The 11th grade chemistry exam is by no means easy. It is required for admission to universities that require further chemical education. First of all, these are chemical-technological universities, medical universities and classical universities. While preparing for the Unified State Exam in Chemistry 2019, you need to do quite a lot of work: systematize and generalize knowledge, repeat the most important chemical concepts and practice solving problems.

Changes in the 2018 Unified State Exam in Chemistry

• The total number of tasks has been increased from 34 to 35 due to the fact that one more task was added in the second part. Now in part No. 2 there are not 5, but 6 tasks. This was achieved in connection with the introduction of a task with a single context.

What do tasks 30 and 31 test? Ability to write redox and ion exchange reactions.

• The grading scale for some tasks in part one has been changed.

This task No. 9 increased level of difficulty, which is now assessed with a maximum of two points.

Task 21 basic level difficulty will be assessed with one point. This is also an oxidation-reduction reaction in the format for establishing correspondence.

Task 26– basic level of complexity – assesses mastery of the experimental fundamentals of chemistry and general understanding of industrial methods obtaining the most important substances. This task is also in the format of matching letters and numbers on the left and right sides. Evaluated by one point.

Task No. 30 high level complexity is in the second part of the exam and is aimed at testing the mastery of tasks on redox reactions. Evaluated with a maximum of 2 points.

Task 31 is aimed at testing the mastery of the topic “Ion exchange reactions” and is also awarded two points.

Structure of CMMs in chemistry

The exam version consists of 2 parts:

The tasks of the 1st part are arranged in order of increasing difficulty level and distributed according to content blocks and lines that are studied in the chemistry course:

• "Structure of Matter"
• "Structure of the Atom"
• "Chemical reaction"
• « Not organic chemistry»
• "Organic chemistry"
• "Chemistry and Life"
• “Methods of cognition and use of substances”
• "Calculations using equations chemical reactions».

To prepare for the exam, it is very important to know the features that it has. Information about this is given on the FIPI website, where you can find a demo version of the Unified State Exam in chemistry and get acquainted with the structure exam tasks.

Second part of the exam

This part causes the greatest difficulties for graduates.

Task No. 30– a new task that appeared in 2018. A list of 5 substances is given. From this list it is necessary to select those substances that will enter into an oxidation-reduction reaction. To do this, you need to find a pair of oxidizing agent and reducing agent. Then, if possible, determine the solution environment (acidic, alkaline or neutral). Then you need to determine the reaction products in accordance with the given starting materials. Next, you need to create an electronic balance of the reaction and, based on it, place the coefficients in the equation.

Task No. 31– this is a task that was not included in the 2017 Unified State Examination. Here they test how eleventh graders can compose ion exchange reactions that occur between electrolytes and always in the direction of binding ions. The student selects an ion exchange pair and shows his understanding of how this reaction occurs. To do this, you need to write down the full and abbreviated ionic equation.

№32 – this task is often called a task to complete thought experiment. There is a description of this or that experiment, and the student must create an equation for the chemical reactions of the ongoing processes. Grading scale – 4 points.

№33 – organic chemistry, where it is necessary to carry out a chain of transformations. When solving a chain, it is necessary to write down the structural formulas of substances that unambiguously reflect the order of connection of atoms in the molecule. It is acceptable to write abbreviated structural formulas of substances such as ethane and acetylene.

Task No. 34– calculation problem requiring knowledge chemical properties substances. It is necessary to draw up an equation of chemical reactions according to the text, and be sure to consider whether all of the substance reacted or whether part of it did not react with one of the reagents. Mathematical calculations that are necessary to find answers to the questions posed in the problem statement can be performed using a calculator or the periodic table. When solving a problem, the graduate must show a logically substantiated answer, taking into account all the physical quantities given by the condition of the problem. The maximum score for completion is 4 points. The expert will deduct only 1 point if an error is made in the calculations.

