Calcium hydroxide is widely used in the production of building materials such as whitewash, plaster and gypsum mortars. This is due to its ability to interact with carbon dioxide CO2 contained in the air. The same property of a calcium hydroxide solution is used to measure the quantitative content of carbon dioxide in the air.

A useful property of calcium hydroxide is its ability to act as a flocculant that purifies wastewater from suspended and colloidal particles (including iron salts). It is also used to increase the pH of water, since natural water contains substances (such as acids) that cause corrosion in plumbing pipes.

Write a molecular equation for the reaction between calcium hydroxide and carbon dioxide that was mentioned in the text.2. Explain what features of this reaction allow it to be used to detect carbon dioxide in the air

Write a shortened ionic equation for the reaction between calcium hydroxide and hydrochloric acid mentioned in the text.2. Explain why this reaction is used to increase the pH of water.

9. The scheme of the redox reaction is given:

Write an electron balance for this reaction.2. Specify the oxidizing agent and the reducing agent.

Arrange the coefficients in the reaction equation.

10. The transformation scheme is given: → → →

Write molecular reaction equations that can be used to carry out these transformations.

Establish a correspondence between the formula of an organic substance and the class/group to which this substance belongs: match the class to each letter

Insert the formulas of the missing substances into the proposed chemical reaction schemes and arrange the coefficients.

1) → 2) →

13. Propane burns with low levels of toxic emissions into the atmosphere, so it is used as an energy source in many applications, such as gas lighters and heating of country houses. What volume of carbon dioxide (CO) is produced when 4.4 g of propane is completely burned? Write down a detailed solution to the problem.

Isopropyl alcohol is used as a universal solvent: it is included in household chemicals, perfumes and cosmetics, and windshield washer fluids for cars. In accordance with the diagram below, create reaction equations for the production of this alcohol. When writing reaction equations, use the structural formulas of organic substances.

15. In medicine, a saline solution is a 0.9% solution of sodium chloride in water. Calculate the mass of sodium chloride and the mass of water required to prepare 500 g of saline solution. Write down a detailed solution to the problem.

7. Response elements:

2) As a result of this reaction, an insoluble substance is formed - calcium carbonate, cloudiness of the original solution is observed, which allows us to judge the presence of carbon dioxide in the air (qualitative reaction to)

8. Response elements:

2) The presence of acid in natural water causes low pH values ​​of this water. Calcium hydroxide neutralizes the acid and pH values ​​increase.

9. Explanation. 1) An electronic balance has been compiled:

2) It is indicated that sulfur in the oxidation state –2 (or) is a reducing agent, and iron in the oxidation state +3 (or) is an oxidizing agent;

3) The reaction equation has been drawn up:

10. The reaction equations corresponding to the transformation scheme are written:

15.Explanation. Answer elements: 1) = 4.5 g 2) = 495.5 g

The test includes 15 tasks. 1 hour 30 minutes (90 minutes) is allotted to complete the chemistry work.

From your chemistry course, you know the following methods for separating mixtures: sedimentation, filtration, distillation (distillation), magnetic action, evaporation, crystallization.

Figures 1-3 present situations in which these methods of cognition are applied.

Which of the methods shown in the figures CANNOT be used to separate the mixture:

1) acetone and butanol-1;

2) clay and river sand;

3) barium sulfate and acetone?

Show answer

The figure shows a model of the electronic structure of an atom of a certain chemical element.

Based on the analysis of the proposed model:

1) Identify the chemical element whose atom has such an electronic structure.

2) Indicate the period number and group number in the Periodic Table of Chemical Elements D.I. Mendeleev, in which this element is located.

3) Determine whether the simple substance formed by this chemical element is a metal or non-metal.

Show answer

Li; 2; 1 (or I); metal

Periodic table of chemical elements D.I. Mendeleev is a rich repository of information about chemical elements, their properties and the properties of their compounds, about the patterns of changes in these properties, about methods of obtaining substances, as well as about their location in nature. For example, it is known that with an increase in the atomic number of a chemical element in periods, the electronegativity of atoms increases, and in groups it decreases.

