II. METHODOLOGY AND TECHNIQUE OF EDUCATIONAL CHEMICAL EXPERIMENT AT SCHOOL

2.1. Definition of the concept of educational experiment,

its classification and place in teaching chemistry

By the concept of "natural educational chemical experiment" we mean a means of teaching chemistry in the form of specially organized and conducted experiments with substances (reagents), included by the teacher in the educational process with the aim of cognizing, verifying or proving by students a chemical fact, phenomenon or law known to science, as well as for the assimilation by students of certain methods of research in chemical science.

The educational chemical experiment should be considered, first of all, as a didactic tool for achieving the main goals of education. With the help of a chemical experiment at school, you can teach children to observe phenomena, form concepts, study new educational material, consolidate and improve knowledge, form and improve practical skills, promote the development of interest in the subject, etc.

Unlike other means of visualization, an educational chemical experiment has a certain dynamics in time, that is, the external manifestation of the process is constantly changing, as a result of the experiment, new substances are obtained that have properties that differ from the original substances, and with which new experiments can be carried out.

The peculiarities and diversity of chemical phenomena, and, consequently, of the educational chemical experiment make it possible to use it literally in all forms and at all stages of the educational process.

Usually, educational experiments performed in chemistry lessons are divided, depending on the subject of their conduct, into demonstration, laboratory experiments and practical work. A demonstration experiment is performed by a teacher or student for the public to see all students in the class; one conducts the experiment, the rest observe the process. Laboratory experiments are performed, as a rule, by all students in the class during the teacher's explanation. These experiments should be simple, short in time (2-3 minutes) and safe to carry out. Everything necessary for laboratory experiments should be prepared in advance on the tables of students. Practical work is an experiment on the study of a specific topic, performed by students under the guidance of a teacher throughout the lesson.

In principle, this classification of the educational experiment is acceptable not only in relation to lessons, but also for other forms of the educational process, such as: electives, workshops, elective courses, chemistry circles and other forms of extracurricular work, etc.

Depending on the number of reagents taken for the experiment and the size of the chemical glassware, the educational chemical experiment is divided into a macro-experiment and a micro-experiment, an experiment with a small number of reagents.

Microexperiment (micromethod) in the form of drop reactions and microscopic examination of precipitates is widely used in analytical chemistry. It has a number of obvious advantages: it simplifies the course of analysis; the desired result is obtained faster, which is especially important in the work of clinical, sanitary and hygienic chemical and technological laboratories; less reagents are consumed; greater sensitivity is achieved, etc.

However, in school conditions, the use of a micro-experiment is in most cases inappropriate. First of all, this applies to demonstration experiments, which do not make sense in the form of drop reactions, since students will not be able to observe either the course of the reaction or its results. In addition, the use of a microexperiment requires the availability of a sufficient amount (for all students) of special equipment: micropipettes, plates for reactions, etc.

In our opinion, in practical classes and when conducting laboratory experiments, methods using small amounts of reagents should be used, and demonstration experiments should be carried out in the form of a macro experiment in order to ensure good visibility for all students.

Due to the fact that it is impossible to show some reactions at school, teachers in the study of chemistry resort to the so-called "thought experiment" - students imagine in their minds, without observation in experience, certain processes that characterize the properties of substances, their production, etc. and mentally predict the results to which this or that experience can lead. We propose to call this kind of experiment not "thought" but "virtual experiment". Since we believe that the word "virtual" is more consonant with the era of computerization, that is, our time, it is modern. In explanatory dictionaries of the Russian language and dictionaries of foreign words, the word "virtual" means "non-existent, but possible", "possible, which can manifest itself under certain conditions."

According to the venue, it is possible to single out a school, home and field educational chemical experiment. In addition, entertaining experiments should play a special role in the school. In general, the classification of educational chemical experiment can be presented in the form of a table.

It goes without saying that each type of educational chemical experiment has its own specific goals and performance features. Demonstration experiments in chemistry can be carried out in the form of natural processes or reactions; in the form of simulation experiments, when some substances are replaced by others for the purpose of greater safety, clarity and economy; in the form of a multimedia experiment, that is, showing experiments on TV, using a movie projector or a computer.

Classification of educational chemical experiment

LABORATORY EXPERIENCES

PRACTICAL WORKS OF STUDENTS

DEMONSTRATION-
EXPERIMENT

Goal: learning new material.

Purpose: consolidation and improvement of knowledge, formation and improvement of practical skills and abilities.

Purpose: to form the concepts of chemistry; learn to observe phenomena.

The action of indicators on acids and bases.

Color reactions to

Simulation experiments

An experiment carried out according to the instructions

Experimental problem

multimedia experiment

Obtaining diamonds from graphite.

Preparation and properties of phenol.

Replacing bromine water with iodine water.

Replacement of formaldehyde with glucose in the silver mirror reaction.

Get copper oxide in three ways and prove that this substance is a basic oxide.

Prove by experience that polyethylene contains carbon and hydrogen.

Obtaining carbon monoxide (IV) and experiments with it.

Obtaining ethyl ester of acetic acid.

EDUCATIONAL CHEMICAL EXPERIMENT

FIELD EXPERIMENT

VIRTUAL EXPERIMENT

HOMEEXPERIMENT

ENTERTAINING EXPERIENCES

Purpose: to make chemical experiments safer, cheaper and more visual; develop the thinking of students.

Purpose: to promote the development of interest in the subject and a more conscious assimilation of scientific knowledge.

Purpose: formation and development of students' interest in chemistry.

Decomposition of mercury oxide or Bertolet salt.

Synthesis of organic
connections.

Obtaining smokeless powder.

Eruption.

Spontaneous combustion
spirit lamps.

Express analysis of soil and water in the field.

Chemistry in
everyday life

Obtaining substances

The study of the properties of substances

Experiments with starch.

Sugar experiments.

Getting indicators.

Getting starch.

Properties of table salt, vinegar, soda, etc.

The main goal of demonstration experiments is the development of observation, the formation of new knowledge and concepts of chemistry. The key advantages of demonstration experiments are their visibility, the ability to promptly direct students' attention to the main link in the process, saving time and reagents. However, this type of experiment does not give students the opportunity to develop special skills.

Laboratory experiments are remarkable in that when they are included in the explanation of new material, students are personally convinced of the correctness of certain statements of the teacher and at the same time acquire some skills in a chemical experiment, develop observation skills. At the same time, preparation for conducting these experiments requires more time, reagents are spent, and the teacher has to pay more attention to ensuring safety in the classroom. The main purpose of laboratory experiments is to provide clarity when learning new material.

Practical work, being an important source of learning new material, also contributes to the formation and improvement of practical skills of students. The main problems in their implementation are the provision of all students with reagents, utensils and equipment, as well as the observance by all students of safety rules.

Performing laboratory experiments and practical work, students independently explore chemical phenomena and patterns, in practice making sure of their reliability. Naturally, this practical activity of students cannot be carried out without the guiding word of the teacher. It is necessary to ensure that when conducting experiments, students show a creative approach, that is, they would apply their knowledge in new conditions. An important advantage of these types of educational experiment is that students, in contrast to demonstration experiments, include almost all sense organs in the process of cognition, which contributes to a stronger and deeper assimilation of the material.

Practical classes are usually held at the end of the study of one or more topics of the course and have specific goals.

Firstly, this is the consolidation of knowledge in chemistry, including the main experimental material, by independently performing certain experiments by students. At the same time, practical exercises conducted at the conclusion of a number of topics make it possible to successfully generalize the experimental and theoretical material, which is not always possible in a regular lesson.

Secondly, there is a further development of practical skills and mastery of the technique of a chemical experiment.

Thirdly, the creative application of knowledge is realized in the process of experimental solution of problems and practical issues, which is of great importance for the formation of the ability to use knowledge in an active form, for expanding the horizons of students about the application of chemistry in life.

The skillful organization of a home chemical experiment contributes to the development of students' interest in chemistry, broadening their horizons, and more conscious assimilation of chemical knowledge. When assisting students in the organization of home laboratories, the teacher must inform the parents in order to avoid undesirable consequences when conducting experiments at home.

