Propane burns with low emissions. It is possible to produce calcium hydroxide on an industrial scale by mixing calcium oxide with water, a process called slaking. The scheme of the redox reaction is given

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. 2 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-electrically 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
C CH
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-mentioned elements of the answer. Two of the above-mentioned elements of the answer are correctly written 2 One of the above-mentioned 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 grading
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 are 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

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 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 (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 equations of reactions 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

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

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.

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 classes in accordance with 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 also 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.