Task No. 35 is the definition of molecular and structural formula organic matter. Sequence of graduate actions:

1. Make a mathematical calculation, that is, the ratio of atoms in the composition of a particular organic substance.
2. Create a structural formula using the conditions given in the problem.
3. Write an equation for a chemical reaction, in which it is necessary to use the structural formula of the substance.

The results of the Unified State Exam in chemistry will help students taking this subject to enter the chosen university and fulfill their dream of becoming a doctor or scientist, chemical technologist or chemistry teacher.

The date of the exam is approved by the Ministry of Education of the Russian Federation and will be published in the next academic year.

More detailed advice on conducting the Unified State Examination 2018 exam. Chemistry" can be viewed here:

One of the elective subjects indicated by the graduate high school in the application is the Unified State Exam in Chemistry 2018. Test materials in chemistry are prepared in accordance with Federal standard complete secondary education. They are completely aimed at the school level. The difficulty is that in secondary schools only one hour a week is allocated for studying chemistry. Therefore, in order to successfully pass the Unified State Exam in Chemistry, you must prepare persistently and purposefully.

Who chooses chemistry for the Unified State Exam?

The Unified State Examination in Chemistry is chosen by 11th grade students who plan to further connect their lives with studying at higher education institutions. educational institutions in this area of ​​training.

• As a rule, these are graduates seeking to enter technical universities that offer chemical specialties as a training profile.
• These could also be guys who want to enroll in medical universities, where good knowledge of chemistry is required.

Basic documents of the Unified State Exam

If we talk about the content of the exam test in chemistry, then here you need to get acquainted with three main documents:

1)Codifier, consisting of two parts.

• The first part of the document presents those elements of content that all tasks included in the option are aimed at checking for completeness.
• The second part of the codifier is called “List of requirements for the level of training of graduates.” Here is a list of skills that an 11th grade student must master in order to complete the assignments.

2) Specification. This is a document that regulates Unified State Exam structure current year. It presents topics that may appear on the exam.

3) Demo version of the Unified State Exam in Chemistry- It is one Unified State Exam option, where you need to start preparing for the state exam in chemistry.
How to prepare? What to read?

There are quite a large number of manuals that are auxiliary materials:

1. The books recommended by the Ministry of Education are chemistry textbooks.
2. Benefits marked “FIPI”.
3. Books by the developers of the Unified State Exam KIMs themselves in chemistry.

How does the Unified State Exam work?

Total 34 tasks
1 part	part 2
29 short answer questions	5 tasks with detailed answers

The time to complete the entire exam is 210 minutes (3 hours 30 minutes).
The maximum primary score is 60.

Part 1 presents tasks of basic and advanced difficulty levels.

Part 2 contains high-level tasks.

Structure and typology of tasks of the 1st part of KIM

Part 1 tasks come in two main forms:

1. short-answer tasks that involve establishing correspondence between the positions of two sets;
2. selecting several answer options from the list provided.

For example, in the 1st task of the basic level a series may be given chemical elements(total 5 elements). Next, questions are asked that the graduate must read carefully and give the appropriate answer. The fact that there are two cells in the answer field indicates that there should be two such answers. And only if you select all the answer options correctly, you can get the maximum score for this task.

The second example of tasks is tasks on correspondence between two sets (5th task). Thus, formulas of substances can be presented in the left column, and in the right column - the class (group) of substances to which this or that substance belongs. Since there are 3 substances in the left column, the student must establish 3 correspondences.

If we talk about tasks of another type, then we can see tasks that contain textual information to a greater extent, where some kind of mental conduct of a chemical experiment is assumed and the choice of formulas of substances that will allow you to correctly answer the task presented in the task conditions.

Multiple-choice tasks often seem quite simple to students and do not require writing down reaction equations or formulas of substances. Unfortunately, it is not. Only if the graduate actually prescribes a solution for each task and is thoughtful about the given conditions of the task, then in this case there is a chance of arriving at the correct answer.