Entertaining experiments can occasionally be carried out in the classroom, but more often used in extracurricular activities in order to form and develop students' interest in chemistry. However, in no case should chemical experiments be turned into tricks, even when they are demonstrated in elementary grades. Therefore, when applying an educational chemical experiment in extracurricular work, it is necessary to widely use all types of experiments, including field experiments.

Qualitative reactions to the content of individual elements in environmental objects can be recommended as field experiments. The chemical reagents and utensils necessary for this are placed in special cases or boxes that allow them to be transferred or transported without any risk or damage. Each package contains instructions on the analysis technique, a pencil and a blank sheet of paper to complete the work.

A virtual experiment is recommended in cases where the initial substances are not available, reactions take a long time, are accompanied by the release of hazardous substances, require complex equipment, etc. In addition, virtual experiences are useful before conducting real processes to ensure that students are fully aware of the course of the upcoming experience. In any case, virtual experiences are based on representations of the imagination, and in order for them to be closer to actual phenomena, it is necessary to first form appropriate memory representations in students. A special form of a virtual chemical experiment are experiments that can be designed and "carried out" using computer programs (Chem. Lab., Virtual Chemical Laboratory, etc.).

As in other natural science disciplines, an educational experiment in teaching chemistry aims to contribute to the solution of basic educational tasks, such as: mastering the basics of chemical science, getting to know its research methods and mastering special skills and abilities; formation and development of students' abilities, their cognitive and mental activity; polytechnic training and orientation of students to chemical professions; the formation of the worldview of students and the natural-science picture of the world in their minds; implementation of labor, moral, environmental education; comprehensive development of personality, etc.

According to many methodologists, a chemical experiment plays a leading role in the successful solution of educational problems in teaching chemistry in many directions as an initial source of knowledge of phenomena, as a necessary, and often the only, means of proving the correctness or erroneousness of the assumption made, as well as confirmation (illustrations ) indisputable provisions reported by the teacher or learned by students from the textbook; as the only means for the formation and improvement of practical skills in handling equipment, substances, in obtaining and recognizing substances; as an important means for the development, improvement and consolidation of theoretical knowledge; as a way to test the knowledge and skills of students; as a means of forming students' interest in the study of chemistry, developing their observation, curiosity, initiative, striving for independent search and improvement of knowledge and their application in practice.

An educational chemical experiment can be successfully applied at all stages of the educational process. First of all, the experiment provides visual acquaintance of students with the studied substances. For this purpose, samples of substances, collections in the form of handouts are demonstrated, experiments are conducted that characterize the physical properties of substances. After that, students begin to get acquainted with its chemical properties.

When explaining new material, the experiment helps to illustrate the topic being studied not only with relevant chemical phenomena, but also with specific practical application, as a result, students perceive the theoretical foundations of chemistry more consciously.

Using the experiment to consolidate a new topic allows the teacher to identify how the new material is learned, and outline the methodology and plan for further study of this issue.

The use of a home experiment helps to attract students to independent work using not only textbooks, but also additional, reference literature.

For the purpose of current, as well as final control and accounting of practical knowledge, one of the means is also a chemical experiment in the form of practical exercises for students and solving experimental problems. With the help of an experiment, many qualities of students can be assessed, ranging from the level of knowledge of theory to the practical skills of students.

Great opportunities in the education and upbringing of schoolchildren lie in the application of an educational experiment on electives, within the framework of specialized education and in extracurricular activities. Here, students are offered more complicated experiments, including those with a more pronounced polytechnic orientation.

The role of the educational chemical experiment in the formation of cognitive interest among students as a motive for cognitive activity should be especially emphasized, since it determines and directs all the mental processes of learning: perception, memory, thinking, attention, etc.

The importance of using a chemical experiment when a teacher uses the method of problematic presentation of the material is great. The activity of the teacher here is to formulate the problem and reveal the evidence-based way to solve it through setting up an experiment. At the same time, it is important that the students themselves come to the conclusion about the need to set up appropriate experiments, take part in their development and implementation. And the experiment here can act as the most important method of proving the truth or falsity of the hypotheses put forward.

The use of a chemical experiment allows students to master the practical skills established by educational standards as mandatory, including: technical (handling reagents, working with equipment, assembling devices and installations from finished parts and assemblies, performing chemical operations, observing safety rules) ; measuring (measurement of temperature, density and volume of liquids and gases, weighing, processing of measurement results); design (manufacturing of instruments and installations, their repair, improvement and graphic design).

With the help of the experiment, many qualities of students can be assessed, ranging from the level of knowledge of theory to the practical skills of students.

With all this, we must not forget that the chemical experiment, performing various didactic functions, can be used in various forms and must be combined with other methods and teaching aids. It is a system that uses the principle of gradually increasing the independence of students: from demonstrating phenomena through conducting laboratory experiments under the guidance of a teacher to independent work when performing practical exercises and solving experimental problems.

A chemical experiment develops thinking, mental activity of students. Often an experiment becomes a source of formed ideas, without which productive mental activity cannot proceed. In mental development, theory plays a leading role, but in unity with experiment, with practice.

2.2. Methodology and technique of educational full-scale experiment

There are certain methodological and technical requirements for conducting a school experiment.

Demonstration experiments are carried out with the aim of creating in students certain ideas about substances, chemical phenomena and processes, followed by the formation of chemical concepts. However, demonstrations of experiments do not develop the required experimental skills and abilities in students, therefore, they must be supplemented by laboratory experiments and practical exercises.

A demonstration experiment is carried out when the experiment is complex and cannot be carried out by the students themselves; students do not have the necessary equipment to conduct this experiment; laboratory experiments do not give the proper result; it is impossible to provide the necessary amount of equipment at the disposal of students; experiments pose some danger to students.

A demonstration experiment, regardless of who conducts it, a teacher or a student, must, first of all, be safe, both for the experimenter and for the observers. Other requirements that the experiment must meet include: visibility, the ability to see all the details and moments of the experience by all students, reliability, expressiveness, emotionality, persuasiveness, quick and simple execution. The demonstration experiment should be combined with the word of the teacher. In connection with these requirements, a number of methodological recommendations can be distinguished.

The teacher is responsible for the safety of students, so the classroom should have fire safety equipment, an exhaust hood for working with harmful and odorous substances, and first aid equipment. Reagents for experiments should be checked in advance, the dishes for the experiment should be clean. When conducting hazardous experiments, a protective screen should be used.

The demonstration experiment should be carried out in flasks, beakers or large test tubes so that the chemical phenomenon can be observed from anywhere in the classroom. There should be nothing superfluous on the demonstration table. The teacher should not obscure the equipment and utensils with which he operates from the views of students with any objects. A lift table or overhead projector can be used.

The equipment for the demonstration of the experiment should not contain unnecessary details so that the attention of the trainees is not distracted from the chemical process. You should not get too carried away with spectacular experiences, as less spectacular experiences will no longer be of interest.

An experiment must always succeed, and for this purpose the technique of the experiment must be carefully worked out before it is carried out; all stages of the experiment should be thought out; negligence in the design of the experiment is unacceptable, it is necessary to foresee possible failures during the experiment and prepare for such cases spare parts of the equipment and reagents. Everything that is necessary for the experience should be at the teacher's fingertips. In case of failure, it is necessary to find out its cause, and repeat the experience in this or the next lesson. If possible, the experiments should be repeated several times so that the students remember them better, otherwise after a while the ideas received once will be erased from the memory of the students.

Any experience should be combined with the word of the teacher, since sensory perceptions alone cannot guarantee the development of correct ideas in students. In the process of observation, they can turn their attention not to the main features of an object or phenomenon, but to secondary or incidentally accompanying ones and, as a result, get an incomplete, fuzzy and even distorted idea of ​​the object under study. A more correct reflection of the real world, a more adequate perception of it becomes when the activity of thinking is added to the sensations, in this case guided by the word of the teacher.

The teacher is obliged to indicate to the students what and how they should observe during the experiment. If it is important for a teacher that students correctly perceive what he shows them, he must organize the observation process in advance, prepare students for it in advance, and then help correct perception during the experiment.

The combination of an experiment with the word of a teacher or a student is carried out in various ways, which are determined by various reasons, which can be illustrated in the form of algorithms.