Considering these patterns, arrange the following elements in order of decreasing electronegativity: B, C, N, Al. Write down the designations of the elements in the required sequence.

Show answer

N → C → B → Al

Listed below are the characteristic properties of substances that have a molecular and atomic structure.

Characteristic properties of substances

molecular structure

fragile;

Refractory;

Non-volatile;

Solutions and melts conduct electric current.

ionic structure

Solid under normal conditions;

fragile;

Refractory;

Non-volatile;

Insoluble in water, do not conduct electric current.

Using this information, determine what structure the substances have: diamond C and potassium hydroxide KOH. Write your answer in the space provided.

1. Diamond S

2. Potassium hydroxide KOH

Show answer

Diamond C has an atomic structure, potassium hydroxide KOH has an ionic structure

Oxides are conventionally divided into four groups, as shown in the diagram. In this diagram, for each of the four groups, fill in the missing names of the groups or chemical formulas of the oxides (one example of formulas) belonging to this group.

Show answer

Response elements:

The names of the groups are written down: amphoteric, basic; Formulas of substances of the corresponding groups are written down.

(Other wording of the answer is allowed without distorting its meaning.)

Read the following text and complete tasks 6-8

Sodium carbonate (soda ash, Na 2 CO 3) is used in glass production, soap making and the production of washing and cleaning powders, enamels, to obtain ultramarine dye. It is also used to soften the water of steam boilers and generally to reduce water hardness. In the food industry, sodium carbonates are registered as a food additive E500 - an acidity regulator, a leavening agent, and an anti-caking agent.

Sodium carbonate can be obtained by reacting alkali and carbon dioxide. In 1861, Belgian chemical engineer Ernest Solvay patented a method for producing soda that is still used today. Equimolar amounts of ammonia and carbon dioxide gases are passed into a saturated sodium chloride solution. The precipitated residue of slightly soluble sodium bicarbonate is filtered and calcined (calcined) by heating to 140-160 ° C, during which it turns into sodium carbonate.

The Roman physician Dioscorides Pedanius wrote about soda as a substance that hissed with the release of gas when exposed to acids known by that time - acetic CH 3 COOH and sulfuric H 2 SO 4.

1) Write down the molecular equation specified in the text for the reaction of producing sodium carbonate by the interaction of alkali and carbon dioxide.

2) What is soap from a chemical point of view?

Show answer

1) 2NaOH + CO 2 = Na 2 CO 3 + H 2 O

2) Soap from a chemical point of view is a sodium or potassium salt of one of the higher carboxylic acids (palmitic, stearic...)

1) Write down in molecular form the equation specified in the text for the decomposition of sodium bicarbonate, leading to the formation of soda ash.

2) What is “water hardness”?

Show answer

1) Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O

2) A sign of a reaction is the formation of a white precipitate of calcium carbonate

1) Write down in abbreviated ionic form the equation for the interaction of soda with acetic acid specified in the text.

2) Which electrolytes - strong or weak - does sodium carbonate belong to?

Show answer

1) Ca(OH) 2 + FeSO 4 = Fe(OH) 2 ↓ + CaSO 4 ↓

2) As a result of the reaction, iron hydroxide precipitates and the iron content in water decreases significantly

The scheme of the redox reaction is given:

HIO 3 + H 2 O 2 → I 2 + O 2 + H 2 O

1) Create an electronic balance for this reaction.

2) Specify the oxidizing agent and reducing agent.

3) Arrange the coefficients in the reaction equation.

Show answer

1) An electronic balance has been compiled:

2) It is indicated that the oxidizing agent is I +5 (or iodic acid), the reducing agent is O -1 (or hydrogen peroxide);

3) The reaction equation has been drawn up:

2НIO 3 + 5Н 2 O 2 = I 2 + 5O 2 + 6Н 2 O

The transformation scheme is given:

P → P 2 O 5 → Ca 3 (PO 4) 2 → Ca (H 2 PO 4) 2

Write molecular reaction equations that can be used to carry out these transformations.

