Chemistry lesson grade 8

Subject: Oxygen, its general characteristics. Being in nature. Getting oxygen and its physical properties.

The purpose of the lesson: to continue the formation of the concepts of "chemical element", "simple substance", "chemical reaction". To form ideas about the methods of obtaining oxygen in the laboratory. Introduce the concept of a catalyst, physical properties, characterize an element according to D.I. Mendeleev. Improve your interactive whiteboard skills.

Basic concepts... Catalysts.

Planned learning outcomes

Subject. To be able to distinguish between the concepts of "chemical element", "simple substance" on the example of oxygen. Be able to characterize the physical properties and methods of oxygen collection.

Metasubject... Develop the ability to work according to plan, formulate, argue, organize educational cooperation and joint activities with teacher and peers.

Personal. To form a responsible attitude towards learning, readiness for self-education.

The main activities of students. Describe a chemical element according to the proposed plan. Describe chemical reactionsobserved during the demo experiment. Participate in a joint discussion of the results. Draw conclusions from the results of experiments.

Demonstrations... Getting oxygen from hydrogen peroxide.

During the classes

Learning new material.

1. Frontal conversation:

What gas supports breathing and combustion?

What information about oxygen do you already know from courses in natural history, botany?

What substances contain oxygen? (water, sand, rocks, minerals, proteins, fats, carbohydrates).

general characteristics chemical element oxygen:

Chemical sign (O).

Relative atomic mass (16).

Valence (II).

Chemical formula simple substance (O2).

Relative molecular weight of a simple substance (32).

Characterize element # 8 based on its position in the periodic table chemical elements DI. Mendeleev. (serial number - 8, atomic mass - 16, IV - group number, period number - 2).

Being in nature.

Oxygen is the most abundant chemical element in the earth's crust (49%). The air contains 21% oxygen gas. Oxygen is an important part of organic compounds that are of great importance for living organisms.

Physical properties: oxygen is a colorless gas, tasteless and odorless, slightly soluble in water (in 100 volumes of water - 3.1 volumes of oxygen). Oxygen is slightly heavier than air (Мr (О2) \u003d 2x16 \u003d 32, p air \u003d 29).

2. Experiments on obtaining oxygen.

Getting in the laboratory.

For the first time, oxygen gas was obtained in 1774 eng. by the scientist Joseph Priestley. Upon calcining mercury (II) oxide, Priestley received "air":

The scientist decided to investigate the effect of the obtained gas on the candle flame: under the influence of this gas, the candle flame became dazzlingly bright, an iron wire burned out in the stream of the obtained gas. Mice, placed in a vessel with this gas, breathed easily, the scientist himself tried to inhale this gas and noted that breathing is easy.

In the school laboratory, we get this gas from hydrogen peroxide. To observe the physical properties of oxygen, we repeat the rules safety precautions.

In a test tube with a solution of hydrogen peroxide, we put a little manganese (IV) oxide MnO2, a violent reaction begins with the release of oxygen. The release of oxygen is confirmed by a smoldering splinter (it flashes and burns). At the end of the reaction, manganese (IV) oxide settles to the bottom, it can be used again. Consequently, manganese (IV) oxide accelerates the decomposition reaction of hydrogen peroxide, but is not consumed in this case.

Definition:

Substances that accelerate chemical reactions, but are not consumed themselves and are not part of the reaction products, are called catalysts.

2Н2О2 MnO2 2Н2О + О2

In the school laboratory, oxygen is obtained in another way:

By heating potassium permanganate

2КМnO4 \u003d К2MnO4 + MnO2 + О2

Manganese (IV) oxide accelerates another reaction for producing oxygen - the decomposition reaction when heated potassium chlorate KClO3 (Berthollet's salt): 2KSlO3 MnO2 2KSl + 3O2

3. Working with the textbook:

On p. 75 read about industrial applications of catalysts.

In fig. 25 and fig. 26 shows methods for collecting oxygen. What physical properties are known to you based on the collection of oxygen by air displacement? (oxygen is heavier than air: 32 29), by water displacement? (oxygen is slightly soluble in water). How to properly assemble a displacement oxygen scavenger? (Fig. 25) Answer: The oxygen collection tube should be positioned bottom down. How can you detect or prove the presence of oxygen in a vessel? (by the flashing of a smoldering splinter).

with. 75 read the textbook article "Getting in the Industry." What physical property of oxygen is such a method of obtaining it based on? (Liquid oxygen has a boiling point higher than liquid nitrogen, so the nitrogen will evaporate and the oxygen will remain).

