Thematic tasks - Chemistry exam: I will pass the GIA for "5"! Relative atomic and molecular masses Average mass of sulfur atoms

1. Fill in the gaps in the sentences.

Absolute atomic mass shows the mass of one twelfth part 1/12 of the mass of one molecule of the carbon isotope 12 6 C is measured in the following units: g, gc, mg, t.

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; does not have a unit of measure.

2. Write down using the notation oku = rounded to an integer value:

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

3. Names of chemical elements are given: mercury, phosphorus, hydrogen, sulfur, carbon, oxygen, potassium, nitrogen. In the empty cells, enter the symbols of the elements in such a way that a series is obtained, in which the relative atomic mass increases.

4. Underline the correct 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. Complete the diagram.

6. Calculate the relative molecular masses of substances according to their formulas:

a) M r (N 2) \u003d 2 * 14 \u003d 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) \u003d 12 + 41 + 35.5 \u003d 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 so 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 choose only the one that is directly adjacent to the previous one.

In response, write down the formulas of the substances of 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, 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

Mark 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.

List the main provisions of the atomic and molecular theory.

1. Substances are made up 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, chemical properties.

2. Molecules are made up of atoms. An atom is the smallest particle of a substance, a chemical element, which 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 (НCl). 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.

Cause of allotropy:

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

b) the 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 one substance are converted into molecules of other substances. Mass is an important property of a substance.

Question #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 in kilograms (kg)

m a () \u003d 1.67 * 10 -24 g

Using such numbers is inconvenient, 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 of the mass of a carbon atom.

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

1 amu \u003d m a (C) / 12 \u003d (1.99 * 10 -23) / 12 g \u003d 1.66 * 10 -24 g

and r () \u003d m a (H) / 1 amu \u003d (1.67 * 10 -27 / 1.66 * 10 -24) \u003d 1

Relative atomic mass, unlike absolute mass, has no unit of measurement.

Question #3

Is it possible to connect the concepts of "mole" and "Avogadro's constant"?

A mole is such an amount of substances that contains 6.02 * 10 23 particles (molecules or atoms).

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

n = N/Na, where

n - amount of substance;

N is the number of atoms or molecules.

Question #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) \u003d 10g

m(N 2) = 10 g

___________

NCl2 – ? N N – ?

Solution

M (Cl 2) \u003d 35.5 * 2 \u003d 71 g / mol

n (Cl 2) \u003d m (Cl 2) / M (Cl 2) \u003d 10 g / 71 g / mol \u003d \u003d 0.14 mol

N (Cl 2) \u003d n (Cl 2) * Na \u003d 0.14 mol

6.02*10 -23 1/mol

M (N 2) \u003d 14 * 2 \u003d 28 g / mol

n (N 2) \u003d m (N 2) / M (Cl 2) \u003d 10 g / 28 g / mol \u003d 0.36 mol

N(N2)=n (N2) * Na \u003d 0.36 mol * 6.02 * 10 23 1 / mol \u003d 2.17 * 10 23

N(N2) /
N (Cl2) \u003d (2.17 * 10 23) / 0.843 * 10 23 \u003d 2.57

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

Question #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 a carbon atom - 12 is 1.993 * 10 -26 kg.

Given:

m a (S) \u003d 5.31 * 10 -26 kg

m a (C) \u003d 1.993 * 10 -26 kg

___________

ar(s) - ?

Solution

1 amu \u003d m a (C) / 12 \u003d (1.993 * 10 -26 kg) \u003d 1.66 * 10-27 kg

ar (s) = m a (S)/1 amu \u003d 5.31 * 10-26 kg \u003d 32

Answer: ar (s) = 32.

Question #6

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

Question #7

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

Initial formulation: characteristic of simple bodies, as well as the forms and properties of compounds of elements are in a periodic dependence on the magnitude of the atomic masses of the elements.

The modern formulation: the properties of simple substances, as well as the forms and properties of compounds of elements, are in a periodic dependence on the charge of the atomic nucleus (atomic number).

In the periodic table, not all elements are arranged in ascending atomic mass, there is an exception that he could not explain. He foresaw that the reason lies 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 do not depend on the atomic mass, but on the charge of the nucleus.

Question #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 counterparts?

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

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

Questions #9

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

1p 3; 3p 6; 3S2; 2S2; 2d5; 5d2; 2p 4 ; 3p7

Question #10

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

This is an element with an atomic number of 92 and a relative mass of 238 - this is uranium.

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

Question #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 as follows:

USED BOOKS

Akhmetov N.S. General and inorganic chemistry.

Pilipenko. Handbook of elementary chemistry.

Khomchenko I.G. general chemistry

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

Average absolute mass of an atom (m) is equal to the relative atomic mass times the a.m.u.

