Kuryseva Nadezhda Gennadievna
chemistry teacher highest category, Municipal educational institution secondary school No. 36, Vladimir

In elective classes, they mainly practice Part C assignments.

To do this, we offer a selection of tasks from versions of open CMMs from past years .

You can practice your skills by completing unit tasks WITH in any order. However, we adhere to the following order: first we solve problems C5 and execute chains C3.(Similar tasks were completed by students in grade X.) In this way, students’ knowledge and skills in organic chemistry are consolidated, systematized and improved.

After studying the topic "Solutions" let's move on to solving problems C4. On topic "Redox reactions"introduce students to the ion-ion method electronic balance (half-reaction method), and then we practice the ability to write redox reactions of tasks C1 And C2.

We offer specific examples to look at the implementation of individual tasks of the part WITH.

Part C1 tasks test the ability to write equations for redox reactions. The difficulty is that some reactants or reaction products are missing. Students, using logical reasoning, must identify them. We offer two options for completing such tasks: the first is logical reasoning and finding missing substances; the second is writing the equation using the ion-electron balance method (half-reaction method - see Appendix No. 3), and then drawing up a traditional electronic balance, because This is what is required of the examinee. In different cases, students themselves determine which method is preferable to use. For both options, you simply need to have a good knowledge of the basic oxidizing and reducing agents, as well as their products. To do this, we offer students a table "Oxidizing agents and reducing agents", introduce with her (Appendix No. 3).

We suggest completing the task using the first method.

Exercise. Using the electron balance method, create an equation for the reactionP + HNO 3 → NO 2 + … Identify the oxidizing agent and the reducing agent.

Nitric acid is a strong oxidizing agent, therefore, the simple substance phosphorus is a reducing agent. Let's write down the electronic balance:

HNO 3 (N +5) is an oxidizing agent, P is a reducing agent.

Exercise. Using the electron balance method, create an equation for the reactionK 2 Cr 2 O 7 + … + H 2 SO 4 → I 2 + Cr 2 ( SO 4 ) 3 + … + H 2 O . Identify the oxidizing agent and the reducing agent.

K 2 Cr 2 O 7 is an oxidizing agent, since chromium is in highest degree oxidation +6, H 2 SO 4 is a medium, therefore, the reducing agent is omitted. It is logical to assume that this is the I ion - .Let's write down the electronic balance:

K 2 Cr 2 O 7 (Cr +6) is an oxidizing agent, KI (I -1) is a reducing agent.

The most difficult tasks C2. They are aimed at testing the assimilation of knowledge about the chemical properties of inorganic substances, the relationship of substances of various classes, the conditions for the irreversible occurrence of metabolic and redox reactions and the availability of skills in drawing up reaction equations. Completing this task involves analyzing the properties of inorganic substances of various classes, establishing a genetic connection between given substances and using the skills to draw up equations of chemical reactions in compliance with Berthollet’s rule and redox reactions.

1. carefully analyze the data in the substance task;
2. using a diagram of the genetic relationship between classes of substances, evaluate their interaction with each other (find acid-base interactions, exchange interactions, metal with acid (or alkali), metal with non-metal, etc.);
3. determine the oxidation states of elements in substances, evaluate which substance can only be an oxidizing agent, only a reducing agent, and some - both an oxidizing agent and a reducing agent. Next, compose redox reactions.

Exercise. Given aqueous solutions: ferric chloride (III), sodium iodide, sodium dichromate, sulfuric acid and cesium hydroxide. Give equations for four possible reactions between these substances.

Among the proposed substances there is acid and alkali. We write the first equation of the reaction: 2 CsOH + H 2 SO 4 = Cs 2 SO 4 + 2H 2 O.

We find an exchange process that occurs with the precipitation of an insoluble base. FeCl 3 + 3CsOH = Fe(OH) 3 ↓ + 3CsCl.

On topic "Chromium" the reactions of conversion of bichromates into chromates in an alkaline medium are studied. Na 2 Cr 2 O 7 + 2CsOH = Na 2 CrO 4 + Cs 2 CrO 4 + H 2 O.

Let us analyze the possibility of the redox process occurring. FeCl 3 exhibits oxidizing properties, because iron in the highest oxidation state is +3, NaI is a reducing agent due to iodine in the lowest oxidation state -1.