II.Consolidation of knowledge, skills.

What substances are called catalysts?

with. 76 test tasks.

Work in pairs. Choose two correct answers:

Chemical element oxygen:

1.colorless gas

2.has serial number 8 (+)

3.Is part of the air

4.included in water (+)

5. slightly heavier than air.

4. Simple substance oxygen:

1.has an atomic mass of 16

2.included in water

3.supports breathing and combustion (+)

4. formed during the decomposition of hydrogen peroxide (+).

5. Fill in the table:

Calculate the mass fraction of the chemical element oxygen in sulfur oxide (VI). SO3

W \u003d (nхAr): Mr х 100%

W (O) \u003d (3x16): 80x100% \u003d 60%

How to recognize which flask is in carbon dioxide and oxygen? (with the help of a smoldering splinter: in oxygen it flashes brightly, in carbon dioxide it goes out).

DEFINITION

Oxygen - the eighth element of the Periodic Table. Designation - O from the Latin "oxygenium". Located in the second period, VIA group. Refers to non-metals. The nuclear charge is 8.

Oxygen is the most abundant element in the earth's crust. In a free state, it is in the atmospheric air, in bound form is a part of water, minerals, rocks and all substances from which organisms of plants and animals are built. The mass fraction of oxygen in the earth's crust is about 47%.

As a simple substance, oxygen is a colorless, odorless gas. It is slightly heavier than air: the mass of 1 liter of oxygen under normal conditions is 1.43 g, and 1 liter of air is 1.293 g. Oxygen dissolves in water, albeit in small amounts: 100 volumes of water at 0 o C dissolve 4.9, and at 20 o C - 3.1 volumes of oxygen.

Atomic and molecular weight of oxygen

DEFINITION

Relative atomic mass A r is the molar mass of an atom of a substance, referred to 1/12 of the molar mass of a carbon-12 atom (12 C).

The relative atomic mass of atomic oxygen is 15.999 amu.

DEFINITION

Relative molecular weight M r is the molar mass of a molecule, referred to 1/12 of the molar mass of carbon-12 (12 C).

This is a dimensionless quantity. It is known that the oxygen molecule is diatomic - O 2. The relative molecular weight of the oxygen molecule will be:

M r (O 2) \u003d 15.999 × 2 ≈32.

Allotropy and allotropic oxygen modifications

Oxygen can exist in the form of two allotropic modifications - oxygen O 2 and ozone O 3 (the physical properties of oxygen are described above).

When normal conditions ozone is a gas. It can be separated from oxygen by strong cooling; ozone condenses into a blue liquid boiling at (-111.9 o C).

The solubility of ozone in water is much greater than that of oxygen: 100 volumes of water at 0 o C dissolve 49 volumes of ozone.

The formation of ozone from oxygen can be expressed by the equation:

3O 2 \u003d 2O 3 - 285 kJ.

Oxygen isotopes

It is known that in nature oxygen can be found in the form of three isotopes 16 O (99.76%), 17 O (0.04%) and 18 O (0.2%). Their mass numbers are 16, 17 and 18, respectively. The nucleus of the oxygen isotope 16 O contains eight protons and eight neutrons, and the isotopes 17 O and 18 O contain the same number of protons, nine and ten neutrons, respectively.

There are twelve radioactive oxygen isotopes with mass numbers from 12 to 24, of which the most stable isotope 15 O with a half-life of 120 s.

Oxygen ions

On the outside energy level oxygen atom has six electrons, which are valence:

1s 2 2s 2 2p 4.

The structure of the oxygen atom is shown below:

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

O 0 + 2e → O 2-;

О 0 -1e → О 1+.

Oxygen molecule and atom

The oxygen molecule consists of two atoms - O 2. Here are some properties that characterize the oxygen atom and molecule:

Examples of problem solving

EXAMPLE 1

Introduction

Every day we breathe in the air we need so much. Have you ever thought about what, or rather what substances, air consists of? Most of it contains nitrogen (78%), followed by oxygen (21%) and inert gases (1%). Although oxygen does not make up the most basic part of the air, without it the atmosphere would be unsuitable for life. Thanks to him, life exists on Earth, because nitrogen, both together and separately, is destructive to humans. Let's take a look at the properties of oxygen.

