Chemistry lesson Grade 8

Topic: Oxygen, its general characteristics. Finding in nature. Obtaining oxygen and physical properties.

The purpose of the lesson: 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 the element according to the table 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" using oxygen as an example. Be able to characterize the physical properties and methods of collecting oxygen.

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

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

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

Demonstrations. Obtaining oxygen from hydrogen peroxide.

During the classes

Learning new material.

1. Frontal conversation:

What gas supports respiration 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 a simple substance(O2).

Relative molecular weight of a simple substance (32).

Describe 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 common chemical element in the earth's crust (49%). 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 (Mr (O2)=2x16=32, p air=29).

2. Experiments on obtaining oxygen.

Obtaining in the laboratory.

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

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

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

We put a little manganese (IV) oxide MnO2 into a test tube with a solution of hydrogen peroxide, a violent reaction begins with the release of oxygen. We confirm the release of oxygen with 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 itself consumed.

Definition:

Substances that speed up chemical reactions, but are not themselves consumed 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=К2MnO4+MnO2+О2

Manganese (IV) oxide accelerates another oxygen production reaction - the decomposition reaction when heated potassium chlorate KClO3 (bertolet salt): 2KSlO3 MnO2 2KSl + 3O2

3. Work with the textbook:

US. 75 read about the use of catalysts in industry.

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

With. 75 read the article of the textbook "obtaining in industry". On what physical property of oxygen is this method of its production based? (liquid oxygen has a higher boiling point than liquid nitrogen, so the nitrogen will evaporate and the oxygen will remain).

II.Consolidation of knowledge and 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. part of the air

4. is part of the water (+)

5. slightly heavier than air.

4. Simple substance oxygen:

1. has an atomic mass of 16

2. is part of the water

3. supports breathing and burning (+)

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

5. Fill in the table:

General characteristics of oxygen
Being in nature
Receipt a) in the laboratory b) in industry
Physical properties

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

W= (nxAr): Mr x 100%

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

How to recognize which flask is carbon dioxide and oxygen? (with the help of a smoldering splinter: in oxygen it flares 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. It is present in the free state in atmospheric air. 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, although in small quantities: 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 the molecule, referred to 1/12 of the molar mass of the carbon-12 atom (12 C).

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

M r (O 2) \u003d 15.999 × 2 ≈32.

Allotropy and allotropic modifications of oxygen

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).

At 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.

Isotopes of oxygen

It is known that in nature oxygen can be 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 an atom 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 isotopes of oxygen with mass numbers from 12 to 24, of which the most stable isotope is 15 O with a half-life of 120 s.

oxygen ions

On the outside energy level The 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 from another atom, i.e. be their acceptor, and turn into negatively charged ions:

O 0 +2e → O 2-;

About 0 -1e → About 1+.

Molecule and atom of oxygen

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. Have you ever thought about what, more precisely, what substances the air consists of? Most of all 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 uninhabitable. Thanks to him, life exists on Earth, because nitrogen, both together and individually, is detrimental to humans. Let's look at the properties of oxygen.

Physical properties of oxygen

In the air, oxygen is simply not distinguishable, since under normal conditions it is a gas without taste, color and 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 a person, and in nature it exists only in a gaseous state. looks like this (photo). And hard 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). The model of an oxygen molecule is shown below.

Oxygen. Chemical properties

The first thing with which the chemical characteristic of an element begins 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 were combined into a separate one - oxides. oxygen can form chemical compounds both metals and non-metals.

Let's talk about getting it in the laboratories.

Oxygen can be produced chemically by the decomposition of potassium permanganate, hydrogen peroxide, berthollet salt, active metal nitrates and heavy metal oxides. Consider the reaction equations for 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 nitrates of active metals (for example, sodium nitrate):

2NaNO 3 \u003d 2NaNO 2 + O 2

Application of oxygen

WITH chemical properties we're done. Now it's time to talk about the use of oxygen in human life. It is needed for fuel combustion in electrical and thermal power plants. It is used to produce steel from cast iron and scrap metal, for welding and cutting metal. Oxygen is needed for firefighters' masks, divers' cylinders, 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. It seems that there is no industry where it is not used, but the most important role he plays in medicine. There he is called "medical oxygen". In order for oxygen to be usable, it is pre-compressed. The physical properties of oxygen contribute to the fact that it can be compressed. In this form, it is stored inside cylinders similar to these.

It is used in resuscitation and operations in equipment to maintain life 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 mankind 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 included in 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: history 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 are now observing. Among all the components, it is oxygen that is more abundant in nature than other elements.

oxygen as separate element was discovered on August 1, 1774. In the course of an experiment on obtaining air from mercury scale by heating with an ordinary lens, he discovered that a candle burns 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, isolated oxygen at the beginning of the 17th century and used it for breathing in his invention. But his experiments did not affect the understanding of the role oxygen plays in the nature of the energy exchange of living organisms. However, the French chemist Antoine Laurent Lavoisier is recognized as the scientist who officially discovered oxygen. He repeated Priestley's experiment and realized that the resulting gas was a separate element.

Oxygen interacts with almost all simple gases, except for 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 in both bound and free form. As a rule, being a strong oxidizing agent, it is in a bound state. The presence of oxygen in nature as a separate unbound element is recorded only in the atmosphere of the planet.

It is contained in the form of a gas and is a combination of two oxygen atoms. It makes up about 21% of the total volume of the atmosphere.

