TABLE OF CONTENTS
Functions and forms of school chemical experiment
Requirements for educational equipment intended for conducting chemical experiments
Functions of a school chemistry experiment
Forms of school chemical experiment
Requirements for educational equipment for a school chemistry experiment
Setting up demonstration experiments
Equipment for demonstration experiments,
Specialized instruments, apparatus, installation
1. Devices for demonstrating experiments with substances harmful to health without exhaust devices
2. Set for demonstrating experiments in electrochemistry
3. Devices for demonstrating experiments using high voltage electric current
4. Piezoelectric high voltage source
5. Device for demonstrating the dependence of the rate of a chemical reaction on various conditions
6. Devices for the production of haloalkanes and esters
7. Equipment for projecting experiences and objects onto a screen
8. Attachment to a graphic projector for demonstrating quantitative experiments
9. Measuring instruments
10. Electric heating devices
11. Electrical supply kit for the chemistry room KEH-10
Demonstration experiments in standard devices and installations
Synthesis of hydrogen chloride and production of hydrochloric acid
Preparation of sulfur (IV) oxide and its oxidation to sulfur oxide
Ammonia synthesis
Catalytic oxidation of ammonia
Obtaining ammonium nitrate
Interaction of iron with water
Study of the electrochemical voltage series of metals
Metal corrosion and corrosion protection
Catalytic decomposition of hydrogen peroxide
Kerosene cracking
Demonstration experiment in special devices and installation
Illustration of the law of conservation of mass of substances
Determination of oxygen content in air
Liquid distillation
Water synthesis
Diffusion of gases through a porous vessel
Adsorption
Electrolysis of water and aqueous solutions
Determination of electrical conductivity of substances
Observing the movement of ions
Experiments in electrical discharges
Obtaining ozoia
Obtaining nitrogen oxides from air
Decomposition of methane in a spark discharge
Study of thermal phenomena
Dependence of the rate of a chemical reaction on conditions
Experiments with toxic substances
Preparation of halondoalcaps and esters
Quantitative experiments projected on a screen
Technique and methodology of student experiment
Characteristics of equipment for student experiment 103
Laboratory experiments and practical exercises 113
Topic 1. Initial chemical concepts
Practical lesson. For an introduction to laboratory equipment, see Safety rules for working in a chemical laboratory
sweat
Practical lesson. Techniques for handling heaters and heaters
Laboratory work. Consideration of substances' chemical properties
Practical lesson. Cleaning contaminated
Topic 2. Oxygen, oxides, combustion
Practical lesson. Production and properties of oxygen
Topic 3. Hydrogen, oxygen, salts
Laboratory work. Production of hydrogen and study of its properties
Practical lesson. Exchange reaction between copper oxide (11) and sulfuric acid 136
Topic 4. Water, solutions, bases 138
Laboratory experience. Electrolysis plants
Practical lesson. Preparation of a solution with a certain mass fraction of the dissolved substance and a given molar concentration 139
Topic 5. Generalization of information about the most important classes of inorganic compounds 141
Solving experimental problems on the topic: Generalization of information about the most important classes of inorganic compounds
Topic 8. Halogens 142
Laboratory experience. Displacement of halogens by each other from solutions of their compounds
Practical lesson. Preparation of hydrochloric acid and experiments with it 143 Practical lesson. Solving experimental problems on the topic “Halogens” 146
Topic 1. Electrolytic dissociation
Laboratory experiments. Testing substances for electrical conductivity
Laboratory experience. Movement of ions in electric field
Practical lesson. Solving experimental problems on the topic “Electrolytic dissociation”
Topic 2. Oxygen subgroup
Laboratory experience. Preparation and properties of ozone.
Practical lesson. Solving experimental problems on the topic “Oxygen subgroup”
Topic 3. Basic laws of chemical reactions. Sulfuric acid production 155
Laboratory work. Dependence of the rate of chemical reactions on conditions
Topic 4. Nitrogen subgroup
Laboratory experiments. Familiarization with nitrogen and phosphorus fertilizers.
Practical lesson. Preparation of ammonia and experiments with it, Understanding the properties of an aqueous solution of ammonia. Practical lesson. Definition mineral fertilizers Practical lesson. Solving experimental problems on the topic “Nitrogen subgroup”
Topic 5. Subgroup of carbon
Practical lesson. Obtaining carbon monoxide and studying its properties
Carbonate recognition
Topic 6. General properties of metals
Laboratory experience. Electrolysis of solutions of copper (P) chloride and potassium iodide
Laboratory experience. Electrochemical corrosion of metals Practical lesson. Solving experimental problems in the sections “Alkali metals. Calcium"
Practical lesson. Iron and its compounds Practical lesson. Solving experimental problems on topics 6, 7, 8
Topic 2. Saturated hydrocarbons
Practical lesson. Qualitative definition carbon, hydrogen and chlorine in organic matter
Topic 3. Unsaturated hydrocarbons
Practical lesson. Preparation of ethylene and experiments with it
Topic 6. Alcohols and phenols
Practical lesson. Synthesis of the bromine phase from alcohol
Topic 7. Aldehydes and carboxylic acids
Practical lesson. Preparation and properties of carboxylic acids Practical lesson. Solving experimental problems on the recognition of organic substances
Topic 8. Esters. Fats
Practical lesson. Synthesis of ethyl acetate Practical lesson Solving experimental problems on obtaining and recognizing organic substances
Topic 12. Synthetic high-molecular substances and polymer materials based on them
Laboratory experiments. Experiments with samples of thermoplastic polymers
Practical lesson. Plastic recognition
Laboratory experiments. The relationship of synthetic fibers to solutions of acids and alkalis
Practical lesson. Fiber recognition
Practical lessons. Solving experimental problems on the completed course
General chemistry
Topic 2. Structure of matter
Laboratory experiments. Preparation and properties of complex compounds of copper, zinc, aluminum, silver and iron
Workshop
Work 1. Determination of the equivalent mass of zinc
Work 2. Determination of the molar mass of carbon monoxide (IV)
Work 3. Softening water using ion exchangers
Work 4. Hydrolysis is salty
Work 5. Study of the reactivity of metals using the semi-micro method
Work 6. Manufacturing a galvanic cell 206
Work 7. Determination of the chemical activity of acids and comparison with the degree of their dissociation 207
Work 8. Study of the effectiveness of inhibitors 208
Work 9. Determination of the heat of solution 210
Work 10. Determination of the heat of hydration 211
Work 11. Hydrolysis of starch 212
Work 12. Production of ethane by electrolysis of a solution of sodium acetate 213
Work 13. Preparation of tetraammine copper (II) sulfate 214
Applications 216
Literature for teachers 235
INTRODUCTION
Teaching the basics of chemistry at school cannot be improved without the appropriate organization of a school chemical experiment.
A chemical experiment - a source of knowledge about matter and chemical reactions - is an important condition for enhancing the cognitive activity of students, cultivating a sustainable interest in the subject, forming a dialectical-materialistic worldview, as well as ideas about the practical application of chemical knowledge.
In the improved chemistry program, the role of all types of school chemical experiments, especially student ones, has been strengthened.
The implementation of the experimental part of the program requires high and comprehensive professional training from the chemistry teacher, a deep understanding of the role of chemical experiment in the educational process, creative activity in the application effective methods training.
Of course, to conduct an experiment at a high scientific, theoretical and methodological level, a variety of equipment is needed, including the latest technical means.
The presence of a set of educational equipment necessary for the implementation of the chemistry program, the teacher’s ability to use it rationally and effectively, select the necessary tools for the lesson, independently produce some of them and correctly include them in the lesson also constitute the most important conditions for organizing a chemical experiment at school.
The book focuses on the issues of material support for a school chemical experiment, the influence of scientific and technological progress on modern equipment, techniques and methods for conducting various types of experiments using traditional and new equipment.
The manual reflects the requirements of the school reform for the chemistry experiment, namely: to include new equipment for the chemical experiment, developed taking into account scientific and technical achievements and the best practices of schools; show the organization and conduct of a chemical experiment based on kits and sets of standardized units and parts for the installation of various instruments and installations; provide for variability in setting up a chemical experiment, carried out using new and modernized equipment, as well as taking into account local conditions and requirements for self-equipment, which is especially important in teaching chemistry; identify the possibilities of using various equipment to implement interdisciplinary connections.
All this is aimed at optimizing chemistry teaching and provides for: reducing the time for preparing and conducting an experiment; convenience, reliability, safety of chemical experiments; expanding the didactic possibilities of student experiment.
In the methodological literature, considerable attention is paid to the chemical experiment. The characteristics of the chemical experiment are carried out in three aspects: equipment for the school chemical experiment; experimental technique; experimental technique. Despite some differences between these works, they discuss the technique and methodology of the experiment simultaneously.
In this manual, to familiarize teachers with the modern arsenal of equipment for chemical experiments, the characteristics of the educational and material base for demonstration and student experiments are given separately from the methods and techniques for performing experiments, many of which can be carried out using kits and multifunctional devices. The characteristics of the educational and material base of chemical experiments include modernized, new and most important promising developments of equipment created on the basis of school practice, analysis of Soviet and foreign literature on this problem, as well as research work of the Scientific Research Institute of Shotso of the Academy of Pedagogical Sciences of the USSR.
Since the issues of equipping a school chemical laboratory are described quite fully in the book “Chemistry Cabinet”, this manual will focus only on those requirements for the classroom and its equipment that determine the inclusion of new and modernized equipment.
The book is intended for chemistry teachers familiar with laboratory techniques. Therefore, it does not contain instructions for performing basic operations. In case of difficulties, readers will be able to refer to numerous manuals on laboratory work techniques, for example, the book by P. I. Voskresensky “Laboratory Work Techniques”. However, when new experiments or experiments with upgraded equipment are recommended, instructions for their implementation are given in sufficient detail. In all cases addressed great attention to conditions ensuring the safe performance of experiments.
The manual presents experiments included in the school chemistry curriculum, as well as those that go beyond its scope. The teacher can use them in extracurricular activities and extracurricular activities. The proposed experimental options make it possible to expand the use of the experiment in different conditions, study the features of chemical processes, present their diversity. This approach will allow teachers to use chemical experiment more effectively, taking into account the specific conditions of each school.
The numbers in square brackets are the numbers of literary sources given at the end of the book.
FUNCTIONS AND FORMS OF SCHOOL CHEMISTRY EXPERIMENT. REQUIREMENTS FOR TRAINING EQUIPMENT DESIGNED FOR CHEMICAL EXPERIMENTS
FUNCTIONS OF SCHOOL CHEMISTRY EXPERIMENT
An experiment allows you to identify and study the most significant aspects of an object or phenomenon using various tools, devices, technical means under given conditions. The experiment can be repeated by the researcher if necessary. This largely determines the main function of a scientific experiment: obtaining reliable data about the surrounding reality. An educational experiment differs from a scientific experiment in that its results are known, the conditions for its conduct are selected so that in the process of conducting experiments or observing them, students must detect known signs of a reaction and arrive at the expected results.
A training experiment is technically simpler and, as a rule, limited in time. In a school chemistry course, experiment is a unique object of study, a research method, a source and means of new knowledge. It is characterized by three main functions: cognitive - for mastering the basics of chemistry, posing and solving practical problems, identifying the meaning of chemistry in modern life; educational - for the formation of a materialistic worldview, conviction, ideological need for work, orientation of students towards working professions; developmental - for acquiring and improving general scientific and practical skills.
Chemical reactions are the main object of study of chemistry. Experiment and related observations are necessary already in the formation of initial chemical concepts. Their role increases in the study of theoretical issues of chemistry (the law of conservation of mass of substances, patterns of chemical reactions, etc.), in determining the properties of simple substances and compounds of elements of groups I - VIII periodic table, the most important classes of organic substances, as well as in identifying the genetic relationship of the most important classes of inorganic and organic substances.
Familiarization with chemical experiment as a method of scientific research, mastering the skills of chemical experimentation to obtain new knowledge and apply it in practical activities play an important role for the formation of a materialistic worldview of students, understanding the role of science and scientific facts in the construction of a communist society.
