What is the absolute mass of sulfur? Thematic tasks - Chemistry exam: I will pass the State Examination Test with a "5"! Examples of problem solving

Chemical phenomena. Substances

Which of the following signs characterize chemical phenomena: a) color change; b) change in state of aggregation; c) change in shape; d) formation of sediment?
Do chemical phenomena occur during the following processes: a) melting of ice; b) water distillation; c) rusting of iron; d) separation of the mixture by filtration; d) rotting food?
Which of the following substances are simple and which are complex: a) carbon dioxide; b) salt; c) copper; d) hydrogen; e) aluminum; e) marble? What is the difference between these groups of substances?
When an unknown complex substance burns in oxygen, carbon dioxide and water are formed. What chemical elements may be present in this complex substance? Which ones are required? Explain your answer.

Relative atomic and molecular masses. Constancy of the composition of matter

The average mass of sulfur atoms is 5.31 ∙ 10 -26 kg. Calculate the relative atomic mass of the element sulfur if the mass of the carbon atom is 1.993 ∙ 10 -26 kg.
Calculate the relative molecular weight of the following complex substances: a) magnesium chloride MgCl 2 ; b) sulfuric acid H 2 SO 4; c) calcium hydroxide Ca(OH) 2; d) aluminum oxide Al 2 O 3; e) boric acid H 3 BO 3; e) copper (II) sulfate CuSO 4 .
Magnesium and sulfur combine in a mass ratio of 3:4. Determine the mass of magnesium that will react with 20 g of sulfur.
21 g of iron and 19 g of sulfur were mixed and the mixture was heated. Considering that iron and sulfur react in a mass ratio of 7:4, determine which of the substances will remain unreacted. Calculate the mass of the substance that did not react.

Chemical formulas and calculations using them

Calculate in what mass ratio sodium and oxygen combine in the Na 2 O compound.
The chemical composition includes calcium (mass fraction 29.4%), sulfur (23.5%) and oxygen (47.1%). Determine the formula of this compound.
Calculate the mass ratios in which calcium, carbon and oxygen are found in the compound CaCO 3.
Copper ore contains the mineral chalcopyrite CuFeS 2 and other impurities, the composition of which does not include copper. The mass fraction of chalcopyrite in the ore is 5%. Calculate the mass fraction of copper in this ore.

Valence

Determine the valence of elements in the following compounds: a) NH 3 ; b) SO 3; c) CO 2; d) H 2 Se; e) P 2 O 3.
Write the formulas of oxygen compounds (oxides) of the following elements: a) beryllium (II); b) silicon (IV); c) potassium (I); d) arsenic (V).
Write formulas for compounds of manganese and oxygen in which manganese is di-, tri-, tetra- and heptavalent.
Draw the formulas of copper (I) chloride and copper (II) chloride, taking into account that chlorine in compounds with metals is monovalent.

Chemical equations. Types of reactions

The reaction scheme CuCl 2 + KOH → Cu(OH) 2 + KCl corresponds to the exchange reaction. Arrange the coefficients in this diagram.
Complete the reaction schemes and make up the equations: a) Li + ... → Li 2 O; b) Al + O 2 → ...; c) Na + S → ... ; d) C + ... → CCl 4.
Give two examples of each type of reaction: decomposition, combination, and substitution. Write the equations for these reactions.
Write the reaction equations between aluminum and the following substances: a) chlorine; b) oxygen; c) sulfur (divalent); d) iodine (monovalent).

Amount of substance. Mol. Molar mass

Calculate the amount of magnesium in a sample of this metal weighing 6 g.
What is the mass of a mixture consisting of 10 moles of hydrogen gas and 5 moles of oxygen?
Calculate the amount of substance contained in 100 g of the following substances: a) lithium fluoride LiF; b) silicon oxide (IV) SiO 2; c) hydrogen bromide HBr; d) sulfuric acid H 2 SO 4.
Determine the mass of a sample of sulfur(IV) oxide that contains the same number of molecules as there are atoms in a 1.4 g piece of iron.