When studying the physical properties of substances, the following algorithm is used: "Look and name (list)", that is, the teacher demonstrates a sample of the substance under study or gives students handouts, for example, aluminum samples, and asks to list the physical properties of the metal, determined directly by the senses (aggregate state, color, smell, etc.). The same technique can also be used when demonstrating the same type of properties of substances of the same class, for example, when demonstrating the effect of phenolphthalein on a KOH solution, if an experiment with a NaOH solution was previously demonstrated.

When studying more complex issues, which, however, can be relatively easily understood by students, the algorithm can be used: "Look; tell what you saw; explain this phenomenon." For example, when learning the concepts of hydrolysis of salts, the teacher demonstrates the effect of the indicator on various salts. Students see that the indicator colors salt solutions in different ways, and note that the environment of the solutions is different. The teacher asks to explain the external signs of the experience, that is, to reveal the essence of the phenomenon, thereby creating a problem situation. Naturally, students cannot always answer the question posed by the teacher. The essence of hydrolysis is explained by the teacher later in the course of the conversation.

In the variants considered, the experiment (demonstration of experience) preceded a verbal discussion of what was seen. These options for combining words and visualization are called research.

Let's consider the reverse. When studying the properties of sulfuric acid, for example, the teacher might say: "Sulfuric acid in aqueous solution has properties typical of inorganic acids and reacts with metals, basic oxides, acids, salts." Then an appropriate demonstration or laboratory experiment is carried out. The algorithm for this combination of words and visualization can be expressed as follows: "The facts are as follows ... now look how it looks." This combination of words and visualization is called illustrative. With its application, the creation of a problem situation in the lesson becomes more difficult.

The illustrative method is useful in explaining complex issues that require complete preliminary reflection and understanding on the part of students. For example, in order to experimentally substantiate the true graphical formula of ethanol, the teacher preliminarily discusses the possible variants of the formulas. Then the teacher poses a problem: how to prove which formula corresponds to ethanol; conducts a thorough discussion of the issue theoretically; and only after that begins the experiment. After the experiment, a conclusion is drawn on the merits of the issue. This option is also illustrative, however, during its implementation, a large mental and cognitive activity of students takes place, which to a certain extent compensates for the main drawback of this approach - duration in time. The algorithm can be expressed as follows: "There is an inexplicable, incomprehensible fact or educational problem; hypotheses are expressed to solve the problem; a variant of the experiment is mentally developed to confirm (or refute) the hypothesis; equipment is installed and an experiment is carried out; observations, necessary measurements, calculations are made; conclusions are drawn to solve the original problem; if necessary, additional experiments are carried out.

The division of the methods of combining words and experience into illustrative and exploratory ones does not mean that the teacher does not say a word during the experiment. In any case, the teacher should explain the course of the experiment and direct the attention of students to the most significant process at the moment.

As a rule, demonstration experiments should not be lengthy. If it is not possible to choose an experience that is short in time, then it is best to demonstrate to students in the lesson several intermediate stages of the experiment and its final result.

Pauses arising while waiting for the result of the experiment should be used to organize a dialogue with schoolchildren, clarify the conditions for the experiment and the signs of chemical reactions.

Of great educational and upbringing importance is the experiment conducted by the students themselves (laboratory experiments, practical exercises, etc.), which also has a number of features. Compared with the teacher's demonstration experiment, it must be, of course, safe and feasible for each student to perform; to promote the development of skills and abilities in laboratory work techniques, accuracy, discretion and careful attitude to materials and equipment; Encourage students to be creative in problem solving.

Laboratory experiments are carried out during the teacher's explanation according to his oral instructions. In this case, the algorithm is most often used: "Add A to substance (solution) B; observe carefully ...; write down your observations and reaction equations." The volumes of reagents used should be minimal so that only the planned reactions are carried out and the corresponding signs are clearly manifested for a sufficient time for the students to notice and fix them in memory.

There are two types of practical work (classes): conducted according to instructions and experimental tasks.

The instruction is an indicative basis for the activities of students. It should describe in detail in writing each stage of the experiments, give instructions on how to avoid possible erroneous actions, safety instructions for this work.

Before the students perform practical work according to the instructions, the teacher needs to clearly and briefly show them the necessary laboratory techniques and manipulations. This can be done in the process of preliminary preparation for practical work.

Experimental tasks do not contain instructions, but only a condition. Students must independently develop a solution plan and put it into practice, thereby obtaining a certain material result.

Before conducting a practical lesson, it is necessary to familiarize students with the designs of devices, methods of laboratory equipment, analyze the goals and content of the work and link this with homework on the analysis of instructions.

At the practical lesson at the beginning of the lesson, there should be a brief conversation about safety rules and the key points of work. On the demonstration table, you need to place assembled all the devices used in the work. Students are required to complete their work accordingly.

The requirements for conducting entertaining experiments and a field experiment and the methodology for their implementation follow from the recommendations described above.

Significant problems in the organization of educational chemical experiments are compliance with safety regulations when performing experiments, cleaning the workplace, washing dishes and disposing of used reagents.

2.3. Unification of the educational experiment

Under the unification of a chemical experiment in education, we mean a rational reduction in the types of instruments and installations with which experiments are carried out. In the proposed device (sometimes with additions or changes), it is possible to successfully carry out various chemical reactions, both during demonstration experiments and during a student experiment.

The basis of the device is a flask or flask with a capacity of 50-200 ml, a stopper with a separating funnel (respectively, a flask) of 25-100 ml, the device must have a gas outlet tube. A variety of modifications of the unified device are possible (using Wurtz, Bunsen flasks, etc.) (Fig. 2).

Rice. 2. Some modifications of the unified device.

The use of this installation ensures the safety of chemical experiments, since the release of gaseous and volatile toxic substances can be quantitatively controlled and sent either directly for reactions involving these gases, or for trapping by absorption devices.

Another advantage of this device is the ability to quickly and accurately dose the initial substances used for the experiment. Substances and solutions are placed in flasks and separating funnels in advance, before the start of classes, in the required amount, and not by eye, as is usually the case when demonstrating experiments in test tubes or glasses, when substances and solutions are collected directly in the lesson during the demonstration of experiments.

When using the device, the perception of experience is achieved by all students, and not only by those who sit at the first desks, as is the case when conducting experiments in test tubes. The recommended device allows you to carry out qualitative and quantitative experiments in chemistry at school, as well as in secondary specialized and higher educational institutions. Let us illustrate the fundamental application of the device on the example of some experiments, grouping them according to similar features.

Getting gases. The production of most gases studied at school is based on heterogeneous reactions between solid and liquid phases. The solid phase is placed in a flask, which is closed with a stopper with a funnel and a gas outlet tube. An appropriate solution or liquid reaction reagent is poured into the funnel, the addition of which to the flask is dosed using a separating funnel tap. If necessary, the flask with the reaction mixture is heated, adjusting the volume of the evolved gas and the reaction rate.

Using the device and appropriate reagents, it is possible to obtain oxygen, ozone, chlorine, hydrogen, carbon dioxide, carbon monoxide and sulfur dioxide, hydrogen halides, nitrogen and its oxides, nitric acid from nitrates, ethylene, acetylene, bromoethane, acetic acid from acetates, acetic anhydride, complex ethers and many other gaseous and volatile substances.

Naturally, at the same time when receiving gases with the help of the device, it is possible to demonstrate their physical and chemical properties.

Reactions between solutions. It is convenient to carry out experiments in this device, in which the addition of a liquid reagent must be carried out in small portions or dropwise, when the course of the reaction is affected by an excess or deficiency of one of the starting substances, etc., for example:

Dissolution of sulfuric acid in water and compliance with safety rules during this operation;

Experiments illustrating the diffusion of substances in liquids or gases;

Determination of the relative density of mutually insoluble liquids and the formation of emulsions;

Dissolution of solids, the phenomenon of flotation and the formation of suspensions;

Salt hydrolysis reactions, if it is important to show the change in the degree of hydrolysis depending on the volume of water added to the salt solution;

Experiments illustrating the color of indicators in various media and neutralization reactions;

Reactions between electrolyte solutions;

Reactions, long in time;

Reactions of organic substances (bromination and nitration of benzene, oxidation of toluene, production of soap and aniline, hydrolysis of carbohydrates).