The school chemical experiment is also of great educational importance for the polytechnic training of students: familiarizing them with the basics of chemical production, its features, the conditions for the occurrence of chemical reactions, and the chemicalization of the national economy.
Based on the perception of observed phenomena, students form ideas and then concepts. This inductive path of knowledge is characteristic of the initial stage of learning chemistry. Gradually, this relatively slow path of knowledge is complemented by another - deductive. After students have armed themselves with theory and acquired practical skills, the experiment becomes not only a source of knowledge of new facts, but also a method of testing judgments and finding the unknown (for example, when solving experimental problems).
The same experiment is used differently at different levels of student preparation. It follows from this that it is advisable to repeat chemical experiments, paying special attention to those aspects of them that are the subject of study in a given educational situation.
In some experiments, the phenomenon is accessible to direct perception. In others, the objects and phenomena being studied are not directly perceived by the senses and can only be detected with the help of instruments or special instruments.
To understand the essence of the subject or phenomenon being studied, a chemical experiment is often supplemented with other visual aids - tables, models, screen aids.
Thus, the chemical experiment permeates all the topics of the school chemistry course, contributing to the disclosure of its content and being a unique teaching method. For the successful manifestation of the cognitive, educational and developmental functions of a chemical experiment, its technical equipment, rational organization of experiments and their inclusion in the educational process play an important role.
It is obvious that the effectiveness of the experiment depends on: setting a specific goal and task that must be solved with the help of experiment; building a rational observation plan; ability to record observation results; ability to analyze and summarize the data obtained; the presence and rational selection of tools and means with which the teacher stimulates and manages student observation. Therefore, organizing targeted observation, developing observation skills, the ability to comprehend the results of observations and retain processed information in memory constitute one of the most important tasks of a chemical experiment.
Comprehension and understanding of educational material involve not only the registration and accumulation of observational and experimental data, but also their correct interpretation, establishing cause-and-effect relationships, patterns, the essence of the objects and phenomena being studied. The success of the work largely depends on how correctly the nature of the activity of the teacher and students, the location of the chemical experiment, and the most appropriate forms and methods of its implementation in the classroom are determined.
FORMS OF SCHOOL CHEMISTRY EXPERIMENT
In the practice of teaching chemistry, it is traditional to divide a chemical experiment into a demonstration experiment, carried out by a teacher, and a student experiment, performed by schoolchildren in the form of laboratory experiments, practical exercises, and solving experimental problems. This classification is based on the activities of the teacher and students.
Demonstrations are used primarily in cases where students have not previously encountered the objects and phenomena being studied and are not prepared for observation. In these cases, one should not only show the object being studied, but also organize observation and direct it in the right direction. Students do not always perceive what is necessary, even with good visibility of an object or phenomenon, if the observation is not organized.
Demonstration is necessary if the objects being studied are dangerous or complex and, therefore, cannot be used for independent work by students.
Correctly conducting demonstrations in chemistry lessons is a necessary prerequisite for organizing various types of independent work. During the process of demonstration, especially a demonstration experiment, the teacher organizes student observation, shows the correct techniques for handling laboratory equipment, and focuses students’ attention on the feasibility and principle of its operation, the conditions for conducting experiments, and safety precautions.
A demonstration is a kind of visual instruction, on which the teacher has to spend a lot of time during the teaching process. Visual instruction based on imitation of the teacher, implemented with the help of various aids, including instruments, tables, diagrams, and screen aids, reduces the time for developing chemical experiment skills and contributes to the correct execution of the student experiment.
The leading role of demonstration also remains in the case when the time allotted by the curriculum does not allow organizing independent work, which usually takes two to three times more time than demonstration. The lack of educational equipment for conducting student experiments and the poor organization of the chemistry laboratory, which does not allow proper independent work, also force teachers to turn to demonstration experiments.
The student experiment consists of laboratory experiments performed frontally or in a group in the process of studying, consolidating and testing new material, as well as practical exercises, solving experimental problems according to options after studying individual topics of the program. A promising form is a workshop conducted in the form of separate generalizing works after completion of the entire chemistry course. Experimentation occupies a special place in elective classes and in extracurricular activities.
In a chemical experiment, both demonstration and student, various masses of substances taken for experiments are used in solid, liquid and gaseous states, which requires appropriate equipment and the ability to handle it.
Conventionally, the following masses of the substance taken for work are distinguished: macroquantities (0.05 - 0.5 g), semi-microquantities (0.01 - 0.05 g), microquantities (0.1 - 10 mg). In this regard, they talk about macro-, semi-micro- and micromethods for determining (analysis) of a substance. In all these cases, the same chemical reactions, the same concentrations of solutions are used, but in different volumes and equipment of different sizes. Thus, in the semi-micro method, volumes of 0.1 - 1 ml of solution are used, for which miniature pipettes, burettes, test tubes (conical), porcelain or glass plates with recesses (for drop analysis), and reactive paper strips (for example, indicator) are used.
As is known, in student experiments they traditionally use the macromethod, in which ordinary test tubes and devices made on their basis are used. Recently, along with the macromethod, school chemistry classrooms have been equipped with devices for conducting experiments with small amounts of substances in small test tubes, on glass or porcelain plates with indentations, etc.
The method of small quantities of substances allows you to combine the macromethod and droplet analysis in a student experiment, while achieving maximum safety of the experiments and their clarity. Solid reagents are taken with special dispensing spoons. The mass of reagents on average does not exceed 1 - 1.5 g (one dispenser contains on average 0.5 g of dry matter). Measuring liquid substances is carried out using pipettes that allow you to take from 1 - 2 drops to 5 ml (the approximate volume of a whole pipette is 1 ml).
Working with small quantities of substances has advantages over the macromethod: the time of conducting the experiment is reduced, the consumption of reagents and materials is reduced, and the possibility of using expensive and highly pure reagents opens up.
Small amounts of substances are also used in demonstration experiments, if experiments are projected onto a screen (for example, in Petri dishes using a graphic projector).
When characterizing an experiment, not only masses are taken into account, but also the features of carrying out physical, physicochemical and chemical operations with solid, liquid and gaseous substances.
In the school chemical laboratory, when preparing an experiment in lessons, elective classes, and club activities, the teacher, laboratory assistant, and students carry out the above operations. Knowledge of these operations and the correct techniques for performing them is necessary for the selection of equipment, proper installation of instruments and installations, and the safe performance of experiments.
Operations with solids: weighing, drying, sublimation, grinding, cracking (dry distillation), heating, determination of physical properties and constants (dielectric properties of polymers, density, melting or solidification temperature, thermal effect of reaction, hardness, electrical conductivity) , calcination, separation of mixtures, grinding (in a mortar), decomposition (pyrolysis), mixing, adding to the flame (determination of lithium, sodium, potassium, calcium, barium, copper ions by the color of the flame).
Operations with solids and gases: roasting, oxidation of metals, adsorption of gases (and vapors), gas chromatography.
Operations with liquid substances: evaporation and evaporation, drying, distillation, heating, purification, determination of density (with a hydrometer, etc.), determination of boiling point, stirring, introduction into a flame (flame coloring), determination of active acidity (with indicators, etc.), obtaining absolute (anhydrous) alcohol, separation of liquids (separating funnel, distillation, chromatography), cracking (pyrolysis), determination of electrical conductivity, electrolysis (water, salts, solutions), storage and transfusion of liquids.
Operations with liquids and gases: dissolution of gases, separation of gases from liquids, atomization of liquids with a gas stream, washing and drying of gases.
Operations with solid and liquid substances: adsorption of solutes, weighing, evaporation, drying, diffusion, ion exchange, crystallization from solution, neutralization, preparation of solutions, dissolution solids, melting and solidification, precipitation, complexation, separation of mixtures (filtration, chromatography, extraction), preparation of colloids, coagulation.
Operations with gases: adsorption, handling of flammable gases, heating, purification and absorption of gases, drying of gases, determination of air composition, production, collection of gases (over water, air displacement), gasometer charging, combustion of gases, interaction of gases with liquids and solids , diffusion, thermal decomposition of gases, electrical discharges in gases, gas corrosion of metals.
This manual does not cover equipment and techniques for performing the listed operations. These issues are covered in detail in laboratory practice manuals. Many of the operations are given below in the description of various experiments.
REQUIREMENTS FOR TEACHING EQUIPMENT FOR A SCHOOL CHEMISTRY EXPERIMENT
The equipment requirements for a school chemical experiment are dictated by the content and features of its organization in a chemistry classroom. Therefore, before determining what school equipment for a chemical experiment should be, it is necessary to consider the general and specific requirements for staging demonstration experiments, organizing laboratory and practical work, as well as the question of the rational combination of these types of experiments in the classroom.
Visualization and expressiveness of experiments is the first requirement for a chemical experiment. Since any chemical experiment is aimed at realizing the clarity of the objects and phenomena being studied, it is necessary to determine in what form it will be most effective: in the form of a laboratory experiment, a regular demonstration, projection on a screen, or in a certain combination thereof.
The educational and material base must provide conditions for the rational choice of the necessary forms of chemical experiment. The purpose of the performance and the content of the experiments should be clear to every student. The experiment must be clearly visible; the dimensions of the instruments, parts, and their placement on the work table must ensure good visibility of the observed phenomena.
The second requirement: chemical experiments must be accessible to perception and always convincing, and should not give students a reason for misinterpretation.
Educational equipment must therefore ensure that chemical experience is simple, demonstrable and reliable. When choosing a device, its design features must be taken into account. So, for example, demonstrating the interaction of sodium with water in a crystallization glass or bowl, as is usually done in schools, does not reveal all the signs of the reaction: the melting of sodium as a result of the released heat of reaction, the transformation of sodium into a ball, its movement along the surface of the water, the release of gas . This makes it difficult to explain the experiment and study the properties of the alkali metal. The combination of conventional demonstration and screen projection makes the experience visual and authentic.
The design of the device or installation must provide not only the conditions for carrying out the chemical reaction, but also the ability to identify and display visible and hidden signs ongoing process. When demonstrating a neutralization reaction, for example, by pouring an acid solution into an alkali solution using litmus or phenolphthalein, the neutralization process is detected by a change in the color of the indicators: litmus becomes violet, and the crimson color of phenolphthalein becomes colorless. The release of heat remains hidden from the observer. The use of an electric thermometer in a demonstration experiment makes it possible to characterize the reaction more conclusively.
The clarity and reliability of the demonstration of experiments is determined by the technique of its production.
In the school chemistry experiment, there were previously no precise measuring instruments. However, today it is impossible to introduce students to scientific methods without them. To use such devices, it is enough to be able to use them correctly, without delving into the details of their design.
These are primarily electrical and electronic devices used in conducting a number of experiments in electrochemistry, including those involving the use of high voltage current.
Each experiment carried out by a teacher or student must be trouble-free, and the equipment for its implementation must be expensive. A failed demonstration disrupts the flow of the lesson, causes frustration among students, and often leads to distrust of the teacher. The reasons for failed experiments are varied. One of them is the technical imperfection of devices, as well as their individual parts and assemblies.
The reliability of instruments and installations thus depends on their technical perfection. To do this, it is necessary to have in each chemistry classroom sets of standardized utensils in strictly necessary and sufficient quantities to carry out various types of chemical experiments; sets of universal units and connecting parts ensuring tightness and ease of installation. These include a variety of connections: rubber, glass joints (ground and bent), rubber and plastic seals.
The reliability of devices and installations also depends on their correct storage and transportation. For example, glassware and accessories often fail due to improper storage in the office (without stacking them in closets).
The reliability and technical excellence of shizhio instruments and installations ensure compliance with safety regulations when carrying out chemical experiments. The implementation of this requirement depends, of course, not only on the state of the educational and material base of the chemistry classroom, but also on the extent to which the teacher has mastered the technique of chemical experiment, on his knowledge of the entire arsenal of educational equipment necessary for the experiments, pt precision and work culture.
The devices in which experiments are carried out must be prepared in advance, tested repeatedly, and the operating manuals or passports of devices and installations must be carefully studied by the teacher.