Features of the tasks of the second part

But the tasks from the second part of the test with a detailed answer suggest a higher level of difficulty. But this does not go beyond the topics presented in the codifier. The complication is due to the fact that if in tasks of a basic level the test is aimed at one element of content, then in tasks of a high level of complexity the mastery of several elements of content or several skills is assumed. For example, you need not only to classify a particular substance into a class or group of substances, but also to remember what properties this group of substances has; sometimes you have to remember the specific properties of the substances discussed in the task.

Five tasks with detailed answers are aimed at the main, most important sections of the chemistry course. The whole option can be divided into certain content blocks, many of which are enlarged topics of the school chemistry course. For example, “Structure of the atom”, “ Periodic laws. Periodic table chemical elements”, “Inorganic substances”, “Organic substances”, “Methods of knowledge in chemistry”, “Chemistry in life”, “Calculations using chemical formulas, reaction equations”.

What can you use during the exam?

The graduate must bring two items to the chemistry exam:

1. non-programmable calculator;
2. black gel pen.

The exam will give you:

• periodic system of chemical elements by D. I. Mendeleev;
• table of solubility of acids, salts and bases;
• electrochemical voltage series of metals (metal activity series).

The Ministry of Education does not intend to make any changes to the Unified State Exam KIM in chemistry in the 2017–2018 academic year.

The date for the Unified State Examination in chemistry will be known in January 2018.

ABOUT Unified State Exam results in chemistry in 2018 can be found at your school or on the official website of the Unified State Exam.

More details about features of the Unified State Exam in chemistry, watch the video:

Already on March 16, the early period for the Unified State Exam 2017 in chemistry starts. This optional subject cannot compete with history and social studies in terms of popularity. However, to enter some higher institutions that are related to medicine, biotechnology and the oil industry, you cannot do without chemistry. Therefore, for a small contingent of high school students and USE applicants on this subject will always be relevant. Our review is dedicated to them, highlighting the main aspects of future state testing in chemistry.

the date of the

First, let’s figure out when to wait for the state exam to begin. In 2017, exams will be held between March and June.

• Early round – March 16.
• The main stage is June 2.
• Reserve – April 3, June 19 and 30.

Changes in the Unified State Examination in Chemistry 2017

Testing material has changed significantly. The emphasis in the new CIMs is on the ability of the examinee to navigate well in all aspects of the school chemistry course.

1. The number of tasks has decreased: 34 instead of the previous 40.
2. The first part of the test work has been modified. Some questions are grouped into separate thematic blocks, and matching tasks have appeared.
3. The maximum primary score has been reduced to 60 (from 64).

Structure of test material

To understand what the new CMM now looks like, let's turn to demo versions of the Unified State Exam in chemistry 2017.

Test takers will have to rack their brains over 34 tasks, which are divided into two unequal blocks. The first part contains 29 tasks, and the second – 5.

First block consists of basic level questions. These are mainly matching tasks. For example, question #5 gives two columns. One consists of a list of formulas:

• A. NH4HCO3;
• B. KF;
• B. NO.

Second is a list of classes/groups of chemical elements:

• medium salt;
• acid oxide;
• non-salt-forming oxide;
• salt is sour.

The examinee will be required to determine which group or class corresponds to which formula. For the second block of exam questions in chemistry 2017, FIPI has prepared complicated tasks. They require not only an answer, but also detailed description solutions. These are questions No. 30 – 34.

The exam lasts exactly 210 minutes. You can use a calculator during the test. In addition, the CMM contains the periodic table, as well as a table of solubility of salts/acids/bases in water and an electrochemical series of metal voltages.

Correct answers are recorded on a special examination form.

Evaluation criteria for the Unified State Examination in Chemistry 2017

The number of tasks has decreased, which has introduced some confusion into the assessment system. However, it is already known that the minimum score remained the same - 36. The maximum primary score decreased to 60. Points are awarded for tasks completed correctly or partially correctly.

• 1 point: questions 1 – 8, 12 – 16, 20 – 21, 27 – 29.
• 2 points: 9 – 11, 17 – 19, 22 – 26.
• 3 points: 30.
• 4 points: 31, 33 and 34.
• 5 points: 32.