Oxygen in the air, in addition to its usual form, has an isotropic form in the form of ozone. is made up 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 short-wavelength radiation from our Sun is absorbed and does not reach the surface.

In the absence of the ozone layer, organic life would be destroyed, like fried food in a microwave oven.

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

In the earth's crust, oxygen is in a bound form and is the most common element. Its share is about 47%. The presence of oxygen in nature is not limited to the shells of the planet, this element is part of all organic beings. Its share on average reaches 67% of the total mass of all elements.

Oxygen is the basis of life

Due to the high oxidative activity, oxygen quite easily combines with most elements and substances, forming oxides. The high oxidizing power of the element ensures the well-known combustion process. Oxygen is also involved in slow oxidation processes.

The role of oxygen in nature as a strong oxidizing agent is indispensable in the life of living organisms. Thereby chemical process substances are oxidized with the release of energy. Living organisms use it for their life activity.

Plants are the 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 appeared that could absorb carbon dioxide.

This process was made possible by the advent 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, thus providing a diverse flora and fauna of our planet.

The importance of oxygen in nature is not just huge, but paramount. The metabolic system of the animal world clearly relies on the presence of oxygen in the atmosphere. Without it, life becomes impossible as we know it. Only anaerobic (capable of living without oxygen) organisms will remain among the inhabitants of the planet.

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

The process of respiration of animals and insects is based on the production of unbound oxygen for redox reactions, followed by the production 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 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, the 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.

Based on the existing "chemistry" of the planet, evolution has come to carbon-based organic life based on water as a solvent for chemicals, as well as using oxygen as an oxidizing agent in order to obtain energy.

Another 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 building an organic molecule. And the medium of the liquid, as a solvent, can be a mixture of liquid ammonia with helium. As for the atmosphere, it can be represented in the form of 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, this direction of the evolution of life is quite acceptable. As time proves, humanity is constantly faced with expanding the boundaries of our understanding of the 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-orbitals. This excludes the possibility of the transition of O atoms to an excited state, therefore oxygen in all compounds exhibits a constant valency equal to II. Having a high electronegativity, oxygen atoms are always negatively charged in compounds (s.o. = -2 or -1). The exception is OF 2 and O 2 F 2 fluorides.

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

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 predominates). Oxygen is part of the atmosphere (20.9% by volume, 23.2% by mass), 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 plant and animal tissues, 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 slightly soluble in water - 5 volumes in 100 volumes of water. However, if all the oxygen dissolved in water passed into the atmosphere, then it would occupy a huge volume - 10 million km 3 (n.c.). This is equal to approximately 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 saltpeter heating, the second - mercury oxide (+2). The name was given by A. Lavoisier ("oxygenium" - "giving birth to acids").

It exists in free form in two allotropic modifications- "ordinary" oxygen O 2 and ozone O 3.

The structure of the ozone molecule

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 - colorless, odorless and tasteless gas, m.p. –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).

Obtaining oxygen

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

2H 2 O → 2H 2 + O 2

2. In the laboratory, oxygen is produced by:
1.Alkaline electrolysis 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 salt KClO 3:
2KClO 3 \u003d 2KCl + 3O 2 (MnO 2 catalyst)

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. Decomposition of hydrogen peroxide:
2H 2 O 2 \u003d H 2 O + O 2 (MnO 2 catalyst)

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

On the 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

Total:
2K 2 O 4 + 2CO 2 \u003d 2K 2 CO 3 + 3O 2

When K 2 O 2 is used, 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 (i.e. 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. Burning - b a rapid process of oxidation of a substance, accompanied by the release of a large amount of heat and light. To prove that the flask contains oxygen, and not some other gas, it is necessary to lower a smoldering splinter into the flask. In oxygen, a smoldering splinter flares brightly. The combustion of various substances in air is a redox process in which oxygen is the oxidizing agent. Oxidizing agents are substances that “take away” electrons from reducing substances. The good oxidizing properties of oxygen can be easily explained by the structure of its outer electron shell.

The valence shell of oxygen 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 before the octet, which oxygen seeks to accept from the electron shells of other elements, entering into reactions with them as an oxidizing agent.

Oxygen has the second (after fluorine) electronegativity on the Pauling scale. Therefore, in the vast majority of its compounds with other elements, oxygen has negative degree of oxidation. A stronger oxidizing agent than oxygen is only its neighbor in the period - fluorine. Therefore, compounds of oxygen 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 system. Most of its most important chemical properties are related to 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 (the so-called pyrophoric iron) spontaneously ignites in air, forming Fe 2 O 3, and steel wire burns in oxygen if it is heated in advance:

3 Fe + 2O 2 → Fe 3 O 4

2Mg + O 2 → 2MgO

2Cu + O 2 → 2CuO

With non-metals (sulfur, graphite, hydrogen, phosphorus, etc.), oxygen reacts 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 a temperature above 1200 o C or in an electrical discharge.

Oxygen is able to oxidize 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.

Compounds containing the dioxygenyl cation O 2 + are known, 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 active than oxygen O 2 . So, ozone oxidizes iodide - ions I - in a solution of Kl:

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, acts as a protector of all life on Earth from the harmful ultraviolet radiation of the sun. The thin ozone layer absorbs this radiation, and it does not reach the Earth's surface. There are significant fluctuations in the thickness and extent of this layer over time (the so-called ozone holes), the reasons for such fluctuations have not yet been elucidated.

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

The use of ozone O 3: for disinfection drinking water, Wastewater, air, for bleaching fabrics.