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 window 5 and nozzle 8 there is a distribution valve 10, which, using a spring 13 and a seat 12 resting on a 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.
Oil contamination of a car 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.
All-Russian Test Work VPR All-Russian Test Work - Chemistry 11th grade
Explanations for the sample of the All-Russian test work
When familiarizing yourself with a sample test work, you should keep in mind that the tasks included in the sample do not reflect all the skills and content issues that will be tested as part of the all-Russian test work. A complete list of content elements and skills that can be tested in the work is given in the codifier of content elements and requirements for the level of training of graduates for the development of an all-Russian test in chemistry. The purpose of the sample test work is to give an idea of the structure of the all-Russian test work, the number and form of tasks, and their level of complexity.
Instructions for performing the work
The test includes 15 tasks. 1 hour 30 minutes (90 minutes) is allotted to complete the chemistry work.
Formulate your answers in the text of the work according to the instructions for the assignments. If you write down an incorrect answer, cross it out and write a new one next to it.
When performing work, you are allowed to use the following additional materials:
– Periodic table of chemical elements D.I. Mendeleev;
– table of solubility of salts, acids and bases in water;
– electrochemical series of metal voltages;
– non-programmable calculator.
When completing assignments, you can use a draft. Entries in draft will not be reviewed or graded.
We advise you to complete the tasks in the order in which they are given. To save time, skip a task that you cannot complete immediately and move on to the next one. If you have time left after completing all the work, you can return to the missed tasks.
The points you receive for completed tasks are summed up. Try to complete as many tasks as possible and score the most points.
We wish you success!
1. From your chemistry course you know the following methods for separating mixtures: settling, filtration, distillation (distillation), magnetic action, evaporation, crystallization. Figures 1–3 show examples of the use of some of the listed methods.
Which of the following methods for separating mixtures can be used for purification:
1) flour from iron filings that got into it;
2) water from inorganic salts dissolved in it?
Write down the figure number and the name of the corresponding method of separating the mixture in the table.
iron filings are attracted by a magnet
During distillation, after condensation of water vapor, salt crystals remain in the vessel
2. The figure shows a model of the electronic structure of an atom of some chemicalelement.
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 Chemical Elements D.I. Mendeleev, in which this element is located;
3) determine whether the simple substance that forms this chemical element is a metal or non-metal.
Write your answers in the table.
Answer:
N; 2; 5 (or V); non-metal
to determine a chemical element, you should count the total number of electrons, which we see in figure (7)
taking the periodic table, we can easily determine the element (the number of electrons found is equal to the atomic number of the element) (N-nitrogen)
after this we determine the group number (vertical column) (5) and the nature of this element (non-metal)
3. Periodic table of chemical elements D.I. Mendeleev– 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 radii of atoms decrease, and in groups they increase.
Considering these patterns, arrange the following elements in order of increasing atomic radii: N, C, Al, Si. Write down the designations of the elements in the required sequence.
Answer: ____________________________
N → C → Si → Al
4. The table below lists the characteristic properties of substances that have a molecular and ionic structure.
Using this information, determine what structure the substances nitrogen N2 and table salt NaCl have. Write your answer in the space provided:
1) nitrogen N2 ________________________________________________________________
2) table salt NaCl ___________________________________________________
nitrogen N2 – molecular structure;
table salt NaCl – ionic structure
5. Complex inorganic substances can be conditionally distributed, that is, classified, 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 substances (one example of formulas) belonging to this group.
The names of the groups are written down: bases, salts;
formulas of substances of the corresponding groups are written down
CaO, bases, HCl, salts
Read the following text and complete tasks 6–8.
The food industry uses the food additive E526, which is calcium hydroxide Ca(OH)2. It is used in the production of: fruit juices, baby food, pickled cucumbers, table salt, confectionery and sweets. It is possible to produce calcium hydroxide on an industrial scale by mixing calcium oxide with water
, this process is called quenching. Calcium hydroxide is widely used in the production of building materials such as whitewash, plaster and gypsum mortars. This is due to his ability interact with carbon dioxide CO2
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 (e.g. acids), causing corrosion in plumbing pipes.
1. Write a molecular equation for the reaction to produce calcium hydroxide, which
mentioned in the text.
2. Explain why this process is called quenching.
Answer:__________________________________________________________________________
________________________________________________________________________________
1) CaO + H 2 O = Ca(OH) 2
2) When calcium oxide interacts with water, a large amount is released
amount of heat, so the water boils and hisses, as if it hits a hot coal, when the fire is extinguished with water (or “this process is called quenching because as a result slaked lime is formed”)
1. Write a molecular equation for the reaction between calcium hydroxide and carbon dioxide
gas, which was mentioned in the text.