Physical properties of oxygen

Oxygen in the air cannot be easily distinguished, since under normal conditions it is a gas without taste, color or smell. But oxygen can be artificially transferred to other states of aggregation. So, at -183 o C it becomes liquid, and at -219 o C it hardens. But solid and liquid oxygen can only be obtained by humans, and in nature it exists only in a gaseous state. looks like this (photo). And solid is like ice.

The physical properties of oxygen are also the structure of the molecule of a simple substance. Oxygen atoms form two such substances: oxygen (O 2) and ozone (O 3). Below is a model of an oxygen molecule.

Oxygen. Chemical properties

The first thing that begins with the chemical characteristics of an element is its position in the periodic system of D.I.Mendeleev. So, oxygen is in the 2nd period of the 6th group of the main subgroup at number 8. Its atomic mass is 16 amu, it is a non-metal.

In inorganic chemistry, its binary compounds with other elements are combined into a separate one - oxides. Oxygen can form chemical compounds with both metals and non-metals.

Let's talk about getting it in laboratories.

Oxygen can be chemically obtained by decomposition of potassium permanganate, hydrogen peroxide, berthollet's salt, active metal nitrates and heavy metal oxides. Consider the reaction equations when applying each of these methods.

1. Water electrolysis:

H 2 O 2 \u003d H 2 O + O 2

5. Decomposition of heavy metal oxides (eg mercury oxide):

2HgO \u003d 2Hg + O 2

6. Decomposition of active metal nitrates (eg sodium nitrate):

2NaNO 3 \u003d 2NaNO 2 + O 2

Oxygen application

WITH chemical properties we're done. Now is the time to talk about the use of oxygen in human life. It is needed to burn fuel in electric and thermal power plants. It is used for making steel from cast iron and scrap metal, for welding and cutting metal. Oxygen is needed for masks for firemen, for divers' cylinders, it is used in ferrous and non-ferrous metallurgy and even in the manufacture of explosives. also in food Industry oxygen is known as food additive E948. There seems to be no industry where it is used, but the most important role he plays medicine. There it is called "medical oxygen". In order for oxygen to be suitable for use, it is pre-compressed. The physical properties of oxygen make it compressible. In this form, it is stored inside cylinders similar to these.

It is used in intensive care and in operations in equipment to maintain vital processes in the body of a sick patient, as well as in the treatment of certain diseases: decompression, pathologies of the gastrointestinal tract. With its help, doctors save many lives every day. The chemical and physical properties of oxygen contribute to its widespread use.

Since the advent of chemistry, it has become clear to humanity that everything around consists of a substance, which includes chemical elements. The variety of substances is provided by various compounds simple elements... To date, 118 chemical elements have been discovered and entered into the periodic table of D. Mendeleev. Among them, it is worth highlighting a number of leading ones, the presence of which determined the emergence of organic life on Earth. This list includes: nitrogen, carbon, oxygen, hydrogen, sulfur and phosphorus.

Oxygen: the story of discovery

All these elements, as well as a number of others, contributed to the development of the evolution of life on our planet in the form in which we now observe. Among all the components, it is oxygen in nature that is more than other elements.

Oxygen as separate element was discovered on August 1, 1774. During an experiment to obtain air from the scale of mercury by heating with an ordinary lens, he discovered that a candle burned with an unusually bright flame.

For a long time Priestley tried to find a reasonable explanation for this. At that time, this phenomenon was given the name "second air". Somewhat earlier, the inventor of the submarine K. Drebbel at the beginning of the 17th century isolated oxygen and used it for breathing in his invention. But his experiments did not influence the understanding of the role oxygen plays in the nature of energy exchange in living organisms. However, the scientist who officially discovered oxygen is the French chemist Antoine Laurent Lavoisier. He repeated Priestley's experiment and realized that the resulting gas was a separate element.

Oxygen interacts with almost all simple and except inert gases and noble metals.