Demonstration of the characteristic properties of the studied substance. With the help of the device, it is possible to demonstrate consistently and clearly, with a minimum expenditure of time, the characteristic physical and chemical properties of the substance under study. At the same time, reagents are saved, the necessary safety of the experiment is achieved (the emitted harmful gases and volatile substances are captured by the appropriate absorption solutions), and a better perception of the experiment by all students of the class is ensured.

Consider the preparation and conduct of an experiment in demonstrating the properties of hydrochloric acid. Before the lesson, the teacher prepares the required number of flasks (according to the number of reactions studied) and one stopper with a separating funnel and a gas outlet tube in it. Substances or solutions (zinc, copper, copper (II) oxide, copper (II) hydroxide, sodium hydroxide solution with phenolphthalein, sodium carbonate, silver nitrate solution, etc.) are placed in the flasks in advance. About 30 ml of a solution (10-20%) of hydrochloric acid is poured into a separating funnel. During the lesson, the teacher only needs to rearrange the cork with a separating funnel filled with acid from one flask to another, spending 3-5 ml of solution for each reaction.

If toxic volatile compounds are formed during the reactions, then the gas outlet tube of the device is lowered into the appropriate solutions to absorb these substances, and the reaction mixture in the flask is neutralized after the end of the experiment.

Solubility of gases in water. Let us consider the demonstration experiment of the solubility of gases in water using the example of sulfur oxide (IV). Two devices are required for the experiment. In the first device (in the flask - sodium sulfite, in the separating funnel - a concentrated solution of sulfuric acid), sulfur oxide (IV) is obtained, which is collected in the flask of the second device by the method of air displacement. After filling this flask with gas, water is poured into the funnel, the gas outlet tube is lowered into a glass of water, tinted with purple litmus or another indicator (Fig. 3).

Rice. 3. Demonstration of the solubility of gases.

If we now open the clamp or valve of the gas outlet tube, then due to the small contact surface (through the inner opening of the tube) of sulfur oxide (IV) and water, a noticeable dissolution of the gas with subsequent fountaining of liquid into the flask does not occur immediately, but after a rather long period of time, until the flask will not create sufficient vacuum.

To speed up this process, 1-2 ml of water is poured from the funnel into the flask (with the clamp on the gas outlet tube closed) and shaken gently.

This volume of water is quite enough for the pressure in the flask to decrease, and the water tinted with the indicator, when the clamp is removed from the gas outlet tube, rushes into the flask with a fountain, changing the color of the indicator. To enhance the effect, the flask can be turned upside down, having previously closed the separating funnel with a stopper and without removing the gas outlet tube from the glass of water.

Discoloration of dyes. About 0.5 g of potassium permanganate is placed in the flask of the device. Two needles are injected into the lower part of the cork, on which a piece of dyed fabric or a strip of litmus paper is pricked. One of the samples is moistened with water, the second is left dry. The flask is closed with a stopper, a few milliliters of concentrated hydrochloric acid are poured into the separating funnel, the gas outlet tube is lowered into a solution of sodium thiosulfate to absorb the excess of released chlorine (Fig. 4).

During the demonstration of the experiment, the faucet of the separating funnel is slightly opened and the acid is poured dropwise into the flask, then the faucet is closed again. In the flask, a reaction takes place between substances with the release of chlorine, a wet cloth or a strip of litmus paper discolors quickly, and a dry sample - later, as it is moistened.

Rice. 4. Demonstration of discoloration of dyes.

Note. Many fabrics are dyed with chlorine- and other bleach-resistant dyes, so pre-testing and pre-selecting appropriate fabric samples is essential. In the same way, the discoloration of dyes by sulfur dioxide can be shown.

Adsorption properties of coal or silica gel. About 0.5 g of powder or shavings of copper is placed in the flask. A piece of metal wire with a bent end is injected into the lower part of the plug, to which a small mesh is attached to hold the activated sorbent weighing 5–15 g (Fig. 5).

Rice. 5. Installation for demonstrating gas adsorption.

The flask of the device is closed with a stopper prepared in this way, and nitric acid is poured into the funnel. A gas outlet tube equipped with a clamp (the clamp is open before the start of the experiment), dropped into a glass with colored water. After assembly, the device is checked for leaks. At the time of the demonstration of the experiment, the faucet of the separating funnel is slightly opened and a few drops are poured out acid into a flask in which a reaction occurs with the release of nitric oxide (IV). Do not add an excess of acid, it is necessary that the volume of the released gas corresponds to the volume of the flask.

After the end of the reaction, which is determined by the cessation of the release of bubbles of air displaced from the flask through the gas outlet tube, the clamp on it is closed. The device is installed in front of a white screen. The adsorption of nitric oxide (IV) in the flask is judged by the disappearance of the color of the gas. In addition, due to the formation of a certain vacuum in the flask, liquid from the glass is sucked into it if the clamp is opened on the gas outlet tube.

Experiments on the study of the electrical conductivity of substances and solutions. If we pass two additional metal or, better, two graphite rods (electrodes) through the stopper of the device, the lower ends of which almost touch the bottom of the flask, and connect them through a light bulb or galvanometer to a current source, we will get an installation for determining the electrical conductivity of solutions of substances and studying the provisions of the theory of electrolytic dissociation (Fig. 6).

Rice. 6. Device for determining the electrical conductivity of solutions.

Quantitative experiments based on reactions occurring with the release of gases. If you bring the gas outlet tube of the device under a graduated cylinder with water installed in a crystallizer with water, and collect the gas released during the reaction by displacing water, then by the volume of the resulting gas, you can carry out quantitative calculations to establish the molar masses of substances, confirm the laws of chemical kinetics and thermochemistry, determining the formula of ethanol and other substances, etc. (Fig. 7). If the gas released during the reaction dissolves or reacts with water, then other liquids and solutions must be used in the experiments. The given examples do not exhaust all the possibilities of the proposed unified device in the educational chemical experiment. If you have in stock plugs with two gas outlet tubes or with two separating funnels, as well as other installation options, then the number of experiments using a unified device can be significantly increased, which will contribute to the scientific organization of labor

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Methodology for the use of electronic publications in extracurricular work in chemistry content

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... certain publisher. All presented principles classification allow to take into account individual characteristics of electronic means educational... parts chemistry, under profile learning in rural school(article). For chemicalexperiment ...

There are the following types of school chemical experiment: demonstration experiment, laboratory experiment, laboratory work, practical work, laboratory workshop and home experiment.

By the nature of the impact on the thinking of students, the methods of organizing a school chemical experiment can be carried out in a research and illustrative form.

The illustrative method is sometimes called the method of ready-made knowledge: the teacher first reports what should be the result of the experiment, and then illustrates what was said with a demonstration, or the material being studied is confirmed by conducting a laboratory experiment.

A research method is called a method, as a result of which students are invited to select reagents and equipment for conducting an experiment, predict the result, highlight the main thing in observations and draw a conclusion on their own. The teacher conducts the experiment, as it were, under the guidance of students, performing the proposed experimental actions, comments on the safety rules for conducting the experiment, and asks clarifying questions.

At the first stage of studying chemistry, the illustrative method of conducting demonstration experiments is more effective than the research one. In this case, students experience less difficulty in the subsequent description of observations, the formulation of conclusions. However, the use of the illustrative method should not be limited to a competent teacher's commentary. Students will have more solid knowledge gained as a result of a heuristic conversation built by the teacher during the demonstration. As the readiness of schoolchildren for independent observation in the process of studying chemistry grows, it is possible to increase the share of the research method in conducting demonstrations. The correct choice of the form of organization of the experiment is an indicator of the pedagogical skill of the teacher.

A school chemistry experiment can be divided into a demonstration experiment, when the teacher shows the experiment, and a student experiment, performed by students.

The most common and difficult in teaching is to conduct demonstration experiments in which objects and processes are observed.