Answer:__________________________________________________________________________
2. Explain what features of this reaction allow it to be used for detection
carbon dioxide in the air.
Answer:__________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
1) Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O
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 CO 2)
1. Write an abbreviated ionic equation for the reaction mentioned in the text between
calcium hydroxide and hydrochloric acid.
Answer:__________________________________________________________________________
2. Explain why this reaction is used to increase the pH of water.
Answer:__________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
1) OH – + H + = H 2 O (Ca(OH)2+ 2HCl = CaCl2 + 2H2O)
2) The presence of acid in natural water causes low pH values of this water. Calcium hydroxide neutralizes the acid and pH values increase
The pH scale exists from 0-14. from 0-6 – acidic environment, 7 – neutral environment, 8-14 – alkaline environment
9. A diagram of the redox reaction is given.
H 2 S + Fe 2 O 3 → FeS + S + H 2 O
1. Make an electronic balance for this reaction.
Answer:__________________________________________________________________________
2. Identify the oxidizing agent and reducing agent.
Answer:__________________________________________________________________________
3. Arrange the coefficients in the reaction equation.
Answer:__________________________________________________________________________
1) An electronic balance has been compiled:
| 2Fe +3 + 2ē → 2Fe +2 | 2 | 1 | |
| 2 | |||
| S -2 – 2ē → S 0 | 2 | 1 |
2) It is indicated that sulfur in the oxidation state –2 (or H 2 S) is a reducing agent, and iron in the oxidation state +3 (or Fe 2 O 3) is an oxidizing agent;
3) The reaction equation has been drawn up:
3H 2 S + Fe 2 O 3 = 2FeS + S + 3H 2 O
10. The transformation scheme is given:
Fe → FeCl 2 → Fe(NO 3) 2 → Fe(OH) 2
Write molecular reaction equations that can be used to carry out
the indicated transformations.
1) _________________________________________________________________________
2) _________________________________________________________________________
3) _________________________________________________________________________
The reaction equations corresponding to the transformation scheme are written:
1) Fe + 2HCl = FeCl 2 + H 2
2) FeCl 2 + 2AgNO 3 = Fe(NO 3) 2 + 2AgCl
3) Fe(NO 3) 2 + 2KOH = Fe(OH) 2 + 2KNO 3
(Other equations that do not contradict the conditions for specifying equations are allowed
reactions.)
11. Establish a correspondence between the formula of an organic substance and the class/group, to which this substance belongs: for each position indicated by a letter, select the corresponding position indicated by a number.
Write down the selected numbers in the table under the corresponding letters.
Answer:
| A | B | IN |
- C3H8 – CnH2n+2 – alkane
- C3H6 – CnH2n-alkene
- C2H6O – CnH2n+2O- alcohol
12. In the proposed schemes of chemical reactions, insert the formulas of the missing substances and arrange the coefficients.
1) C 2 H 6 + ……………..… → C 2 H 5 Cl + HCl
2) C 3 H 6 + ……………..… → CO 2 + H 2 O
1) C 2 H 6 + Cl 2 → C 2 H 5 Cl + HCl
2) 2C 3 H 6 + 9O 2 → 6CO 2 + 6H 2 O
(Fractional odds are possible.)
13. Propane burns with low levels of toxic emissions into the atmosphere Therefore, it is used as an energy source in many areas, for example in gas lighters and for heating 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.
Answer:__________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
1) The equation for the propane combustion reaction has been compiled:
C 3 H 8 + 5 O 2 → 3 CO 2 + 4 H 2 O
2) n(C 3 H 8) = 4.4/44 = 0.1 mol
n(CO 2) = 3n(C 3 H 8) = 0.3 mol
3) V(O 2) = 0.3 22.4 = 6.72 l
14. 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.
1) _______________________________________________________
2) _______________________________________________________
3) _______________________________________________________
The reaction equations corresponding to the scheme are written:
(Other reaction equations that do not contradict the conditions for specifying reaction equations are allowed.)
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.