Show answer

1) 4P + 5O 2 = 2P 2 O 5

2) P 2 O 5 + ZCaO = Ca 3 (PO 4) 2

3) Ca 3 (PO 4) 2 + 4H 3 PO 4 = ZCa (H 2 PO 4) 2

Establish a correspondence between the class of organic substances and the formula of its representative: for each position indicated by a letter, select the corresponding position indicated by a number.

CLASS OF SUBSTANCES

A) 1,2-dimethyl benzene

Test No. 1 11th grade

Option 1.

From your chemistry course you know the following:ways separation of mixtures:

.

ways.

Fig.1 Fig.2 Fig.3

1) flour from iron filings that got into it;

2) water from inorganic salts dissolved in it?

mixtures. (

iron filings

Water with inorganic salts dissolved in it

element.

this chemical element.

Write your answers in the table

chemical

element

Period No.

Group number

Metal/non-metal

3. Periodic table of chemical elements D.I. Mendeleev - a rich repository

about their occurrence in nature. For example, it is known that with increasing serial number

of a chemical element, in periods the radii of atoms decrease, and in groups they increase.

Considering these patterns, arrange in order of increasing atomic radii

the following elements:C, Si, Al, N.

sequences.

4.

state;



boiling and melting;

 non-conductive;





 fragile;

 refractory;

 non-volatile;



electricity

Using this information, determine what structure the substances nitrogen N have 2

and table salt NaCl. (give a detailed answer).

2

products and sweets.

by

CO2

carbon dioxide in the air.

contains substances (for example,acids

mentioned in the text .

6.

.

9. Although plants and animals need phosphorus compounds as an element that is part of vital substances, pollution of natural waters with phosphates has an extremely negative effect on the condition of water bodies. The discharge of phosphates with wastewater causes the rapid development of blue-green algae, and the vital activity of all other organisms is inhibited. Determine the number of cations and anions formed during the dissociation of 25 mol of sodium orthophosphate.

10. Give an explanation:Sometimes in rural areas, women combine henna hair coloring with washing in a Russian bath. Why does the color become more intense?

11.

H 2 S + Fe 2 O 3 → FeS + S + H 2 O.

12. Propane burns with low levels of toxic emissions into the atmosphere, so it is used as an energy source in many applications, such as gas

What volume of carbon dioxide (CO) is formed during the complete combustion of 4.4 g of propane?

13. In medicine, a saline solution is a 0.9% solution of sodium chloride in water. Calculate the mass of sodium chloride and the mass of water required to prepare 500 g of saline solution.

Write down a detailed solution to the problem .

Test No. 1 11th grade

Option 2.

1. From the chemistry course you know the followingways separation of mixtures:

sedimentation, filtration, distillation (distillation), magnetic action, evaporation, crystallization .

Figures 1–3 show examples of the use of some of the listed

ways.

Fig.1 Fig.2 Fig.3

Which of the following methods for separating mixtures can be used for purification:

1) sulfur from iron filings that got into it;

2) water from particles of clay and sand?

Write down the figure number and the name of the corresponding division method in the table

mixtures. (copy the table into your notebook)

2. The figure shows a model of the electronic structure of an atom of some chemical

element.

Based on the analysis of the proposed model, complete the following tasks:

1) identify the chemical element whose atom has such an electronic structure;

2) indicate the period number and group number in the Periodic Table of Chemicals

elements D.I. Mendeleev, in which this element is located;

3) determine whether the simple substance that forms is a metal or non-metal

this chemical element.

Write your answers in the table(draw the table into your notebook)

chemical

element

Period No.

Group number

Metal/non-metal

3. Periodic table of chemical elements D.I. Mendeleev - a rich repository

information about chemical elements, their properties and the properties of their compounds,

about the patterns of changes in these properties, about methods of obtaining substances, as well as

about their occurrence in nature. For example, it is known that the electronegativity of a chemical element increases in periods and decreases in groups.

Given these patterns, arrange in order of increasing electronegativity

the following elements:F, Na, N, Mg. Write down the designations of the elements in the required

sequences.