Calculations using chemical equations

The interaction of hydrogen and oxygen produced 450 g of water. What is the mass of the gases that reacted?
When limestone (calcium carbonate) is calcined with CaCO 3, calcium oxide and carbon dioxide are formed. What mass of limestone must be taken to obtain 7 kg of calcium oxide?
When 13.44 g of iron interacted with chlorine, one of the iron chlorides weighing 39 g was formed. Determine the valence of iron in the resulting chloride and write the formula of the compound.
Aluminum weighing 10.8 g was fused with a gray mass of 22.4 g. Calculate the amount of aluminum sulfide Al 2 S 3 that is formed as a result of the reaction.

List the main provisions of atomic-molecular teaching.

1. Substances consist of molecules. A molecule is the smallest particle of a substance that retains its chemical properties. Molecules of different substances have different mass, size, composition, and chemical properties.

2. Molecules are made up of atoms. An atom is the smallest particle of a substance, a chemical element, that retains its chemical properties. A chemical element is a separate type of atom. The chemical properties of an element are determined by the structure of its atoms. All chemical elements are divided into metals and non-metals.

3. Substances whose molecules consist of atoms of one element are called simple (H 2 ; O 2). Substances whose molecules consist of atoms of different elements are called complex (HCl). Allotropic changes are changes in which different simple substances are formed by one element. Allotropy is the formation of different simple substances by one element.

Reason for allotropy:

a) different numbers of atoms (O 2 and O 3);

b) formation of crystals of various modifications (diamond and graphite);

4. Molecules and atoms are in continuous motion. The speed of movement depends on the state of aggregation of the substance. Chemical reactions are the chemical form of movement of atoms and molecules.

As a result of chemical reactions, molecules of some substances are transformed into molecules of other substances. An important characteristic of a substance is mass.

Question No. 2

What are the similarities and differences in the concepts of “atomic mass” and “relative mass”?

1. Absolute atomic mass is the mass of a gram, expressed in grams (g) or kilograms (kg)

m a () =1.67*10 -24 g

It is inconvenient to use such numbers, so relative atomic masses are used.

2. Relative atomic mass shows how many times the mass of a given atom is greater than 1/12 the mass of a carbon atom.

1/12 of the mass of a carbon atom is called an atomic mass unit (a.u.m.)

1 amu = m a (C)/12 =(1.99*10 -23)/12 g = 1.66*10 -24 g

a r () = m a (H)/1 a.u.m = (1.67*10 -27 / 1.66*10 -24) = 1

Relative atomic mass, unlike absolute mass, does not have a unit of measurement.

Question No. 3

Is it possible to connect the concepts “mole” and “Avogadro’s constant”?

A mole is the amount of substance that contains 6.02 * 10 23 particles (molecules or atoms).

The value 6.02 * 10 23 mol-1 is called Avogadro’s constant, which is denoted Na

n = N/Na, where

n – amount of substance;

N is the number of atoms or molecules.

Question No. 4

Compare the number of atoms contained in chlorine and nitrogen weighing 10 g each. In which case and how many times is the number of atoms greater?

Given:

m(Cl 2)= 10g

m(N 2) = 10 g

___________

N Cl2 – ? N N – ?

Solution

M(Cl 2) = 35.5 *2 = 71 g/mol

n (Cl 2) = m(Cl 2)/ M(Cl 2) = 10 g/71 g/mol = = 0.14 mol

N (Cl 2) = n (Cl 2) * Na = 0.14 mol

6.02*10 -23 1/mol

M(N 2) =14*2 = 28 g/mol

n (N 2) = m(N 2)/ M(Cl 2) = 10 g/28 g/mol = 0.36 mol

N(N2) = n (N2) * Na = 0.36 mol * 6.02 * 10 23 1/mol = 2.17 * 10 23

N(N2)/
N (Cl2) =(2.17*10 23) /0.843*10 23 =2.57

Answer: N (N2) > N (Cl2) 2.57 times

Question No. 5

The average mass of sulfur atoms is 5.31 * 10-26 kg. Calculate the relative atomic mass of the element sulfur. The mass of carbon atom – 12 is equal to 1.993 * 10 -26 kg.

Given:

m a (S)= 5.31*10 -26 kg

m a (C) = 1.993*10 -26 kg

___________

ar(s) – ?