Answer:__________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
1) m(NaCl) = 4.5 g
2) m(water) = 495.5 g
m(solution) = 500g m(salt) = x
x/500 * 100%= 0.9%
m(salt) = 500* (0.9/100) = 4.5 g
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation
Despite the fact that in the practice of heating homes we are constantly faced with the need to ensure safety due to the presence of toxic combustion products in the atmosphere of premises, as well as the formation of explosive gas mixtures (due to leaks of natural gas used as fuel), these problems are still relevant . The use of gas analyzers can prevent adverse consequences.
G Burning, as is known, is a special case of an oxidation reaction accompanied by the release of light and heat. When burning carbon fuels, including gas, carbon and hydrogen, which are part of organic compounds, or predominantly carbon (when burning coal) are oxidized to carbon dioxide (CO 2 - carbon dioxide), carbon monoxide (CO - carbon monoxide) and water (H2O). In addition, nitrogen and impurities contained in the fuel and (or) in the air, which is supplied to the burners of heat generators (boiler units, stoves, fireplaces, gas stoves, etc.) for fuel combustion, enter into reactions. In particular, the product of nitrogen (N 2) oxidation is nitrogen oxides (NO x) - gases that are also classified as harmful emissions (see table).
Table. Permissible content of harmful emissions in gases discharged from heat generators by equipment class according to the European standard.
Carbon monoxide and its dangers
The risk of carbon monoxide poisoning today is still quite high, which is due to its high toxicity and lack of public awareness.
Most often, carbon monoxide poisoning occurs due to improper operation or malfunction of fireplaces and traditional stoves installed in private homes, baths, but there are also frequent cases of poisoning, even death, with individual heating with gas boilers. In addition, carbon monoxide poisoning is often observed, and often fatal, in fires and even in localized fires of things indoors. The common and determining factor in this case is combustion with a lack of oxygen - it is then that instead of carbon dioxide, which is safe for human health, carbon monoxide is formed in dangerous quantities.
Rice. 1 Replaceable gas analyzer sensor along with its control board
Entering the blood, carbon monoxide binds to hemoglobin, forming carboxyhemoglobin. In this case, hemoglobin loses its ability to bind oxygen and transport it to the organs and cells of the body. The toxicity of carbon monoxide is such that when it is present in the atmosphere in a concentration of only 0.08%, up to 30% of the hemoglobin in a person breathing this air turns into carboxyhemoglobin. In this case, the person already feels the symptoms of mild poisoning - dizziness, headache, nausea. At a CO concentration in the atmosphere of 0.32%, up to 40% of hemoglobin is converted into carboxyhemoglobin, and the person is in moderate severity of poisoning. His condition is such that he does not have the strength to leave the room with the poisoned atmosphere on his own. When the CO content in the atmosphere increases to 1.2%, up to 50% of blood hemoglobin passes into carboxyhemoglobin, which corresponds to the development of a comatose state in a person.
Nitrogen oxides - toxicity and environmental harm
When fuel is burned, the nitrogen present in the fuel or air supplied for combustion forms nitrogen monoxide (NO) with oxygen. After some time, this colorless gas is oxidized by oxygen to form nitrogen dioxide (NO2). Of the nitrogen oxides, NO 2 is the most dangerous to human health. It severely irritates the mucous membranes of the respiratory tract. Inhaling toxic nitrogen dioxide fumes can cause serious poisoning. A person feels its presence even at low concentrations of only 0.23 mg/m 3 (detection threshold). However, the body's ability to detect the presence of nitrogen dioxide disappears after 10 minutes of inhalation. There is a feeling of dryness and soreness in the throat, but these symptoms disappear with prolonged exposure to gas in a concentration 15 times higher than the detection threshold. Thus, NO 2 weakens the sense of smell.
Fig 2 Carbon monoxide alarm
In addition, at a concentration of 0.14 mg/m 3, which is below the detection threshold, nitrogen dioxide reduces the ability of the eyes to adapt to darkness, and at a concentration of only 0.056 mg/m 3 it makes breathing difficult. People with chronic lung diseases experience difficulty breathing even at lower concentrations.
People exposed to nitrogen dioxide are more likely to suffer from respiratory diseases, bronchitis and pneumonia.
Nitrogen dioxide itself can cause lung damage. Once in the body, NO 2 upon contact with moisture forms nitrous and nitric acids, which corrode the walls of the alveoli of the lungs, which can result in pulmonary edema, often leading to death.
In addition, emissions of nitrogen dioxide into the atmosphere under the influence of ultraviolet radiation, part of the spectrum of sunlight, contribute to the formation of ozone.
The formation of nitrogen oxides depends on the nitrogen content in the fuel and the combustion air supplied, the residence time of nitrogen in the combustion zone (flame length) and flame temperature.