You can only receive these points for answers that fully meet all the criteria.

How to independently prepare for the Unified State Exam in Chemistry

Here is a list of web resources and educational materials which will help you prepare for the chemistry exam.

• Demo version. The simplest option. After studying the demo CMM, you will be aware of the structure of the future exam. You can also solve the tasks presented in it. Fortunately, the demo version also contains answers.
• Examer.ru. Online tutor consisting of large quantity training tasks.
• 4ege.ru. The largest portal dedicated to the Unified State Exam. In it you will find samples, collections of solved tests and various training works. In general, everything you need to satiate self-training preparatory material for the Unified State Exam in Chemistry 2017.
• Egeiria.ru. In the special section of this educational site you can find the largest selection educational literature, which is dedicated to the state exam in chemistry.

Afterword

So, we have looked at the main aspects of the upcoming chemistry test. Now you know the exact date of the state exam, the structure of the CIM and the latest changes related to this subject. Moreover, the list of educational web portals and educational materials presented to your attention will help you start preparing for the exam now. At the same time, most materials from sites dedicated to the Unified State Examination in Chemistry can be downloaded for free. So self-training won’t cost you a pretty penny!

The total duration of the examination work is 3.5 hours (210 minutes).
The approximate time allotted for completing individual tasks is:
1) for each task of the basic level of complexity of part 1 – 2–3 minutes;
2) for each task of an increased level of difficulty in part 1 – 5–7 minutes;
3) for each task of a high level of difficulty in part 2 – 10–15 minutes.

Additional materials and equipment

The following are attached to each version of the examination paper:
materials:
− Periodic table of chemical elements D.I. Mendeleev;
− table of solubility of salts, acids and bases in water;
− electrochemical series of metal voltages.
You are permitted to use a non-programmable calculator during the examination.

Grading system

Answers to tasks in Part 1 are automatically processed after scanning answer forms No. 1. Answers to tasks in Part 2 are checked by a subject commission.
For the correct answer to each of tasks 1–6, 11–15, 19–21, 26–29, 1 point is given. The task is considered completed correctly if the examinee gave the correct answer in the form of a sequence of numbers or a number with a given degree of accuracy.
Tasks 7–10, 16–18, 22–25 are considered completed correctly if the sequence of numbers is indicated correctly. For a complete correct answer in tasks 7–10, 16–18, 22–25, 2 points are given; if one mistake is made, –1 point; for an incorrect answer (more than one error) or lack thereof – 0 points.
Part 2 tasks (with a detailed answer) involve checking from two to five answer elements. Assignments with extended answers can be completed by graduates different ways. The presence of each required element of the answer is scored 1 point, so the maximum score for a correctly completed task is from 2 to 5 points, depending on the degree of complexity of the task:

tasks 30 and 31 – 2 points;
32 – 4 points;
33 – 5 points;
34 – 4 points;
35 – 3 points.

Checking the tasks of part 2 is carried out on the basis of an element-by-element analysis of the graduate’s answer in
in accordance with the assignment assessment criteria.
The maximum primary score is 60.

Points for admission to universities are calculated on a 100-point scale
based on an analysis of the results of completing all exam tasks
work.

Changes in CMM 2018 compared to 2017

In the 2018 exam paper compared to the 2017 paper
The following changes have been adopted.
1. In order to more clearly distribute tasks into individual thematic blocks and content lines, the order of tasks of basic and advanced levels of complexity in
Part 1 of the examination paper.
2. In the 2018 examination paper, the total number of tasks was increased from 34 (in 2017) to 35 due to an increase in the number of tasks in part 2 of the examination paper from 5 (in 2017) to 6 tasks. This has been achieved
through the introduction of tasks with a single context.
In particular, this format presents tasks No. 30 and No. 31, which are aimed at testing the assimilation of important content elements: “Redox reactions” and “Reactions
ion exchange".
3. The grading scale for some tasks has been changed due to the clarification of the level of difficulty of these tasks based on the results of their completion in the 2017 examination paper:

