Education Centre"Paramita" presents a large collection of video materials on chemistry. Along with conducting laboratory workshops at the Center, students are offered chemical programs (video), interesting experiments- for the possibility of additional independent training and better memorization thematic material. The idea of creating something like this interactive program was implemented in 2010 by teachers of our center.
For ease of searching on the website, chemical experiments and programs are divided into three sections: “ general chemistry", "Inorganic Chemistry" and "Organic Chemistry". Each section contains all the video material that is used during the study of the chemistry course.
An interesting video on chemistry for 9th grade students is presented with experiments in the course of inorganic chemistry. Collected on the site. These are entertaining video lessons in chemistry - demonstration of chemical reactions of basic classes inorganic compounds: bases, acids, oxides and salts. For example, a video experiment with chrome, which is a collection of color reactions, is quite popular.
The experiments are classified in the order in which they are considered in curriculum in chemistry. Video experiments in chemistry grade 9 include characteristic chemical reactions elements, according to which the subsections of experiments on the site are named: Hydrogen, Halogens, Oxygen, Sulfur, Nitrogen, Phosphorus, Carbon, Silicon, Alkaline and alkaline earth metals, Aluminium, Iron, Copper, Silver, Chrome and Manganese.
Video experiments in chemistry. presented with course material organic chemistry. According to each class of organic compounds, the sections are arranged in order: Alkanes, Alkenes, Alkynes, Aromatic hydrocarbons, Alcohols, Phenols, Aldehydes and ketones, Amines, Amino acids and Proteins, Fatty acid, Carbohydrates and Polymers.
In fact, the demo video materials of the site are a video tutor in chemistry for an applicant - lessons and experiments for self-study in a chemistry course. This course is taught in grades 8-11 secondary schools. Video lessons in chemistry for the Unified State Exam are a section on the Paramita center website dedicated to demonstrating experiments that are carried out to familiarize students with general patterns and properties of substances (inorganic and organic). Video experiments in chemistry also introduce the basic principles and characteristics of chemical reactions, which is necessary not only in the process successful preparation to the Unified State Exam/State Examination and to the Olympiads, but in the formation of a scientific and practical basis for a deep understanding of chemistry.
Methodology chemical experiment V high school.
Types of chemical experiment
The chemical experiment has important when studying chemistry. There is a distinction between an educational demonstration experiment, performed mainly by a teacher on a demonstration table, and a student experiment - practical work, laboratory experiments And experimental tasks which are carried out by students at their workplaces. A unique type of experiment is a thought experiment.
A 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 understandable in a short period of time important conclusions or generalizations from the field of chemistry, teach how to perform laboratory experiments and individual techniques and operations. Students' attention is directed to performing the experiment and studying its results. They will not passively observe the conduct of experiments and perceive the material presented if the teacher, demonstrating the experiment, accompanies it with explanations. Thus, he focuses attention on experience and teaches him to observe the phenomenon in all its details. In this case, all the teacher’s techniques and actions are perceived not as magical manipulations, but as a necessity, without which it is almost impossible to complete the experiment. During demonstration experiments, compared to laboratory experiments, observations of phenomena take place in a more organized manner. But demonstrations do not develop the necessary experimental skills and abilities, and therefore must be supplemented by laboratory experiments, practical work and experimental tasks.
The demonstration experiment is carried out in the following cases:
It is not possible to provide students with required amount equipment;
The experiment is complex and 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 electric current high voltage, etc.);
It is necessary to increase the pace of work in the lesson.
Naturally, each demonstration experience has its own characteristics depending on the nature of the phenomenon being studied and the specific educational task. At the same time, the chemical demonstration experiment must meet the following requirements:
Be visible (everything that is done on the demonstration table should be clearly visible to all students);
Be simple in technique and easy to understand;
Proceed successfully, without disruptions;
Prepare in advance by the teacher so that the children can easily perceive its content;
Be safe.
The pedagogical effectiveness of a demonstration experiment, its influence on knowledge and experimental skills depend on the experimental technique. This means a set of instruments and devices specially created and used in a demonstration experiment. The teacher should study the classroom equipment as a whole and each device separately, and practice demonstration techniques. The latter is a set of techniques for handling instruments and apparatus in the process of preparing and conducting demonstrations, which ensure their success and expressiveness. Demonstration methodology is a set of techniques that ensure the effectiveness of the demonstration and its best perception. The methodology and demonstration technique are closely related and can be called the technology of demonstration experiment.
When conducting demonstration experiments, a preliminary check of each experiment is very important in terms of technique, quality of reagents, good visibility by students of instruments and the phenomena occurring in them, and guarantees of safety. Sometimes it is advisable to display two devices on the demonstration table: one - assembled and ready for use, the other - disassembled, so that, using it, it is better to explain the structure of the device, for example, a Kipp apparatus, a refrigerator, etc.