Safe work determined by regulatory documents, in particular the “Safety Rules for Chemistry Classrooms (Laboratory) secondary schools MP systems of the USSR". It should be noted that in most cases the danger is caused by the negligence of the experimenter, violation or direct disregard of the operating instructions for devices or installations. Heating flammable liquids over an open flame, incorrect choice quantities, concentrations and volumes of reacting substances, storage of flammable and explosive gases in glass gasometers, demonstration of the explosion of gases in glass vessels, the inclusion of electrical appliances designed for low voltage in the network, the use of technically imperfect home-made electrical appliances are the most common causes of dangerous situations.
In industrial devices and installations, safety requirements are determined by the relevant regulatory documents V. are reflected in the design features of this device. For example, providing electrical appliances with protective covers, pole plugs (preventing the device from being plugged into a regular power outlet), mechanical locking of sockets (locking them in the desired position), etc.
Homemade devices and installations can only be used in schools if they are technically reliable and safe. One of the requirements for a school chemical experiment is its short duration, which is determined by the limited time of the lesson.
When setting up an experiment in a lesson, the following must be taken into account: the feasibility of including experiments at a certain stage of the lesson, the need to explain them (including using other teaching tools), the possibility of repeating the experiment to correct the observation and obtain reliable results.
The rational design of devices and installations, their correct use in accordance with the pace and stages of the lesson ensure the achievement of set goals in a precisely calculated time frame. For example, savings in teaching time can be achieved not only by reducing auxiliary operations when installing a device or installation, but also due to the convenience and speed of their implementation. This is greatly facilitated by the well-thought-out design of the device. For example, heating is one of the most frequently repeated operations. Therefore, it is necessary to create heaters that would provide the ability to operate in predetermined modes.
The average duration of a laboratory experiment and a separate demonstration should not exceed 5 - 6 minutes of a lesson, and when performing practical work - 15 - 20 minutes. Delaying the experiment time beyond the given norms reduces interest in the experiment, disrupts the rhythm and structure of the lesson, and does not allow the results of the research to be formalized.
Some experiments (for example, on metal corrosion) require a long time. Such an experiment is carried out in stages; in the first lesson, the conditions of the experiment are discussed and the implementation is carried out; in the next one or two lessons, the results obtained are recorded. To carry out such experiments in parallel classes, a larger amount of equipment of the same type is required, which can be replaced with a similar one for its intended purpose (for example, beakers can be used instead of flasks).
It must be taken into account that educational equipment for a chemical experiment can function successfully if certain conditions are created in the chemistry classroom; in particular, there are appropriate communications connections, halo, water and electricity supplies have been established, teacher and student workplaces have been rationally organized, and the system for placing and storing educational equipment has been carefully thought out.
These and other questions are covered in the book “Chemistry Cabinet”. Therefore, here we consider mainly new issues regarding the implementation of methodological requirements and safety rules when performing a chemical experiment. These primarily include modern electrical equipment in the chemistry classroom, since conducting experiments in electrochemistry, as well as the operation of electric heaters, require not only reliable, but also safe instruments, as well as appropriate conditions for their use in the learning process.
The composition of electrical equipment and the rules for its operation in a school chemistry classroom are determined by the following regulatory documents; “Standard lists of educational visual aids and educational equipment for secondary schools” for the XII five-year plan (hereinafter referred to as “Lists-12”), Section; chemistry; Safety regulations for chemistry classrooms (laboratories) in secondary schools of the USSR Ministry of Education; GOST “School equipment. General safety requirements."
The electrical equipment of the chemistry classroom includes stationary equipment (electrical supply kits for the chemistry classroom, KHE, power input panel, water distillation apparatus) and portable equipment (various electrical appliances and installations, projection equipment). All electrical appliances are divided into four classes according to the method of protection against electric shock: OT, I, II, III. In the chemistry classroom, the teacher works with electrical equipment belonging to classes I, II, III.
The first class includes stationary devices and installations that require grounding. The second class includes all kinds of electrical appliances (stoves, demonstration heaters) that are connected to the network, but they are not grounded, since they have double or reinforced insulation.
The third class includes devices that do not have either internal or external electrical circuits with a voltage exceeding 42 V (heaters laboratory type NLSH, NPU, NPESH, cm, p. 108, 109).
Teachers and laboratory assistants work with instruments and installations of the first and second grades. Students use only third grade equipment for laboratory and practical work.
In new buildings, stationary equipment powered by three-phase current is installed construction organizations. However, in most schools, specialists have yet to install it. The most convenient for this purpose is the wall adjacent to the laboratory room.
Using the power supply kit for the chemistry classroom (KEC), the teacher’s demonstration table is powered with electric current AC voltage 220 V and 42 V and student workplaces with electric current of alternating voltage 42 V. K.EH is equipped with a residual current device of the UZOSH type.
To perform electrochemistry experiments requiring voltage direct current up to 12 V, you should use the “Practicum” power supply (from the physics room).
To power electrical appliances, two sockets are installed on the demonstration table specialized for the chemistry classroom: 220 V and 42 V at a distance of at least 1.5 m from the water tap (for example, on the side wall of the demonstration part of the table).
To power electrical appliances, one 42 V outlet is placed at students’ workplaces (for example, on the side panel of the table). It has slot-like holes located perpendicular to each other and designed to accept a plug with a corresponding arrangement of flat plugs.
When creating and using homemade and industrial devices, you must remember the following safety requirements (according to the above GOST):
1. In closed current-carrying systems, the permissible voltage for students is no higher than 42 V AC and DC; for the teacher - -220 V AC and 110 V DC.
2. In open current-carrying systems (in devices with bare parts of conductors and when working with electrolytes), a voltage of no higher than 12V AC and DC is allowed for teachers and students.
3. When working with electrolytes in vessels closed with special devices (casings, lids, etc.), voltage for student experiments is allowed up to 42 V AC and DC and for teacher experiments - PO V.
4. The maximum value of electric power consumption in the chemistry classroom should not exceed 2.2 kW (for example, 20 test tube heaters, a projection apparatus and a distillation apparatus cannot be turned on simultaneously).
The teacher should take note that in the chemistry classroom, sockets (220 V) and switches, according to the rules for electrical installations, must be located at a height of 1.8 m from the floor.
A mandatory requirement when working with electrical equipment is a preliminary thorough study of the instructions for its operation.
It must also be remembered that electric current is turned on at students’ laboratory tables only during experiments. During non-working hours, workplaces must be de-energized.
The electric current is switched on using a switchboard located in the laboratory room. The shield is equipped with a general power switch and a power indicator.
To carry out all types of experiments, it is necessary that in each office sets of instruments, installations, glassware and laboratory supplies are created, always ready for use.
The equipment supplied to schools in accordance with the current List of educational equipment allows each chemistry classroom to independently create such kits if it was not possible to purchase them ready-made.
To successfully implement a chemical experiment using the new program, the following kits are required.
For the demonstration experiment: a set of low-inertia electric heaters for liquids and solids up to a temperature of 300°C (in flasks, beakers, crucibles, cups); a set of utensils, parts and assemblies for the installation of devices and installations in which chemical reactions are carried out under normal conditions; a set of parts and assemblies for experiments with harmful substances without traction; counting and measuring kit (measurement of mass, temperature, time, voltage, pI and carrying out arithmetic calculations on a demonstration light display); a kit for carrying out catalytic reactions (a set of catalyst tubes and heaters, catalysts on carriers); kit for experiments with gases (flammable and explosive); kit for experiments with high voltage electric current; a set of specialized instruments and apparatus (for obtaining and storing gases, obtaining distilled water, illustrating some laws, etc.); a set of components and parts for projecting experiments on the screen; a set of 250 ml bottles for reagent solutions; a set of bottles with a lower tube of 1 - 2 liters for storing a supply of reagent solutions.
For a student experiment: a set for laboratory experiments and practical work, including a set of dry reagents in jars and their solutions in flasks for constant and occasional use; small set of accessories; small volume set of dishes (25 - 50 ml); a set of joints and assemblies for mounting various instrument options; a set of auxiliary laboratory equipment (washing bowls, waste jars, test tube racks and laboratory racks for fixing instruments, glassware and accessories).
These kits should provide the opportunity for students to variably and safely perform laboratory and practical work in various ways: using macro and micro amounts of reagents, the drop method, using substances in various states of aggregation.
When organizing students’ workplaces, the teacher must determine the equipment placement option that best suits his style of work: sets permanently attached to the laboratory table or handouts provided in trays before practical work.
The system for placing reagents, glassware and accessories on laboratory tables or when stored in a laboratory should provide students with a quick and correct selection of bottles with reagents, the necessary components for installing instruments, order and convenience in the workplace.
The same requirements apply to the teacher’s workplace, and above all to the demonstration table.
Particular attention should be paid to the organization of the preparation table in the laboratory, storage and placement of reagents, glassware, accessories, trays with handouts in sectional cabinets.
Dishes and glassware must be stored in containers (made of foam rubber or polystyrene), which can be made by students under the guidance of chemistry and vocational education teachers.
According to the requirements of the school reform, the range of demonstration experiments (projecting chromatography experiments on a screen, etc.) and student experiments (electrolysis, ozone production, etc.) has been expanded.
The requirements of scientific and technological progress - to raise experiment as the basis for the study of chemistry to a higher level, to ensure its clarity, evidence, reliability, safety, to show with the help of educational equipment the application of the laws of chemistry in chemical technology, as well as the connection of chemistry with physics and biology - determine the main directions for the development of educational equipment for school chemical experiments:
creation of multifunctional devices that allow several experiments to be carried out in one device. These devices include standardized units and parts (modules), which provide the student teacher with the opportunity to quickly and conveniently install necessary settings for demonstrations and independent work of students;
creation of new electrical appliances: specialized low-inertia heaters; automatic and auxiliary devices(For forced ventilation, regulation of lighting, shading, etc.);
optimal miniaturization of educational equipment, which ensures savings in materials and allows students to rationally carry out independent work with small quantities of substances;
the use of electronic technology to record not only qualitative, but also quantitative results of experiments;
creation of instruments and installations for interdisciplinary connections between chemistry and physics and biology;
the use of new structural materials and technologies in the production of educational equipment: germanium semiconductors, strain gauges that convert gas pressure into an electrical signal, plastics, glass parts with a curved surface, and in the future - liquid crystals, optical fiber materials;
carrying out a school chemical experiment based on typical, standard equipment that ensures rational compatibility individual parts and units, kits in general and the ability to quickly and correct installation various options for instruments and installations in a school chemistry classroom.
In this manual, the authors focus mainly on the use of new and modernized equipment, which makes it possible to improve the technique and methodology of school chemical experiments.
CONSTITUTION OF DEMONSTRATION EXPERIMENTS
EQUIPMENT FOR DEMONSTRATION EXPERIMENTS
Typical components and parts, sets of utensils and accessories for installation of devices and installations
In school practice, various chemical laboratory glassware and laboratory supplies (glass and rubber tubes, taps, screw and spring clamps, fireproof gaskets, triangles for crucibles, etc.) are used to conduct a chemical demonstration experiment. This equipment is used to conduct both simple and more complex experiments in devices and installations. The first group of experiments includes: separation of a mixture of substances; interaction of water with phosphorus and calcium oxides and testing of the resulting hydroxides with indicators; sublimation of iodine; exchange reactions (production of insoluble hydroxides and study of their properties, salt precipitation, etc.); the ratio of saturated hydrocarbons to potassium permanganate solution, alkalis, acids; interaction of glycerol with sodium; solubility of phenol in water at normal temperature and when heated; the ratio of stearic and oleic acids to bromine water and a solution of potassium permanganate and some other experiments. To set them up, flasks, beakers, cylinders with plates, demonstration tubes with a capacity of 50 ml (type PH-21), crucibles, evaporation bowls, etc. are used.
The technique for working with this equipment is simple and well known to the chemistry teacher, and therefore the authors do not disclose it.
Another group of demonstration experiments (about 40) requires the use, along with chemical glassware and laboratory supplies, of special parts and assemblies, which are usually installed by the teacher (laboratory assistant) himself, if the school does not have special kits industrial production.
The preparation of such parts and assemblies in the form of kits for various purposes, their rational placement in the chemistry classroom are necessary conditions for the successful implementation of experiments of varying complexity.