• task No. 9 of an increased level of complexity, aimed at testing the assimilation of the content element “Characteristic chemical properties inorganic substances"and presented in a format for establishing correspondence between reacting substances and reaction products between these substances, will be assessed with a maximum of 2 points;
• task No. 21 of a basic level of complexity, aimed at testing the assimilation of the content element “Redox reactions” and presented in a format for establishing
  correspondence between elements of two sets will be scored 1 point;
• task No. 26 of a basic level of complexity, aimed at testing the assimilation of the content lines “Experimental foundations of chemistry” and “ General views on industrial methods for obtaining essential substances” and presented in a format for establishing correspondence between the elements of two sets, will be assessed 1 point;
  task No. 30 of a high level of complexity with a detailed answer, aimed at testing the assimilation of the content element “Redox reactions”, will be assessed with a maximum of 2 points;
• task No. 31 of a high level of complexity with a detailed answer, aimed at testing the assimilation of the content element “Ion exchange reactions”, will be assessed with a maximum of 2 points.

From the draft Test Specifications
measuring materials for carrying out in 2018
unified state exam in chemistry

Demo version of the Unified State Examination Chemistry 2018 download:

Specification of KIM Unified State Examination in Chemistry 2018:

Municipal budget educational institution

“Secondary school No. 4, Shebekino, Belgorod region”

Features of solving and evaluating tasks 30-35 of the Unified State Exam in chemistry

Prepared by: Arnautova Natalya Zakharovna,

teacher of chemistry and biology

MBOU "Secondary school No. 4, Shebekino, Belgorod region"

2017

Methodology for assessing tasks with a detailed answer (main approaches to determining criteria and rating scales for completing tasks)

The basis of the methodology for assessing tasks with a detailed answer is a number of general provisions. The most important among them are the following:

Testing and evaluation of tasks with a detailed answer is carried out only through an independent examination based on the method of element-by-element analysis of the examinees' answers.

The use of the element-by-element analysis method makes it necessary to ensure that the wording of the task conditions clearly corresponds to the content elements being checked. The list of content elements tested by any assignment is consistent with the standard requirements for the level of preparation of high school graduates.

The criterion for assessing the completion of a task using the method of element-by-element analysis is to establish the presence in the answers of the examinees of the answer elements given
in the response model. However, another answer model proposed by the examinee may be accepted if it does not distort the essence of the chemical component of the task conditions.

The rating scale for task performance is established depending on the number of content elements included in the response model, and taking into account such factors as:

Level of complexity of the content being tested;

A specific sequence of actions that should be carried out when completing a task;

Unambiguous interpretation of the task conditions and possible options wording of the answer;

Compliance of the assignment conditions with the proposed assessment criteria for individual content elements;

Approximately the same level of difficulty for each of the content elements tested by the task.

When developing assessment criteria, the features of the content elements of all five long-answer tasks included in the examination paper are taken into account. It is also taken into account that the records of the examinees’ answers can be either very general, streamlined and not specific, or too brief
and insufficiently reasoned. Close attention is paid to highlighting the elements of the answer that are worth one point. This takes into account the inevitability of a gradual increase in the difficulty of obtaining each subsequent point
for a correctly formulated element of content.

When drawing up a scale for grading calculation problems (33 and 34), the possibility of different ways of solving them is taken into account, and therefore, the presence in the examinee’s answer of the main stages and results of completing the tasks indicated
in the evaluation criteria. Let us illustrate the methodology for assessing tasks with a detailed answer using specific examples.

2017-2018 academic year

Tasks

Maximum score

Job Level

Task 30

2016-2017

Tasks 30 are aimed at testing the ability to determine the degree of oxidation of chemical elements, determine the oxidizing agent and the reducing agent, predict the products of redox reactions, establish the formulas of substances missed in the reaction scheme, draw up an electronic balance, and on its basis assign coefficients in reaction equations.