4. The table below lists the characteristic properties of substances that have a molecular and ionic structure.

gaseous and solid aggregate

state;

 have low temperatures

boiling and melting;

 non-conductive;

 have low thermal conductivity

 solid under normal conditions;

 fragile;

 refractory;

 non-volatile;

 carried out in melts and solutions

electricity

Using this information, determine what structure the substances oxygen O have 2

and soda Na 2 CO 3 . (give a detailed answer).

The food industry uses the food additive E526, which

is calcium hydroxide Ca(OH)2 . It finds application in production:

fruit juices, baby food, pickled cucumbers, table salt, confectionery

products and sweets.

It is possible to produce calcium hydroxide on an industrial scaleby

mixing calcium oxide with water , this process is called quenching.

Calcium hydroxide is widely used in the production of such construction materials.

materials such as whitewash, plaster and gypsum mortars. This is due to his ability

interact with carbon dioxide CO2 contained in the air. This is the same property

calcium hydroxide solution is used to measure the quantitative content

carbon dioxide in the air.

A useful property of calcium hydroxide is its ability to act as

flocculant that purifies wastewater from suspended and colloidal particles (including

iron salts). It is also used to increase the pH of water, since natural water

contains substances (for example,acids ), causing corrosion in plumbing pipes.

5. Write a molecular equation for the reaction to produce calcium hydroxide, which

mentioned in the text .

6. Explain why this process is called quenching.

7. Write a molecular equation for the reaction between calcium hydroxide and carbon dioxide

gas, which was mentioned in the text. Explain what features of this reaction make it possible to use it to detect carbon dioxide in the air.

8. Write an abbreviated ionic equation for the reaction mentioned in the text between

calcium hydroxide and hydrochloric acid .

9. Although plants and animals need phosphorus compounds as an element that is part of vital substances, pollution of natural waters with phosphates has an extremely negative effect on the condition of water bodies. The discharge of phosphates with wastewater causes the rapid development of blue-green algae, and the vital activity of all other organisms is inhibited. Determine the number of cations and anions formed during the dissociation of 15 mol of potassium orthophosphate.

10. Give an explanation:Why are all types of hair styling usually done using heat?

11. The scheme of the redox reaction is given

Arrange the coefficients. Record your electronic balance.

Specify the oxidizing agent and the reducing agent.

12. Propane burns with low levels of toxic emissions into the atmosphere, so it is used as an energy source in many areas, such as gas

lighters and when heating country houses.

What volume of carbon dioxide (CO) is formed during the complete combustion of 5 g of propane?

Write down a detailed solution to the problem.

13. The pharmacist needs to prepare a 5% iodine solution, which is used to treat wounds.

What volume of solution can a pharmacist prepare from 10 g of crystalline iodine if the density of the solution should be 0.950 g/ml?

From 1965 to 1980, of the 1307 deaths worldwide in major accidents involving fires, explosions or toxic releases, either in fixed installations or during transport, 104 deaths (8%) involved the release of a toxic substance. Statistics on non-fatal cases are as follows: the total number of people affected is 4,285 people; those affected by toxic emissions are 1,343 people (32%). Before 1984, the ratio of casualties to deaths from toxic releases was very different from the ratio of accidents involving fires and explosions. However, the accident that occurred on December 3, 1984 in Bhopal (India) claimed about 4 thousand lives and made a significant adjustment to this ratio. Accidents involving the release of toxic substances are of great concern to the public in all industrialized countries.

Many toxic substances widely used in industry, of which the most important are chlorine and ammonia, are stored in the form of liquefied gases under a pressure of at least 1 MPa. In case of loss of tightness of the tanks where such a substance is stored, instantaneous evaporation of part of the liquid occurs. The amount of liquid evaporated depends on the nature of the substance and its temperature. Some toxic substances, which are liquids at ordinary temperatures, are stored in tanks (at atmospheric pressure) equipped with breathing equipment and appropriate devices to prevent leakage to the atmosphere, such as a special activated carbon trap. One of the possible reasons for the loss of tank tightness may be the appearance of excess pressure of an inert gas, such as nitrogen, inside the vapor space of the tank, which occurs as a result of failure of the pressure relief valve in the absence of an automatic pressure control system in the tank. Another reason is that the remaining toxic substance is carried away along with water, for example when washing a tank.