You must always remember that any experiment that fails during demonstration undermines the authority of the teacher.
Laboratory experiments - view independent work, which involves performing chemical experiments at any stage of the lesson for more productive learning of the material and obtaining specific, conscious and lasting knowledge. In addition, during laboratory experiments, experimental skills are improved, since students work mainly independently. Performing experiments does not take up the entire lesson, but only part of it.
Laboratory experiments are most often carried out to get acquainted with the physical and chemical properties of substances, as well as to specify theoretical concepts or provisions, less often - to obtain new knowledge. The latter always contain a certain cognitive task that students must solve experimentally. This introduces an element of exploration that activates mental activity schoolchildren. Laboratory experiments, unlike practical work, introduce a small number of facts. In addition, they do not fully capture the attention of students, as practical lessons, because after a short time self-execution work (experience), students must again be ready to perceive the teacher’s explanation.
Laboratory experiments accompany the presentation of educational material by the teacher and, just like demonstrations, create in students visual representations about the properties of substances and chemical processes, they are taught to generalize observed phenomena. But unlike demonstration experiments, they also develop experimental skills. However, not every experiment can be carried out as a laboratory one (for example, ammonia synthesis, etc.). And not every laboratory experiment is more effective than a demonstration one - many laboratory experiments require more time, and the duration directly depends on the quality of the developed experimental skills. The purpose of laboratory experiments is to introduce students to what is being studied as quickly as possible. specific phenomenon(substance). The technique used in this case is reduced to students performing 2-3 operations, which naturally limits the possibilities of forming practical skills and skills.
The preparation of laboratory experiments should be carried out more carefully than demonstration ones. This is due to the fact that any negligence and omission can lead to a violation of the discipline of the entire class.
We must strive to laboratory work each student performed individually. As a last resort, you can allow no more than two people to have one set of equipment. This contributes to better organization and activity of children, as well as to the achievement of the goal of laboratory work.
After completing the experiments, they should be analyzed and a brief record of the work done should be made.
Practical work is a type of independent work when students perform chemical experiments on specific lesson after studying a topic or section of a chemistry course. It helps to consolidate acquired knowledge and develop the ability to apply this knowledge, as well as the formation and improvement of experimental skills.
Practical work requires students to be more independent than laboratory experiments. This is due to the fact that the children are invited to get acquainted at home with the content of the work and the order of their implementation, and repeat theoretical material that is directly related to the work. The student performs practical work independently, which helps to increase discipline, composure and responsibility. And only in some cases, if there is a lack of equipment, can you be allowed to work in groups of two people, but preferably no more.
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.
During practical work Students write down the results of experiments, and at the end of the lesson they draw appropriate conclusions and generalizations.
Methodology for a demonstration experiment in organic chemistry [Tsvetkov L.A., 2000]
The characteristic features of a demonstration experiment in organic chemistry are the following:
Experiment in teaching organic chemistry in to a large extent is a means of “questioning nature,” i.e. a means of experimental research into the issues being studied, and not just by illustrating information about substances reported by the teacher. This is determined by the characteristics of the academic subject, and the fact that organic chemistry is studied on the basis of significant chemical training of students.
The most significant demonstration experiments in most cases turn out to be longer in time than experiments on inorganic chemistry. Sometimes they take almost whole lesson, and in some cases do not fit into the framework of a 45-minute lesson.
Demonstration experiments in some cases are less visual and expressive than in the course of inorganic chemistry, since there is little in the observed processes external changes, and the resulting substances often do not have sharp differences in properties from the original substances.
In experiments in organic chemistry great importance have reaction conditions: even minor change These conditions can lead to a change in the direction of the reaction and the production of completely different substances.
When conducting experiments in organic chemistry, there is a significant danger of students not understanding them sufficiently. This is explained by the fact that experiments occur frequently long time, and sometimes several demonstrations are staged in parallel, which forces students to distribute their attention to several objects simultaneously. In addition, the path from phenomenon to essence is often more difficult here than in the study of inorganic chemistry.
Due to the fact that in school conditions a significant number of important chemical processes cannot be demonstrated; it is inevitable that students will become familiar with a number of facts without demonstrating experiments, based on the teacher’s story, diagrams, drawings, etc.
Let us consider in this sequence what methodological conclusions follow from here.
1. The organic chemistry experiment provides very useful material for the mental development of students and education creativity to solving the problems raised. If we want to use these possibilities, the experiments demonstrated cannot be reduced to just a visual illustration of the teacher’s words. Such teaching is hardly capable of awakening independent thought in students. The experiment is especially valuable as a means of studying nature and since it is a source of knowledge, it develops students’ powers of observation and stimulates their mental activity, and also forces them to compare and analyze facts, create hypotheses and find ways to test them, and be able to come to correct conclusions and generalizations. From this point of view, experiments showing genetic connection classes of organic substances; experiments testing assumptions about the properties of substances and methods for their preparation based on the theory of structure; experiments leading to a conclusion about a particular structure of the molecule of a substance.