The scale for assessing the performance of such tasks includes the following elements:

 an electronic balance has been compiled – 1 point;

 the oxidizing agent and the reducing agent are indicated – 1 point.

 formulas of missing substances are determined and coefficients are assigned
in the equation of redox reaction – 1 point.

Example task:

Using the electron balance method, create an equation for the reaction

Na 2 SO 3 + … + KOH K 2 MnO 4 + … + H 2 O

Identify the oxidizing agent and the reducing agent.

Points

Possible answer

Mn +7 + ē → Mn +6

S +4 – 2ē → S +6

Sulfur in the +4 oxidation state (or sodium sulfite due to sulfur in the +4 oxidation state) is a reducing agent.

Manganese in oxidation state +7 (or potassium permanganate due to manganese
in the oxidation state +7) – oxidizing agent.

Na 2 SO 3 + 2KMnO 4 + 2KOH = Na 2 SO 4 + 2K 2 MnO 4 + H 2 O

The answer is correct and complete:

the degree of oxidation of elements that are, respectively, an oxidizing agent and a reducing agent in the reaction is determined;

oxidation and reduction processes were recorded, and an electronic (electron-ion) balance was compiled on their basis;

the missing substances in the reaction equation are determined, all the coefficients are placed

Maximum score

When assessing the examinee’s answer, it is necessary to take into account that there are no uniform requirements for the formatting of the answer to this task. As a result, the compilation of both electronic and electron-ion balances is accepted as the correct answer, and the indication of the oxidizing agent and reducing agent can be done in any clearly understandable way. However, if the answer contains elements of the answer that are mutually exclusive in meaning, then they cannot be considered correct.

2018 format tasks

1. Task 30 (2 points)

To complete the task, use the following list of substances: potassium permanganate, hydrogen chloride, sodium chloride, sodium carbonate, potassium chloride. It is permissible to use aqueous solutions of substances.

From the proposed list of substances, select substances between which an oxidation-reduction reaction is possible, and write down the equation for this reaction. Make an electronic balance, indicate the oxidizing agent and reducing agent.

Explanation.

Let's write the reaction equation:

Let's create an electronic balance:

Chlorine in oxidation state −1 is a reducing agent. Manganese in the oxidation state +7 is an oxidizing agent.TOTAL 2 points

substances are selected, the equation of the redox reaction is written, and all the coefficients are set.

oxidation and reduction processes were recorded, and an electronic (electron-ion) balance was compiled on their basis; which are respectively the oxidizing agent and the reducing agent in the reaction;

There was an error in only one of the response elements listed above

There were errors in two of the above response elements

All elements of the answer are written incorrectly

Maximum score

2018 format tasks

1. Task 31 (2 points)

To complete the task, use the following list of substances: potassium permanganate, potassium bicarbonate, sodium sulfite, barium sulfate, potassium hydroxide. It is permissible to use aqueous solutions of substances.

Explanation.

Possible answer:

2. Task 31

To complete the task, use the following list of substances: hydrogen chloride, silver(I) nitrate, potassium permanganate, water, nitric acid. It is permissible to use aqueous solutions of substances.

From the proposed list of substances, select substances between which an ion exchange reaction is possible. Write down the molecular, complete and abbreviated ionic equations for this reaction.

Explanation.

Possible answer:

Task 32. 2018 format tasks

In the condition of task 32, testing knowledge of the genetic relationship of various classes of inorganic substances, a description of a specific chemical experiment is proposed, the progress of which the examinees will have to illustrate using the equations of the corresponding chemical reactions. The grading scale for the task remains, as in 2016, equal to 4 points: each correctly written reaction equation is scored 1 point.

Example task:

Iron was dissolved in hot concentrated sulfuric acid. The resulting salt was treated with an excess of sodium hydroxide solution. The brown precipitate that formed was filtered and calcined. The resulting substance was heated with iron.

Write equations for the four reactions described.

