Home Preparations for the winter Deciphering formulas in chemistry. Chemistry formulas. Examples of molecular and ionic reaction equations

Preparations for the winter

Deciphering formulas in chemistry. Chemistry formulas. Examples of molecular and ionic reaction equations

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A chemical formula is a reflection of information about the composition and structure of substances using chemical signs, numbers and separating brackets. Currently, the following types of chemical formulas are distinguished: The simplest formula. Can be obtained by experienced ... ... Wikipedia

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A chemical equation (chemical reaction equation) is a conditional record of a chemical reaction using chemical formulas, numerical coefficients and mathematical symbols. The chemical reaction equation gives qualitative and quantitative ... ... Wikipedia

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several basic concepts and formulas.

All substances have different mass, density and volume. A piece of metal from one element can weigh many times more than exactly the same size piece from another metal.

mole(number of moles)

designation: mole, international: mol is a unit of measure for the amount of a substance. Corresponds to the amount of the substance that contains NA particles (molecules, atoms, ions) Therefore, a universal value was introduced - the number of mol. A frequently encountered phrase in tasks is “it was received ... mole of substance"

NA= 6.02 1023

NA is Avogadro's number. Also "number by agreement". How many atoms are there in the tip of a pencil? About a thousand. It is not convenient to operate with such values. Therefore, chemists and physicists around the world agreed - let's denote 6.02 1023 particles (atoms, molecules, ions) as 1 mol substances.

1 mol = 6.02 1023 particles

It was the first of the basic formulas for solving problems.

Molar mass of a substance

Molar mass matter is the mass of one mole of substance.

Referred to as Mr. It is located according to the periodic table - this is simply the sum of the atomic masses of a substance.

For example, we are given sulfuric acid - H2SO4. Let's calculate the molar mass of a substance: atomic mass H = 1, S-32, O-16.
Mr(H2SO4)=1 2+32+16 4=98 g/mol.

The second necessary formula for solving problems is

mass formula:

That is, to find the mass of a substance, you need to know the number of moles (n), and we find the molar mass from the Periodic system.

The law of conservation of mass is The mass of substances that enter into a chemical reaction is always equal to the mass of the formed substances.

If we know the mass (masses) of substances that have entered into a reaction, we can find the mass (masses) of the products of this reaction. And vice versa.

The third formula for solving problems in chemistry is

volume of matter:

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Where did the number 22.4 come from? From Avogadro's law:

equal volumes of different gases, taken at the same temperature and pressure, contain the same number of molecules.

According to Avogadro's law, 1 mole of an ideal gas under normal conditions (n.o.) has the same volume Vm\u003d 22.413 996 (39) l

That is, if we are given normal conditions in the problem, then, knowing the number of moles (n), we can find the volume of the substance.

So, basic formulas for solving problems in chemistry

Avogadro's numberNA

6.02 1023 particles

Amount of substance n (mol)

n=V\22.4 (l\mol)

Mass of matter m (g)

Volume of matter V(l)

V=n 22.4 (l\mol)

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These are formulas. Often, to solve problems, you must first write the reaction equation and (required!) Arrange the coefficients - their ratio determines the ratio of moles in the process.

Key words: Chemistry 8th grade. All formulas and definitions, symbols of physical quantities, units of measurement, prefixes for designating units of measurement, relationships between units, chemical formulas, basic definitions, briefly, tables, diagrams.

1. Symbols, names and units of measurement
some physical quantities used in chemistry

Physical quantity	Designation	unit of measurement
Time	t	from
Pressure	p	Pa, kPa
Amount of substance	ν	mole
Mass of matter	m	kg, g
Mass fraction	ω	Dimensionless
Molar mass	M	kg/mol, g/mol
Molar volume	V n	m 3 / mol, l / mol
Volume of matter	V	m 3, l
Volume fraction		Dimensionless
Relative atomic mass	A r	Dimensionless
	M r	Dimensionless
Relative density of gas A over gas B	D B (A)	Dimensionless
Matter density	R	kg / m 3, g / cm 3, g / ml
Avogadro constant	N A	1/mol
Temperature absolute	T	K (Kelvin)
Celsius temperature	t	°С (degree Celsius)
Thermal effect of a chemical reaction	Q	kJ/mol