Solution

1 amu = m a (C) /12 = (1.993*10 -26 kg) = 1.66*10-27 kg

ar (s) = m a (S)/1 a.m.u. = 5.31*10-26 kg=32

Answer: ar(s) = 32.

Question No. 6

A sample of a substance weighing 6.6 g contains 9.03 * 10 22 molecules. Determine the molecular mass of this substance.

Question No. 7

Give the initial and modern formulation of the periodic law. What is the reason for their difference?

Initial formulation: characteristic of simple bodies, and the shapes and properties of compounds of elements are periodically dependent on the magnitude of the atomic masses of the elements.

Modern formulation: the properties of simple substances, as well as the forms and properties of compounds of elements, are periodically dependent on the magnitude of the charge of the atomic nucleus (atomic number).

In the periodic table, not all elements are arranged in order of increasing atomic mass; there are exceptions that he could not explain. He foresaw that the reason lay in the complexity of the structure of atoms. The discovery and study of isotopes showed that the chemical properties of all isotopes of one element are the same, which means that the chemical properties of an element depend not on the atomic mass, but on the charge of the nucleus.

Question No. 8

Imagine the electronic configurations of aluminum and scandium. Explain why they are placed in the same group of the “Periodic Table?” Why are they placed in different subgroups? Are they electronic analogues?

aL and Se each have three valence electrons, so they are in the same group.

aL refers to p-elements, and Se refers to d-elements, so they are located in different subgroups and are not electronic analogues.

Questions No. 9

Among the electronic configurations given below, indicate the impossible ones and explain the reason for the impossibility of their implementation

1р 3; 3p 6; 3S 2 ; 2S 2 ; 2d 5 ; 5d 2 ; 2p 4 ; 3p 7

Question No. 10

Element isotope symbol. Specify the name of the element; number of neutrons and protons; the number of electrons in the electron shell of an atom.

This element with atomic number 92 and relative mass 238 is uranium.

The number of protons is 92, and the number of neutrons is determined by the difference between the relative atomic mass and the atomic number, equal to 238 – 92 = 146. Number e is determined by the serial number of the element and is equal to 92.

Question No. 11

The nucleus of an atom of some element contains 16 neutrons, and the electron shell contains 15 electrons. Name the element of which this atom is an isotope. Give the symbol of this chemical element and indicate the nuclear charge and mass number.

Phosphorus (P) is an element containing 15 electrons.

The mass of an atom is determined by the sum of the masses of protons and neutrons.

Since the nucleus of an atom contains 16 neutrons and 15 protons, its mass number is 31. And this can be written in the following form:

USED BOOKS

Akhmetov N.S. General and inorganic chemistry.

Pilipenko. Handbook of elementary chemistry.

Khomchenko I.G. general chemistry

1. Fill in the gaps in the sentences.

Absolute atomic mass shows the mass of one twelve part 1/12 of the mass of one molecule of the carbon isotope 12 6 C measured in the following units: g, gk, mg, i.e.

Relative atomic mass shows how many times the mass of a given substance of an element is greater than the mass of a hydrogen atom; has no unit of measurement.

2. Using the notation, write down the value rounded to an integer:

a) relative atomic mass of oxygen - 16:
b) relative atomic mass of sodium - 23;
c) relative atomic mass of copper - 64.

3. The names of the chemical elements are given: mercury, phosphorus, hydrogen, sulfur, carbon, oxygen, potassium, nitrogen. Write the symbols of the elements into the empty cells so that you get a row in which the relative atomic mass increases.

4. Underline the true statements.

a) The mass of ten oxygen atoms is equal to the mass of two bromine atoms;
b) The mass of five carbon atoms is greater than the mass of three sulfur atoms;
c) The mass of seven oxygen atoms is less than the mass of five magnesium atoms.

5. Fill out the diagram.

6. Calculate the relative molecular masses of substances based on their formulas:

a) M r (N 2) = 2*14=28
b) M r (CH 4) = 12+4*1=16
c) M r (CaCO 3) = 40+12+3*16=100
d) M r (NH 4 Cl) = 12+41+35.5=53.5
e) M r (H 3 PO 4) = 3*1+31+16*4=98

7. Before you is a pyramid, the “building stones” of which are the formulas of chemical compounds. Find a path from the top of the pyramid to its base such that the sum of the relative molecular masses of the compounds is minimal. When choosing each next “stone”, you need to take into account that you can only choose the one that is directly adjacent to the previous one.