A possible cause of leakage from tanks can be an excessive amount of heat supplied to the tank, for example in the form of solar radiation or the heat load of a fire in the storage area. The entry of substances into the tank that react chemically with the contents can also cause a toxic release, even if the contents themselves were of low toxicity. There are known cases where at enterprises, as a result of unintentional actions, for example, when mixing hydrochloric acid and bleach (sodium hypochlorite), the resulting chlorine leaked. The introduction of substances that accelerate polymerization or decomposition into the tank may release an amount of heat that will cause some of the contents to boil off and result in toxic emissions.

Increasing motorization brings with it the need for environmental protection measures. The air in cities is increasingly polluted with substances harmful to human health, especially carbon monoxide, unburned hydrocarbons, nitrogen oxides, lead compounds, sulfur compounds, etc. To a large extent, these are products of incomplete combustion of fuels used in enterprises, in everyday life, and also in automobile engines.

Along with toxic substances during the operation of cars, their noise also has a harmful effect on the population. Recently, in cities, the noise level has increased by 1 dB annually, so it is necessary not only to stop the increase in the overall noise level, but also to reduce it. Constant exposure to noise causes nervous diseases and reduces the ability to work of people, especially those engaged in mental activity. Motorization brings noise to previously quiet, remote places. Unfortunately, the reduction of noise generated by woodworking and agricultural machines has not yet been given due attention. A chainsaw creates noise in a large part of the forest, which causes changes in the living conditions of animals and often causes the extinction of certain species.

The most common source of criticism, however, is air pollution from vehicle exhaust gases.

During busy traffic, exhaust gases accumulate near the soil surface and in the presence of solar radiation, especially in industrial cities located in poorly ventilated basins, so-called smog is formed. The atmosphere is polluted to such an extent that staying in it is harmful to health. Traffic officers stationed at some busy intersections use oxygen masks to maintain their health. Particularly harmful is the relatively heavy carbon monoxide located near the earth's surface, which penetrates into the lower floors of buildings and garages and has more than once led to deaths.

Legislative regulations limit the content of harmful substances in vehicle exhaust gases, and they are constantly becoming more stringent (Table 1).

Regulations are a big concern for car manufacturers; they also indirectly affect the efficiency of road transport.

For complete combustion of the fuel, some excess air can be allowed to ensure good movement of the fuel with it. The required excess air depends on the degree of mixing of fuel with air. In carburetor engines, considerable time is allocated for this process, since the fuel path from the mixture-forming device to the spark plug is quite long.

A modern carburetor allows the formation of various types of mixtures. The richest mixture is needed for a cold start of the engine, since a significant portion of the fuel condenses on the walls of the intake manifold and does not immediately enter the cylinder. In this case, only a small part of the light fractions of the fuel evaporates. When the engine warms up, a rich mixture is also required.

When the vehicle is moving, the composition of the air-fuel mixture should be poor, which will ensure good efficiency and low specific fuel consumption. To achieve maximum engine power, you need to have a rich mixture in order to fully utilize the entire mass of air entering the cylinder. To ensure good dynamic qualities of the engine when the throttle valve is quickly opened, it is necessary to additionally supply a certain amount of fuel into the intake pipeline, which compensates for the fuel that has settled and condensed on the walls of the pipeline as a result of the increase in pressure in it.

To ensure good mixing of fuel with air, high air speed and rotation must be created. If the cross-section of the carburetor diffuser is constant, then at low engine speeds, for good mixture formation, the air speed in it is low, and at high speeds, the resistance of the diffuser leads to a decrease in the mass of air entering the engine. This disadvantage can be eliminated by using a carburetor with a variable diffuser cross-section or fuel injection into the intake manifold.