Depending on the place and time of formation, fast and fuel nitrogen oxides are released. Fast NOx is formed during the reaction of nitrogen with free oxygen (excess air) in the reaction zone of the flame.
Fuel NOx is formed at high combustion temperatures as a result of the combination of nitrogen contained in the fuel with oxygen. This reaction absorbs heat and is typical for the combustion of diesel and solid organic fuels (wood, pellets, briquettes). During the combustion of natural gas, fuel NO x is not formed, since natural gas does not contain nitrogen compounds.
The decisive criteria for the formation of NO x are the oxygen concentration during the combustion process, the residence time of the combustion air in the combustion zone (flame length) and the flame temperature (up to 1200 °C - low, from 1400 °C - significant and from 1800 ° C - maximum formation of thermal NOx).
NOx formation can be reduced by modern combustion technologies such as cold flame, flue gas recirculation and low excess air levels.
Non-combustible hydrocarbons and soot
Unburnable hydrocarbons (C x H y) are also formed as a result of incomplete combustion of fuel and contribute to the formation of the greenhouse effect. This group includes methane (CH 4), butane (C 4 H 10) and benzene (C 6 H 6). The reasons for their formation are similar to the reasons for the formation of CO: insufficient atomization and mixing when using liquid fuels and lack of air when using natural gas or solid fuels.
In addition, as a result of incomplete combustion in diesel burners, soot is formed - essentially pure carbon (C). At normal temperatures, carbon reacts very slowly. For complete combustion of 1 kg of carbon (C) 2.67 kg of O 2 is required. Ignition temperature - 725 °C. Lower temperatures lead to soot formation.
Natural and liquefied gas
Gas fuel itself poses a separate danger.
Natural gas consists almost entirely of methane (80-95%), the rest is mostly ethane (up to 3.7%) and nitrogen (up to 2.2%). Depending on the area of production, it may contain sulfur compounds and water in small quantities.
The danger comes from gas fuel leaks due to damage to the gas pipeline, faulty gas fittings, or simply being left open when supplying gas to the gas stove burner (“human factor”).
Fig 3 Checking for natural gas leaks
Methane in the concentrations in which it can be present in the atmosphere of residential premises or outdoors is not toxic, but unlike nitrogen, it is very explosive. In the gaseous state, it forms an explosive mixture with air in concentrations from 4.4 to 17%, the most explosive concentration of methane in air is 9.5%. In domestic conditions, such concentrations of methane in the air are created when it accumulates during leaks in confined spaces - kitchens, apartments, entrances. In this case, an explosion can be caused by a spark that jumps between the contacts of the power switch when trying to turn on the electric lighting. The consequences of explosions are often catastrophic.
A particular danger in natural gas leaks is the absence of odor from its components. Therefore, its accumulation in a confined space occurs unnoticed by people. To detect leaks, an odorant is added to natural gas (to simulate the smell).
In autonomous heating systems, liquefied hydrocarbon gas (LPG), which is a by-product of the oil and fuel industries, is used. Its main components are propane (C 3 H 8) and butane (C 4 H 10). LPG is stored in a liquid state under pressure in gas cylinders and gas holders. It also forms explosive mixtures with air.
LPG forms explosive mixtures with air at a concentration of propane vapor from 2.3 to 9.5%, normal butane - from 1.8 to 9.1% (by volume), at a pressure of 0.1 MPa and a temperature of 15-20 °C . The auto-ignition temperature of propane in air is 470 °C, normal butane is 405 °C.
At standard pressure, LPG is gaseous and heavier than air. When evaporating from 1 liter of liquefied hydrocarbon gas, about 250 liters of gaseous gas are formed, so even a slight leak of LPG from a gas cylinder or gas holder can be dangerous. The density of the gas phase of LPG is 1.5-2 times greater than the density of air, so it is poorly dispersed in the air, especially in enclosed spaces, and can accumulate in natural and artificial depressions, forming an explosive mixture with air.
Gas analyzers as a means of gas safety
Gas analyzers allow you to detect the presence of hazardous gases in the indoor atmosphere in a timely manner. These devices can have different designs, complexity and functionality, depending on which they are divided into indicators, leak detectors, gas detectors, gas analyzers, and gas analysis systems. Depending on the design, they perform different functions - from the simplest (supplying audio and/or video signals), to such as monitoring and recording with data transmission via the Internet and/or Ethernet. The former, usually used in safety systems, signal that concentration threshold values are exceeded, often without quantitative indication; the latter, which often include several sensors, are used in setting up and regulating equipment, as well as in automated control systems as components responsible not only for safety, but also for efficiency.