Typical components of educational instruments and installations include various reactors, devices for transferring reaction products (plugs with tubes, joints, extensions, cones, etc.), and receivers. Somewhat less commonly used are vessels for cleaning, drying gases, refrigerators, a Buchner funnel and a Bunsen flask for filtering under vacuum (Fig. 1).
Reactors. Among the reactors, the most common are two types: the first type is a reactor in the form of various flasks (round-bottom flasks, flasks with an extension - Wurtz flasks, etc.); the second type is a reactor in the form of a tube located horizontally or vertically (see flyleaf I).
In complex installations, both types of reactors are sometimes used.
Flyleaf I presents reactors in the form of various flasks with the most commonly used components: a stopper with tubes, a funnel, a thermometer. In devices assembled using the appropriate parts, it is possible to carry out a number of demonstration experiments with the production of gases or volatile substances: the production of chlorine, hydrogen chloride, ammonia, sulfur oxide (IV), acetylene by the carbide method, nitration of benzene, etc. (see flyleaf P).
The choice of reactor flask is determined by the nature of the demonstration experiment. As a rule, round-bottomed flasks (flask capacity 200 - 250 ml) are used because they are more durable and can withstand gentle heating directly from the burner flame. For many experiments (distillation of liquids, production of gases, etc.), flasks with an extension (Wurtz flasks) are convenient. The flasks must be tightly closed with rubber stoppers or stoppers with the necessary parts.
A dropping funnel with a stopper (endpaper G) is the part most often used in the production of gases. Often, to equalize the pressure inside the flask and atmospheric pressure, the end of the funnel is immersed in a small test tube located at the bottom of the reactor flask. However, the most convenient to use is a reactor flask, equipped with a spherical funnel with a gas outlet tube (endpaper I): In a two-neck flask, an industrially manufactured funnel for working with harmful substances (type VVRV) is used (endpaper I) The presence of a thin section, unfortunately, limits it application, since the funnel is supplied to schools complete with a flask that has the same grind.
In some cases - (for the distillation of liquids) a thermometer inserted into the stopper is required (endpaper I). A stopper connected by a small test tube through glass and rubber tubes is convenient for introducing small amounts of powdery substances into the reactor flask.
* Using an electric spiral, you can perform a number of experiments in flasks, for example, the thermal decomposition of wood, peat, oil shale, coal, petroleum products.
Various types of tubes v (see flyleaf I) can also be used as a reactor: straight, calcium chloride (with a ball and arc-shaped), straight reaction tubes with a length of 200 mm and a diameter of 15 - 20 mm (for some experiments longer tubes are required - 400 mm with 25 mm in diameter) made of heat-resistant or quartz glass, as well as iron (straight and curved at right angles) and porcelain.
A number of experiments can be carried out in ordinary glass tubes (tubular reactors) using heating with an open flame. They carry out, for example; demonstrating the decomposition of basic copper carbonate; reduction of copper (II) oxide with hydrogen; catalytic oxidation of sulfur oxide (IV) to sulfur oxide and ammonia to nitrogen oxide (II); quantitative experiment: determination of the mass of sulfur (IV) oxide formed during the combustion of a certain mass of sulfur by increasing the mass of sodium hydroxide that absorbed the resulting reaction product.
Tubular reactors are needed, as a rule, for high-temperature experiments, for reactions in a flow (gas, liquid).
Not possible to use in all cases gas burners; Therefore, electric heaters have long been used, the description of which is given in manuals for chemical experiments.
It is often recommended to use asbestos to make homemade electrically heated tube furnaces. However, its use in school chemistry classrooms has recently been prohibited. Electric heating using a spiral. Can be used without asbestos. Some experiments are carried out in electrically heated glass tubes (oxidation of sulfur oxide (IV) to sulfur oxide (VI) in the presence of a solid catalyst, ammonia synthesis, catalytic oxidation of ammonia).
The electric spiral can be used in another way. The tube through which the electric spiral is pulled (endpaper L) is filled with a catalyst. In such a reactor, ammonia is oxidized to nitrogen oxides, in the presence of the same catalyst - chromium (III) oxide.
On a ceramic carrier in the same reactor, sulfur oxide (IV) can be oxidized into sulfur oxide (VI).
Reactors should also include special devices for burning gases in each other. They own a universal industrial burner.
Devices for transferring and collecting reaction products. For quick and reliable assembly and disassembly of devices, connecting elements are used in the form of transitions, bends, couplings, lengths, closures, and attachments. From a limited number of such parts, especially when they have ground surfaces, a whole range of devices can be assembled. The most common are interchangeable cone joints. Cones can be made not thick by grinding methods, but also by hot calibration - bending. Thus, a distinction is made between cones with a ground surface (KS) and cones with an unpolished surface (KN). Bent products have a number of advantages over ground ones: greater mechanical strength, do not jam and are easily separated, become less dirty, can work even without lubrication, and are transparent.
Various washing bottles are used to clean and dry gases (see flyleaf I). They are filled with liquid (concentrated sulfuric acid and an alkali solution are most often used) with solid (sodium and calcium hydroxides, calcium chloride) absorbers.
For solid absorbers, calcium chloride tubes with a ball and absorption columns are also used. The latter can be receivers of reaction products, for example, hydrogen chloride and synthetic hydrochloric acid. Various chemical vessels can also be used as receivers: test tubes, flasks, beakers.
Bottles for liquid washers (Drexel, two-necked and three-necked Wulf) are used like this. same as safety vessels for vacuum filtration. To perform this operation, you must have a thick-walled flask with an extension (Bunsen) and a porcelain funnel with holes (Buchner).
Typical units for collecting gases and dissolving them are presented on flyleaf II.
Currently, all typical parts and assemblies for the installation of various instruments and installations are included in special sets produced by industry: a set of chemical laboratory glassware and accessories for demonstration experiments in chemistry (NPH) for incomplete and complete secondary schools and a set of parts and assemblies for installation of devices illustrating chemical production(NDHP-M).
These kits include more than 50 different parts that ensure the installation of not only traditional, but also special instruments and installations for staging all demonstration chemical experiments in chemistry courses in junior and senior high schools.
Specialized instruments, devices, installations
To carry out certain demonstration experiments, specialized instruments, devices, and installations are used. As a rule, these are stationary instruments: an apparatus for producing gases (Kippa), a gasometer, an instrument for electrolysis, a device for demonstrating the dependence of the rate of chemical reactions on conditions, etc.
The installations are assembled from instruments, parts and assemblies of kits and sets of industrial production (sets for experiments with electric current, kits for projecting experiments onto a screen, etc.).
1. Devices for demonstrating experiments with substances harmful to health without exhaust devices. In the school chemistry course there are many experiments on studying the properties of volatile substances harmful to health (chlorine, bromine, hydrogen chloride, hydrogen sulfide, nitrogen oxides, ammonia, carbon monoxide (I) , some organic substances).
It is usually recommended to obtain these substances and become familiar with their properties using iodine traction. The distance of fume hoods from students' work stations and the presence of glare on the glazed surface of the cabinet impair the visibility of demonstrations, but ensure their safety.
One of the directions for improving such demonstrations was the creation of devices closed to an absorber. The use of these devices achieves clarity, reliability, safety, accessibility, and simplicity of the demonstration experiment.
In connection with the new technology for manufacturing glass parts and units with curved surfaces, it has become possible to implement all of the specified requirements, including the idea of vertical installation of educational instruments in chemistry.
It should be noted that the instruments and devices that make up the system closed on the absorber seem to be more complex compared to conventional devices due to the introduction of new design details, but from a methodological point of view this is advisable.
Number of new structural elements small, and they can be used in many devices for carrying out reactions with volatile substances.
END OF PARAGMEHTA BOOKS
To successfully teach chemistry, a teacher must master a school chemical experiment, as a result of which students acquire the necessary knowledge and skills. A school chemical experiment can be divided into a demonstration experiment, when the experiment is shown by the teacher, and a student experiment, performed by students. In turn, student experiment is divided into two types:
- laboratory experiments conducted by students in the process of acquiring new knowledge;
- practical work that students do after completing one or two topics
In many cases, practical work is carried out in the form of experimental problem solving, in high school - in the form of a workshop, when, after completing a number of topics, practical work is carried out in several lessons.
The development of students’ cognitive interests in the learning process is of great importance for any academic subject. The study of chemistry has its own characteristics that are important for teachers to keep in mind. First of all, this concerns the use of educational chemical experiments, which are widely used in schools in various forms. The experiment requires a lot of time from the teacher to prepare and conduct. Only in this case can the expected pedagogical effect be achieved. In this case, it is necessary to take into account both your work experience and the experience of other teachers, known from literature and personal communication. If a teacher is fluent in a chemical experiment and uses it to help students acquire knowledge and skills, then students study chemistry with interest. In the absence of a chemical experiment in chemistry lessons, students' knowledge may acquire a formal connotation - interest in the subject drops sharply.
A chemistry teacher needs to master not only the technique and methodology of demonstration experiments, but also student experiments. Sometimes the best things may not work out simple experiments when the required concentration of reactants in solutions is not observed or the conditions for conducting chemical reactions are not taken into account. That is why it is necessary to study simple test tube experiments in detail in order to guide the conduct of student experiments in the classroom and provide assistance to students.
Recently, more and more often, student experiments are carried out either by working with a small amount of reagents in small flasks and test tubes, or by the semi-micro method, when experiments are carried out in cells for droplet analysis, solutions are taken with a pipette in a few drops. If you take a paper clip and lower its end into a cell with a solution of copper chloride (11), then after a few seconds the paper clip will be covered with a bright coating of copper. The semi-micromethod saves not only the time of the teacher and students, but also material assets - expensive reagents, materials, and utensils.
Demonstration experiments are the most common type of school chemical experiment, which has a strong influence on the process of students acquiring knowledge in chemistry. When demonstrating experiments, students are especially affected by the following three aspects of the experiment:
1. Direct impact of the chemical reaction itself.
If we arrange in order of importance the factors influencing students during the demonstration of experiments, then first of all they will be influenced by the light stimulus (flashes, combustion, color of the initial and resulting substances). Of great importance are the various odors characteristic of the substances being demonstrated and formed.
during the experiment. They can be pleasant and unpleasant, strong and weak. In cases where substances are poisonous and harmful to health, experiments are carried out under draft or absorption of these substances. The third place will be occupied by auditory stimuli: strong explosions or light sounds that occur during the flash of various substances. Students usually like beeps a lot. Unfortunately, they are not always accompanied by the desired pedagogical effect.
Motor processes (moving liquid and solid substances, rearranging parts when assembling devices) have an important impact on students. For example, students watch with interest the bubbling of gas bubbles in a liquid and the movement of colored solutions. If the processes occurring during a demonstration are little noticeable or poorly perceived by the senses, then the demonstrations are reproduced using various devices. Thus, poorly visible chemical reactions are projected onto a screen using a graphic projector, computer, multimedia, interactive whiteboard, or video. Sometimes it is advisable to combine demonstrations - clearly visible operations are shown in glassware, and individual, poorly visible details are projected onto the screen.
2. The word and actions of the teacher.
It is known that demonstrations are almost never carried out in silence. The teacher guides the students' observation and directs their thoughts depending on the purpose of the demonstration. The nature of this manual most often results in a different pedagogical effect of the demonstration.
The actions of the teacher are also significant: assembling the device, adding solutions, mixing substances, gesturing, etc.
Often these actions have a great influence on students, and they sometimes take them as the main, primary sign, indicating in detail in their notes how the teacher adds solutions and mixes substances.
3. Various visual aids (drawings and diagrams by the teacher, formulas and chemical equations, models, etc.)
All of them help students correctly perceive and comprehend a chemical experiment, emphasize poorly visible details, and contribute to the correct disclosure of the chemistry of the demonstrations.
How do these three aspects of the demonstration experiment affect students? The chemical reactions demonstrated have essential and non-essential features. An essential feature is one without which it is impossible to correctly perceive a chemical process. For example, when demonstrating the interaction of sodium with water, the essential features are the evolution of hydrogen and the formation of alkali. Non-essential features complement the overall picture of the demonstration and make it more complete. In the above example, an insignificant feature is the movement of a piece of sodium along the surface of the water.