Contents of the correct answer and assessment instructions(other wording of the answer is allowed that does not distort its meaning)

Points

Possible answer

Four equations for the described reactions are written:

1) 2Fe + 6H 2 SO 4
Fe 2 (SO 4 ) 3 + 3SO 2 + 6H 2 O

2) Fe 2 (SO 4 ) 3 + 6NaOH = 2Fe(OH) 3 + 3Na 2 SO 4

3) 2Fe(OH) 3
Fe 2 O 3 + 3H 2 O

4) Fe 2 O 3 + Fe = 3FeO

All reaction equations are written incorrectly

Maximum score

It should be noted that the absence of coefficients (at least one) before the formulas of substances in reaction equations is considered an error. No points are awarded for such an equation.

Task 33. 2018 format tasks

Tasks 33 test the assimilation of knowledge about the relationship of organic substances and provide for checking five elements of content: the correctness of writing five reaction equations corresponding to the diagram - a “chain” of transformations. When writing reaction equations, examinees must use the structural formulas of organic substances. The presence of each checked content element in the answer is scored 1 point. The maximum number of points for completing such tasks is 5.

Example task:

Write the reaction equations that can be used to carry out the following transformations:

When writing reaction equations, use the structural formulas of organic substances.

Contents of the correct answer and assessment instructions
Other wording of the answer is allowed that does not distort its meaning)

Points

Possible answer

Five reaction equations have been written corresponding to the transformation scheme:

Five reaction equations written correctly

Four reaction equations written correctly

Three reaction equations written correctly

Two reaction equations written correctly

One reaction equation written correctly

All elements of the answer are written incorrectly

Maximum score

Note that in the examinee’s answer it is permissible to use structural formulas different types(expanded, contracted, skeletal), unambiguously reflecting the order of connection of atoms and mutual arrangement substituents and functional groups
in a molecule of organic matter.

Task 34. 2018 format tasks

Tasks 34 are calculation problems. Their implementation requires knowledge of the chemical properties of substances and involves the implementation of a certain set of actions to ensure that the correct answer is obtained. Among such actions we name the following:

– drawing up equations of chemical reactions (according to the data of the problem conditions) necessary to perform stoichiometric calculations;

– performing calculations necessary to find answers to questions
in the problem statement there are questions;

– formulating a logically substantiated answer to all questions posed in the task conditions (for example, establishing a molecular formula).

However, it should be borne in mind that not all of the named actions must necessarily be present when solving any calculation problem, and in some cases some of them can be used more than once.

The maximum score for completing the task is 4 points. When checking, you should first of all pay attention to the logical validity of the actions performed, since some tasks can be solved in several ways. At the same time, in order to objectively evaluate the proposed method for solving the problem, it is necessary to check the correctness of the intermediate results that were used to obtain the answer.

Example task:

Determine the mass fractions (in%) of iron(II) sulfate and aluminum sulfide
in a mixture if, when 25 g of this mixture is treated with water, a gas is released, which completely reacts with 960 g of a 5% solution of copper sulfate.

In your answer, write down the reaction equations that are indicated in the problem statement,
and provide all the necessary calculations (indicate the units of measurement of the required physical quantities).

Points

Possible answer

The reaction equations were compiled:

The amount of hydrogen sulfide is calculated:

The amount of substance and mass of aluminum sulfide and iron(II) sulfate are calculated:

The mass fractions of iron(II) sulfate and aluminum sulfide in the initial mixture were determined:

ω(FeSO 4 ) = 10 / 25 = 0.4, or 40%

ω(Al 2 S 3 ) = 15 / 25 = 0.6, or 6 0%

The answer is correct and complete:

the answer correctly contains the reaction equations corresponding to the conditions of the task;

calculations have been carried out correctly using the necessary physical quantities specified in the task conditions;

a logically substantiated relationship between the physical quantities on the basis of which calculations are carried out is demonstrated;

in accordance with the task conditions, the required physical quantity is determined

There was an error in only one of the response elements listed above

All elements of the answer are written incorrectly

Maximum score

When checking the answer, the examinee must take into account the fact that if the answer contains an error in calculations in one of the three elements (second, third or fourth), which led to an incorrect answer, the mark for completing the task is reduced by only 1 point.