There are several types of gasoline injection systems into the intake manifold. In the most commonly used systems, fuel is supplied through a separate nozzle for each cylinder, which ensures uniform distribution of fuel between the cylinders and eliminates sedimentation and condensation of fuel on the cold walls of the intake manifold. It is easier to bring the amount of injected fuel closer to the optimal amount required by the engine at the moment. There is no need for a diffuser, and energy losses that occur when air passes through it are eliminated. An example of such a fuel supply system is the frequently used Bosch K-Jetronic injection system used on.

The diagram of this system is shown in Fig. 1. The conical pipe 1, in which the valve 3 swings on the lever 2, moves, is designed so that the lift of the valve is proportional to the mass air flow. Windows 5 for the passage of fuel are opened by spool 6 in the regulator body when the lever moves under the influence of the incoming air flow. The necessary changes in the mixture composition in accordance with the individual characteristics of the engine are achieved by the shape of the conical pipe. The lever with the valve is balanced by a counterweight; inertial forces during vehicle vibrations do not affect the valve.

Rice. 1. Bosch K-Jetronic gasoline injection system:
1 - inlet pipe; 2 - lever of the air plate valve; 3 - air plate valve; 4 - throttle valve; 5 - windows; 6 - metering spool; 7 - adjusting screw; 8 - fuel injector; 9 - lower chamber of the regulator; 10 - distribution valve; 11 - steel membrane; 12 - valve seat; 13 - distribution valve spring; 14 - pressure reducing valve; 15 - fuel pump; 16 - fuel tank; 17 - fuel filter; 18 - fuel pressure regulator; 19 - additional air supply regulator; 20 - fuel bypass valve; 21 - cold start fuel injector; 22 - thermostat water temperature sensor.

The air flow entering the engine is controlled by the throttle valve 4. Damping of valve vibrations, and with it the spool, which occur at low engine speeds due to air pressure pulsations in the intake manifold, is achieved by jets in the fuel system. To regulate the amount of fuel supplied, screw 7 located in the valve lever is also used.

Between the window 5 and the nozzle 8 there is a distribution valve 10, which, using a spring 13 and a seat 12 resting on the membrane 11, maintains a constant injection pressure in the nozzle nozzle of 0.33 MPa at a pressure in front of the valve of 0.47 MPa.

Fuel from tank 16 is supplied by an electric fuel pump 15 through a pressure regulator 18 and a fuel filter 17 into the lower chamber 9 of the regulator housing. Constant fuel pressure in the regulator is maintained by pressure reducing valve 14. Diaphragm regulator 18 is designed to maintain fuel pressure when the engine is not running. This prevents the formation of air pockets and ensures a good start of a hot engine. The regulator also slows down the increase in fuel pressure when starting the engine and dampens its fluctuations in the pipeline.

Cold starting of the engine is facilitated by several devices. Bypass valve 20, controlled by a bimetallic spring, opens the drain line into the fuel tank during a cold start, which reduces the fuel pressure on the end of the spool. This upsets the balance of the lever and the same amount of incoming air will correspond to a larger volume of injected fuel. Another device is the additional air supply regulator 19, the diaphragm of which is also opened by a bimetallic spring. Additional air is needed to overcome the increased frictional resistance of a cold engine. The third device is the cold start fuel injector 21, controlled by a thermostat 22 in the engine water jacket, which keeps the injector open until the engine coolant reaches a set temperature.

The electronics equipment of the considered gasoline injection system is limited to the minimum. When the engine is stopped, the electric fuel pump is turned off and there is less excess air than with direct fuel injection, however, the large cooling surface of the walls leads to large heat losses, which causes a drop.

Formation of carbon monoxide CO and hydrocarbons CH x

When a mixture of stoichiometric composition is burned, harmless carbon dioxide CO 2 and water vapor should be formed, and if there is a lack of air due to the fact that part of the fuel burns incompletely, additional toxic carbon monoxide CO and unburned hydrocarbons CH x should be formed.

These harmful components of exhaust gases can be burned and rendered harmless. For this purpose, it is necessary to supply fresh air with a special compressor K (Fig. 2) to a place in the exhaust pipeline where harmful products of incomplete combustion can be burned. Sometimes this is done by blowing air directly onto the hot exhaust valve.