In order for demonstration experiments to produce adequate results, it is necessary to strive to fulfill following conditions: a) clearly state the problem that requires an experimental solution, and develop with students the main idea of the experiment; Students must understand the purpose and idea of the experiment before the experiment and be guided by them during the experiment; b) students must be prepared for the experiment, i.e. must have the necessary stock of knowledge and ideas for correct observation and further discussion of experience; c) students should know the purpose of individual parts of the device, the properties of the substances used, what to observe during the experiment, by what signs one can judge the process and the appearance of new substances; d) a chain of reasoning based on the material of experience must be correctly constructed, and students must come to the necessary conclusions based on the experiments themselves under the guidance of the teacher.
It is especially important to ensure the conscious and active participation of students in conducting the experiment and discussing its results. This can be achieved by a system of questions that the teacher poses in connection with the experiment, for example: “What do we want to learn with the help of this experiment?”, “What substances should we take for the experiment?”, “Why do we use this or that part in the device? ", "What was observed in this experiment?", "By what signs can we judge that a chemical reaction was taking place?", "What conditions are necessary for the reaction"?, "Why do you think that such and such a substance was obtained?", " How can one draw this or that conclusion based on this experience?”, “Is it possible to draw such and such a conclusion?” etc. This method of chemical experiment accustoms students to observe correctly, develops sustained attention and rigor of judgment, helps firmly consolidate correct ideas, and develops interest in the subject.
2. Experiments in organic chemistry require great methodological thoroughness due to their duration. Of the experiments recommended by the program and textbooks, over 60% are “long”, requiring from 10 minutes to 1 hour to perform, and in some cases more. Among such experiments are the following: fractional distillation of petroleum, production of bromobenzene, fermentation of glucose, production of bromoethane, nitration of fiber, synthesis of nitrobenzene and aniline, production of acetaldehyde from acetylene, polymerization of methyl methacrylate or other monomer, quantitative experiments in connection with the proof structural formulas and etc.
Some teachers try to avoid lengthy experiments, fearing to delay the pace of the course, others allow significant methodological inaccuracies in setting up such experiments, while others, on the contrary, highly value these experiments, which are characteristic of organic chemistry, and do not deviate from the experiment they have begun. At the same time, the lesson drags on tediously while waiting for the result of the experiment, i.e. there is a waste of time, and pedagogical value lesson again turns out to be low.
How to build a lesson using a long experiment? Where possible, one should strive first of all to reduce the time required to conduct the experiment. This can be achieved in various ways. Sometimes you can limit yourself to obtaining a small amount of a substance, sufficient only for its recognition, or not extract the product into pure form, if he can be identified with conviction as a result of the reaction. It is possible to recommend preheating the reaction mixture or to judiciously reduce the amount of starting materials.
The following techniques also provide a significant reduction in time. Having carried out this or that experiment, you can not wait for its end in this lesson, but, having noted the beginning of the reaction, show the finished products, so that in the next lesson you can present the substances obtained in the experiment started, or, having started the experiment in the lesson, use a similar experience prepared in advance, where the reaction has already largely taken place, and here in the lesson we will focus on the extraction of the resulting substances. Such an organization of experiments will not mean a departure from clarity into dogmatism, since the main stages of the process are preserved here and find the necessary explanation. Students see the slowness of the process and have full confidence in the demonstration of the final stage of the experiment. Experiments are carried out with special care, which cannot be significantly reduced in time using the methods indicated above. Here is one of possible options methodological design similar experiences. Structure is discussed in class ethyl alcohol. Students are asked the question: “What reaction can confirm the presence of a hydroxyl group in an alcohol molecule?” By asking leading questions about which hydroxyl-containing substances were studied in inorganic chemistry and with which substances they reacted, the teacher prompts students to propose a reaction with hydrochloric or hydrobromic acid. If there is a hydroxyl group, you can expect the formation of water and ethyl chloride (bromide), known to students. The starting substances are named, the structure of the device is explained, and the corresponding experiment is carried out. A hypothetical reaction equation is drawn up.
During the experiment, the question is asked: “What reactions can alcohol of the structure we have established still undergo?” Students recall the production of ethylene. The teacher asks how this experiment was carried out in class and offers to create an equation for the reaction. Next, the teacher asks to summarize Chemical properties alcohol The called student indicates the reaction of alcohol with sodium, the reaction to produce ethylene, gives the corresponding equations, writes the equation for the reaction with hydrogen bromide, and names the product formed. At this point, the teacher draws the class's attention to the experience. A significant amount of ethyl bromide has already collected in the receiver. The teacher separates it from the water (without rinsing) and carries it around the class. At the same time he asks: “What is the name of this substance and how was it obtained?” In such cases, students should know very well the purpose of the experiment, the starting substances, the direction of the experiment, so that when returning to it after some distraction they do not have to strain to remember which substances react in in this case and what to expect. The experience should become so firmly ingrained in the mind that students can refer to it at any time, paying, however, their main attention to the issue being discussed in class.
