, use the Periodic Table to clarify the molar mass of each component and calculate the exact molar mass of this complex substance (taking into account the elemental indices if necessary).

Well, then find out the number of moles in the sample under study (by dividing the mass of the sample by the molar mass) and multiply the result by the value of Avogadro’s number.

In chemistry, the mole is used as a unit of quantity of a substance. A substance has three characteristics: mass, molar mass, and amount of substance. Molar mass is the mass of one mole of a substance.

Instructions

One mole of a substance represents its quantity, which contains as many structural units as there are atoms contained in 0.012 kg of an ordinary (non-radioactive) isotope. The structural units of matter are molecules, atoms, ions. When the conditions of the problem are given with the relative atomic mass of Ar, from the formula of the substance, depending on the formulation of the problem, either the mass of one mole of the same substance or its molar mass is found by performing calculations. The relative atomic mass of Ar is a value equal to the ratio of the average mass of an isotope of an element to 1/12 of the mass of carbon.

Both organic and inorganic substances have molar mass. For example, calculate this parameter in relation to water H2O and methane CH3. First find the molar mass of water:
M(H2O)=2Ar(H)+Ar(O)=2*1+16=18 g/mol
Methane is a gas of organic origin. This means that its molecule contains hydrogen and carbon atoms. Just one molecule of this gas contains three hydrogen atoms and one carbon atom. Calculate the molar mass of this substance as follows:
M(CH3)=Ar(C)+2Ar(H)=12+3*1=15 g/mol
Calculate the molar masses of any other substances in the same way.

Also, the mass of one mole of a substance or molar mass is found by knowing the mass and quantity of the substance. In this case, molar mass is calculated as the ratio of the mass of a substance to its quantity. The formula looks like this:
M=m/ν, where M is molar mass, m is mass, ν is the amount of substance.
The molar mass of a substance is expressed in grams or kilograms per mole. If the mass of a molecule of a substance is known, then, knowing Avogadro’s number, you can find the mass of one mole of the substance as follows:
Mr=Na*ma, where Mr is the molar mass, Na is Avogadro's number, ma is the mass of the molecule.
So, for example, knowing the mass of a carbon atom, you can find the molar mass of this substance:
Mr=Na*ma=6.02*10^23*1.993*10^-26=12 g/mol

Video on the topic

The mass of 1 mole of a substance is called its molar mass and is designated by the letter M. The units of measurement of molar mass are g/mol. The method for calculating this value depends on the specified conditions.

You will need

• - periodic table of chemical elements D.I. Periodic table (periodic table);
• - calculator.

Instructions

If a substance is known, its molar mass can be calculated using the periodic table. The molar mass of a substance (M) is equal to its relative molecular mass (Mr). In order to calculate it, find in the periodic table the atomic masses of all elements that make up the substance (Ar). Typically this is a number written in the lower right corner of the cell of the corresponding element under its serial number. For example, the atomic mass is 1 - Ar (H) = 1, the atomic mass of oxygen is 16 - Ar (O) = 16, the atomic mass of sulfur is 32 - Ar (S) = 32.

In order to find out the molecular and molar mass of a substance, you need to add up the relative atomic masses of the elements included in it, taking into account their number. Mr = Ar1n1+Ar2n2+…+Arxnx. Thus, the molar mass of water (H2O) is equal to the sum of the atomic mass of hydrogen (H) multiplied by 2 and the atomic mass of oxygen (O). M(H2O) = Ar(H)?2 + Ar(O) = 1?2 +16=18(g/mol). The molar mass of (H2SO4) is equal to the sum of the atomic mass of hydrogen (H) multiplied by 2, the atomic mass of sulfur (S) and the atomic mass of oxygen (O) multiplied by 4. M (H2SO4) = Ar (H) ?2 + Ar( S) + Ar (O) ?4=1?2 + 32 + 16?4 = 98(g/mol). The molar mass of simple substances consisting of one element is calculated in the same way. For example, the molar mass of oxygen gas (O2) is equal to the atomic mass of the element oxygen (O) multiplied by 2. M (O2) = 16?2 = 32 (g/mol).

If the chemical formula of a substance is unknown, but its quantity and mass are known, the molar mass can be found using the formula: M = m/n, where M is the molar mass, m is the mass of the substance, n is the amount of the substance. For example, it is known that 2 moles of a substance have a mass of 36 g, then its molar mass is M = m/n = 36 g? 2 mol = 18 g/mol (most likely this is water H2O). If 1.5 moles of a substance has a mass of 147 g, then its molar mass is M = m/n = 147 g? 1.5 mol = 98 g/mol (most likely this is sulfuric acid H2SO4).

Video on the topic

Sources:

• Talitsa Mendeleev