Ar(Mg) = 24.312

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

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

M g \u003d 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) \u003d 2 A r (B) + 3 A r (O) \u003d 2 11 + 3 16 \u003d 70

M g (KAl (SO 4) 2) \u003d 1 A r (K) + 1 A r (Al) + 1 2 A r (S) + 2 4 A r (O) \u003d
= 1 39 + 1 27 + 1 2 32 + 2 4 16 = 258

Absolute mass of a molecule is equal to the relative molecular weight times the a.m.u. 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). Denotedn , measured in moles. A mole is the amount of a substance that contains as many particles as there are atoms in 12 g of carbon.

Avogadro's number (NA ). The number of particles in 1 mole of any substance is the same and equal to 6.02 10 23. (The Avogadro 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 a substance in 6.4 g of sulfur:

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

Let us 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 value has the dimension g / mol, and the second is dimensionless.

M = N A m (1 molecule) = N A M g 1 a.m.u. = (N A 1 amu) M g = M g

This means that if the mass of a certain molecule is, for example, 80 a.m.u. ( SO 3 ), then the mass of one mole of molecules is 80 g. Avogadro's constant is a proportionality factor that ensures the transition from molecular to molar ratios. All statements regarding molecules remain valid for moles (with the replacement, if necessary, of a.m.u. 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.

Navigation

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

DEFINITION

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

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

Of the sulfur compounds in nature, sulfates are also common, mainly calcium and magnesium. Finally, sulfur compounds are found in plant and animal organisms.

Atomic and molecular weight of sulfur

Relative molecular weight of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of 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 of 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 - rhombic and monoclinic.

At ordinary pressures, sulfur forms brittle yellow crystals, melting at 112.8 o C; the density is 2.07 g/cm 3 . It is insoluble in water, but quite soluble in carbon disulfide, benzene, and some other liquids. During the evaporation of these liquids, sulfur is released from the solution in the form of yellow crystals of the rhombic system, having 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 form are obtained if molten sulfur is slowly cooled and, when it partially solidifies, the liquid that has not yet solidified is drained. Under these conditions, the walls of the vessel are covered from the inside with long dark yellow acicular crystals of the monoclinic system. This modification of sulfur is called monoclinic. It has a density of 1.96 g / cm 3, melts at 119.3 o C and is stable only at temperatures above 96 o C.

Sulfur isotopes

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

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

Sulfur ions

On the outer energy level of the sulfur atom, there are six electrons that are valence:

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- .

Molecule and atom of sulfur

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

Examples of problem solving

EXAMPLE 1

The task

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

We write the reaction equation for the production of sulfur sulfide:

2Al + 3S \u003d Al 2 S 3.

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

n (Al 2 S 3) \u003d 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) \u003d 1: 3, which 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 to (molar mass - 32 g / mol):

m(S) = n(S) × M(S);

chemical phenomena. Substances

Which of the following signs characterize chemical phenomena: a) color change; b) change in aggregate state; c) shape change; d) precipitate formation?
Do chemical phenomena occur during the following processes: a) ice melting; b) distillation of water; c) iron rusting; d) separating the mixture by filtration; e) food rotting?
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 compound burns in oxygen, carbon dioxide and water are formed. What chemical elements can be present in this complex substance? Which ones are required? Explain the answer.

Relative atomic and molecular masses. The 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 sulfur element if the mass of a 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; f) copper sulfate (II) 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.
Mixed 21 g of iron and 19 g of sulfur, the mixture was heated. Given that iron and sulfur interact 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 on them

Calculate in what mass ratio sodium and oxygen combine in the compound Na 2 O.
The composition of the chemical includes calcium (mass fraction 29.4%), sulfur (23.5%) and oxygen (47.1%). Determine the formula for this compound.
Calculate the mass ratios in which calcium, carbon and oxygen are in the CaCO 3 compound.
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 valency of the 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 the formulas of compounds of manganese and oxygen, in which manganese is two-, three-, four- and heptavalent.
Draw the formulas of copper (I) chloride and copper (II) chloride, given that chlorine in compounds with metals is monovalent.

Chemical equations. Reaction types

The reaction scheme CuCl 2 + KOH → Сu(OH) 2 + KCl corresponds to the exchange reaction. Arrange the coefficients in this scheme.
Add reaction schemes and make equations: a) Li + ... → Li 2 O; b) Al + O 2 → ...; c) Na + S → ... ; d) C + ... → CCl 4 .
Give two examples of reactions of each type: 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 (bivalent); d) iodine (monovalent).

The amount of substance. Moth. Molar mass

Calculate the amount of magnesium substance in a sample of this metal weighing 6 g.
What is the mass of a mixture 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 oxide (IV), which contains as many molecules as there are atoms in a piece of iron weighing 1.4 g.

Calculations by chemical equations

The interaction of hydrogen and oxygen formed 450 g of water. What is the mass of the gases that reacted?
When limestone (calcium carbonate) is calcined, CaCO 3 produces calcium oxide and carbon dioxide. 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 what the valence of iron in the resulting chloride is 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 substance Al 2 S 3 that is formed as a result of the reaction.