At correct positioning Long-term experiments develop in students the ability to keep several objects in their field of vision at the same time, which is undoubtedly important in further education and in life. In a higher educational institution, already in the first lectures, the ability to distribute attention between listening to the lecture and recording it, between mastering the content of the lecture, recording it and observing the experiments demonstrated is required.
3. Many experiments in organic chemistry fail significantly due to the low visibility of the processes and the resulting substances. In fact, when booking benzene, students from a distance can see neither the manifestation of the reaction nor the bromobenzene formed; during the hydrolysis of sucrose, starch, and fiber, neither a reaction nor new substances are visible (the presence of which can only be determined later indirectly); when producing ether, the same colorless liquid is distilled off from a colorless mixture of substances; when demonstrating receipt esters no changes visible to students occur in the reacting mixture, etc. At incorrect positioning From such experiences, students may not only fail to form the necessary ideas, but may easily form the wrong ideas. Therefore, when observing the separation of liquids, you can tint one of them so that the dividing line is clearly marked. In the same way, it is possible to color water when collecting gases above water and in experiments involving changes in the volume of gases. Coloring liquids is permissible, however, only if the teacher provides clear understanding students of the artificiality of this technique. When distilling liquids, the fall of drops into the receiver can be made more noticeable using a backlight, a white or black screen, etc.; it is necessary to sharply emphasize what properties differ in appearance between the initial and resulting substances, and immediately demonstrate this difference. Where the progress of a reaction can be inferred from the formation of by-products, the latter should be made clearly visible to students (absorption of hydrogen bromide alkaline solution phenolphthalein in the preparation of bromobenzene, etc.).
4. It should be especially noted that for reactions in organic chemistry crucial have the conditions for their occurrence. In inorganic chemistry, these conditions play a lesser role, since many processes already occur at normal conditions and proceed almost unambiguously. Observing chemical reactions without a clear understanding of the conditions for their occurrence negatively affects the quality and strength of knowledge. When the conditions of a reaction are not sufficiently clarified, students may get the wrong idea that the direction of reactions is not determined by anything, is completely arbitrary and does not obey any laws. For example, soon after learning about the production of ethylene from alcohol, students encounter the production of ethyl ether from essentially the same mixture of substances (alcohol and concentrated sulfuric acid). It is completely incomprehensible to them why ether is produced here and not ethylene. To clarify this and thus prevent mistrust of science, we have to return to the experiment with ethylene and now report the conditions for its production. If these conditions had been emphasized in a timely manner, the conditions for the formation of the ether could be compared with them, and knowledge could be more firmly consolidated in this comparison. Therefore, when demonstrating experiments, you should pay attention to the conditions for the reaction and then require students to indicate these conditions in their experiments. This approach organizes students’ observation in the process of experimentation, gives the right direction for studying the material from the book and helps to consolidate specific ideas about phenomena in memory. This helps to check the quality of the students’ assimilation of the material. Constantly emphasizing the conditions of the experiment, showing with some examples negative results failure to comply with experimental conditions, recognition of an answer as incomplete when an equation of reactions is given without a description of the phenomenon itself - all these techniques help the correct study of chemistry. Even in performing exercises and solving problems, whenever possible and appropriate, the conditions under which the corresponding process occurs should be indicated.
5. Modern theory the structure of organic compounds allows us to reveal the essence more deeply than was the case in the study of inorganic chemistry chemical phenomena. From observations of phenomena, the student must move on to an idea of the order of connection of atoms in a molecule, their location in space, the mutual influence of atoms or groups of atoms on the properties of the substance as a whole, and the rearrangement of these atoms during a reaction. If the experiment is used incorrectly, it may turn out that, despite the seemingly complete observance of the principle of clarity, educational material will be presented in a largely dogmatic manner, divorced from experiment, and students’ knowledge may turn out to be formal. This situation may exist, for example, in cases where the teacher strives to begin the study of each substance always strictly according to a certain scheme.