Fig 4 Setting up the operation of a gas boiler using a gas analyzer
The most important components of all gas analytical instruments are sensors - small-sized sensitive elements that generate a signal depending on the concentration of the component being determined. To increase the selectivity of detection, selective membranes are sometimes placed at the input. There are electrochemical, thermocatalytic/catalytic, optical, photoionization and electrical sensors. Their weight usually does not exceed several grams. One gas analyzer model may have modifications with different sensors.
The operation of electrochemical sensors is based on the transformation of the component being determined in a miniature electrochemical cell. Inert, chemically active or modified, as well as ion-selective electrodes are used.
Optical sensors measure the absorption or reflection of the primary light flux, luminescence, or the thermal effect when light is absorbed. The sensitive layer can be, for example, the surface of a light guide fiber or a phase containing a reagent immobilized on it. Fiber optic light guides allow operation in the IR, visible and UV ranges.
The thermocatalytic method is based on the catalytic oxidation of molecules of controlled substances on the surface of the sensitive element and the conversion of the generated heat into an electrical signal. Its value is determined by the concentration of the controlled component (the total concentration for the totality of flammable gases and liquid vapors), expressed as a percentage of the LFL (lower concentration limit of flame propagation).
The most important element of a photoionization sensor is a source of vacuum ultraviolet radiation, which determines the sensitivity of detection and ensures its selectivity. Photon energy is sufficient to ionize most common pollutants, but is low for components of clean air. Photoionization occurs in volume, so the sensor easily tolerates large concentration overloads. Portable gas analyzers with such sensors are often used to monitor the air in a work area.
Electrical sensors include metal oxide electronically conducting semiconductors, organic semiconductors, and field-effect transistors. The measured quantities are conductivity, potential difference, charge or capacitance, which change when exposed to the substance being determined.
Various devices use electrochemical, optical, and electrical sensors to determine CO concentration. To determine gaseous hydrocarbons and, above all, methane, photoionization, optical, thermocatalytic, catalytic and electrical (semiconductor) sensors are used.
Figure 5. Gas analyzer
The use of gas analyzers on gas distribution networks is regulated by regulatory documents. Thus, SNiP 42-01-2002 “Gas distribution systems” provides for the mandatory installation of a gas analyzer on internal gas networks, which issues a signal to the shut-off valve to close in the event of gas accumulation in a concentration of 10% of the explosive concentration. According to clause 7.2. SNiP, “premises of buildings for all purposes (except for residential apartments) where gas-using equipment is installed, operating in automatic mode without the constant presence of maintenance personnel, should be equipped with gas monitoring systems with automatic shutdown of the gas supply and output of a signal about gas contamination to a control center or to a room with permanent presence of personnel, unless other requirements are regulated by the relevant building codes and regulations.
Systems for monitoring indoor gas pollution with automatic shutdown of gas supply in residential buildings should be provided when installing heating equipment: regardless of the installation location - with a power of over 60 kW; in basements, ground floors and in extensions to the building - regardless of the thermal power.”
Preventing harmful emissions and increasing the efficiency of boiler equipment
In addition to the fact that gas analyzers allow you to warn about dangerous gas concentrations in the volume of premises, they are used to adjust the operation of boiler equipment, without which it is impossible to ensure the efficiency and comfort indicators declared by the manufacturer, and reduce fuel costs. For this purpose, flue gas analyzers are used.
Using a flue gas analyzer, it is necessary to configure wall-mounted condensing boilers running on natural gas. The concentration of oxygen (3%), carbon dioxide (20 ppm) and carbon dioxide (13% vol.), excess air ratio (1.6), NO x should be monitored.
In fan burners operating on natural gas, it is also necessary to control the concentration of oxygen (3%), carbon dioxide (20 ppm) and carbon dioxide (13% vol.), excess air ratio (1.6), NO x.
In fan burners operating on diesel fuel, in addition to everything above, before using a gas analyzer, it is necessary to measure the soot number and sulfur oxide concentration. The soot number must be less than 1. This parameter is measured using a soot number analyzer and indicates the quality of the spray through the nozzles. If it is exceeded, the gas analyzer cannot be used for adjustment, as the gas analyzer path will become contaminated and it will become impossible to achieve optimal performance. The concentration of sulfur oxide (IV) - SO 2 indicates the quality of the fuel: the higher it is, the worse the fuel; with local excesses of oxygen and humidity, it turns into H 2 SO 4, which destroys the entire fuel-burning system.