Finding oxygen in nature

Among all the elements of our planet, oxygen occupies the largest share. The distribution of oxygen in nature is very diverse. It is present both in bound form and in free form. As a rule, being a strong oxidizing agent, it stays in a bound state. The presence of oxygen in nature as a separate unbound element is recorded only in the atmosphere of the planet.

Contained as a gas, it is a compound of two oxygen atoms. It makes up about 21% of the total volume of the atmosphere.

Oxygen in air, in addition to its usual form, has an isotropic form in the form of ozone. consists of three oxygen atoms. The blue color of the sky is directly related to the presence of this compound in upper layers atmosphere. Thanks to ozone, the hard shortwave radiation from our Sun is absorbed and does not hit the surface.

Without the ozone layer, organic life would be destroyed like toasted food in the microwave.

In the hydrosphere of our planet, this element is associated with two and forms water. The proportion of oxygen in oceans, seas, rivers and groundwater estimated at about 86-89%, taking into account the dissolved salts.

Oxygen is bound in the earth's crust and is the most abundant element. Its share is about 47%. Finding oxygen in nature is not limited to the shells of the planet, this element is included in all organic creatures. Its share on average reaches 67% of the total mass of all elements.

Oxygen is the basis of life

Due to its high oxidative activity, oxygen easily combines with most elements and substances to form oxides. The high oxidizing capacity of the element ensures the well-known combustion process. Oxygen also participates in slow oxidation processes.

The role of oxygen in nature as a strong oxidant is irreplaceable in the life of living organisms. Thereby chemical process oxidation of substances occurs with the release of energy. Its living organisms use it for their life.

Plants are a source of oxygen in the atmosphere

At the initial stage of the formation of the atmosphere on our planet, the existing oxygen was in a bound state, in the form of carbon dioxide (carbon dioxide). Over time, plants have appeared that can absorb carbon dioxide.

This process became possible due to the occurrence of photosynthesis. Over time, during the life of plants, over millions of years, a large amount of free oxygen has accumulated in the Earth's atmosphere.

According to scientists, in the past its mass fraction reached about 30%, one and a half times more than now. Plants, both in the past and now, have significantly influenced the oxygen cycle in nature, thereby providing a diverse flora and fauna of our planet.

The importance of oxygen in nature is not just enormous, but paramount. The metabolic system of the animal world is clearly based on the presence of oxygen in the atmosphere. In its absence, life becomes impossible in the form in which we know. Among the inhabitants of the planet, only anaerobic (capable of living without oxygen) organisms will remain.

Intensive in nature is provided by the fact that it is in three states of aggregation in combination with other elements. Being a strong oxidizing agent, it very easily passes from free to bound form. And only thanks to plants, which, through photosynthesis, break down carbon dioxide, it is available in free form.

The respiration process of animals and insects is based on the production of unbound oxygen for redox reactions with the subsequent receipt of energy to ensure the vital activity of the organism. The presence of oxygen in nature, bound and free, ensures the full functioning of all life on the planet.

Evolution and "chemistry" of the planet

The evolution of life on the planet was based on the peculiarities of the composition of the Earth's atmosphere, the composition of minerals and the presence of water in a liquid state.

The chemical composition of the crust, atmosphere and the presence of water became the basis for the origin of life on the planet and determined the direction of the evolution of living organisms.

Building on the existing "chemistry" of the planet, evolution has come to carbon-based organic life based on water as a solvent for chemicals, and the use of oxygen as an oxidizing agent for energy.

Different evolution

At this stage modern science does not refute the possibility of life in other environments, different from terrestrial conditions, where silicon or arsenic can be taken as the basis for the construction of an organic molecule. And the medium of a liquid, as a solvent, can be a mixture of liquid ammonia with helium. As for the atmosphere, it can be represented as gaseous hydrogen with an admixture of helium and other gases.

What metabolic processes can be under such conditions, modern science is not yet able to model. However, such a direction in the evolution of life is quite acceptable. As time proves, humanity is constantly faced with the expansion of the boundaries of our understanding of the surrounding world and life in it.

Oxygen O It has atomic number 8, located in the main subgroup (subgroup a) VI group, in the second period. In oxygen atoms, valence electrons are located at the 2nd energy level, which has only s- and p-orbital. This excludes the possibility of transition of O atoms to an excited state, therefore oxygen in all compounds exhibits a constant valence equal to II. Having a high electronegativity, oxygen atoms are always negatively charged in compounds (s.r. \u003d -2 or -1). The exception is fluorides OF 2 and O 2 F 2.