In response, write down the formulas of the substances in the winning path.

Answer: C 2 H 6 - H 2 CO 3 - SO 2 - Na 2 S

8. Citric acid is found not only in lemons, but also in unripe apples, currants, cherries, etc. Citric acid is used in cooking and in the household (for example, to remove rust stains from fabric). The molecule of this substance consists of 6 carbon atoms, 8 hydrogen atoms, 7 oxygen atoms.

C 6 H 8 O 7

Check the correct statement:

a) the relative molecular weight of this substance is 185;
b) the relative molecular weight of this substance is 29;
c) the relative molecular weight of this substance is 192.

DEFINITION

Sulfur- the sixteenth element of the Periodic Table. Designation - S from the Latin "sulfur". Located in the third period, group VIA. Refers to non-metals. The nuclear charge is 16.

Sulfur occurs in nature both in a free state (native sulfur) and in various compounds. Sulfur compounds with various metals are very common. Many of them are valuable ores (for example, lead luster PbS, zinc blende ZnS, copper luster Cu 2 S) and serve as a source for non-ferrous metals.

Among sulfur compounds, sulfates are also common in nature, mainly calcium and magnesium. Finally, sulfur compounds are found in the organisms of plants and animals.

Atomic and molecular mass of sulfur

Relative molecular mass of the substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 the mass of a carbon atom.

The values of the atomic and molecular masses of sulfur are the same; they are equal to 32.059.

Allotropy and allotropic modifications of sulfur

Sulfur exists in the form of two allotropic modifications - orthorhombic and monoclinic.

At normal pressures, sulfur forms brittle yellow crystals that melt at 112.8 o C; the density is 2.07 g/cm3. It is insoluble in water, but quite soluble in carbon disulfide, benzene and some other liquids. When these liquids evaporate, sulfur is released from the solution in the form of yellow crystals of the orthorhombic system, in the shape of octahedrons, in which usually some of the corners or edges are cut off (Fig. 1). This modification of sulfur is called rhombic.

Rice. 1. Allotropic modifications of sulfur.

Crystals of a different shape are obtained if molten sulfur is slowly cooled and, when it partially solidifies, the liquid that has not yet had time to solidify is drained. Under these conditions, the walls of the vessel are covered from the inside with long dark yellow needle-shaped crystals of the monoclinic system. This modification of sulfur is called monoclinic. It has a density of 1.96 g/cm3, melts at 119.3 o C and is stable only at temperatures above 96 o C.

Sulfur isotopes

It is known that in nature sulfur can be found in the form of four stable isotopes 32 S, 33 S, 34 S and 36 S. Their mass numbers are 32, 33, 34 and 36, respectively. The nucleus of an atom of the sulfur isotope 32 S contains sixteen protons and sixteen neutrons, and the isotopes 33 S, 34 S and 36 S contain the same number of protons, seventeen, eighteen and twenty neutrons, respectively.

There are artificial isotopes of sulfur with mass numbers from 26 to 49, among which the most stable is 35 S with a half-life of 87 days.

Sulfur ions

The outer energy level of the sulfur atom has six electrons, which are valence electrons:

1s 2 2s 2 2p 6 3s 2 3p 4 .

As a result of chemical interaction, sulfur can lose its valence electrons, i.e. be their donor, and turn into positively charged ions or accept electrons from another atom, i.e. be their acceptor and turn into negatively charged ions:

S 0 -6e → S 6+ ;

S 0 -4e → S 4+ ;

S 0 -4e → S 2+ ;

S o +2e → S 2- .

Sulfur molecule and atom

The sulfur molecule is monatomic - S. Here are some properties that characterize the sulfur atom and molecule:

Examples of problem solving

EXAMPLE 1

Exercise

What mass of sulfur will be required to obtain aluminum sulfide Al 2 S 3 weighing 30 g? Under what conditions can this sulfide be obtained from simple substances?