In pellet boilers, the concentration of oxygen (5%), carbon monoxide (120 ppm) and carbon dioxide (17% vol.), excess air ratio (1.8), NO x should be monitored. Preliminary protection of the fine filtration from dust contamination by flue gases and protection from exceeding the operating range through the CO channel are necessary. In a matter of seconds it can exceed the operating range of the sensor and reach 10,000-15,000 ppm.
VPR. Chemistry. 11th grade Code
CLASS 11 Explanations for the sample of the all-Russian test work When familiarizing yourself with the sample test work, you should keep in mind that the tasks included in the sample do not reflect all the skills and content issues that will be tested as part of the all-Russian test work. A complete list of content elements and skills that can be tested in the work is given in the codifier of content elements and requirements for the level of training of graduates for the development of an all-Russian test in chemistry. The purpose of the sample test work is to give an idea of the structure of the all-Russian test work, the number and form of tasks, and their level of complexity.
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation ALL-RUSSIAN TESTING WORK CHEMISTRY
CLASS 11 SAMPLE Instructions for completing the work The test work includes 15 tasks. 1 hour 30 minutes (90 minutes) are allotted to complete the work in chemistry. Write the answers in the text of the work according to the instructions for the tasks. If you write down an incorrect answer, cross it out and write a new one next to it. When completing the work, you are allowed to use the following additional materials
– Periodic table of chemical elements D.I. Mendeleev
– table of solubility of salts, acids and bases introducing the electrochemical series of metal voltages
– non-programmable calculator. When completing assignments, you can use a draft. Entries in draft will not be reviewed or graded. We advise you to complete the tasks in the order in which they are given. To save time, skip a task that you cannot complete immediately and move on to the next one. If you have time left after completing all the work, you can return to the missed tasks. The points you receive for completed tasks are summed up. Try to complete as many tasks as possible and score the most points. We wish you success
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision of Education and Science of the Russian Federation From your chemistry course, you know the following methods for separating mixtures: sedimentation, filtration, distillation (distillation, magnetic action, evaporation, crystallization. Figures 1–3 show examples of the use of some of these methods. Fig. 1 Fig. 3
Which of the following methods for separating mixtures can be used for purification?
1) flour from trapped iron filings
2) water from inorganic salts dissolved in it. Write down the figure number and the name of the corresponding method of separating the mixture in the table. Mixture Figure number Method of separating the mixture Flour and trapped iron filings Water with inorganic salts dissolved in it 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, complete the following tasks) determine 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 that forms this chemical element is a metal or non-metal. Write your answers in the table. Answer Chemical element symbol
Period No.
Group No. Metal non-metal
1
2
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation 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, the patterns of changes in these properties, methods of obtaining substances, and their location in nature. For example, it is known that with an increase in the atomic number of a chemical element in periods, the radii of atoms decrease, and in groups they increase. Taking these regularities into account, arrange the following elements in order of increasing atomic radii: N, C, Al, Si. Write down the designations of the elements in the required sequence. Answer ____________________________ The table below lists the characteristic properties of substances that have a molecular and ionic structure. Characteristic properties of substances Molecular structure Ionic structure under normal conditions they have a liquid, gaseous and solid state of aggregation have low boiling and melting points
non-conductive; have low thermal conductivity
solid under normal conditions, brittle, refractory, non-volatile in melts and solutions conduct electric current. Using this information, determine what structure the substances nitrogen and table salt NaCl have. Write your answer in the space provided.
1) nitrogen N
2
________________________________________________________________
2) table salt NaCl ___________________________________________________
3
4
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation Complex inorganic substances can be conditionally distributed, that is, classified, into four groups, as shown in the diagram. In this diagram for each of the four groups, fill in the missing group names or chemical formulas of substances (one example of formulas belonging to this group. Read the following text and complete tasks 6–8. The food industry uses food additive E, which is calcium hydroxide Ca(OH)
2
. It is used in the production of fruit juices, baby food, pickled cucumbers, table salt, confectionery and sweets. It is possible to produce calcium hydroxide on an industrial scale by mixing calcium oxide with water, a process called quenching. Calcium hydroxide is widely used in the production of building materials such as whitewash, plaster and gypsum mortars. This is due to the ability to interact with carbon dioxide CO
2
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 (for example, acids that cause corrosion in plumbing fixtures). pipes
5
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation
6 1. Write a molecular equation for the reaction to produce calcium hydroxide, which was mentioned in the text. Answer
2. Explain why this process is called quenching. Answer
________________________________________________________________________________
1. Write a molecular equation for the reaction between calcium hydroxide and carbon dioxide, which was mentioned in the text. Answer
2. Explain what features of this reaction make it possible to use it to detect carbon dioxide in the air. Answer
________________________________________________________________________________
________________________________________________________________________________
1. Write a shortened ionic equation for the reaction between calcium hydroxide and hydrochloric acid mentioned in the text. Answer
2. Explain why this reaction is used to increase the pH of water. Answer
________________________________________________________________________________
________________________________________________________________________________
6
7
8
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation A scheme of the redox reaction is given.