Task 35. 2018 format tasks

Tasks 35 involve determining the molecular formula of a substance. Completing this task includes the following sequential operations: carrying out the calculations necessary to establish the molecular formula of an organic substance, writing the molecular formula of an organic substance, drawing up a structural formula of a substance that uniquely reflects the order of bonds of atoms in its molecule, writing a reaction equation that meets the conditions of the task.

The grading scale for task 35 in part 2 of the examination paper will be 3 points.

Tasks 35 use a combination of tested content elements - calculations, on the basis of which they come to determine the molecular formula of a substance, compile a general formula of a substance, and then determine the molecular and structural formula of a substance on its basis.

All these actions can be performed in different sequences. In other words, the examinee can come to the answer in any logical way available to him. Therefore, when assessing a task, the main attention is paid to the correctness of the chosen method for determining the molecular formula of a substance.

Example task:

When burning a sample of some organic compound weighing 14.8 g, 35.2 g of carbon dioxide and 18.0 g of water were obtained.

It is known that the relative vapor density of this substance with respect to hydrogen is 37. During the study of the chemical properties of this substance, it was established that when this substance interacts with copper(II) oxide, a ketone is formed.

Based on the data of the task conditions:

1) make the calculations necessary to establish the molecular formula of an organic substance (indicate the units of measurement of the required physical quantities);

write down the molecular formula of the original organic substance;

2) draw up a structural formula of this substance, which unambiguously reflects the order of bonds of atoms in its molecule;

3) write the equation for the reaction of this substance with copper(II) oxide using the structural formula of the substance.

Contents of the correct answer and assessment instructions

(other wording of the answer is allowed that does not distort its meaning)

Points

Possible answer

The amount of combustion product substance found:

General formula substances – C x H y O z

n(CO2) = 35.2 / 44 = 0.8 mol; n (C) = 0.8 mol

n(H 2 O) = 18.0 / 18 = 1.0 mol; n(H) = 1.0 ∙ 2 = 2.0 mol

m(O) = 14.8 – 0.8 ∙ 12 – 2 = 3.2 g; n(O) = 3.2 ⁄ 16 = 0.2 mol

The molecular formula of the substance was determined:

x:y:z = 0.8:2:0.2 = 4:10:1

The simplest formula– C4H10O

M simple (C 4 H 10 O) = 74 g/mol

M source (C x H y O z ) = 37 ∙ 2 = 74 g/mol

Molecular formula of the starting substance – C 4 H 10 O

The structural formula of the substance has been compiled:

The equation for the reaction of a substance with copper(II) oxide is written:

The answer is correct and complete:

the calculations necessary to establish the molecular formula of a substance have been correctly performed; the molecular formula of the substance is written down;

the structural formula of an organic substance is written down, which reflects the bond order and relative arrangement of substituents and functional groups in the molecule in accordance with the assignment conditions;

the equation of the reaction, which is indicated in the task conditions, is written using the structural formula of an organic substance

There was an error in only one of the response elements listed above

There were errors in two of the above response elements

There were errors in three of the above response elements

All elements of the answer are written incorrectly

All elements of the answer are written incorrectly

Maximum score

TOTAL part 2

2+2+ 4+5+4 +3=20 points

Bibliography

1. Methodological materials for chairmen and members of subject commissions of subjects Russian Federation for checking the completion of tasks with detailed exam answers Unified State Examination works 2017. Article " Guidelines for assessing the completion of Unified State Examination tasks with a detailed question.” Moscow, 2017.

2. FIPI control and measuring project Unified State Exam materials 2018.

3. Demo versions, specifications, codifiers of the Unified State Exam 2018. FIPI website.

4. Information about planned changes to the 2018 CMM. FIPI website.

5.Site “I will solve the Unified State Exam”: chemistry, for an expert.