As a rule, a thermal reactor for afterburning CO and CH x is located immediately behind the engine directly at the exhaust gas outlet. Exhaust gases M are supplied to the center of the reactor and removed from its periphery into the exhaust pipeline V. The outer surface of the reactor has thermal insulation I.

In the hottest central part of the reactor there is a fire chamber, heated by exhaust gases, where the products of incomplete combustion of fuel are burned. This releases heat, which maintains the high temperature of the reactor.

Unburned components in the exhaust gases can be oxidized without combustion using a catalyst. To do this, it is necessary to add secondary air to the exhaust gases, necessary for oxidation, the chemical reaction of which will be carried out by the catalyst. This also releases heat. The catalyst is usually rare and precious metals, so it is very expensive.

Catalysts can be used in any type of engine, but they have a relatively short service life. If lead is present in the fuel, the surface of the catalyst is quickly poisoned and it becomes unusable. Producing high-octane gasoline without lead anti-knock agents is a rather complex process that consumes a lot of oil, which is not economically feasible if there is a shortage of oil. It is clear that afterburning fuel in a thermal reactor leads to energy losses, although combustion releases heat that can be utilized. Therefore, it is advisable to organize the process in the engine in such a way that when fuel burns in it, a minimum amount of harmful substances is formed. At the same time, it should be noted that in order to comply with future legislative requirements, the use of catalysts will be inevitable.

Formation of nitrogen oxides NO x

Nitrogen oxides, which are harmful to health, are formed at high combustion temperatures under conditions of a stoichiometric mixture composition. Reducing the emission of nitrogen compounds is associated with certain difficulties, since the conditions for their reduction coincide with the conditions for the formation of harmful products of incomplete combustion and vice versa. At the same time, the combustion temperature can be reduced by introducing some inert gas or water vapor into the mixture.

For this purpose, it is advisable to recirculate cooled exhaust gases into the intake manifold. The resulting decrease in power requires a richer mixture, a larger opening of the throttle valve, which increases the overall emission of harmful CO and CH x from the exhaust gases.

Exhaust gas recirculation, combined with a reduction in compression ratio, variable valve timing and retarded ignition, can reduce NO x by up to 80%.

Nitrogen oxides are removed from exhaust gases using also catalytic methods. In this case, the exhaust gases are first passed through a reduction catalyst, in which the NO x content is reduced, and then, together with additional air, through an oxidation catalyst, where CO and CH x are eliminated. A diagram of such a two-component system is shown in Fig. 3.

To reduce the content of harmful substances in exhaust gases, so-called α-probes are used, which can also be used in conjunction with a two-component catalyst. The peculiarity of the system with an α-probe is that additional air for oxidation is not supplied to the catalyst, but the α-probe constantly monitors the oxygen content in the exhaust gases and controls the fuel supply so that the mixture composition always corresponds to the stoichiometric one. In this case, CO, CH x and NO x will be present in the exhaust gases in minimal quantities.

The principle of operation of the α-probe is that in a narrow range near the stoichiometric composition of the mixture α = 1, the voltage between the inner and outer surfaces of the probe changes sharply, which serves as a control pulse for the device that regulates the fuel supply. The sensitive element 1 of the probe is made of zirconium dioxide, and its surfaces 2 are coated with a layer of platinum. The voltage characteristics U between the inner and outer surfaces of the sensing element are shown in Fig. 4.

Other toxic substances

Antiknock agents, such as tetraethyl lead, are usually used to increase the octane number of fuel. To prevent lead compounds from depositing on the walls of the combustion chamber and valves, so-called scavengers are used, in particular dibromoethyl.

These compounds enter the atmosphere with exhaust gases and pollute vegetation along roads. When lead compounds enter the human body with food, they have a harmful effect on human health. Lead deposition in exhaust gas catalysts has already been mentioned. In this regard, an important task currently is the removal of lead from gasoline.

Oil entering the combustion chamber does not burn completely, and the content of CO and CH x in the exhaust gases increases. To eliminate this phenomenon, high tightness of the piston rings and maintaining good technical condition of the engine are necessary.