When observing essential and non-essential attributes, students are influenced by strong and weak stimuli resulting from a chemical reaction. Sometimes the strong excitement students receive from the action of a powerful stimulus allows them to “shade out” the weak components associated with the essential side of the demonstration of experience. So, in the above example of demonstrating the interaction of an alkali metal with water, students are greatly influenced by a strong stimulus associated with an insignificant feature - the movement of the metal on the surface of the water, and the formation of alkali and hydrogen remains without much attention. When demonstrating an ozonizer, students get the most vivid impression of the noise of the induction coil, which obscures the essence of the chemical process - the formation of ozone. When an explosive mixture (hydrogen and oxygen) explodes in a tin can, the loudest explosion (an insignificant sign) makes the strongest impression on the students, and the main one - the formation of water - passes by the attention of the students, although the teacher informs them about it. It is known that to recognize acids and alkalis, various indicators are used (litmus, phenolphthalein, etc.), which indicate the additional properties of these substances. When demonstrating indicators, as established by D.M. Kiryushin [3], as a result of an incorrect combination of words and actions of the teacher, students indicate a change in the color of acids and alkalis, and not the indicators themselves.
What to do in cases when students, when demonstrating an experiment, mistake unimportant additional features for essential, main ones? Psychologists note that to prevent students from misperceptions or change them, it is necessary to use various verbal instructions from the teacher. Two main types of instructions must be distinguished. You can indicate to students exactly which features of the subject they should pay attention to (positive instructions), and you can indicate which features they should not pay attention to (negative instructions). When teaching chemistry, when students perceive bright flashes and strong explosions as the main sign of a reaction, it is not enough to use only verbal instructions; it is necessary to use various visual aids, for example, color drawings and diagrams in combination with the teacher’s word.
When demonstrating the interaction of alkali metals with water, students’ attention should be drawn to the fact that alkali and hydrogen are formed here. The movement of a piece of metal on the surface of the water should not be ignored. It is advisable for the teacher to ask students the following questions: why is he moving? If hydrogen had not been released, would this phenomenon have been observed? To emphasize the second essential feature of this chemical reaction – the formation of an alkali, students’ attention is drawn to the change in color of the phenolphthalein solution.
An important issue in chemistry demonstration is the number of experiments that the teacher demonstrates in the lesson. V.N. Verkhovsky pointed out the danger of overloading lessons with demonstration chemical experiments. A large number of experiments interferes with the clarity and distinctness of students’ assimilation of the material; unnecessary experiments distract their attention. Even worse results are obtained if the teacher demonstrates an insufficient number of experiences on the basis of which he draws theoretical conclusions. If you show students only the interaction of iron and zinc with acid, then they make a mistake that is difficult to correct even in high school: to produce hydrogen, students offer nitric acid and zinc.
How many experiments should be demonstrated in class? In each individual case, the teacher needs to think about this issue, guided by the fact that their number should be optimal. Students need to be shown all the essential aspects of the demonstrated process with an economical expenditure of time during the lesson, so that as a result they receive conscious and lasting knowledge, not forgetting that a chemical experiment has a great influence on consciousness, sometimes stronger than the teacher’s word.
The cognitive interest of students arises in the process of a fascinating story from the teacher, for example, about a situation in which he once found himself. The story evokes positive emotions in the children, without which, according to psychologists, fruitful learning is impossible. It should be borne in mind that it is always necessary to tell the truth (even if it is unpleasant for the teacher himself), since students do not tolerate falsehood. The life interpretation of the chemical experiment turns out to be the most convincing. Especially in cases where the experiment is unsafe.
While studying white phosphorus, I recalled an incident from my student life when, in a chemical laboratory, a student sitting next to me took a piece of white phosphorus with her hand, which instantly flared up. The student was confused and rubbed the burning phosphorus with her palm over her robe, which also flared up. The fire was extinguished, but the phosphorus severely burned the skin of the hand and, having penetrated the body, caused its poisoning.
While preparing a mixture of berthollet salt with red phosphorus for a demonstration at a chemistry evening, I pressed hard on a lump of berthollet salt, an outbreak occurred - eyebrows, eyelashes, part of the hair were singed, the burning phosphorus got on my hands and caused burns that did not heal for a long time.
A laboratory assistant at the Department of Inorganic Chemistry threw the remaining reagents, including potassium metal, into the sink - an explosion occurred and the ceramic sink shattered into pieces.
A colleague from a neighboring school told me that when she conducted an experiment on the interaction of sodium with water not in a glass, not in a crystallizer, but in a test tube - it burst in her hands from an explosion of detonating gas.
Since the reception of the teacher’s personal experience is limited, the historical experience of chemist scientists should be used more widely, not only based on their achievements, but also without remaining silent about mistakes. Thanks to this, students will understand that the development of chemical science does not follow a smooth, well-trodden path. Usually this is a difficult path of struggle between opinions and evidence.
So, a demonstration experiment in chemistry must be carried out in such a way that it has an emotional impact on the student and contributes to the development of their interest in studying chemistry.
As A. Einstein stated: “A beautiful experiment in itself is often much more valuable than twenty formulas obtained in the retort of abstract thought.”
Literature
- Polosin V.S., Prokopenko V.G. Workshop on methods of teaching chemistry - M.: Education, 1989.
- Polosin V.S. School experiment in inorganic chemistry - M.: Education, 1970.
- Kiryushkin D.M. Experience in researching the interaction of words and visuals in teaching - M.: Publishing house APN, 1980.
- Khomchenko G.P., Platonov F.P., Chertkov I.N. Demonstration experiment in chemistry - M.: Education, 1978.
- Verkhovsky V.N., Smirnov A.D. Technique of chemical experiment at school - M.: Education, 1975.
- Moshchansky V.N. On the pedagogical ideas of Albert Einstein (on the 100th anniversary of his birth) - Soviet Pedagogy, 1979, No. 10
Olga school
Pavlodar district
Report
“Chemical experiment as one of the active forms of learning in chemistry lessons”
(August Teachers' Conference)
teacher of chemistry and biology: Pavina O.A.
2014-2015 academic year
Table of contents:
Introduction
Using student experiment in teaching chemistry
1.1 . Substances for household use proposed for organizing a chemistry experiment
1.2 . .
1.3 . Application in
2. Conclusion.
3. Literature.
Introduction.
Today, in our rural schools, insufficient attention is paid to conducting chemical experiments, since not every school has reagents for conducting experiments. Therefore, students often have only a formal understanding of chemical objects, sometimes having no idea about the true tasks facing chemical knowledge, about chemical research methods. As a result, some schoolchildren who have a potential inclination to work in the natural sciences receive an incomplete, one-sided idea about it in their school.
Wide popularization of chemical knowledge contributes to the growth positive attitude to the subject and improving the quality of students’ knowledge.
Most of the experiments offered do not require special equipment and reagents, so they can be carried out in any school and even at home. Experiments can be shown directly in class or used in extracurricular activities in chemistry.
1. Using student experiment in teaching chemistry
A student experiment is a type of independent work. The school chemistry curriculum stipulates what experimental work must be performed.
The experiment not only enriches students with new concepts, skills, and abilities, but is also a way to test the truth of the knowledge they have acquired, contributes to a deeper understanding of the material, and the assimilation of knowledge. It allows for a more complete connection with life, with the future practical activities of students.
Student experiment is divided into laboratory experiments and practical exercises. They differ in didactic purpose. The purpose of laboratory experiments is to acquire new knowledge and study new material. Practical classes are usually held at the end of studying a topic and serve to consolidate and improve, concretize knowledge, develop practical skills, and improve students’ existing skills and abilities.
The implementation of a student experiment from the point of view of the learning process should take place in the following stages:
Awareness of the purpose of the experience;
Study of substances;
Assembly or use of a finished device;
Performing the experience;
Analysis of results and conclusions;
Explaining the results obtained and drawing up chemical equations;
Compilation of a report.
The student must understand why he is doing the experiment and what he must do to solve the problem posed to him. He studies substances organoleptically or using instruments or indicators, examines the parts of the device or the device itself. Performing the experiment requires mastery of techniques and manipulations, the ability to observe and notice the features of the process, and distinguish important changes from unimportant ones.
After analyzing the work, which the student must do independently, he draws a conclusion based on the appropriate theoretical concept. The role of the report that students write immediately after completing the experiment should not be underestimated. He teaches concise and precise formulation of thoughts, correct recording.
1.1 Household substances offered for organizing a home chemistry experiment
Substance name
Chemical name
Household purposes
Where can I buy
Office silicate glue
Sodium silicateNa 2 SiO 4
Bonding paper and cardboard
Stationery
Table salt
Sodium chlorideNaCl
Eating, canning
Food stores
Copper sulfate
Copper sulfate pentahydrateCuSO 4 *5 H 2 O
Disinfection, pest and plant disease control
Gardening shops
Sodium nitrate
Sodium nitrate
NaNO 3
Nitrogen fertilizer
Gardening shops
Potassium nitrate
Potassium nitrate
KNO 3
Nitrogen and potash fertilizer
Gardening shops
Ammonium nitrate
Ammonium nitrate
N.H. 4 NO 3
Concentrated nitrogen fertilizer
Gardening shops
Ammonium sulfate
Ammonium sulfate
(NH 4 ) 2 SO 4
Nitrogen fertilizer
Gardening shops
Calcium nitrate
Calcium nitrate
Ca(NO 3 ) 2
Nitrogen fertilizer
Gardening shops
Urea
Urea, carbamide
(NH 2 ) 2 CO
Nitrogen fertilizer
Gardening shops
10.
Slaked lime, fluff
Calcium hydroxideCa(OH) 2
Whitening agent, component mortars
11.
Quicklime, boiling water
Calcium oxideCaO
Means for whitewashing, disinfection, component of mortars
Construction stores and markets
12.
Plaster, alabaster
Calcium sulfate dihydrate or hemihydrateCaSO 4 *2 H 2 O, CaSO 4 *0,5 H 2 O
Fastening composition or component thereof
Construction stores and markets
13.
Chalk
Calcium carbonateCaCO 3
For educational needs or as part of whitewash
Stationery store
14.
Trisodium phosphate
Technical sodium phosphateNa 3 P.O. 4
Detergent and cleaning product
15.
Washing (soda ash)
Anhydrous sodium carbonateNa 2 CO 3
Detergent and cleaning product
Soap, detergent and household goods stores
16.
Technical borax
Sodium tetraborateNa 2 B 4 O 7
Product for controlling household insects
hardware store
17.
Baking soda (drinking soda)
Sodium bicarbonateNaHCO 3
Dishwashing liquid, dough loosening agent
Grocery store. Pharmacy (in the form of “Becarbon” tablets)
18.
Baking powder ammonium carbonate
Ammonium carbonate(NH 4 ) 2 CO 3
Leavening agent for unleavened dough
Grocery store
19.
Vinegar essence
Acetic acid 70-80%CH 3 COOH
Product for home canning and marinating of kebabs
Grocery store
20.
Glycerin for external or internal use
GlycerolCH 2 OH-CHOH-CH 2 OH
Cosmetic and dehydrating agent
Pharmacy
21.
Lapis
Silver nitrateAgNO 3
Mole and wart remover, antiseptic
Pharmacy
22.
Potassium permanganate, potassium permanganate
Potassium permanganateKMnO 4
Antiseptic
Pharmacy
23.
Epsom salt
Magnesium sulfateMgSO 4
Laxative
Pharmacy
24.
Magnesia 25%
Decongestant and antihypertensive agent
25.
Calcium chloride 10%
Calcium chlorideCaCl 2
In the form of intravenous injections - as an anti-inflammatory and dehydrating agent, orally - for allergies and skin diseases
Pharmacy
26.
Ammonia water
Ammonium hydroxideN.H. 4 OH
For cleaning painted floors, washing clothes, relieving fainting
Hardware store (25% solution), pharmacy (10% solution)
27.
Mirabilite, Glauber's salt
Sodium sulfate decahydrateNa 2 SO 4 *10 H 2 O
Laxative
Pharmacy
28.
Boric acid
Boric (orthoboric) acidH 3 B.O. 3
Eye wash
Pharmacy
29.