The topic "Ethylene" is being studied. The teacher intends to describe physical properties ethylene, then show its reactions. At the very beginning, he tells the students: “In order to be able to observe ethylene and become familiar with its reactions, we will get it in the laboratory.” An experiment is being carried out to obtain ethylene from ethyl alcohol using sulfuric acid. It would seem that in this case it was necessary to explain the structure of the device, indicate which substances were taken for the reaction, etc. But according to the teacher’s plan, the production of ethylene should be studied after studying the properties, and he does not deviate from this plan here. Students wait tediously while the mixture is heated. What should happen in the experiment, what to follow, what to observe - the students do not know. Only after gas begins to collect in the test tube above the water does the teacher tell the students what ethylene is in terms of its physical properties. Thus, part of the time was wasted uselessly - the students looked at an incomprehensible device and saw nothing of substance. With such a study plan, of course, it would be more expedient to prepare ethylene in cylinders in advance in order to immediately begin demonstrating it in class.
6. When studying organic chemistry, it is neither possible nor necessary to demonstrate all the phenomena about which we're talking about at the lesson. This statement has already been sufficiently substantiated above. Here it is important to consider how to approach the selection of experiments required for demonstration, and how to determine which experiences students can get an idea of from diagrams, drawings, teacher stories, etc.
First of all, it should be assumed that students, of course, must observe in real life all the substances indicated in the program, their most important chemical reactions. In this case, there is no need to reproduce reactions studied many times. Having familiarized students with the reaction of a silver mirror on one representative of aldehydes, they can then use this reaction for practical recognition of substances (for example, to determine aldehyde group in glucose), and after that there is no longer any need to demonstrate this reaction every time it comes up in class.
In each new case, the mention of it evokes in students a fairly vivid image of the phenomenon. Having demonstrated the explosion of methane and ethylene with oxygen, there is no particular need to demonstrate the explosion of acetylene.
It will be enough to refer to previous experiments, pointing out that the explosion of acetylene occurs with even greater force. Similarly, having demonstrated the oxidation of ethyl and methyl alcohol, there is no need to oxidize other alcohols to create students necessary concept. If reactions of acetic acid are indicated, all reactions may not be repeated when studying other acids, etc.
However, in cases where a substance is the direct object of study (butane and isobutane were considered for the sake of the concept of isomerism), one cannot limit oneself to referring to its physical properties without introducing the substance itself. For example, it is impossible not to show benzene on the grounds that students imagine a colorless liquid that freezes at +5°C, boils easily, etc. To form a fairly complete concept of benzene, you also need to become familiar with its smell, consistency, its relationship to other substances, etc. It would be absurd not to show students the reaction of a silver mirror on the basis that they have an idea of a mirror in general. It is impossible, for example, not to show the production and collection of methane or ethylene over water on the basis that previously students observed the production of oxygen, collected nitrogen oxides, etc. The object of study here is not the collection of gas, but the method of obtaining the substance, its properties, and from this angle the corresponding experiment is demonstrated.
In some cases it is necessary to limit verbal description experience without demonstrating it, although students do not yet have the necessary basis for a correct representation of the process. This may be necessary in cases where the new phenomenon being studied cannot be reproduced in school (for example, when the process requires the use of high pressure or when changing conditions for school teaching purposes would distort the picture of the production process being studied).
From the above it follows that the methodology for demonstrating experiments requires careful thought for each lesson. Any experience should be so woven into the logical structure of the lesson that every student can maximum degree understand the meaning and grasp the significance of the experience. In this case, all the possibilities of the experiment will be more fully used to set up proper study substances, phenomena, theories and laws of this science.
In conclusion, it should be recalled here once again that since the basics of a demonstration experiment in organic chemistry are common to the experiment of inorganic chemistry and even to the experiment of other related sciences, it is fully subject to those General requirements, which are presented for any educational experiment. Let us list at least some of these requirements.
The experiment must be “fail-safe”, i.e. turn out for sure and at the same time give the expected, and not unexpected, result. To do this, each experiment is tested before the lesson with the reagents that will be used in the class. The reliability of reagents here often has higher value than in inorganic chemistry. The experiment must be expressive, clearly representing what they want to get from it. To do this, the experiment must be carried out on an appropriate scale, without cluttering the device with unnecessary details and without side effects that distract the attention of students: the experiment must be, as they say, “naked.” Of course, getting rid of unnecessary details should be appropriate. If it is necessary, for example, to show the almost colorless flame of methane, then it is impossible not to pass the gas through at least one wash with alkali before lighting it at the outlet tube. The experiment must be safe to perform in the classroom. If there is any danger (acetylene synthesis, nitro-fiber production), it should only be performed by a teacher and with proper precautions.
Name: Organic chemistry experiment in high school. 2000.
The manual focuses on the experimental methodology used in the study of organic chemistry at school. It provides recommendations for demonstration and laboratory experiment, and useful tips when setting up practical work.
The manual is intended for teachers of secondary schools and specialized classes, lyceums, gymnasiums and other secondary schools. educational institutions. It can also be recommended for students pedagogical universities biological and chemical profile.