2. Relations between units of physical quantities

3. Chemical formulas in grade 8

4. Basic definitions in grade 8

Atom- the smallest chemically indivisible particle of a substance.
Chemical element a certain type of atom.
Molecule- the smallest particle of a substance that retains its composition and chemical properties and consists of atoms.
Simple substances Substances whose molecules are made up of atoms of the same type.
Complex Substances Substances whose molecules are made up of different types of atoms.
The qualitative composition of the substance shows what atoms it consists of.
The quantitative composition of the substance shows the number of atoms of each element in its composition.
Chemical formula- conditional record of the qualitative and quantitative composition of a substance by means of chemical symbols and indices.
Atomic mass unit(amu) - a unit of measurement of the mass of an atom, equal to the mass of 1/12 of a carbon atom 12 C.
mole- the amount of a substance that contains the number of particles equal to the number of atoms in 0.012 kg of carbon 12 C.
Avogadro constant (Na \u003d 6 * 10 23 mol -1) - the number of particles contained in one mole.
Molar mass of a substance (M ) is the mass of a substance taken in an amount of 1 mol.
Relative atomic mass element BUT r - the ratio of the mass of an atom of a given element m 0 to 1/12 of the mass of a carbon atom 12 C.
Relative molecular weight substances M r - the ratio of the mass of a molecule of a given substance to 1/12 of the mass of a carbon atom 12 C. The relative molecular mass is equal to the sum of the relative atomic masses of the chemical elements that form the compound, taking into account the number of atoms of this element.
Mass fraction chemical element ω(X) shows what part of the relative molecular weight of substance X is accounted for by this element.

ATOMIC-MOLECULAR STUDIES
1. There are substances with a molecular and non-molecular structure.
2. There are gaps between the molecules, the dimensions of which depend on the state of aggregation of the substance and temperature.
3. Molecules are in continuous motion.
4. Molecules are made up of atoms.
6. Atoms are characterized by a certain mass and size.
In physical phenomena, molecules are preserved, in chemical phenomena, as a rule, they are destroyed. Atoms in chemical phenomena rearrange, forming molecules of new substances.

THE LAW OF CONSTANT COMPOSITION OF A SUBSTANCE
Each chemically pure substance of molecular structure, regardless of the method of preparation, has a constant qualitative and quantitative composition.

VALENCE
Valency is the property of an atom of a chemical element to attach or replace a certain number of atoms of another element.

CHEMICAL REACTION
A chemical reaction is a process in which another substance is formed from one substance. Reagents are substances that enter into a chemical reaction. Reaction products are substances that are formed as a result of a reaction.
Signs of chemical reactions:
1. Release of heat (light).
2. Color change.
3. The appearance of a smell.
4. Precipitation.
5. Gas release.

Value and its dimension	Ratio
Atomic mass of element X (relative)
Element number	Z= N(e –) = N(R +)
Mass fraction of element E in substance X, in fractions of a unit, in%)
Amount of substance X, mol
Amount of gas substance, mol	V m= 22.4 l/mol (n.o.) well. - R= 101 325 Pa, T= 273 K
Molar mass of substance X, g/mol, kg/mol
Mass of substance X, g, kg	m(X)= n(X) M(X)
Molar volume of gas, l / mol, m 3 / mol	V m= 22.4 l / mol at n.o.
Gas volume, m 3	V = V m × n
Product yield
Substance density X, g / l, g / ml, kg / m 3
Density of a gaseous substance X by hydrogen
Density of a gaseous substance X in air	M(air) = 29 g/mol
United gas law
Mendeleev-Clapeyron equation	PV = nRT, R= 8.314 J/mol×K
Volume fraction of a gaseous substance in a mixture of gases, in fractions of a unit or in%
Molar mass of a mixture of gases
Mole fraction of substance (X) in the mixture
The amount of heat, J, kJ	Q = n(X) Q(X)
Thermal effect of the reaction	Q =–H
Heat of formation of substance X, J/mol, kJ/mol
Chemical reaction rate (mol/lsec)
Mass action law (for a simple reaction)	a A+ in B= from C + d D u = k from a(A) from in(B)
Van't Hoff's rule
Solubility of substance (X) (g/100 g solvent)
Mass fraction of substance X in a mixture A + X, in fractions of a unit, in%
Mass of solution, g, kg	m(rr) = m(X) + m(H2O) m(rr) = V(rr)  (rr)
Mass fraction of the dissolved substance in the solution, in fractions of a unit, in %
Solution Density
The volume of the solution, cm 3, l, m 3
Molar concentration, mol/l
The degree of dissociation of the electrolyte (X), in fractions of a unit or%
Ionic product of water	K(H 2 O) =
Hydrogen indicator	pH = –lg

Main:

Kuznetsova N.E. and etc. Chemistry. 8 cells-10 cells .. - M .: Ventana-Graf, 2005-2007.