Glucose
GlucoseC 6 H 12 O 6
In the form of 40%, 20%, 10%, 5% solutions for injection, in dry form for oral use
Pharmacy
30.
Bleaching powder
Calcium hypochloriteCa(ClO) 2
For rough disinfection
Pharmacy, soap and cleaning products store
31.
Bleaching agent "Whiteness"
Mixture of sodium chloride and hypochloriteNaCl + NaClO
For washing, cleaning, bleaching, disinfection
Soap and cleaning products store
32.
Dry fuel
Urotropine technical (hexamethylenetetraamine)
To produce a flame in the laboratory and field conditions
Household goods store or market
33.
Hexamine 40% solution
Hexamethylenetetraamine (hexamethylenetetraamine)
Osmotic diuretic
Pharmacy
34.
Paraffin
Higher aliphatic hydrocarbons (for example, C 35 N 72 )
Paraffin candles
Household goods store or market
35.
Gelatin
Gelatin, protein substance
For making jellies, jellies, jelly
Grocery store
36.
Starch
Starch, a complex carbohydrate with the general formula (C 6 N 5 ABOUT 10 ) n
For making jelly, paste, starching linen
Grocery store
37.
Phenolphthalein, purgen
Phenolphthalein
Previously used as a laxative, now - only as an indicator in laboratories and health care facilities.
Pharmacies, medical institutions
38.
Ethanol
EthanolC 2 H 5 OH
For treating the skin before injection
Pharmacy
39.
Acetone
AcetoneCH 3 -CO-CH 3
Solvent for paints and varnishes
Hardware stores and markets
40.
Hydrogen peroxide
H 2 O 2
For wound treatment, disinfection, bleaching
Pharmacy
41.
H 2 SO 4
In batteries
42.
Hydrochloric acid
HCl
For soldering and etching
Hardware stores and markets
43.
Ethylene glycol, antifreeze
Ethylene glycol, the simplest dihydric alcohol
As antifreeze - lowers the freezing point of water
44.
Sulfur
SulfurS
Feed additive and treatment for skin diseases
Pet shops, veterinary pharmacies
45.
Reduced iron powder
IronFe
For the treatment of iron deficiency anemia
At the pharmacy
46.
Alcohol tincture of iodine
IodineI
For treating wounds
At the pharmacy
47.
Aluminum foil or powder
AluminumAl
Foil - for baking or wrapping, powder - for making silver paint
In grocery, hardware, construction stores
1.2 . Experiments using silicate glue .
A). Seaweed (or Co-hydrolysis). Add a few crystals to office silicate glue copper sulfate(or a few drops of its concentrated aqueous solution). Observe the appearance of fancy blue-green stains reminiscent of seaweed.
The essence of the process is the joint hydrolysis of two salts: strong foundation and a weak acid (sodium silicate) and a weak base and a strong acid (copper sulfate). When they interact in an aqueous solution, copper silicate is formed, which exists for a very short time and is quickly decomposed by water into silicic acid and copper hydroxide.
Na 2 SiO 3 + CuSO 4 → Na 2 SO 4 + CuSiO 3
CuSiO 3 + 2H 2 O → Cu(OH) 2 ↓+H 2 SiO 3 ↓
Similar experiments were recommended by D.I. Shkurko in the book “Funny Chemistry”: however, the author pointed out that it is possible to carry out the interaction of silicate glue with crystals of salts of copper, iron, cobalt, nickel, aluminum in order to obtain multi-colored “algae”. However, not everyone has the opportunity to find salts of these metals at home.
B) Look for acid at the bottom. For the experiment, you will need silicate glue and a little citric acid solution (you can use diluted acetic acid - in the concentration of table vinegar). A little acid is added to a test tube with silicate glue, and a gelatinous precipitate of silicic acid will immediately fall to the bottom. This is the weakest inorganic acid, even weaker than carbonic acid. It is easily displaced from silicates by organic acids, and, being insoluble, precipitates. This precipitate can only be dissolved by adding alkali.
Reaction equation:
Na 2 SiO 3 + 2 CH 3 COOH ↔ 2 CH 3 COONa + H 2 SiO 3 ↓
IN). We are not friends with salt (or the cation of the same name). Add a few drops of a saturated solution of table salt to the silicate glue. Observe the gradual appearance of a white gelatinous precipitate. This is silicic acid released as a result of increased hydrolysis of sodium silicate.
The presence of the cation of the same name (sodium from table salt) enhances the process of hydrolysis of sodium silicate, bringing it almost to completion - to the formation of insoluble silicic acid. As we can see from the equations for the dissociation of salts in an aqueous solution, the strong base cation of the same name (sodium) shifts the equilibrium of the hydrolysis process to the right, that is, towards the formation of silicic acid.
Dissociation:
Na 2 SiO 3 ↔ 2 Na + + SiO 3 2-
NaCl ↔ Na + + Cl -
Hydrolysis (general equation):
Na 2 SiO 3 + 2 HOH ↔ 2 NaOH + H 2 SiO 3 ↓
1.3 Application in items for household purposes in chemistry lessons.
In educational activities, a chemical experiment not only allows one to establish facts, but also serves as an active means of forming many chemical concepts. For example, the initial formation of the concept of “catalyst” is based on a simple chemical experience of the decomposition of hydrogen peroxide in the presence of manganese (IV) oxide.
Five granules of manganese (IV) oxide are placed in a test tube with 2 ml of a 10% hydrogen peroxide solution. An intense release of oxygen begins, the presence of which is checked using a smoldering splinter. As soon as the smoldering splinter has stopped igniting, carefully drain the liquid from the test tube and again add 2 ml of the original hydrogen peroxide solution to it. Again they prove the presence of oxygen. The experiment is repeated a third time.
Based on observations, students come to the conclusion that manganese (IV) oxide is not consumed during the reaction. Then they independently form a definition of the concept of “catalyst” (a substance that changes the rate of a chemical reaction, but is not consumed during its implementation).
The heuristic function of a school chemical experiment in the development of educational activities is associated, first of all, with the establishment of new factors. Already in the first chemistry lessons in 8th grade, students become familiar with chemicals, study their properties, their application in life, learn a lot of new things, learn to explain, for example, in the 8th grade, by adding a few drops of alkali solution to a phenolphthalein solution, the student is convinced that this indicator changes its color under the influence of alkali. Phenolphthalein can be replaced purgenom. The above example is the simplest case of establishing a fact based on experience.
To realize the goals of developmental education, the conclusions of dependencies and patterns in chemistry are of significant interest. For example, when studying the rate of a chemical reaction, it is necessary to organize the educational process in such a way that students themselves establish the dependence of the reaction rate on the concentration of the reacting substances. For this purpose, they can be asked to react a solution of potassium iodide with a solution of hydrogen peroxide in the presence of starch.
A 3% solution of hydrogen peroxide is poured into three test tubes containing a solution of potassium iodide with starch: in the first test tube - with the original concentration, in the second - diluted two times, and in the third - 4 times. Using a clock, the completion of the reaction is recorded: in the second test tube, the reaction proceeds 2 times slower than in the first, and in the third - 4 times.
Based on their experience, students come to the conclusion that the rate of a reaction is directly proportional to the concentration of the reacting substances.
When studying ion exchange reactions, citric acid and acetic acid can be used to obtain a reaction with precipitation.A little acid is added to a test tube with silicate glue, and a gelatinous precipitate of silicic acid will immediately fall to the bottom. This is the weakest inorganic acid, even weaker than carbonic acid. It is easily displaced from silicates by organic acids, and, being insoluble, precipitates. This precipitate can only be dissolved by adding alkali.
Reaction equation:
Na 2 SiO 3 + 2 CH 3 COOH ↔ 2 CH 3 COONa + H 2 SiO 3 ↓
A gas-evolving reaction is obtained using calcium carbonate (chalk) and a solution of acetic acid.
2. Conclusion .
A chemical experiment serves as a source of knowledge, a means of consolidating knowledge and skills, and a method of monitoring the assimilation of educational material and the development of skills.
Chemistry experiment in high school- a unique opportunity to develop in the student’s thinking the abilities to analyze, synthesize, specify, generalize and systematize new educational material and, as a result, form in the mind of the subject of educational and cognitive activity a harmonious structure of the chemical picture of the world that he has comprehended.
LITERATURE
1. Nazarova T.S., Grabetsky A.A., Lavrova V.N. Chemical experiment at school. - M.: Education, 1987.
2. Pletner Yu.V., Polosin V.S. Workshop on methods of teaching chemistry. - M.: Education, 1981.
3. Polosin V.S. School experiment in inorganic chemistry. - M.: Enlightenment
4. Tarasovskaya N.E., Syzdykova G.K. Visual aids and demonstration material in teaching natural science disciplines in humanitarian and technical universities // Pedagogical Bulletin of Kazakhstan. – Pavlodar, 2007. - No. 2. – P. 76-83.
Chemistry in human life
The experiment covers many areas human activity and is expressed in a controlled change in the conditions for the implementation of a phenomenon for the purpose of studying it.
Chemical experiment is important both in chemical science and in teaching chemistry. The origins of the school chemical experiment methodology were such famous methodologists as V.N. Verkhovsky, K.Ya. Parmenov, V.S. Polosin, L.A. Tsvetkov, A.A. Grabetsky and others.
Let us characterize the triune functions of a chemical experiment. The educational function is that students receive information about the properties of substances, the occurrence of chemical reactions, the methods of chemical science, and the formation of practical skills. Only in close interaction between experiment and theory in the educational process can high quality chemistry teaching be achieved.
The educational function of the experiment includes the formation of beliefs in the objectivity of scientific knowledge in the world, in the possibility of knowledge and transformation of the world.
A chemical experiment promotes the development of independence and increases interest in chemistry, because in the process of performing it, students become convinced not only of the practical significance of such work, but also have the opportunity to creatively apply their knowledge.
A chemical experiment develops students' thinking and mental activity; it can be considered as a criterion for the correctness of the results obtained and the conclusions drawn. A chemical experiment opens up great opportunities both for creating and solving problem situations, and for testing the correctness of the hypothesis put forward. During the experiment, students master general organizational skills in planning and monitoring their own activities. Consequently, the experiment has a positive effect on the development of students, and the teacher has the opportunity to control the processes of thinking, learning and knowledge acquisition.
Heuristic function chemical experiment manifests itself in the establishment of new a) facts; b) concepts and c) patterns.
Corrective function of a chemical experiment manifests itself in overcoming difficulties mastering theoretical material and bug fixes students. Very hour
Generalizing function of a chemical experiment allows us to develop the prerequisites for building various types empirical generalizations. Using a series of experiments, one can draw a general conclusion, for example, about the belonging of various classes of substances to electrolytes.
Research function of a chemical experiment most clearly manifested in problem-based learning.
Types of chemical experiment
There are educational demonstration experiment, performed primarily by the teacher on a demonstration table, and student experiment– it is carried out by students at their workplaces.
Demonstration experiment is carried out mainly when presenting new material to create in schoolchildren specific ideas about substances, chemical phenomena and processes, and then to form chemical concepts. It allows you to make clear important conclusions or generalizations from the field of chemistry in a short period of time, teach you how to perform laboratory experiments and individual techniques and operations.
The demonstration experiment is carried out in the following cases:
– it is impossible to provide the required amount of equipment at the disposal of students;
– the experiment is complex, it cannot be carried out by schoolchildren themselves;
– students do not have the necessary equipment to conduct this experiment;
– experiments with small amounts of substances or on a small scale do not give the desired result;
– experiments are dangerous (working with alkali metals, using high voltage electric current, etc.);
– it is necessary to increase the pace of work in the lesson.
The chemical demonstration experiment must meet following requirements:
– compliance with the goals and objectives of the lesson;
– visibility
– technical simplicity
As a rule, in chemistry the object of study is not the device itself, but the process occurring in it. The complexity of the device and unimportant details of the experiment should not distract students’ attention from the essence of the experiment.
– reliability: the experiment must proceed successfully, without failures, for this it is prepared in advance by the teacher; a failed demonstration experience undermines the teacher's authority. If the experiment still did not work out, you need to find out the reasons for the failure, eliminate them and demonstrate the experience in the next lesson.