There are a number of valuable manuals on experimental issues in teaching inorganic chemistry at school. Outstanding among them is the remarkable work of the late Vadim Nikandrovich Verkhovsky, “Techniques and Methods of Chemical Experiments at School.” There is no special manual on experimental issues in organic chemistry designed for the school curriculum.
As a result, teachers in the process of teaching organic chemistry are often forced to limit themselves chemical experiments, described in the appendix to the stable textbook. But the experiments in the textbook are designed to be performed by students in the classroom and therefore cannot fully provide a demonstration experiment, much less extracurricular activities in chemistry.
It is also significant that the technique and methodology of experiments in organic chemistry in some cases turn out to be more complex than in inorganic chemistry. This is due to some features of experiments with organic substances, for example: the expenditure of often considerable time to carry out reactions, not always sufficient external expressiveness of the processes, etc.
CONTENT:
PART I
GENERAL ISSUES OF THE METHODS OF SCHOOL EXPERIMENTS IN ORGANIC CHEMISTRY
Educational significance school course organic chemistry (6). Scientific and educational experiment in organic chemistry (8). Objectives and content of the experiment in teaching organic chemistry (11). Varieties of educational experiment (14). Methodology for demonstration experiment in organic chemistry (17).
PART II
TECHNIQUES AND METHODS OF SCHOOL EXPERIMENTS IN ORGANIC CHEMISTRY
Chapter I. Saturated hydrocarbons
Methane (26). Producing methane in the laboratory (27). Methane is lighter than air (29). Methane combustion (29). Determination of the qualitative composition of methane (30). Explosion of a mixture of methane and oxygen (31). Replacement of hydrogen in methane with chlorine (32). Other ways to produce methane (33). Experiments with natural gas (35).
Homologues of methane. Experiments with propane (36). Evidence of the qualitative composition of higher hydrocarbons (38).
Halogen derivatives of saturated hydrocarbons. Interaction of halogen derivatives with silver nitrate (38). Displacement of each other by halogens from compounds (39). Thermal decomposition iodoform (39). Discovery of halogens in organic matter (39).
Chapter II. Unsaturated hydrocarbons
Ethylene (40). Combustion of ethylene (41). Explosion of a mixture of ethylene and oxygen (41). Reaction of ethylene with bromine (42). Oxidation of ethylene with permanganate solution (45). Reaction of ethylene with chlorine (addition reaction) (45). Combustion of ethylene in chlorine (46). Preparation of ethylene from ethyl alcohol in the presence of sulfuric acid (46). Preparation of ethylene from dibromoethane (49). Experiments with polyethylene (49). Experiments with other hydrocarbons containing double bond (50).
Acetylene (50). Preparation of acetylene (51). Dissolution of acetylene in water (52). Dissolving acetylene in acetone (52). Combustion of acetylene (52). Explosion of acetylene with oxygen (52). Reaction of acetylene with bromine and potassium permanganate solution (53). Combustion of acetylene in chlorine (53). Experiments with polyvinyl chloride (54).
Rubber (54). Relation of rubber and rubber to solvents (55). Reaction of rubber with bromine (55). Decomposition of rubber when heated (55). Experiments with rubber glue (56). Discovery of sulfur in vulcanized rubber (56). Extraction of rubber from the milky sap of plants (56).
Chapter III. Aromatic hydrocarbons
Benzene (57). Benzene solubility (57). Benzene as a solvent (57). Freezing point of benzene (58). Combustion of benzene (58). The ratio of benzene to bromine water and potassium permanganate solution (58). Bromination of benzene (59). Nitration of benzene (61). Addition of chlorine to benzene (62). Preparation of benzene from benzoic acid and its salts (63).
Benzene homologues. Oxidation of toluene (64). Halogenation of toluene (64). Mobility of halogen atoms in benzene ring and in the side chain (65). Synthesis of benzene homologues (66).
Naphthalene. Sublimation of naphthalene (67).
Styrene Unsaturated properties of styrene (67). Preparation of styrene from polystyrene (68). Experiments with polystyrene (68). Polymerization of styrene (69).
Chapter IV. Oil
Specific gravity and oil solubility (69). Comparative volatility of petroleum products (69). Gasoline and kerosene as solvents (70). Combustion of higher hydrocarbons (70). Explosion of gasoline vapor with air (70). Relation of petroleum hydrocarbons to chemical reagents (71). Fractional distillation of oil (71). Purification of gasoline and kerosene (73).
Chapter V. Alcohols. Phenol. Ethers
Ethanol (ethyl alcohol) (74). Specific gravity of alcohol and change in volume when mixed with water (74). Detection of water in alcohol (74). Detection of higher alcohols (fusel oil) in alcohol (74). Concentrating the alcohol solution (75). Preparation of absolute alcohol (75). Solvent alcohol (76). Burning alcohol (76). Detection of alcohol in wine or beer (76). Interaction of alcohol with sodium (77). Ethanol dehydration (77). Reaction of alcohol with hydrogen bromide (79). Preparation of iodoethane (79). Qualitative reaction for alcohol (81). Preparation of ethyl alcohol from bromoethane (82). Preparation of ethyl alcohol by fermentation of sugar (82). Preparation of ethanol from ethylene in the presence of sulfuric acid (83).