A demonstration experiment is an experiment that a teacher, laboratory assistant, or sometimes one of the students conducts in the classroom. The teacher uses this experiment at the beginning of the course in order to teach students to observe processes, work methods, and manipulations. This arouses students' interest in the subject, begins to form their practical skills, introduces them to chemical glassware, instruments, substances, etc. Then a demonstration experiment is used when it is too complicated for students to perform on their own.

The school uses a demonstration experiment of two types:

Demonstrations, when the student observes the objects of demonstrations directly. In this case, substances are shown and various chemical operations are carried out with them, for example, heating, burning, or experiments are demonstrated in large vessels - glasses, flasks, etc.

2. Indirect demonstrations are used in cases where the ongoing processes are little noticeable or poorly perceived by the senses. In these cases, chemical processes are reproduced using various devices. Thus, poorly visible chemical reactions are projected onto a screen using a graph projector, electrolytic dissociation processes are detected using probes, and the density of solutions is determined using hydrometers.

One should skillfully use these two types of demonstrations, not exaggerate the significance of one of them, for example, it is impossible to show all experiments only by projecting onto a screen, since in this case students will not directly see the substances and ongoing processes. Therefore, they will not acquire specific ideas about them. Sometimes it turns out to be appropriate to use a combined technique involving direct and indirect demonstrations, when clearly visible operations are shown in glassware, and individual, poorly visible details are projected onto a screen. Or, in an indirect demonstration, taken and received substances are put on the demonstration table (or tables of students), and the processes between them are projected onto the screen.

The didactic effect of demonstration experiments depends on such factors as the technique of conducting the experiment and the creation of optimal conditions for visualization of what the teacher wants to show and prove, i.e. achieving the goal of the experiment.

Demonstration requirements:

the safety of the experiment;

observance of the condition of a certain distance from the objects of observation to the observer, lighting conditions, volumes of substances, sizes and shapes of dishes, appliances;

a combination of a demonstration of experience with a teacher's commentary.

The last requirement plays a major role in the demonstration, when the teacher directs the observation of the experiment through commentary. Conducting an experiment by a teacher can be carried out both by a purely illustrative method, and by a partially research method.

Thus, in the process of demonstration, three functions of the educational process are carried out: educational, educational and developing. Demonstration experience allows students to form the basic theoretical concepts of chemistry, provides a visual perception of chemical phenomena and specific substances, develops logical thinking, and reveals the practical significance of chemistry. With its help, students are posed cognitive problems, put forward hypotheses that can be tested experimentally. It contributes to the consolidation and further application of the studied material.

A student experiment is a type of independent work. It not only enriches students with new knowledge, concepts, skills, but also proves the truth of the knowledge they have acquired, which provides a deeper understanding and assimilation of the material. It allows you to more fully implement the principle of polytechnics - connection with life, with practical activities.

The student experiment is divided into two types: 1) laboratory experiments conducted by students in the process of acquiring new knowledge; 2) practical work that students do after passing one or two topics.

Laboratory experiments are educational and developmental in nature and their role in the study of chemistry is the most important.

The purpose of laboratory experiments is the acquisition of new knowledge, the study of new material. In them, methods of action are initially worked out, while students usually work in pairs.

Practical classes, as a rule, are carried out at the end of the study of the topic in order to consolidate, concretize knowledge, form practical skills and improve the existing skills of students. In practical classes, they conduct experiments on their own, using the instructions, more often individually.

Conducting practical work allows students to apply the acquired knowledge and skills in independent work, draw conclusions and generalizations, and the teacher - to assess the level of knowledge and skills of students. Practical work is a kind of result, the final stage in the study of topics and sections.

For practical work, students must prepare and independently think through the experiment. In many cases, practical work is carried out in the form of an experimental problem solving, in high school - in the form of a workshop, when after passing through a number of topics, practical work is carried out in several lessons. A skillfully used chemical experiment is of great importance not only for achieving the set educational and upbringing tasks in teaching chemistry, but also for developing the cognitive interests of students. If the teacher is fluent in a chemical experiment and applies it to students to acquire knowledge and skills, then students study chemistry with interest. In the absence of a chemical experiment in chemistry lessons, students' knowledge of chemistry can acquire a formal shade - interest in the subject drops sharply.

A student experiment from the point of view of the learning process should go through the following stages: 1) understanding the purpose of the experiment; 2) study of the proposed substances; 3) assembly or use of the finished device; 4) performance of experience; 5) analysis of results and conclusions; 6) explanation of the results obtained and the use of chemical equations; 7) drawing up a report.

Each student must understand why he is doing the experiment and how to solve the problem assigned to him. He studies substances organoleptically or with the help of devices and indicators, examines the details of the device or the entire device. Performing the experiment, the student masters the techniques and manipulations, observes and notices the features of the process, distinguishes important changes from insignificant ones. Having done the experiment, he must draw up a report.

In practical classes, much attention is paid to the development of practical skills, since their foundations are laid from the very first stages of studying chemistry, and in subsequent classes they are developed and improved.

Practical exercises are of two types: conducted according to the instructions and experimental tasks.

Instruction is an indicative basis for the activities of students. It details each stage of the experiments, gives instructions on how to avoid erroneous actions, and contains information on safety measures when performing work. Instructions for laboratory experiments and practical tasks should be clear and consistent. However, when performing work, one written instruction is not enough, the teacher needs to competently and clearly show laboratory techniques and manipulations in the process of preliminary preparation of students for practical work.

Experimental tasks do not contain instructions, but only include conditions. Students must develop a solution plan and implement it on their own.

Preparation for practical exercises is of a general nature. At the same time, the material studied in different sections of the topic is used, and practical skills are also formed. In previous lessons, the teacher used the devices that students will use in the practical lesson, the conditions and features of the experiment were considered, etc.

At the beginning of the practical session, it is necessary to conduct a brief conversation about safety rules and the key points of work. All devices used in the work are placed on the demonstration table in assembled form.

A practical lesson devoted to solving experimental problems is a kind of control work, so it is carried out a little differently than a practical lesson according to the instructions.

Preparation of students for solving experimental problems can be carried out in stages.

1. First, the whole class solves the problem theoretically. To do this, it is necessary to analyze the condition of the problem, formulate questions that need to be answered in order to obtain the final result, and offer experiments necessary to answer each question.

2. One of the students solves the problem theoretically at the blackboard.

3. The student at the blackboard performs an experiment. After that, the class proceeds to solve similar problems in the workplace.

It is advisable to distribute experimental tasks by options in order to achieve greater independence and activity of students in the process of work.

The experimental solution of chemical problems provides for the independent use of students' skills to conduct chemical experiments to acquire knowledge or confirm assumptions. This ensures the development of their cognitive activity in the process of performing a chemical experiment.

When is a demonstration experiment used in a lesson? At the beginning of the school course - to instill experimental skills and abilities, interest in chemistry, familiarization with utensils, substances, equipment. When it is difficult for students to independently complete. When it is dangerous for students (explosion of hydrogen with oxygen). There is no appropriate equipment and reagents.

V i s s u b s t Simplicity S e c u r i t i o n d e m o n s t r a t i o n about the experiment. Requirements for a demonstration experiment

Methodology for conducting demonstration experiments 1. Setting the goal of the experiment: why this experiment is being carried out, what students should make sure of, what to understand. 2. Description of the device where the experiment is carried out, and the conditions for its implementation. 3. Organization of students' observations: the teacher should guide the students on which part of the device should be observed. 4. Conclusions.

Stages of a student experiment 1) understanding the purpose of the experiment; 2) the study of substances; 3) installation of the device (where necessary); 4) performance of experience; 5) analysis of the results; 6) explanation of the results obtained, writing chemical equations; 7) formulation of conclusions and preparation of a report.

Functions of a chemical experiment The heuristic function is manifested in the establishment of new a) facts; b) concepts and c) regularities. The corrective function is manifested in overcoming the difficulties of mastering theoretical material and correcting students' mistakes. The generalizing function makes it possible to develop prerequisites for constructing various types of empirical generalizations. Research function
14 REFERENCES 1. Zlotnikov E.G. On the content of the concept of "educational chemical experiment" in the system of intensive education. In: Improving the content and methods of teaching chemistry in secondary school. Leningrad: LGPI im. A.I. Herzen, Surin Yu.V. Methodology for conducting problem experiments in chemistry. Development experiment. Moscow: School-Press, 1998

graduate work

§2.1 School chemical experiment: types, requirements, technique

Methods of chemical experiment in high school.