H
2
S + Fe
2
O
3
→ FeS + S + H
2
O
1. Make an electronic balance for this reaction. Answer
2. Identify the oxidizing agent and reducing agent. Answer
3. Arrange the coefficients in the reaction equation. Answer The transformation scheme is given
Fe Write the molecular reaction equations that can be used to carry out the indicated transformations.
1) _________________________________________________________________________
2) _________________________________________________________________________
3) __________________________________________________________________________ Establish a correspondence between the formula of an organic substance and the class/group to which this substance belongs to each position indicated by a letter, select the corresponding position indicated by a number. FORMULA OF THE SUBSTANCE
CLASS/GROUP A)
CH
3
-SN
2
-SN
3
B) C)
CH
3
-CH
2
OH
1) saturated hydrocarbons
2) alcohols
3) unsaturated hydrocarbons
4) carboxylic acids Write the selected numbers in the table under the corresponding letters. A B C Answer
9
10
11
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision in Education and Science of the Russian Federation Insert the formulas of the missing substances into the proposed schemes of chemical reactions and arrange the coefficients.
1) C
2
N
6
+ ……..........… → C
2
N
5
Cl+HCl
2) C
3
H
6
+ ……..........… → CO
2
+H
2
O 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 home heating. What volume of carbon dioxide is formed during the complete combustion of 4.4 g of propane? Write down a detailed solution to the problem. Answer
________________________________________________________________________________
______________________________________________________________________________ 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.
CH
2
CH CH
3
CH
3
CCH
3
O
CH
3
CH CH
3
Br
CH
3
CH
CH
3
OH
1) _______________________________________________________
2) _______________________________________________________
3) _______________________________________________________
12
13
14
VPR. Chemistry. 11th grade Code
© 2017 Federal Service for Supervision of Education and Science of the Russian Federation A saline solution in medicine is a 0.9% sodium chloride solution in water. Calculate the mass of sodium chloride and the mass of water needed for preparation
500 g of saline solution. Write down a detailed solution to the problem. Answer
________________________________________________________________________________
________________________________________________________________________________
15
VLOOKUP
. Chemistry. Grade 11. Answers 2017 Federal Service for Supervision in Education and Science of the Russian Federation ALL-RUSSIAN INSPECTION WORK
CHEMISTRY
, 11
CLASS
Reply
ety
and evaluation criteria
ania
№
tasks
Reply
no
1
Mixture
Number
drawing
Way
separation
mixtures
Flour and trapped iron filings Magnetic action
Water with inorganic salts dissolved in it
Distillation
(distillation
2
N; 2; 5 (or V); non-metal N
→
C
→
Si
→
Al
4 nitrogen N
2
– molecular structure of table salt NaCl – ionic structure 132 The correct answer to task 3 is scored one point
Completion of tasks 1, 2, 4, 11 is assessed as follows: 2 points - no errors
1 point – one mistake was made 0 points – two or more mistakes were made, or there was no answer
Content
correct answer and instructions for assessment
n
Iyu
Points
Answer elements The names of the base and salt groups are written down, the formulas of the substances of the corresponding groups are written down
The answer is correct and complete, contains all the elements mentioned above. Three cells of the diagram are filled out correctly. 1 Two or more errors were made. Maximum score.