Kuznetsova N.E., Litvinova T.N., Levkin A.N. Chemistry. Grade 11 in 2 parts, 2005-2007.

Egorov A.S. Chemistry. A new textbook for preparing for universities. Rostov n/a: Phoenix, 2004.– 640 p.

Egorov A.S. Chemistry: a modern course to prepare for the exam. Rostov n / a: Phoenix, 2011. (2012) - 699 p.

Egorov A.S. Self-instruction manual for solving chemical problems. - Rostov-on-Don: Phoenix, 2000. - 352 p.

Chemistry / manual-tutor for university applicants. Rostov-n/D, Phoenix, 2005– 536 p.

Khomchenko G.P., Khomchenko I.G. Tasks in chemistry for university students. M.: Higher school. 2007.–302p.

Additional:

Vrublevsky A.I.. Educational and training materials for preparation for centralized testing in chemistry / A.I. Vrublevsky - Mn .: Unipress LLC, 2004. - 368 p.

Vrublevsky A.I.. 1000 tasks in chemistry with chains of transformations and control tests for schoolchildren and university entrants.– Mn.: Unipress LLC, 2003.– 400 p.

Egorov A.S.. All types of computational tasks in chemistry for preparing for the Unified State Examination.–Rostov n/D: Phoenix, 2003.–320p.

Egorov A.S., Aminova G.Kh. Typical tasks and exercises to prepare for the exam in chemistry. - Rostov n / D: Phoenix, 2005. - 448 p.

Unified state exam 2007. Chemistry. Educational and training materials for the preparation of students / FIPI - M .: Intellect-Center, 2007. - 272 p.

USE-2011. Chemistry. Training kit, ed. A.A. Kaverina. - M .: National Education, 2011.

The only real options for tasks to prepare for the unified state exam. USE.2007. Chemistry/V.Yu. Mishina, E.N. Strelnikov. M.: Federal Testing Center, 2007.–151p.

Kaverina A.A.. The optimal bank of tasks for preparing students. Unified State Exam 2012. Chemistry. Textbook./ A.A. Kaverina, D.Yu. Dobrotin, Yu.N. Medvedev, M.G. Snastina. - M .: Intellect-Center, 2012. - 256 p.

Litvinova T.N., Vyskubova N.K., Azhipa L.T., Solovieva M.V.. Test tasks in addition to tests for students of 10-month correspondence preparatory courses (guidelines). Krasnodar, 2004. - S. 18 - 70.

Litvinova T.N.. Chemistry. USE-2011. Training tests. Rostov n/a: Phoenix, 2011.– 349 p.

Litvinova T.N.. Chemistry. Tests for the exam. Rostov n / D .: Phoenix, 2012. - 284 p.

Litvinova T.N.. Chemistry. Laws, properties of elements and their compounds. Rostov n / D .: Phoenix, 2012. - 156 p.

Litvinova T.N., Melnikova E.D., Solovieva M.V.., Azhipa L.T., Vyskubova N.K. Chemistry in tasks for applicants to universities. - M .: LLC "Publishing House Onyx": LLC "Publishing House "World and Education", 2009.- 832 p.

Educational and methodological complex in chemistry for students of medical and biological classes, ed. T.N. Litvinova. - Krasnodar: KSMU, - 2008.

Chemistry. USE-2008. Entrance tests, teaching aid / ed. V.N. Doronkin. - Rostov n / a: Legion, 2008. - 271 p.