Types of chemical experiment

A chemical experiment is essential in the study of chemistry. A distinction is made between an educational demonstration experiment, performed mainly by a teacher on a demonstration table, and a student experiment - practical work, laboratory experiments and experimental tasks that students carry out at their workplaces. A thought experiment is a kind of experiment.

A demonstration experiment is carried out mainly when presenting new material to create concrete ideas about substances, chemical phenomena and processes in schoolchildren, and then to form chemical concepts. It allows for a short period of time to make clear important conclusions or generalizations from the field of chemistry, to teach how to perform laboratory experiments and individual techniques and operations. The attention of students is directed to the implementation of the experiment and the study of its results. They will not passively observe the conduct of experiments and perceive the material presented if the teacher, demonstrating the experience, accompanies it with explanations. Thus, he focuses attention on experience, accustoms to observe the phenomenon in all its details. In this case, all the techniques and actions of the teacher are perceived not as magical manipulations, but as a necessity, without which it is almost impossible to complete the experiment. In demonstration experiments, in comparison with laboratory observations of phenomena are more organized. But the demonstrations do not develop the necessary experimental skills and abilities, so they must be supplemented by laboratory experiments, practical work and experimental tasks.

A demonstration experiment is carried out in the following cases:

It is impossible to provide the necessary amount of equipment at the disposal of students;

The experience is complex, it cannot be carried out by schoolchildren themselves;

Students do not have the necessary equipment to conduct this experiment;

Experiments with a small amount of substances or on a small scale do not give the desired result;

Experiments are dangerous (work with alkali metals, using high voltage electric current, etc.);

It is necessary to increase the pace of work in the classroom.

Naturally, each demonstration experience has its own characteristics, depending on the nature of the phenomenon being studied and the specific educational task. At the same time, the chemical demonstration experiment must meet the following requirements:

Be visual (everything that is done on the demonstration table should be clearly visible to all students);

Be simple in technique and easy to understand;

Pass successfully, without disruption;

To be prepared in advance by the teacher so that the children can easily perceive its content;

Be safe.

The pedagogical effectiveness of a demonstration experiment, its influence on knowledge and experimental skills and abilities depend on the technique of the experiment. This is understood as a set of instruments and devices specially created and used in a demonstration experiment. The teacher should study the equipment of the classroom as a whole and each device separately, work out the demonstration technique. The latter is a set of techniques for handling instruments and apparatus in the process of preparing and conducting demonstrations, which ensure their success and expressiveness. Demonstration technique - a set of techniques that ensure the effectiveness of the demonstration, its best perception. The methodology and technique of demonstration are closely related and can be called the technology of a demonstration experiment.

When conducting demonstration experiments, it is very important to check each experiment in terms of technique, quality of reagents, good visibility by students of the instruments and the phenomena occurring in them, and safety guarantees. Sometimes it is advisable to put two devices on a demonstration table: one is assembled and ready for action, the other is disassembled in order to better explain the device device, for example, a Kipp apparatus, a refrigerator, etc.

It must always be remembered that any experiment that fails during the demonstration undermines the authority of the teacher.

Laboratory experiments are a type of independent work that involves performing chemical experiments at any stage of the lesson for more productive assimilation of the material and obtaining specific, conscious and solid knowledge. In addition, during laboratory experiments, experimental skills and abilities are improved, since students work mostly independently. Performing experiments does not take up the entire lesson, but only part of it.

Laboratory experiments are carried out most often to get acquainted with the physical and chemical properties of substances, as well as to specify theoretical concepts or provisions, less often to gain new knowledge. The latter always contain a specific cognitive task that students must solve experimentally. This introduces an element of research that activates the mental activity of schoolchildren.
Laboratory experiments, unlike practical work, introduce a small number of facts. In addition, they do not fully capture the attention of students, like practical exercises, because after a short time of independent work (experiment), students should be ready to accept the teacher's explanation again.

Laboratory experiments accompany the presentation of educational material by the teacher and, like demonstrations, create visual representations of the properties of substances and chemical processes in students, teach them to generalize the observed phenomena. But unlike demonstration experiments, they also develop experimental skills and abilities. However, not every experiment can be carried out as a laboratory one (for example, the synthesis of ammonia, etc.). And not every laboratory experiment is more effective than a demonstration one - many laboratory experiments require more time, and the duration directly depends on the quality of the formed experimental skills and abilities. The task of laboratory experiments is to introduce students to the particular phenomenon (substance) being studied as soon as possible. The technique used in this case is reduced to the performance of 2-3 operations by students, which naturally limits the possibilities for the formation of practical skills and abilities.

The preparation of laboratory experiments should be carried out more carefully than demonstration ones. This is due to the fact that any negligence and omission can lead to a violation of the discipline of the entire class.

It is necessary to strive to ensure that laboratory work is performed by each student individually. In extreme cases, one set of equipment can be allowed for no more than two. This contributes to better organization and activity of children, as well as the achievement of the goal of laboratory work.

After the experiments are completed, they should be analyzed and a brief record of the work done should be made.

Practical work is a type of independent work when students perform chemical experiments at a certain lesson after studying a topic or section of a chemistry course. It helps to consolidate the acquired knowledge and develop the ability to apply this knowledge, as well as the formation and improvement of experimental skills and abilities.

Practical work requires more independence from students than laboratory experiments. This is due to the fact that the children are invited to get acquainted with the content of the work and the order of their implementation at home, to repeat the theoretical material that is directly related to the work. The student performs practical work independently, which helps to increase discipline, composure and responsibility. And only in some cases, with a lack of equipment, can work be allowed in groups of two people, but preferably no more.

The role of the teacher in practical work is to monitor the correct implementation of experiments and safety rules, to keep order on the desktop, to provide individually differentiated assistance.

During practical work, students write down the results of experiments, and at the end of the lesson they draw the appropriate conclusions and generalizations.

Methodology for a demonstration experiment in organic chemistry [Tsvetkov L.A., 2000]

The characteristic features of a demonstration experiment in organic chemistry are as follows:

Experiment in the teaching of organic chemistry is to a large extent a means of "questioning nature", i.e. a means of experimental study of the issues being studied, and not just an illustration of information about substances reported by the teacher. This is determined both by the peculiarities of the subject itself and by the fact that organic chemistry is already studied on the basis of significant chemical training of students.

The most significant demonstration experiments in most cases turn out to be longer in time than experiments in inorganic chemistry. Sometimes they take almost a whole lesson, and in some cases they do not fit into the framework of a 45-minute lesson.

Demonstration experiments in a number of cases are less visual and expressive than in the course of inorganic chemistry, since there are few external changes in the observed processes, and the resulting substances often do not have sharp differences in properties from the starting materials.

In organic chemistry experiments, the reaction conditions are of great importance: even a slight change in these conditions can lead to a change in the direction of the reaction and the production of completely different substances.

When setting up experiments in organic chemistry, there is a significant danger of insufficient comprehension by students. This is due to the fact that experiments often take a long time, and sometimes several demonstrations are staged in parallel, which forces students to distribute their attention simultaneously to several objects. In addition, the path from phenomenon to essence is often more difficult here than in the study of inorganic chemistry.

Due to the fact that a significant number of important chemical processes cannot be demonstrated in school conditions, it is inevitable that students become familiar with a number of facts without demonstrating experiments, according to the teacher's story, according to diagrams, drawings, etc.

Let us consider in this sequence what methodological conclusions follow from this.

1. The experiment of organic chemistry provides very grateful material for the mental development of students and the education of creative abilities to solve the problems put forward. If we want to use these opportunities, the experiments demonstrated cannot be reduced to a visual illustration of the words of the teacher. Such teaching is hardly capable of awakening the independent thought of students. The experiment is especially valuable as a means of studying nature, and since it is a source of knowledge, it develops the observation of students and stimulates their mental activity, and also makes them compare and analyze facts, create hypotheses and find ways to test them, be able to come to the right conclusions and generalizations. From this point of view, experiments showing the genetic connection between classes of organic substances are of great importance; experiments that test assumptions about the properties of substances and methods for their preparation based on the theory of structure; experiments leading to a conclusion about a particular structure of a molecule of a substance.