– safety
Methods for ensuring the safety of an experiment include: cleanliness of glassware, preliminary checking of reagents, use of reagents in certain quantities, strict adherence to instructions on the experimental technique. If strong effects are expected during the experiment (flash, loud sound), then students are warned in advance.
Student experiment enriches students with knowledge; in the course of it, various skills and abilities are developed. General laboratory skills include: handling chemical glassware and instruments, performing laboratory operations (dissolving, dissolving, filtering, weighing, etc.), obtaining substances, collecting them, recognizing them. Organizational skills are also developed: planning an experiment, self-control, maintaining order in the workplace, etc.
The main types of student experiment include: laboratory experiments, practical classes, workshops. All of them represent types of independent work for students, involving the performance of chemical experiments, and differ primarily in didactic tasks.
Laboratory experiments carried out primarily to study new material or consolidate it.
Practical work have the main didactic task - improving and applying knowledge and skills, as well as their control, each student receives a mark for completing practical work and preparing a report.
Organization of a chemical experiment
A chemistry teacher must be able to plan an experiment on the entire topic and for a specific lesson, apply it methodically correctly, select experimental options, guide the cognitive activity of students, analyze and evaluate their own activities during demonstrations and the activities of students when they independently perform experimental work.
In thematic planning, in accordance with the curriculum, the sequence of demonstrations, laboratory experiments, and practical classes is established. Knowing in advance the timing of the experiment, the teacher has the opportunity to prepare equipment for lessons in advance, teaching aids and etc.
When drawing up lesson plans, the teacher needs to think about at what stage of the lesson, in what sequence, with what reagents and instruments to conduct experiments, determine their place during the lesson depending on the significance of the tasks, as well as the form for recording the results obtained (figure, table, equation reactions, etc.).
The role of the teacher in practical work is to monitor the correct execution of experiments and safety rules, the order on the work table, and the provision of individually differentiated assistance.
Students' performance in practical work is assessed on the basis of a written report and observation results. Such criteria could be:
– error-free and accurate execution of experiments;
– correct recording of explanations, conclusions and reaction equations;
– skillful handling of reagents and equipment;
– quality of report design;
– compliance with safety precautions and discipline during classes.
The quality and strength of acquired skills and abilities depend on the frequency of their use in practical work.
23
II. METHODS AND TECHNIQUES OF TEACHING CHEMICAL EXPERIMENT AT SCHOOL
2.1. Definition of the concept of educational experiment,
its classification and place in teaching chemistry
By the concept of “full-scale 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 for the purpose of knowledge, verification or proof by students of a chemical fact, phenomenon or law known to science, as well as for students to master certain methods of research in chemical science.
An educational chemical experiment should be considered, first of all, as a didactic tool for achieving the main learning goals. 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 over 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 different from the original substances, and with which new experiments can be carried out.
The features and diversity of chemical phenomena, and, consequently, the educational chemical experiment allow it to be used in literally all forms and at all stages of the educational process.
Typically, educational experiments performed in chemistry lessons are divided, depending on the subject of their implementation, into demonstration, laboratory experiments and practical work. A demonstration experiment is performed by a teacher or student for public viewing by all students in the class; one conducts the experiment, the rest observe the progress of the process. Laboratory experiments are carried out, 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 students’ desks. Practical work is an experiment to study a specific topic, performed by students under the guidance of a teacher throughout the lesson.
In principle, this classification of 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 clubs 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 amount of reagents.
Micro-experiment (micro-method) in the form of droplet reactions and microscopic examination of sediments is widely used in analytical chemistry. He has a number obvious advantages: the analysis process is simplified; the desired result is obtained faster, which is especially important in the work of clinical, sanitary and hygienic chemical and technological laboratories; Reagents are consumed less; greater sensitivity is achieved, etc.
However, in school settings, the use of micro-experiments is in most cases impractical. First of all, this applies to demonstration experiments, conducting which in the form of droplet reactions does not make sense, since students will not be able to observe either the course of the reaction or its results. In addition, the use of a microexperiment presupposes the availability of sufficient quantities (for all students) of special equipment: micropipettes, reaction plates, 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 to ensure good visibility of it by all students.
Due to the fact that it is impossible to demonstrate some reactions at school, when studying chemistry, teachers resort to the so-called “thought experiment” - students imagine in their minds, without experimental observation, certain processes characterizing the properties of substances, their production, etc. etc., and mentally predict the results to which this or that experience can lead. We propose to call this type of experiment not a “thought” but a “virtual experiment.” Because we believe that the word “virtual” is more in tune 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”.
Depending on the location, we can distinguish school, home and field educational chemical experiments. In addition, entertaining experiences should play a special role in school. In general, the classification of educational chemical experiments 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 implementation 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 efficiency; in the form of a multimedia experiment, that is, displaying experiments on TV, using a film projector or computer.
Classification of educational chemical experiment
LABORATORY EXPERIMENTS
PRACTICAL WORK OF STUDENTS
DEMONSTRATION-
EXPERIMENT
Goal: learning new material.
Goal: consolidation and improvement of knowledge, formation and improvement of practical skills.
Goal: to form concepts of chemistry; teach to observe phenomena.
Action of indicators on acids and bases.
Color reactions to
Simulation experiments
Experiment carried out according to instructions
Experimental task
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.
Prepare copper oxide in three ways and prove that this substance is a basic oxide.
Prove experimentally that polyethylene contains carbon and hydrogen.
Preparation of carbon (IV) oxide and experiments with it.
Preparation of ethyl acetic acid.
EDUCATIONAL CHEMICAL EXPERIMENT
FIELD EXPERIMENT
VIRTUAL EXPERIMENT
HOMEEXPERIMENT
FUN EXPERIENCES
Goal: to make chemical experiments safer, cheaper and more visual; develop students' thinking.
Goal: to promote the development of interest in the subject and a more conscious assimilation of scientific knowledge.
Goal: formation and development of students’ interest in chemistry.
Decomposition of mercuric oxide or bertholite salt.
Synthesis of organic
connections.
Making smokeless powder.
Eruption.
Spontaneous combustion
alcohol lamps.
Express analysis of soil and water in field conditions.
Chemistry in
everyday life
Obtaining substances
Study of the properties of substances
Experiments with starch.
Experiments with sugar.
Getting indicators.
Obtaining starch.
Properties of table salt, vinegar, soda, etc.
The main goal of demonstration experiments is the development of observation skills, the formation of new knowledge and concepts of chemistry. The key advantages of demonstration experiments are their clarity, the ability to promptly direct students’ attention to the main link of the process, saving time and reagents. However, this type of experiment does not provide the opportunity to develop special skills in students.
Laboratory experiments are remarkable in that when they are included in the explanation of new material, students are convinced with their own eyes of the correctness of certain statements of the teacher and at the same time acquire some skills in a chemical experiment and develop observation skills. At the same time, preparation for conducting these experiments requires more time, reagents are consumed, and the teacher has to pay more attention to ensuring safety in the lesson. The main purpose of laboratory experiments is to provide clarity when studying new material.
Practical work, being an important source of knowledge of new material, also contributes to the formation and improvement of students’ practical skills. The main problems during their implementation are the provision of reagents, utensils and equipment to all students, as well as the implementation of safety rules by all students.
By performing laboratory experiments and practical work, students independently investigate chemical phenomena and patterns, making sure of their reliability in practice. 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 creativity, that is, they would apply their knowledge in new conditions. An important advantage of these types of educational experiments is that students, in contrast to demonstration experiments, include almost all senses in the learning process, which contributes to a more durable and deeper assimilation of the material.
Practical classes are usually held at the end of studying one or more topics of the course and pursue specific goals.
Firstly, it is the consolidation of knowledge in chemistry, including basic experimental material, by independently performing certain experiments by students. At the same time, practical classes conducted at the end of a number of topics make it possible to successfully summarize experimental and theoretical material, which is not always possible in a regular lesson.
Secondly, there is further development of practical skills and mastery of chemical experiment techniques.
Thirdly, the creative application of knowledge in the process is realized experimental solution tasks and practical questions, which is of great importance for developing the ability to use knowledge in an active form, for expanding students’ horizons about the use of chemistry in life.
Skillful organization of a home chemical experiment helps develop students' interest in chemistry, broaden their horizons, and more consciously master chemical knowledge. When helping students organize home laboratories, the teacher needs to inform parents in order to avoid undesirable consequences when conducting experiments at home.
Entertaining experiments can be carried out occasionally in class, but more often used in extracurricular activities in order to form and develop students’ interest in chemistry. However, under no circumstances should chemical experiments be turned into magic tricks, even when demonstrating them in elementary grades. Therefore, when using educational chemical experiments in extracurricular activities, it is necessary to widely use all types of experiments, including field experiments.
As field experiments, we can recommend qualitative reactions to the content of individual elements in environmental objects. Necessary for this chemical reagents and the dishes are placed in special cases or boxes that allow them to be carried or transported without any risk or damage. Each package contains instructions for the analysis technique, a pencil and a blank sheet of paper for drawing up the work.
It is recommended to conduct a virtual experiment in cases where the starting materials 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 actual processes to ensure that students are fully aware of the flow of the upcoming experience. In any case, virtual experiences are based on 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 virtual chemical experiment are experiments that can be designed and “conducted” using computer programs (Chem. Lab., Virtual Chemical Laboratory, etc.).
As in other natural science disciplines, an educational experiment in the teaching of chemistry aims to contribute to the solution of basic educational tasks, such as: mastering the fundamentals of chemical science, becoming familiar with its research methods and mastering special skills; formation and development of students’ abilities, their cognitive and mental activity; polytechnic training and orientation of students to chemical professions; formation of students’ worldview and natural science picture of the world in their minds; implementation of labor, moral, environmental education; comprehensive personality development, 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 the initial source of knowledge of phenomena, as a necessary, and often the only, means of proving the correctness or error of the assumption made, as well as confirmation (illustrations ) indisputable provisions communicated by the teacher or gleaned by students from the textbook; as the only means for developing and improving practical skills in handling equipment, substances, in obtaining and recognizing substances; as an important means for developing, improving and consolidating theoretical knowledge; as a way to test students' knowledge and skills; as a means of developing students’ interest in studying chemistry, developing their powers of observation, curiosity, initiative, and the desire to independently search for and improve knowledge and apply it in practice.
An educational chemical experiment can be successfully used at all stages of the educational process. First of all, the experiment provides students with a visual introduction to the substances being studied. For this purpose, samples of substances and collections in the form of handouts are demonstrated, and experiments are performed to characterize the physical properties of substances. After this, students begin to become familiar with its chemical properties.
When explaining new material, an experiment helps to illustrate the topic being studied not only with relevant chemical phenomena, but also with specific practical applications, as a result, students more consciously perceive the theoretical foundations of chemistry.
Using the experiment when consolidating new topic allows the teacher to identify how new material has been learned and to outline a 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 ongoing, as well as final control and accounting of practical knowledge, one of the means is also a chemical experiment in the form of practical classes for students and solving experimental problems. Using an experiment, you can evaluate many qualities of students, ranging from the level of knowledge of theory to the practical skills of students.
Great opportunities in the training and education of schoolchildren lie in the use of educational experiments in electives, as part of specialized training and in extracurricular activities. Here students are offered more complex experiments, including those with a more pronounced polytechnic focus.
Particular emphasis should be placed on the role of the educational chemical experiment in the formation of cognitive interest among students as a motive for cognitive activity, since it determines and directs all mental processes teachings: perception, memory, thinking, attention, etc.
The importance of using a chemical experiment is great when the teacher uses the method of problem-based presentation of the material. The activity of the teacher here is to pose the problem and reveal an evidence-based way to solve it through setting up an experiment. At the same time, it is important that students themselves come to the conclusion about the need to stage appropriate experiments and take part in their development and implementation. And 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 practical skills established by educational standards as mandatory, including: technical (handling reagents, working with equipment, assembling instruments and installations from finished parts and assemblies, performing chemical operations, observing safety regulations) ; measuring (measurement of temperature, density and volume of liquids and gases, weighing, processing of measurement results); design (production of devices and installations, their repair, improvement and graphic design).
With the help of an experiment, you can evaluate many qualities of students, ranging from the level of knowledge of theory to the practical skills of students.