Solution

Let us write the reaction equation for the production of sulfur sulfide:

2Al + 3S = Al 2 S 3.

Let's calculate the amount of aluminum sulfide substance (molar mass - 150 g/mol):

n(Al 2 S 3) = m(Al 2 S 3) / M(Al 2 S 3);

n(Al 2 S 3) = 30 / 150 = 0.2 mol.

According to the reaction equation n(Al 2 S 3) : n(S) = 1:3, it means:

n(S) = 3 × n(Al 2 S 3);

n(S) = 3 × 0.2 = 0.6 mol.

Then the mass of sulfur will be equal (molar mass - 32 g/mol):

m(S) = n(S) × M(S);

Relative atomic mass (A r) - dimensionless quantity equal to the ratio of the average mass of an atom of an element (taking into account the percentage of isotopes in nature) to 1/12 of the mass of an atom 12 C.

Average absolute atomic mass (m) equal to the relative atomic mass times the amu.

Ar(Mg) = 24.312

m(Mg) = 24.312 1.66057 10 -24 = 4.037 10 -23 g

Relative molecular weight (M r) - a dimensionless quantity showing how many times the mass of a molecule of a given substance is greater than 1/12 the mass of a carbon atom 12 C.

M g = m g / (1/12 m a (12 C))

m r - mass of a molecule of a given substance;

m a (12 C) - mass of a carbon atom 12 C.

M g = S A g (e). The relative molecular mass of a substance is equal to the sum of the relative atomic masses of all elements, taking into account the indices.

Examples.

M g (B 2 O 3) = 2 A r (B) + 3 A r (O) = 2 11 + 3 16 = 70

M g (KAl(SO 4) 2) = 1 A r (K) + 1 A r (Al) + 1 2 A r (S) + 2 4 A r (O) =
= 1 39 + 1 27 + 1 2 32 + 2 4 16 = 258

Absolute molecular mass equal to the relative molecular mass multiplied by the amu. The number of atoms and molecules in ordinary samples of substances is very large, therefore, when characterizing the amount of a substance, a special unit of measurement is used - the mole.

Amount of substance, mol . Means a certain number of structural elements (molecules, atoms, ions). Designatedn , measured in moles. A mole is the amount of a substance containing as many particles as there are atoms in 12 g of carbon.

Avogadro's number (N A ). The number of particles in 1 mole of any substance is the same and equals 6.02 10 23. (Avogadro's constant has the dimension - mol -1).

Example.

How many molecules are there in 6.4 g of sulfur?

The molecular weight of sulfur is 32 g/mol. We determine the amount of g/mol of substance in 6.4 g of sulfur:

n ( s) = m(s)/M(s ) = 6.4 g / 32 g/mol = 0.2 mol

Let's determine the number of structural units (molecules) using the constant Avogadro N A

N(s) = n (s)N A = 0.2 6.02 10 23 = 1.2 10 23

Molar mass shows the mass of 1 mole of a substance (denotedM).

M = m / n

The molar mass of a substance is equal to the ratio of the mass of the substance to the corresponding amount of the substance.

The molar mass of a substance is numerically equal to its relative molecular mass, however, the first quantity has the dimension g/mol, and the second is dimensionless.

M = N A m (1 molecule) = N A M g 1 amu = (N A 1 amu) M g = M g

This means that if the mass of a certain molecule is, for example, 80 amu. ( SO 3 ), then the mass of one mole of molecules is equal to 80 g. Avogadro’s constant is a proportionality coefficient that ensures the transition from molecular relationships to molar ones. All statements regarding molecules remain valid for moles (with replacement, if necessary, of amu by g). For example, the reaction equation: 2 Na + Cl 2 2 NaCl , means that two sodium atoms react with one chlorine molecule or, which is the same thing, two moles of sodium react with one mole of chlorine.

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Quantitative characteristics of the substance
Solving combined problems based on quantitative characteristics of a substance
Problem solving. The law of constancy of the composition of substances. Calculations using the concepts of “molar mass” and “chemical amount” of a substance
Solving calculation problems based on quantitative characteristics of matter and stoichiometric laws
Solving calculation problems based on the laws of the gas state of matter