In order for demonstration experiments to give proper results, it is necessary to strive to fulfill the following conditions: a) clearly state the problem that requires an experimental solution, and develop with students the main idea of ​​\u200b\u200bthe experiment; the purpose and idea of ​​the experiment, students must learn before the experiment and be guided by them during the experiment; b) students must be prepared for the experiment, i.e. must have the necessary stock of knowledge and ideas for correct observation and further discussion of experience; c) students should know the purpose of the individual parts of the device, the properties of the substances used, what to observe during the experiment, by what signs one can judge the process and the appearance of new substances; d) a chain of reasoning must be correctly built on the material of experience, and students must come to the necessary conclusions on the basis of experiments themselves under the guidance of a teacher.

It is especially important to ensure the conscious and active participation of students in the conduct of the experiment and the discussion of its results. This can be achieved by a system of questions that the teacher poses in connection with the experiment, for example: “What do we want to learn with the help of this experiment?”, “What substances should we take for the experiment?”, “Why do we use this or that part in the device? "," What did you observe in this experiment? "," By what signs can we judge that a chemical reaction was going on? How, on the basis of this experience, can one or another conclusion be drawn?", "Is it possible to draw such and such a conclusion?" etc. Such a technique of a chemical experiment teaches students to observe correctly, cultivates steady attention, strictness of judgment, contributes to the firm consolidation of correct ideas, and develops interest in the subject.

2. Experiments in organic chemistry require great methodical thoroughness in view of their length in time. Of the experiments recommended by the program and textbooks, more than 60% are "long-term", requiring from 10 minutes to 1 hour, and in some cases more. Among such experiments are the following: fractional distillation of oil, production of bromobenzene, fermentation of glucose, production of bromoethane, nitration of fiber, synthesis of nitrobenzene and aniline, production of acetaldehyde from acetylene, polymerization of methyl methacrylate or another monomer, quantitative experiments in connection with the proof of structural formulas, etc.

Some teachers try to avoid lengthy experiments, being afraid to delay the pace of the course, while others make significant methodological inaccuracies in staging such experiments, while others, on the contrary, highly appreciate these experiments, which are characteristic of organic chemistry, and do not deviate from the experiment they have begun. At the same time, the lesson drags on tediously in anticipation of the result of the experiment, i.e. there is a wasteful waste of time, and the pedagogical value of the lesson again turns out to be low.

How to build a lesson using a long experiment? Where possible, one should strive primarily to reduce the time for conducting the experiment. This can be achieved in various ways. Sometimes it is possible to confine ourselves to obtaining a small amount of a substance, sufficient only for its recognition, or not to extract the product in its pure form, if it can be identified with conviction as a result of the reaction. It can be recommended to preheat the reaction mixture or reasonably reduce the amount of starting materials.

The following methods also give a significant reduction in time. Having put this or that experiment, you can not wait for it to end in this lesson, but, having noted the beginning of the reaction, show the finished products in order to present the substances obtained in the experiment started in the next lesson, or, having started the experiment in the lesson, use the same experience prepared in advance, where the reaction has already largely passed, and here in the lesson to put the extraction of the resulting substances. Such an organization of experiments will not mean a departure from visualization into dogmatism, since the main stages of the process are preserved here and find the necessary explanation. Students see the slowness of the process and with full confidence relate to the demonstration of the final stage of the experience. Experiments are carried out with special care, which cannot be shortened in time by the methods indicated above. Here is one of the possible options for the methodological design of such experiments. The class discusses the structure of ethyl alcohol. The students are asked the question: "What reaction can confirm the presence of a hydroxyl group in an alcohol molecule?" By leading questions about which hydroxyl-containing substances were studied in inorganic chemistry and with which substances they reacted, the teacher calls on the students to suggest a reaction with hydrochloric or hydrobromic acid. In the case of the presence of a hydroxyl group, one can expect the formation of water and ethyl chloride (bromide) known to students. The initial substances are named, the structure of the device is explained and the corresponding experience is put. A hypothetical reaction equation is drawn up.

During the experiment, the question is posed: "What other reactions can alcohol of the structure we have established?" Students remember getting ethylene. The teacher asks how this experiment was set up in the class, and suggests compiling an equation for the reaction. Next, the teacher asks to summarize the chemical properties of alcohol. The called student indicates the reaction of alcohol with sodium, the reaction for obtaining ethylene, gives the corresponding equations, writes the equation for the reaction with hydrogen bromide, names the resulting product. At this point, the teacher draws the attention of the class to the experience. A significant amount of ethyl bromide has already accumulated in the receiver. The teacher separates it from the water (without rinsing) and carries it around the class. At the same time he asks: "What is the name of this substance and how is it obtained?" In such cases, students must know very well the purpose of the experiment, the initial substances, the direction of the experiment, so that when they return to it after some distraction, they do not have to remember with tension which substances are reacting in a given case and what to expect. Experience must be so firmly established in consciousness that students can refer to it at any time, however, paying their main attention to the issue that is being discussed in the class.

Properly set up, lengthy experiments instill in students the ability to keep several objects in their field of vision at the same time, which is undoubtedly important in further education and in life. In a higher educational institution, already at the first lectures, the ability to distribute attention between listening to a lecture and recording it, between mastering the content of a lecture, recording it and observing the experiments demonstrated is required.

3. Many experiments in organic chemistry lose significantly due to the low visibility of the processes and substances obtained. In fact, when booking benzene, students from a distance do not see either the manifestation of the reaction or the resulting bromobenzene; during the hydrolysis of sucrose, starch, cellulose, neither reaction nor new substances are visible (the presence of which can only be determined indirectly later); upon receipt of ether from a colorless mixture of substances, the same colorless liquid is distilled off; when demonstrating the preparation of esters in the reacting mixture, there are no visible changes for students, etc. If such experiments are not set up correctly, students may not only fail to form the necessary ideas, but false ideas can easily form. Therefore, when observing the separation of liquids, one of them can be tinted so that the dividing line is clearly indicated. In the same way it is possible to color water when collecting gases above water and in experiments involving changes in the volumes of gases. Coloring liquids is acceptable, however, only if the teacher ensures that the students clearly understand the artificiality of this technique. When distilling liquids, the falling of drops into the receiver can be made more visible by means of a backlight, a white or black screen, etc.; it should be sharply emphasized by what properties outwardly similar starting and resulting substances differ, and immediately demonstrate this difference. Where the course of the reaction can be judged by the formation of by-products, the latter should be clearly visible to students (absorption of hydrogen bromide by an alkaline solution of phenolphthalein in the preparation of bromobenzene, etc.).

4. It should be especially noted that for reactions in organic chemistry, the conditions under which they occur are of decisive importance. In inorganic chemistry, these conditions play a lesser role, since many processes already take place under ordinary conditions and proceed almost unambiguously. Observation of chemical reactions without a clear understanding of the conditions of their occurrence adversely affects the quality and strength of knowledge. When the reaction conditions are not clarified enough, students may get the wrong idea that the direction of the reactions is not determined by anything, is completely arbitrary and does not obey any laws. So, for example, shortly after getting acquainted with the production of ethylene from alcohol, students meet with the production of ethyl ether from the same mixture of substances (alcohol and concentrated sulfuric acid). It is completely incomprehensible to them why ether is obtained here, and not ethylene. In order to explain this, and thus prevent distrust of science, we have to return to the experiment with ethylene and now give the conditions for its preparation. If these conditions were emphasized in a timely manner, it would be possible to compare the conditions for the formation of the ether with them, and in this comparison, knowledge would be more firmly consolidated. Therefore, when demonstrating experiments, one should pay attention to the conditions for the course of the reaction and then demand that these conditions be indicated in the experiments of students. This approach organizes the observation of students in the process of experimentation, gives the right direction to the study of material from the book, and helps to consolidate specific ideas about phenomena in memory. This helps, and check the quality of assimilation of the material by students. Constant emphasizing the conditions of the experiment, showing on some examples the negative results of non-compliance with the conditions of the experiment, recognizing the answer as inferior when the reaction equation is given without describing the phenomenon itself - all these techniques help the correct study of chemistry. Even in performing exercises and solving problems, whenever possible and appropriate, one should indicate the conditions under which the corresponding process occurs.