For oxygen, the oxidation states are -2, -1, +1, +2

General characteristics of the element

Oxygen is the most abundant element on Earth, accounting for slightly less than half, 49% of the total mass of the earth's crust. Natural oxygen consists of 3 stable isotopes 16 O, 17 O and 18 O (16 O prevails). Oxygen is part of the atmosphere (20.9% by volume, 23.2 by weight), water and more than 1400 minerals: silica, silicates and aluminosilicates, marbles, basalts, hematite and other minerals and rocks. Oxygen makes up 50-85% of the mass of tissues of plants and animals, because it is contained in proteins, fats and carbohydrates that make up living organisms. The role of oxygen for respiration and for oxidation processes is well known.

Oxygen is relatively little soluble in water - 5 volumes in 100 volumes of water. However, if all the oxygen dissolved in water passed into the atmosphere, it would occupy a huge volume - 10 million km 3 (n.u). This is equal to about 1% of all oxygen in the atmosphere. The formation of an oxygen atmosphere on earth is due to the processes of photosynthesis.

Discovered by the Swede K. Scheele (1771 - 1772) and the Englishman J. Priestley (1774). The first used heating of nitrate, the second - mercury oxide (+2). The name was given by A. Lavoisier ("oxygenium" - "giving birth to acids").

Freely exists in two allotropic modifications - "ordinary" oxygen O 2 and ozone O 3.

Ozone molecule structure

3O 2 \u003d 2O 3 - 285 kJ
Ozone in the stratosphere forms a thin layer that absorbs most of the biologically harmful ultraviolet radiation.
During storage, ozone spontaneously converts to oxygen. Chemically, oxygen O 2 is less active than ozone. The electronegativity of oxygen is 3.5.

Physical properties of oxygen

O 2 - gas without color, odor and taste, so pl. –218.7 ° С, b.p. –182.96 ° C, paramagnetic.

Liquid O 2 blue, solid - of blue color... O 2 is soluble in water (better than nitrogen and hydrogen).

Oxygen production

1. Industrial method - liquid air distillation and water electrolysis:

2H 2 O → 2H 2 + O 2

2. In the laboratory, oxygen is obtained:
1.Electrolysis of alkaline aqueous solutions or aqueous solutions of oxygen-containing salts (Na 2 SO 4, etc.)

2. Thermal decomposition of potassium permanganate KMnO 4:
2KMnO 4 \u003d K 2 MnO4 + MnO 2 + O 2,

Berthollet's salt KClO 3:
2KClO 3 \u003d 2KCl + 3O 2 (catalyst MnO 2)

Manganese oxide (+4) MnO 2:
4MnO 2 \u003d 2Mn 2 O 3 + O 2 (700 o C),

3MnO 2 \u003d 2Mn 3 O 4 + O 2 (1000 o C),

Barium peroxide BaO 2:
2BaO 2 \u003d 2BaO + O 2

3. By decomposition of hydrogen peroxide:
2H 2 O 2 \u003d H 2 O + O 2 (catalyst MnO 2)

4. Decomposition of nitrates:
2KNO 3 → 2KNO 2 + O 2

On spaceships and submarines oxygen is obtained from a mixture of K 2 O 2 and K 2 O 4:
2K 2 O 4 + 2H 2 O \u003d 4KOH + 3O 2
4KOH + 2CO 2 \u003d 2K 2 CO 3 + 2H 2 O

In total:
2K 2 O 4 + 2CO 2 \u003d 2K 2 CO 3 + 3О 2

When using K 2 O 2, the overall reaction looks like this:
2K 2 O 2 + 2CO 2 \u003d 2K 2 CO 3 + O 2

If you mix K 2 O 2 and K 2 O 4 in equal molar (ie equimolar) amounts, then one mole of O 2 will be released per 1 mole of absorbed CO 2.