List of sites on chemistry:

1. Alchemist. http:// www. alchemist. en

2. Chemistry for everyone. Electronic reference book for a complete course of chemistry.

http:// www. informika. en/ text/ database/ chemy/ START. html

3. School chemistry - a reference book. http:// www. school chemistry. by. en

4. Tutor in chemistry. http://www. chemistry.nm.ru

Internet resources

Alchemist. http:// www. alchemist. en

Chemistry for everyone. Electronic reference book for a complete course of chemistry.

http:// www. informika. en/ text/ database/ chemy/ START. html

School chemistry - a reference book. http:// www. school chemistry. by. en

http://www.classchem.narod.ru

Chemistry tutor. http://www. chemistry.nm.ru

http://www.alleng.ru/edu/chem.htm- Internet educational resources in chemistry

http://schoolchemistry.by.ru/- school chemistry. On this site there is an opportunity to pass On-line testing on various topics, as well as demo versions of the Unified State Exam

Chemistry and life–XX1st century: popular scientific journal. http:// www. hij. en

>> Chemical formulas

Chemical formulas

The paragraph will help you:

> find out what a chemical formula is;
> read the formulas of substances, atoms, molecules, ions;
> correctly use the term "formula unit";
> make chemical formulas of ionic compounds;
> characterize the composition of a substance, molecule, ion by chemical formula.

Chemical formula.

Everyone has it substances there is a name. However, by name it is impossible to determine what particles the substance consists of, how many and what atoms are contained in its molecules, ions, what charges the ions have. Answers to such questions are given by a special record - a chemical formula.

A chemical formula is the designation of an atom, molecule, ion, or substance using symbols chemical elements and indexes.

The chemical formula of an atom is the symbol of the corresponding element. For example, an aluminum atom is denoted by the symbol Al, and a silicon atom by the symbol Si. Simple substances also have such formulas - the metal aluminum, the non-metal of the atomic structure silicon.

Chemical formula molecule of a simple substance contains the symbol of the corresponding element and a subscript - a small number written below and to the right. The index indicates the number of atoms in the molecule.

An oxygen molecule consists of two oxygen atoms. Its chemical formula is O 2 . This formula is read by pronouncing first the symbol of the element, then the index: “o-two”. The formula O 2 denotes not only the molecule, but also the substance oxygen itself.

The O 2 molecule is called diatomic. Of these molecules (their general formula is E 2), the simple substances of Hydrogen, Nitrogen, Fluor, Chlorine, Bromine, Iodine are composed.

Ozone contains three-atom molecules, white phosphorus - four-atom, and sulfur - eight-atom. (Write the chemical formulas of these molecules.)

H 2
O2
N 2
Cl2
Br2
I 2

In the formula of a molecule of a complex substance, the symbols of the elements whose atoms are contained in it, as well as the indices, are written. The carbon dioxide molecule consists of three atoms: one carbon atom and two oxygen atoms. Its chemical formula is CO 2 (read "tse-o-two"). Remember: if there is one atom of any element in the molecule, then the corresponding index, i.e. I, is not written in the chemical formula. The formula of the carbon dioxide molecule is also the formula of the substance itself.

In the formula of an ion, its charge is additionally recorded. To do this, use the superscript. In it, a number indicates the amount of charge (they do not write a unit), and then a sign (plus or minus). For example, a Sodium ion with a charge of +1 has the formula Na + (read "sodium plus"), a Chlorine ion with a charge - I - SG - ("chlorine minus"), a hydroxide ion with a charge - I - OH - (" o-ash-minus"), a carbonate ion with a charge of -2 - CO 2- 3 ("tse-o-three-two-minus").

Na + , Cl -
simple ions

OH -, CO 2- 3
complex ions

In the formulas of ionic compounds, they first write down, without indicating charges, positively charged ions, and then - negatively charged (Table 2). If the formula is correct, then the sum of the charges of all ions in it is equal to zero.

table 2
Formulas of some ionic compounds

In some chemical formulas, a group of atoms or a complex ion is written in brackets. As an example, take the formula for slaked lime Ca (OH) 2. This is an ionic compound. In it, for every Ca 2+ ion, there are two OH - ions. The compound formula reads " calcium-o-ash-twice", but not "calcium-o-ash-two".

Sometimes in chemical formulas, instead of the symbols of the elements, "foreign" letters are written, as well as index letters. Such formulas are often called general. Examples of formulas of this type: ECI n , E n O m , Fe x O y. First
the formula denotes a group of compounds of elements with Chlorine, the second - a group of compounds of elements with Oxygen, and the third is used if the chemical formula of the Ferrum compound with Oxygen unknown and
it should be installed.

If you need to designate two separate neon atoms, two oxygen molecules, two carbon dioxide molecules or two sodium ions, use the notation 2Ne, 20 2, 2CO 2 , 2Na +. The number in front of the chemical formula is called the coefficient. The coefficient I, like the index I, is not written.

formula unit.