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LECTURE PLAN 1. Types of experiment and methods of its use. 2. Functions of a chemical experiment. 3. Problem experiment.

1. Types of experiment and methods of its use. demonstration student laboratory experiments practical exercises home experiments

When is a demonstration experiment used in a lesson? At the beginning of the school course - to instill experimental skills, interest in chemistry, familiarization with utensils, substances, equipment. When it is difficult for students to independently complete. When it is dangerous for students. There is no appropriate equipment and reagents.

REQUIREMENTS FOR THE DEMONSTRATION EXPERIMENT 1. Visibility - a large amount of reagents and utensils, visible from the last rows, there should be no extra details on the table. 2. Simplicity - there should not be a pile of unnecessary details in the devices. 3. Safety - a chemistry teacher is responsible for the lives of students. 4. Reliability - A failed experience causes frustration among students. 5. The technique of performing the experiment must be impeccable. 6. The need to explain the demonstration experiment.

METHODOLOGY OF DEMONSTRATION EXPERIMENTS 1. Setting the purpose of the experiment: why this experiment is being carried out, what students should make sure of, what to understand. 2. Description of the device where the experiment is carried out, and the conditions for its implementation. 3. Organization of students' observations: the teacher should guide the students on which part of the device should be observed. 4. Conclusions.

TOPIC "OXYGEN" sequence of demonstrations: combustion of coal combustion of sulfur combustion of phosphorus combustion of iron When selecting experiments, it is necessary to optimally and harmoniously include them in the outline of the lesson.

STAGES OF PERFORMANCE understanding the purpose of the experiment studying substances installing the device performing the experiment analyzing the results explaining the results obtained writing chemical equations formulating conclusions writing a report

RECORDING SHEET Content of the operation Evaluation of the performance of the operation Ivanov Take a bottle with a solution of sulfuric acid so that the label is under the palm of your hand Pour 20 ml of a solution of sulfuric acid into a glass Remove a drop of acid from the neck of the bottle Assemble the tripod correctly and place a glass of sulfuric acid on the grid Place an alcohol burner under grid so that the top of the flame touches the grid Cleanliness of the workplace Compliance with safety regulations Petrov Sidorov Dmitriev

HOME CHEMICAL EXPERIMENT - one of the types of independent work of students The reagents used must be safe and purchased at hardware stores or pharmacies.

THE EXPERIMENT MAKES THOUGHTS ON A NUMBER OF QUESTIONS: 1) What is the cause of the observed phenomenon? 2) Why does the addition of nitric acid affect the evolution of hydrogen from a hydrochloric acid solution? 3) Why does hydrogen evolution resume after a certain time?

WORKING HYPOTHESIS Hydrogen released from hydrochloric acid is used to reduce nitric acid. HNO 3 + 8 H \u003d NH 3 + ZH 2 O NH 3 + HCl \u003d NH 4 Cl 4 Zn + 10 HNO 3 \u003d 4 Zn (NO 3) 2 + NH 4 NO 3 + 3 H 2 O Conclusion: hydrogen is consumed for reduction nitric acid.

SCHEME OF RESEARCH OF THE PROPERTIES OF SUBSTANCES - actualization of knowledge; - setting research goals; - carrying out theoretical analysis; - building a hypothesis; - drawing up a plan for experimental testing of the hypothesis; - execution of the experiment; - discussion of the results and formulation of conclusions.

EXAMPLES OF PARADOXICAL EXPERIMENTS A weak acid displaces a strong one from its salt. Reagents. Boric acid, sodium chloride, universal indicator or blue litmus paper. Explanation of experience. 2 Na. Cl + 4 H 3 BO 3 \u003d Na 2 B 4 O 7 + 5 H 2 O + 2 HCl

THERMODYNAMIC CALCULATIONS CHANGING THE ENTHALPY OF A CHEMICAL REACTION ∆Н°(p-tion) 2 Na. Cl + 4 H 3 BO 3 \u003d Na 2 B 4 O 7 + 5 H 2 O + 2 HCl ∆H ° 298 -410 k. J / mol -1087, 6 -3290 -241, 84 -92, 3 ACCORDING TO THE CONSEQUENCE FROM HESS'S LAW: ∆Н (r-tion) = ∑∆Н (prod. r-tion) - ∑ ∆Н (ref. in-in) ∆Н ° (r-tion) = [(-3290) + (-241 , 84 5) + (-92, 3 2)] - [(-1087, 6 4) + (-410 2)] \u003d \u003d 486.6 k. J.

CHANGES IN THE ENTROPY OF THE CHEMICAL REACTION ∆S°(p-tion) 2 Na. Cl + 4 H 3 BO 3 \u003d Na 2 B 4 O 7 + 5 H 2 O + 2 HCl ∆S ° 298 72.36 (w / (mol K) 89. 49 189. 5 188. 74 186. 7 ∆S ° (r-tion) \u003d ∑∆S (prod. r-tion) - ∑∆S (original in-in) ∆S ° (r-tion) \u003d (189, 5 + 188, 74 -5 + 186, 7 -2) - - (72, 36 2 + 89, 49 4) = 1003. 9 J/K = =1 k. 6 - 298 1 = 188.6 k. J.

TEMPERATURE AT WHICH THE REACTION IS POSSIBLE Т= ∆Н/∆S = 486.6/1 = 486.6 K, or 213.6 °C. CONCLUSION: This chemical reaction proceeds with relatively little heating.

Dissolution of copper in iron(III) chloride solution Reagents. Freshly precipitated copper, 10% iron (III) chloride solution. Explanation of experience. Cu + Fe. Cl 3 = Cu. C 12 + Fe. Cl 2 The iron ion Fe 3+ is an oxidizing agent, the copper atom is a reducing agent.

Src="https://present5.com/presentation/131736652_437384195/image-33.jpg" alt="(!LANG: EMF (E) of the redox element is: E = E(ok-la) - E(in-la ) If E>0, then"> ЭДС (Е) окислительновосстановительного элемента равна: Е = E(ок-ля) - E(в-ля) Если Е>0, то данная реакция возможна. Окислительно-восстановительные потенциалы пар равны: E°(Fe 3+/Fe 2+) = 0, 771 В E°(Cu 2+/Cu°) = 0, 338 В ЭДС = 0, 771 - 0, 338 = 0, 433 В ВЫВОД: Положительное значение ЭДС подтверждает возможность протекания данной реакции в стандартных условиях.!}

Dissolution of copper in ammonia solution Reagents. 15-25% ammonia solution, freshly deposited copper. Explanation of experience. 2 Cu + 8 NH 3 + O 2 + 2 H 2 O = = 22+ + 4 OH-

CALCULATION OF EMF: Cu + 4 NH 3 - 2ē = 22+ E° = - 0.07 V O 2 + 2 H 2 O + 4ē = 4 OH- E° = 0.401 V EMF = 0.401 - (-0 , 07) = 0.408 V CONCLUSION: The positive value of the EMF confirms the possibility of this reaction occurring under standard conditions.

Vanilla is a fragrant additive to confectionery. Vanilla is the name given to the dried fruits, the pods of a tropical plant from the orchid family Vanilla plantifonia.

2. Place a few milliliters of a 3% aqueous solution of vanillin in a test tube and add 1 ml of a 10% sodium hydroxide solution and 2 ml of a 30% hydrogen peroxide solution to it. After some time, the solution will turn pink, since the oxidation produces a colored 3-methoxy-1, 4-dioxobenzene.

3. Since vanillin contains an aldehyde group, it can give a silver mirror reaction. First, prepare a solution of silver ammonia: to 2-3 ml of a 1% solution of silver nitrate, add, shaking, a 5% solution of ammonia until the precipitate formed at first is completely dissolved. Now place 2-3 ml of silver ammonia in a clean, fat-free test tube and add 3 ml of a 3% aqueous solution of vanillin to it. Immerse the test tube in a glass of boiling water, after 10 minutes pour out the contents of the test tube and rinse it with water. On the walls there will be a touch of silver.