Chemical properties of oxygen

Oxygen supports combustion. Combustion - b rapid oxidation process of a substance, accompanied by the release of a large amount of heat and light. To prove that the bottle contains oxygen, and not some other gas, a smoldering splinter must be dipped into the bottle. In oxygen, a smoldering splinter flares up brightly. Combustion of various substances in air is a redox process in which oxygen is the oxidizing agent. Oxidants are substances that "take" electrons from reducing substances. The good oxidizing properties of oxygen can be easily explained by the structure of its outer electron shell.

The oxygen valence shell is located at the 2nd level - relatively close to the nucleus. Therefore, the nucleus strongly attracts electrons to itself. On the valence shell of oxygen 2s 2 2p 4 there are 6 electrons. Consequently, two electrons are missing to the octet, which oxygen seeks to take from the electron shells of other elements, entering into reactions with them as an oxidizing agent.

Oxygen has the second (after fluorine) electronegativity in the Pauling scale. Therefore, in the overwhelming majority of its compounds with other elements, oxygen has negative oxidation state. A stronger oxidant than oxygen is only its neighbor in the period - fluorine. Therefore, oxygen compounds with fluorine are the only ones where oxygen has positive degree oxidation.

So, oxygen is the second most powerful oxidizing agent among all elements. Periodic table... Most of its most important chemical properties are associated with this.
All elements react with oxygen, except for Au, Pt, He, Ne and Ar, in all reactions (except for interaction with fluorine) oxygen is an oxidizing agent.

Oxygen easily reacts with alkali and alkaline earth metals:

4Li + O 2 → 2Li 2 O,

2K + O 2 → K 2 O 2,

2Ca + O 2 → 2CaO,

2Na + O 2 → Na 2 O 2,

2K + 2O 2 → K 2 O 4

Fine iron powder (so-called pyrophoric iron) ignites spontaneously in air, forming Fe 2 O 3, and steel wire burns in oxygen if heated in advance:

3 Fe + 2O 2 → Fe 3 O 4

2Mg + O 2 → 2MgO

2Cu + O 2 → 2CuO

Oxygen reacts with non-metals (sulfur, graphite, hydrogen, phosphorus, etc.) when heated:

S + O 2 → SO 2,

C + O 2 → CO 2,

2H 2 + O 2 → H 2 O,

4P + 5O 2 → 2P 2 O 5,

Si + O 2 → SiO 2, etc.

Almost all reactions involving oxygen O 2 are exothermic, with rare exceptions, for example:

N 2 + O 2 → 2NO - Q

This reaction takes place at temperatures above 1200 o C or in an electric discharge.

Oxygen is capable of oxidizing complex substances, for example:

2H 2 S + 3O 2 → 2SO 2 + 2H 2 O (excess oxygen),

2H 2 S + O 2 → 2S + 2H 2 O (lack of oxygen),

4NH 3 + 3O 2 → 2N 2 + 6H 2 O (without catalyst),

4NH 3 + 5O 2 → 4NO + 6H 2 O (in the presence of a Pt catalyst),

CH 4 (methane) + 2O 2 → CO 2 + 2H 2 O,

4FeS 2 (pyrite) + 11O 2 → 2Fe 2 O 3 + 8SO 2.

Known compounds containing dioxygenyl cation O 2 +, for example, O 2 + - (the successful synthesis of this compound prompted N. Bartlett to try to obtain compounds of inert gases).

Ozone

Ozone is chemically more reactive than oxygen O 2. So, ozone oxidizes iodide - ions I - in a Kl solution:

O 3 + 2Kl + H 2 O \u003d I 2 + O 2 + 2KOH

Ozone is highly toxic, its toxic properties are stronger than, for example, hydrogen sulfide. However, in nature, ozone contained in the high layers of the atmosphere plays the role of a protector of all life on Earth from the harmful ultraviolet radiation of the sun. A thin ozone layer absorbs this radiation, and it does not reach the Earth's surface. Significant fluctuations in the thickness and length of this layer are observed over time (the so-called ozone holes) the reasons for such fluctuations have not yet been clarified.

Oxygen application O 2: to intensify the processes of obtaining iron and steel, when smelting non-ferrous metals, as an oxidizing agent in various chemical industries, for life support on submarines, as an oxidizer for rocket fuel (liquid oxygen), in medicine, when welding and cutting metals.

Ozone O 3 application: for disinfection drinking water, wastewater, air, for bleaching fabrics.