With all this, we must not forget that a chemical experiment, performing various didactic functions, can be used in various forms and must be combined with other methods and means of teaching. It is a system that uses the principle of gradually increasing student independence: from demonstrating phenomena through conducting laboratory experiments under the guidance of a teacher to independent work in performing practical exercises and solving experimental problems.
A chemical experiment develops students' thinking and mental activity. Often an experiment becomes a source of formed ideas, without which productive mental activity cannot take place. In mental development, theory plays a leading role, but in unity with experiment and practice.
2.2. Methodology and technology 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 with the subsequent formation of chemical concepts. However, demonstrations of experiments do not develop the required experimental skills in students, and therefore must be supplemented with 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 desired result; it is impossible to provide the required 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 for both the experimenter and observers. Other requirements that the experiment must meet include: clarity, the ability to see all the details and moments of the experiment by all students, reliability, expressiveness, emotionality, persuasiveness, quick and simple execution. The demonstration experiment must be combined with the teacher's word. In connection with these requirements, a number of methodological recommendations can be identified.
The teacher is responsible for the safety of students, therefore the classroom must have fire safety equipment, a fume hood for working with harmful and odorous substances, and first aid equipment. Reagents for experiments must be checked in advance, and the glassware for the experiment must be clean. When conducting dangerous experiments, a protective shield should be used.
The demonstration experiment should be conducted 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 he operates with any objects from the view of the students. You can use a lifting table or an overhead projector.
The equipment for demonstrating the experiment should not contain unnecessary parts so that the students’ attention is not distracted from the chemical process. You should not get too carried away with spectacular experiments, as less spectacular experiments will cease to arouse interest.
The experiment must always be successful, and for this purpose the technique of the experiment must be carefully worked out before it is carried out; all stages of the experiment must be thought out; Negligence in the design of the experiment is unacceptable; it is necessary to foresee possible failures during the experiment in advance and prepare spare equipment parts and reagents for such cases. Everything needed for the experiment should be at hand by the teacher. In case of failure, it is necessary to find out its reason and repeat the experiment in this or the next lesson. If possible, experiments should be repeated several times so that students remember them better, otherwise after some time the ideas obtained once will be erased from the students’ memory.
Any experience must be combined with the teacher’s word, since sensory perceptions alone cannot guarantee the development of correct ideas in students. In the process of observation, they may turn their attention not to the main features of an object or phenomenon, but to secondary or incidentally accompanying ones, and as a result receive an incomplete, unclear and even distorted idea of the object being studied. Perception becomes a more correct reflection of the real world, more adequate to it, when the activity of thinking is added to sensations, in this case guided by the word of the teacher.
The teacher is obliged to indicate to 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, pre-prepare students for it, and then help correct perception during the experiment.
The combination of an experiment with the word of a teacher or 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 algorithm is used: “Look and name (list),” that is, the teacher demonstrates a sample of the substance being studied or gives students handouts, for example, samples of aluminum, and asks them 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 repeatedly 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 me what you saw; explain this phenomenon.” For example, when learning the concepts of hydrolysis of salts, the teacher demonstrates the effect of an indicator on various salts. Students see that the indicator colors salt solutions in different ways and note that the solution environment 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 problematic situation. Naturally, students cannot always answer the question posed by the teacher. The essence of hydrolysis is explained by the teacher further during the conversation.
In the considered options, the experiment (demonstration of experience) was preceded by a verbal discussion of what was seen. These combinations of words and visuals are called research.
Let's consider the opposite options. When studying the properties of sulfuric acid, for example, a teacher might say: “Sulfuric acid in aqueous solution has properties typical of inorganic acids and reacts with metals, basic oxides, acids, and salts.” An appropriate demonstration or laboratory experiment is then conducted. The algorithm for this combination of words and visuals can be expressed as follows: “The facts are as follows..., now look how it looks.” This version of the combination of words and clarity is called illustrative. When using it, creating a problem situation in the lesson becomes more difficult.
The illustrative method is appropriate when explaining complex issues that require complete preliminary understanding and understanding on the part of students. For example, to experimentally substantiate the true graphical formula of ethanol, the teacher first discusses possible variants of the formulas. The teacher then 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 essence of the issue. This option is also illustrative, however, during its implementation, a lot of mental and cognitive activity of students takes place, which to a certain extent compensates for the main drawback of this approach - the duration in time. The algorithm can be expressed as follows: “There is an inexplicable, incomprehensible fact or educational problem; hypotheses are expressed to resolve 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 resolve the original problem; if necessary, additional experiments are carried out."
Dividing the methods of combining words and experience into illustrative and exploratory does not mean that the teacher does not say a word during the experiment. In any case, the teacher must explain the course of the experiment and direct the students’ attention to the most important thing at the given moment of the process.
As a rule, demonstration experiments do not need to be lengthy. If it is not possible to choose an experiment that will not last long, then it is best to demonstrate to students in class several intermediate stages of the experiment and its final result.
The pauses that arise while waiting for the result of an experiment should be used to organize a dialogue with schoolchildren, clarify the conditions of the experiment and signs of chemical reactions.
The experiment conducted by the students themselves (laboratory experiments, practical exercises, etc.), which also has a number of features, is of great educational and educational importance. Compared to the teacher's demonstration experiment, it should certainly be safe and feasible for each student to perform; promote the development of skills and abilities in laboratory work techniques, accuracy, prudence and careful handling of materials and equipment; to teach students to take a creative approach to resolving emerging issues.
Laboratory experiments are carried out during the teacher’s explanation according to his oral instructions. In this case, the algorithm most often used is: “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 occur and the corresponding signs are clearly visible for a sufficient time for students to notice and record them in memory.
Practical work (classes) are of two types: those carried out according to instructions and experimental tasks.
The instructions are the indicative basis for students’ activities. It must detail in writing each stage of the experiment, provide instructions on how to avoid possible erroneous actions, and safety instructions for this work.
Before students perform practical work according to instructions, the teacher must clearly and concisely 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 implement it in practice, thereby obtaining a certain material result.
Before conducting a practical lesson, it is necessary to familiarize students with the designs of instruments, laboratory techniques, analyze the goals and content of the work, and link this with homework on analyzing instructions.
During a practical lesson, at the beginning of the lesson there should be a short conversation about safety rules and key points of work. All instruments used in the work must be assembled on the demonstration table. Students must format their work accordingly during the lesson.
The requirements for conducting entertaining experiments and field experiments and the methodology for their implementation follow from the recommendations described above.
Significant problems in organizing an educational chemical experiment are compliance with safety rules when performing experiments, cleaning the workplace, washing dishes and disposing of used reagents.
2.3. Unification of educational experiment
By unifying chemical experiments in teaching, 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 modifications) it is possible to successfully carry out various chemical reactions, both during demonstration experiments and during student experiments.
The basis of the device is a flask or flask with a capacity of 50-200 ml, a stopper with a separating funnel (corresponding to the 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, etc. flasks) (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 directed either directly to reactions involving these gases, or for capture by absorption devices.
Another advantage of this device is the ability to quickly and accurately dose the starting 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 quantities, and not by eye, as is usually the case when demonstrating experiments in test tubes or beakers, when substances and solutions are collected directly in class during the demonstration of experiments.
When using the device, the perception of experience is achieved by all students, and not just those who sit on 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 use of the device using the example of some experiments, grouping them according to similar characteristics.
Obtaining gases. The production of most gases studied in 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. The appropriate solution or liquid reaction reagent is poured into the funnel, the addition of which to the flask is dosed using the tap of the separating funnel. If necessary, the flask with the reaction mixture is heated, adjusting the volume of gas released and the reaction rate.
Using the device and the corresponding reagents, it is possible to obtain oxygen, ozone, chlorine, hydrogen, carbon dioxide, carbon dioxide and sulfur dioxide, hydrogen halides, nitrogen and its oxides, nitric acid from nitrates, ethylene, acetylene, bromoethane, acetic acid from acetates, acetic anhydride, esters and many other gaseous and volatile substances.
Naturally, at the same time, when obtaining gases using the device, it is possible to demonstrate their physical and Chemical properties.
Reactions between solutions. This device is convenient for conducting experiments in which the addition of a liquid reagent must be carried out in small portions or drops, when the course of the reaction is affected by an excess or deficiency of one of the starting substances, etc., for example:
Dissolving sulfuric acid in water and following safety rules for 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 that last for a long 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 substance being studied. Using the device, you can consistently and clearly demonstrate the characteristic physical and chemical properties of the substance being studied with minimal time. At the same time, reagents are saved, the necessary safety of the experiment is achieved (emitted harmful gases and volatile substances are captured by appropriate absorption solutions), and a better perception of the experiment by all students in the class is ensured.
Let's consider preparing and conducting an experiment to demonstrate the properties of hydrochloric acid. Before the lesson, the teacher prepares the required number of flasks (according to the number of reactions being 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 flasks in advance. About 30 ml of a solution (10-20%) of hydrochloric acid is poured into a separatory funnel. During the lesson, the teacher only needs to move the stopper 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 reactions, then the gas outlet tube of the device is lowered into 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 a demonstration experiment on the solubility of gases in water using the example of sulfur (IV) oxide. The experiment will require two devices. In the first device (in a flask - sodium sulfite, in a separating funnel - a concentrated solution of sulfuric acid) sulfur oxide (IV) is obtained, which is collected into the flask of the second device by displacing air. 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 gas solubility.
If you now open the clamp or tap of the gas outlet tube, then due to the small contact surface (through the internal hole of the tube) of sulfur (IV) oxide and water, noticeable dissolution of the gas with subsequent flow 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, pour 1-2 ml of water from the funnel into the flask (with the clamp closed on the gas outlet tube) and shake lightly.
This volume of water is quite enough for the pressure in the flask to decrease, and the water tinted by the indicator, when the clamp is removed from the gas outlet tube, rushes into the flask like a fountain, changing the color of the indicator. To enhance the effect, the flask can be turned upside down by first closing 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 stuck into the bottom of the cork, onto which a piece of dyed fabric or strips of litmus paper are pricked. One of the samples is moistened with water, the second is left dry. The flask is closed with a stopper, several milliliters of concentrated hydrochloric acid are poured into the separating funnel, the gas outlet tube is immersed in a solution of sodium thiosulfate to absorb the excess chlorine released (Fig. 4).
During the demonstration of the experiment, the tap of the separatory funnel is opened slightly and the acid is poured dropwise into the flask, then the tap is closed again. In the flask, a reaction occurs between substances with the release of chlorine; a damp cloth or strip of litmus paper becomes discolored quickly, and a dry one sample - later, as it is moistened.
Rice. 4. Demonstration of dye decolorization.
Note. Many fabrics are dyed with dyes that are resistant to chlorine and other bleaches, so it is necessary to carry out preliminary tests and select appropriate fabric samples in advance. The decolorization of dyes by sulfur dioxide can be shown in the same way.
Adsorption properties of coal or silica gel. About 0.5 g of copper powder or shavings is placed in the flask. A piece of metal wire with a curved end is stuck into the lower part of the plug, to which a small mesh is attached, designed to hold an 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), dipped into a glass with tinted water. After assembly, the device is checked for leaks. At the moment of demonstration of the experiment, the tap of the separating funnel is opened slightly and a few drops are poured out. acid into a flask in which the reaction occurs to release nitric oxide (IV). You should not add excess acid; it is necessary that the volume of gas released 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 placed in front of a white screen. The adsorption of nitrogen 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 on the gas outlet tube is opened.
Experiments on studying the electrical conductivity of substances and solutions. If we pass two additional metal or, better yet, two graphite rods (electrodes) through the plug 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 obtain a setup 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 place the gas outlet tube of the device under a graduated cylinder of water installed in a crystallizer with water, and collect the gas released during the reaction by displacing water, then based on the volume of the resulting gas, you can carry out quantitative calculations to determine molar masses substances, confirmation of the laws of chemical kinetics and thermochemistry, determination of the formula of ethanol and other substances, etc. (Fig. 7). If the gas released during the reaction dissolves or reacts with water, then it is necessary to use other liquids and solutions in the experiments. The given examples do not exhaust all the capabilities of the proposed unified device in an 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 work
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