The combustion of large amounts of oil is especially typical for two-stroke engines, in which it is added to the fuel. The negative consequences of using gasoline-oil mixtures are partially mitigated by dosing the oil with a special pump in accordance with the engine load. Similar difficulties exist when using the Wankel engine.

Gasoline vapors also have a harmful effect on human health. Therefore, crankcase ventilation must be carried out in such a way that gases and vapors penetrating into the crankcase due to poor sealing do not enter the atmosphere. Leakage of gasoline vapors from the fuel tank can be prevented by adsorption and suction of vapors into the intake system. Leakage of oil from the engine and gearbox and contamination of the vehicle as a result with oils are also prohibited in order to maintain a clean environment.

Reducing oil consumption is just as important from an economic point of view as saving fuel, since oils are significantly more expensive than fuel. Regular inspection and maintenance will reduce oil consumption due to engine malfunctions. Oil leaks in the engine can be observed, for example, due to poor sealing of the cylinder head cover. Due to oil leakage, the engine becomes dirty, which can cause a fire.

Oil leakage is also dangerous due to low tightness of the crankshaft seal. In this case, oil consumption increases noticeably, and the car leaves dirty marks on the road.

Contaminating a car with oil is very dangerous, and oil stains under the car are grounds for prohibiting its operation.

Oil leaking from the crankshaft seal can get into the clutch and cause it to slip. However, more negative consequences are caused by oil entering the combustion chamber. And although oil consumption is relatively small, its incomplete combustion increases the emission of harmful components with exhaust gases. Oil burning manifests itself in excessive smoking of the car, which is typical for, as well as significantly worn four-stroke engines.

In four-stroke engines, oil penetrates into the combustion chamber through the piston rings, which is especially noticeable when there is a lot of wear on them and the cylinder. The main reason for oil penetration into the combustion chamber is the uneven fit of the compression rings to the cylinder circumference. Oil is drained from the cylinder walls through the slots of the oil scraper ring and holes in its groove.

Through the gap between the rod and the intake valve guide, oil easily penetrates into the intake manifold, where there is a vacuum. This is especially common when using low viscosity oils. Oil consumption through this unit can be prevented by using a rubber seal on the end of the valve guide.

Engine crankcase gases, which contain many harmful substances, are usually discharged through a special pipeline into the intake system. Entering the cylinder from it, crankcase gases burn together with the air-fuel mixture.

Low-viscosity oils reduce friction losses, improve engine performance and reduce fuel consumption. However, it is not recommended to use oils with a viscosity lower than that prescribed by standards. This can cause increased oil consumption and increased engine wear.

Due to the need to conserve oil, waste oil collection and use are becoming increasingly important issues. By regenerating old oils, it is possible to obtain a significant amount of high-quality liquid lubricants and at the same time prevent environmental pollution by stopping the discharge of used oils into water streams.

Determination of the permissible amount of harmful substances

Removing harmful substances from exhaust gases is a rather difficult task. In high concentrations, these components are very harmful to health. Of course, it is impossible to immediately change the current situation, especially with regard to the vehicle fleet in use. Therefore, legal requirements for monitoring the content of harmful substances in exhaust gases are designed for new vehicles produced. These regulations will be gradually improved taking into account new advances in science and technology.

Exhaust gas purification is associated with an increase in fuel consumption by almost 10%, a decrease in engine power and an increase in the cost of the vehicle. At the same time, the cost of vehicle maintenance also increases. Catalysts are also expensive because their components are made of rare metals. The service life should be calculated for 80,000 km of vehicle mileage, but this has not yet been achieved. Currently used catalysts last about 40,000 km, and they use gasoline without lead impurities.

The current situation calls into question the effectiveness of strict regulations on the content of harmful impurities, since this causes a significant increase in the cost of the car and its operation, and ultimately leads to increased oil consumption.

It is not yet possible to meet the stringent requirements for the purity of exhaust gases put forward in the future with the current state of gasoline and diesel engines. Therefore, it is advisable to pay attention to a radical change in the power plant of mechanical vehicles.