Methanol. Reaction of methanol with hydrogen chloride (85). Production of methanol by dry distillation of wood (86). Comparison of the properties of monohydric alcohols (88).
Glycerol. Solubility of glycerol in water (88). Lowering the freezing point of aqueous solutions of glycerol (89). Hygroscopicity of glycerol (89). Combustion of glycerol (89). Reaction of glycerol with sodium (89). Reaction with copper hydroxide (90).
Phenol. The solubility of phenol in water and alkalis is (90). Phenol - weak acid(91). Reaction of phenol with bromine water(91). Qualitative reaction of phenol (92). Disinfectant effect of phenol (92). Nitration of phenol (92). Preparation of phenol from salicylic acid (92).
Ethers. Low temperature ether boiling (93). Cooling during ether evaporation (93). Ether vapor is heavier than air (94). Mutual solubility of ether and water (94). Ether as a solvent (95). Preparation of ester from alcohol (95). Checking the purity of ether (96). Comparison of the properties of diethyl ether and butanol (97).
Chapter VI. Aldehydes and ketones
Formaldehyde (methanal). Smell of formaldehyde (98). Flammability of formaldehyde (98). Preparation of formaldehyde (98). Reaction of formaldehyde with silver oxide (99). Oxidation of formaldehyde with copper(II) hydroxide (101). Disinfectant effect of formaldehyde (102). Polymerization and depolymerization of aldehyde (102). Reaction of formaldehyde with ammonia (102). Preparation of phenol-formaldehyde resins (103).
Acetaldehyde (ethanal). Preparation of acetaldehyde by oxidation of ethanol (105). Preparation of acetaldehyde by hydration of acetylene (106).
Benzoaldehyde. The smell of benzaldehyde and oxidation by atmospheric oxygen (108). Silver mirror reaction (108).
Acetone (dimethylprolanone). Combustion of acetone (109). The solubility of acetone in water is (109). Acetone as a solvent for resins and plastics (109). Relation to ammonia solution of silver oxide (109). Oxidation of acetone (109). Preparation of bromoacetone (110). Preparation of acetone (III).
Chapter VII. Carboxylic acids
Acetic acid. Crystallization of acetic acid (112). Combustion of acetic acid (113). The ratio of acetic acid to oxidizing agents (113). Effect of acetic acid on indicators (113). Reaction of acid with methyls (113). Interaction with bases (113). Interaction with salts (114). Acetic acid is a weak acid (114). Basicity of acetic acid (115). Quantitative production of methane and* acetic acid salts (115). Acid production by oxidation of ethanol (116). Preparation of acetic acid from its salts (118). Obtaining acid from the products of dry distillation of wood (118). Preparation of acetic anhydride (118). Preparation of acetyl chloride (119). Study of acetic acid sample (120).
Formic acid. Decomposition formic acid to carbon monoxide (II) and water (121). Oxidation of formic acid (122). Preparation of formic acid (122). Reaction of sodium formate with soda lime (124).
Stearic acid. Properties of stearic acid (124). Stearic acid is a weak acid (125). Preparation of soap (sodium stearate) from stearin (125). Obtaining stearic acid from soap (125). Cleansing effect of soap (126). The effect of hard water on soap (126).
Unsaturated acids. Preparation of methacrylic acid (127). Properties of methacrylic acid (128). Unsaturation of oleic acid (128).
Oxalic acid. Preparation of oxalic acid from formic acid (129). Decomposition of oxalic acid when heated with sulfuric acid (129). Oxidation of oxalic acid (130). Formation of acidic and intermediate salts of oxalic acid (131).
Benzoic acid. Solubility of benzoic acid in water (131). Solubility of benzoic acid in alkalis (132). Sublimation of benzoic acid (132). Preparation of benzoic acid by oxidation of benzaldehyde (132). Preparation of benzene from benzoic acid (132).
Lactic and salicylic acids. Properties of lactic acid (133). Experiments with salicylic acid (133).
Chapter VIII. Esters. Fats
Esters (134). Synthesis of ethyl acetate (ethyl acetate) (135). Preparation of benzoic acid ethyl ester (ethyl benzoate) (137). Synthesis of aspirin (137). Hydrolysis of esters (138). Hydrolysis of aspirin (139). Preparation of methacrylic acid methyl ester (methyl methacrylate) from organic glass (140). Preparation of polymethyl methacrylate (141). Experiments with gulimethyl methacrylate (141).