5
VLOOKUP
. Chemistry. Grade 11. Answers 2017 Federal Service for Supervision in Education and Science of the Russian Federation Contents of the correct answer and instructions for assessment
n
Iyu
(Additionally, find other wordings of the answer that do not distort its meaning
Points
Response Elements
1) CaO + H
2
O = Ca(
OH)
2 2) When calcium oxide interacts with water, a large amount of heat is released, so the water boils and hisses, as if it hits hot coal, when the fire is extinguished with water (
or
“This process is called slaking because as a result slaked lime is formed
»)
The answer is correct and complete, contains all the above elements The answer includes one of the above elements 1 All elements of the answer are written incorrectly 0 Maximum score 2 Contents of the correct answer and instructions for scoring
n
Iyu
(Additionally, find other wordings of the answer that do not distort its meaning
Points
Response Elements
1) Ca(OH)
2
+ CO
2
= CaCO
3
↓+H
2
O
2) As a result of this reaction, an insoluble substance, calcium carbonate, is formed, turbidity of the original solution is observed, which allows us to judge the presence of carbon dioxide in the air. The qualitative reaction to The answer is correct and complete, contains all the above elements. The answer includes one of the above elements 1 All elements answers written down incorrectly 0 Maximum score 2 Contents of the correct answer and instructions for scoring
n
Iyu
(Additionally, find other wordings of the answer that do not distort its meaning
Points
Response Elements
1) OH
–
+H
+
= H
2
O
2) The presence of acid in natural water causes low values of this water
Calcium hydroxide
neutralize
no
sour
otu
, and the values increase The answer is correct and complete, contains all the above elements The answer includes one of the above elements 1 All elements of the answer are written incorrectly 0 Maximum score 2
6
7
8
VLOOKUP
n
Iyu
(Additionally, find other wordings of the answer that do not distort its meaning
Points
1) An electronic balance has been compiled) It is indicated that sulfur in the oxidation state –2 (or H
2
S) is a reducing agent, and iron is in the +3 oxidation state or Fe
2
O
3
) – oxidizing agent
3) The reaction equation has been compiled
3H
2
S + Fe
2
O
3
= 2FeS + S + 3
H
2
O The answer is correct and complete, contains all the above elements. Two of the above elements of the answer are correctly written 2 One of the above elements of the answer is written correctly 1 All elements of the answer are written incorrectly 0 Maximum score Contents of the correct answer and instructions for scoring
n
Iyu
Points
Reaction equations corresponding to the transformation scheme have been written
1) Fe + 2HCl = FeCl
2
+H
2 2) FeCl
2
+ 2AgNO
3
= Fe(NO
3
2
+ 2Ag
C
l
3) Fe(NO
3
2
+ 2KOH = F
e(OH)
2
.)
n
Iyu
Points
Response Elements
1)
WITH
2
N
6
+ Cl
2
→
WITH
2
N
5
Cl+HCl
2) 2C
3
H
6
+ 9O
2
→
6C
O
2
+ 6
H
2
O Fractional coefficients are possible) The answer is correct and complete, contains all the above elements An error was made in one of the elements of the answer 1 All elements of the answer were written incorrectly 0 Maximum score
9
10
12
VLOOKUP
. Chemistry. Grade 11. Answers 2017 Federal Service for Supervision in Education and Science of the Russian Federation Contents of the correct answer and instructions for assessment
n
Iyu
(Additionally, find other wordings of the answer that do not distort its meaning
Points
1) The equation for the propane combustion reaction has been compiled
WITH
3
N
8
+ O →
CO + HO) n(
WITH
3
N
8
) = 4.4/44 = 0.1 mol SOCH mol) O) = 0.3 · 22.4 = 6.72 l The answer is correct and complete, contains all the above elements, two of the above elements of the answer are written correctly 2 Correct one of the above elements of the answer is written down 1 All elements of the answer are written down incorrectly 0 Maximum score 3 Contents of the correct answer and instructions for scoring
n
Iyu
Points
Reaction equations corresponding to the diagram have been written
1)
C
H
3
CH
CH
2
+H
2
O
H
2
SO
4
, t
°
CH
3
CH
CH
3
OH
CH
3
CC
H
3
O
+ cat+ water n. r-r,
t
°
+ Other reaction equations that do not contradict the conditions for specifying reaction equations are allowed
.)
Three reaction equations are written correctly Two reaction equations are written correctly 2 One reaction equation is written correctly 1 All equations are written incorrectly or there is no answer 0 Maximum score Contents of the correct answer and instructions for scoring
n
Iyu
(Additionally, find other wordings of the answer that do not distort its meaning
Points
Response Elements
1)m
(NaCl) = 4.5 g
2) water) = 495.5 g
The answer is correct and complete, contains all the above elements The answer includes one of the above elements 1 All elements of the answer are written incorrectly 0 Maximum score 2
13
14
15
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 schemes of chemical reactions 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