Using the technique of writing redox reactions, considered when completing the tasks of the part C1, let's write:

2FeCl 3 + 2NaI = 2NaCl + 2FeCl 2 + I 2

Fe +3 + 1e - →Fe +2 2I -1 - 2 e - →I 2

The work consists of two parts:
- part 1 - tasks with a short answer (26 - basic level, 9 advanced),
- part 2 - tasks with detailed answers (5 high-level tasks).
The maximum number of primary points remains the same: 64.
However, some changes will be made:

1. In tasks of basic difficulty level(formerly Part A) will include:
a) 3 tasks (6,11,18) with multiple choice (3 out of 6, 2 out of 5)
b) 3 tasks with an open answer (calculation problems), the correct answer here will be the result of the calculations, recorded with a specified degree of accuracy;
Like other basic level assignments, these assignments will be worth 1 initial point.

2. Advanced level tasks (formerly Part B) will be of one type: compliance assignments. They will be scored 2 points (if there is one error - 1 point);

3. The question on the topic: “Reversible and irreversible chemical reactions. Chemical equilibrium. Shift of equilibrium under the influence of various factors” has been moved from the tasks of the basic level to the advanced level.
However, the issue of nitrogen-containing compounds will be checked at a basic level.

4. The time for the unified exam in chemistry will be increased from 3 hours to 3.5 hours(from 180 to 210 minutes).

To pass final exams at school. It will need to be taken for admission to universities in the following areas: chemistry and chemical technology, medicine, construction, biotechnology and others. In general, the exam is not very popular - only one student out of ten graduates chooses chemistry.

Read the general information about the exam and start preparing. The KIM version of the Unified State Exam 2019 has some differences from last year: 1) in part 2 a task of a high level of difficulty with a detailed answer was added, 2) for four questions the level of difficulty and the maximum primary score were revised (for the entire test the maximum score did not change), 3) for To ensure a clearer distribution of tasks into thematic blocks, the developers slightly changed their order in Part 1.

Unified State Examination

Last year, to pass the Unified State Examination in chemistry with at least a C grade, it was enough to score 37 primary points. They were given, for example, for correctly completing the first 15 tasks of the test.

It is not yet known exactly what will happen in 2019: we need to wait for the official order from Rosobrnadzor on the correspondence of primary and test scores. Most likely it will appear in December. Considering that the maximum primary score for the entire test remains the same, most likely the minimum score will not change either. Let's focus on these tables for now:

Structure of the Unified State Exam test

In 2019, the test consists of two parts, including 35 tasks.

• Part 1: 29 tasks (1–29) with a short answer (number or sequence of numbers);
• Part 2: 6 tasks (30–36) with detailed answers, complete solutions to the tasks are written down on answer sheet 2.

Preparation for the Unified State Exam

• Take the Unified State Exam tests online for free without registration or SMS. The tests presented are identical in complexity and structure to the actual exams conducted in the corresponding years.

• Download demo versions of the Unified State Examination in Chemistry, which will allow you to better prepare for the exam and pass it easier. All proposed tests have been developed and approved for preparation for the Unified State Exam by the Federal Institute of Pedagogical Measurements (FIPI). All official versions of the Unified State Exam are developed in the same FIPI.
  The tasks that you will see most likely will not appear on the exam, but will be similar to the demo ones, on the same topic or simply with different numbers.
• Familiarize yourself with the basic exam prep formulas to help refresh your memory before attempting the demos and test options.

General Unified State Examination figures

Year	Minimum Unified State Examination score	Average score	Number of participants	Failed, %	Qty 100 points	Duration - Exam length, min.
2009	33
2010	33	56,04	83 544	6,2	275	180
2011	32	57,75	77 806	8,6	331	160
2012	36	57,3	93 181	11	365	180
2013	36	67,8	93 802	7,3	3220	180
2014	36	55,3				180
2015	36	56,3				180
2016	36					180
2017	36					180
2018

Option No. 1357842

Unified State Exam in Chemistry - 2016. Main wave (Part C).

When completing tasks with a short answer, enter in the answer field the number that corresponds to the number of the correct answer, or a number, a word, a sequence of letters (words) or numbers. The answer should be written without spaces or any additional characters. Separate the fractional part from the whole decimal point. There is no need to write units of measurement. The answer to tasks 1-29 is a sequence of numbers or a number. 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.

If the option is specified by the teacher, you can enter or upload answers to tasks with a detailed answer into the system. The teacher will see the results of completing tasks with a short answer and will be able to evaluate the downloaded answers to tasks with a long answer. The scores assigned by the teacher will appear in your statistics.

Version for printing and copying in MS Word

Using the electron balance method, create the reaction equation:

Identify the oxidizing agent and the reducing agent.