What does 2NaCl mean? There are no NaCl molecules; table salt is an ionic compound that consists of Na + and Cl - ions. A pair of these ions is called the formula unit of matter (it is highlighted in Fig. 44, a). Thus, the notation 2NaCl represents two formula units of table salt, i.e., two pairs of Na + and C l- ions.

The term "formula unit" is used for complex substances not only of ionic, but also of atomic structure. For example, the formula unit for quartz SiO 2 is the combination of one silicon atom and two oxygen atoms (Fig. 44, b).

Rice. 44. formula units in compounds of ionic (a) atomic structure (b)

A formula unit is the smallest "brick" of a substance, its smallest repeating fragment. This fragment can be an atom (in simple matter), molecule(in simple or complex matter),
a collection of atoms or ions (in a complex substance).

The exercise. Compose the chemical formula of a compound that contains Li + i SO 2- 4 ions. Name the formula unit of this substance.

Solution

In an ionic compound, the sum of the charges of all ions is zero. This is possible provided that there are two Li + ions for each SO 2- 4 ion. Hence the formula of the compound is Li 2 SO 4.

The formula unit of a substance is three ions: two Li + ions and one SO 2- 4 ion.

Qualitative and quantitative composition of the substance.

A chemical formula contains information about the composition of a particle or substance. Characterizing the qualitative composition, they name the elements that form a particle or substance, and characterizing the quantitative composition, indicate:

The number of atoms of each element in a molecule or complex ion;
the ratio of atoms of different elements or ions in a substance.

The exercise. Describe the composition of methane CH 4 (molecular compound) and soda ash Na 2 CO 3 (ionic compound)

Solution

Methane is formed by the elements Carbon and Hydrogen (this is a qualitative composition). The methane molecule contains one carbon atom and four hydrogen atoms; their ratio in the molecule and in the substance

N(C): N(H) = 1:4 (quantitative composition).

(The letter N denotes the number of particles - atoms, molecules, ions.

Soda ash is formed by three elements - Sodium, Carbon and Oxygen. It contains positively charged Na + ions, since Sodium is a metallic element, and negatively charged CO -2 3 ions (qualitative composition).

The ratio of atoms of elements and ions in a substance is as follows:

conclusions

A chemical formula is a record of an atom, molecule, ion, substance using the symbols of chemical elements and indices. The number of atoms of each element is indicated in the formula with a subscript, and the charge of the ion is indicated with a superscript.

Formula unit - a particle or a collection of particles of a substance, represented by its chemical formula.

The chemical formula reflects the qualitative and quantitative composition of a particle or substance.

?
66. What information about a substance or particle does a chemical formula contain?

67. What is the difference between a coefficient and a subscript in chemical records? Complete your answer with examples. What is superscript used for?

68. Read the formulas: P 4 , KHCO 3 , AI 2 (SO 4) 3 , Fe(OH) 2 NO 3 , Ag + , NH + 4 , CIO - 4 .

69. What do the entries mean: 3H 2 0, 2H, 2H 2, N 2, Li, 4Cu, Zn 2+, 50 2-, NO - 3, ZCa (0H) 2, 2CaC0 3?

70. Write down chemical formulas that read like this: es-o-three; boron-two-o-three; ash-en-o-two; chrome-o-ash-thrice; sodium-ash-es-o-four; en-ash-four-twice-es; barium-two-plus; pe-o-four-three-minus.

71. Make a chemical formula of a molecule that contains: a) one Nitrogen atom and three Hydrogen atoms; b) four hydrogen atoms, two phosphorus atoms and seven oxygen atoms.

72. What is the formula unit: a) for soda ash Na 2 CO 3; b) for the ionic compound Li 3 N; c) for the compound B 2 O 3, which has an atomic structure?

73. Make formulas for all substances that can contain only such ions: K + , Mg2 + , F - , SO -2 4 , OH - .

74. Describe the qualitative and quantitative composition:

a) molecular substances - chlorine Cl 2, hydrogen peroxide (hydrogen peroxide) H 2 O 2, glucose C 6 H 12 O 6;
b) ionic substance - sodium sulfate Na 2 SO 4;
c) H 3 O +, HPO 2- 4 ions.

Popel P. P., Kriklya L. S., Chemistry: Pdruch. for 7 cells. zahalnosvit. navch. zakl. - K .: Exhibition Center "Academy", 2008. - 136 p.: il.

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