Copper(II) oxide was heated in a hydrogen atmosphere. The resulting solid was dissolved in concentrated sulfuric acid. The resulting salt reacted with potassium iodide, and the released gas was mixed with chlorine and passed through a solution of potassium hydroxide.

Solutions to long-answer tasks are not automatically checked.
The next page will ask you to check them yourself.

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.

Solutions to long-answer tasks are not automatically checked.
The next page will ask you to check them yourself.

Zinc nitrate was heated. Some of it decomposed and 5.6 liters of gas mixture was released. The solid residue weighing 64.8 g was dissolved in a strict amount of 28% sodium hydroxide solution (that is, sufficient for dissolution and without excess). Determine the mass fraction of sodium nitrate.

Solutions to long-answer tasks are not automatically checked.
The next page will ask you to check them yourself.

What to pay attention to when preparing for the Unified State Exam 2017

In 2016, 75,096 graduates took the chemistry exam, which is approximately the same as in the previous two years.

Did not cross the established minimum threshold for the number of points scored (less than 34) - 13.2%, passed satisfactorily (up to 60) - 47.3%, good (up to 80) - 33.7%, excellent (up to 100) - 5, 8%.

In total, there were 40 tasks in the work: 35 with a short answer made up the first part, five with a detailed answer - the second.

In the examination paper in chemistry in 2016 (compared to 2015), changes were made to six tasks. Instead of choosing one answer, you had to choose 2-3 or give the answer as a number with a given degree of accuracy. In two tasks of increased complexity (34 and 35), instead of multiple choice, it was necessary to establish correspondences between elements of two sets. Unfortunately, these changes resulted in poor results in completing the listed tasks.

The tasks of increased complexity turned out to be too difficult for the examinees, and the percentage of those who coped with them was small. This was, for example, task 39. It turned out that only a few well-prepared graduates can carry out calculations using reaction equations. Even among the guys who had good training, only 19.6% were able to cope with this task. Apparently, those who are now preparing for the Unified State Exam 2017 need to pay special attention to such tasks and work out the algorithm for completing them.

At the same time, another task of increased complexity (number 36) on redox reactions based on electronic balance was completed by 61.5% of the examinees.

In 2017, some changes are planned for the chemistry exam. This is caused by the desire to more objectively check the success of mastering the subject.

Fewer tasks are expected: instead of 40, as in 2016, only 34. The primary score from 64 in 2016 will drop to 58-60.

Graduates need to be prepared to demonstrate not only successful mastery of the general education program in the subject, but also the ability to apply acquired knowledge, skills, and abilities in educational situations. For example, classify organic and inorganic substances, describe their chemical properties. In the task, it may be necessary to indicate the numbers of acids from the listed substances, that is, it is necessary to show knowledge of the characteristics of this class of substances - the presence of only hydrogen ions as cations. Or, for example, the following task: with which of the listed substances will phosphorus and magnesium react (the main thing here is to remember that these two substances can be reducing agents, and therefore can react with an oxidizing substance).

There will also be tasks to establish correspondence between the two groups of proposed substances. For example, determine which substances from one group can react with substances from another.

From these examples it is clear that nothing overly difficult, beyond the school curriculum, will be required from the graduate, but the knowledge must be systematic, and not fragmentary - this is the main factor for successfully passing any exam, not only in chemistry.

Familiarize yourself with the codifier of tested content elements and specifications posted on the FIPI website, and let your child try the demo version of the Unified State Exam. After that, together, honestly assess your chances of passing this very difficult exam. You can’t beat it in one sitting even by the minimum score. If you completed the demo version with a low score, it may be worth looking for other options for continuing your studies, and therefore choosing other disciplines, the scores for which are passing to the newly chosen university, taking into account your real abilities and acquired knowledge base.

Yes, high scores on the Unified State Exam in chemistry will open the doors of many prestigious educational institutions. However, in this case, before cutting off, that is, deciding to take chemistry, you need to measure not just seven times, but seventy-seven. After all, the child’s future depends on success in the exam. As they say, whatever you studied for, that’s what you were good for. In the eleventh grade it is too late to start studying this complex subject from scratch. To repeat - yes, but to teach as a completely new, completely unfamiliar discipline - no. Be realistic.

But if the child still chooses to take the Unified State Exam in Chemistry, it is necessary to make every effort to thoroughly master the educational program for this course, which will be rewarded by receiving the maximum number of points, admission to the chosen university and successful studies there.