Fats. Fat solubility (141). Extraction of fats and oils (142). Melting and solidification of fats (143). Reaction of unsaturated fats (oils) (144). Determination of the degree of unsaturation of fats (144). Determination of acid content in fats (145). Saponification of fats (145).
Chapter IX. Carbohydrates
Glucose. Physical properties of glucose (147). Reaction of alcohol groups of glucose (148). Reaction of aldehyde group (149). Detection of glucose in fruits and berries (150). Fermentation of glucose (150).
Sucrose. Change in sugar when heated (150). Carbonization of sugar with concentrated sulfuric acid (151). Detection of hydroxyl groups in sugar (151). The ratio of sucrose to a solution of silver oxide and copper (II) hydroxide (152). Hydrolysis of sucrose (152). Obtaining sugar from beets (153).
Starch. Preparation of starch paste (1.55). Reaction of starch with iodine (155). Study various products for the presence of starch (156). Hydrolysis of starch (156). Obtaining molasses and glucose from starch (158). Obtaining starch from potatoes (159).
Fiber (cellulose). Hydrolysis of fiber to glucose (160), Nitration of fiber and experiments with nitrofiber (162).
Chapter X. Amines. Dyes
Fatty amines. Preparation of amines from herring brine (164). Preparation of methylamine from hydrochloride salt and experiments with it (165).
Aniline (166). Relation of aniline to indicators (167). Interaction of aniline with acids (167). Reaction of aniline with bromine water (168). Oxidation of aniline (168). Preparation of aniline (169).
Dyes (171). Synthesis of dimethylaminoazobenzene (171). Synthesis of helianthin (methyl orange) (173).
Chapter XI. Acid amides
Urea. Hydrolysis of urea (175). Interaction of urea with nitric acid(175). Interaction of urea with oxalic acid (176). Biuret formation (176).
Capron. Recognition of polymers. Experiments with nylon (177). Recognition of plastics (177).
Squirrels. Discovery of nitrogen in proteins (178). Discovery of sulfur in proteins (179). Denaturation of proteins by heating (179). Denaturation of proteins upon exposure various substances(179). Color reactions of proteins (180). Xanthoprotein reaction (180). Biuret reaction (181). Combustion as a method for recognizing protein materials (181).
Features of conducting an experiment in organic chemistry.
When teaching organic chemistry, the teacher is given ample opportunities to solve individual educational objectives and more effective development and education of students. The educational experiment, as in inorganic chemistry, in the teaching of organic chemistry is aimed at facilitating the solution of basic educational tasks.
Consideration of phenomena with substances when studying organic chemistry helps students to better understand the processes occurring in the surrounding plant and animal world, to learn the essence and patterns of life. A characteristic feature of organic chemistry is the dependence of the chemical properties of substances on the internal structure of molecules, and not only on the qualitative and quantitative composition.
Students performing experiments in organic chemistry, often more complex than experiments with inorganic substances, contribute to the development of the ability to apply practical knowledge and skills in handling substances and laboratory equipment, which is also important in the professional orientation of students.
An experiment in organic chemistry helps students develop attention, accuracy, observation, perseverance in overcoming difficulties and a number of other qualities.
A purely descriptive study of organic chemistry, when students are required only to list information about individual substances and write equations of chemical reactions, seems to them like a heap of an infinite number of random facts. Structural formulas introduced dogmatically become for students only diagrams that must be memorized and be able to draw.
In general, if the technique of an educational school experiment when studying organic chemistry becomes somewhat more complicated than when studying inorganic chemistry, then the method of using it in the educational process does not differ significantly. Under no circumstances should a chemical experiment in organic chemistry be excluded from the educational process.
At the beginning of the study of organic chemistry, it is useful to experimentally prove that the elements hydrogen and carbon are present in the composition of organic substances.
Discovery of carbon and hydrogen in organic matter. Grind a pea-sized piece of paraffin in a mortar with an equal volume of copper oxide powder. For the experiment, freshly obtained fine oxide powder obtained by calcination of malachite is best suited.
Place the mixture in a test tube, pour a little more CuO powder on top and strengthen the test tube almost horizontally in a stand, slightly tilting it towards the hole, at the edge of which place a pinch of anhydrous copper sulfate. Close the test tube with a stopper with a gas outlet tube, the end of which is placed in a glass of lime water
Picture 1. Discovery of hydrogen and carbon in organic compounds
- CuO with analyte
- Anhydrous CuSO 4
- Glass with lime water.
Heat the mixture in a test tube and observe the formation of drops of liquid on the walls of the test tube, a change in the color of copper sulfate, the release of gas and turbidity lime water. Explain these phenomena, write the corresponding reaction equations, and draw conclusions.
In order to form concepts about the properties of hydrocarbons and other organic compounds, it is convenient and methodologically correct to use a unified approach when explaining them. Simultaneously with the preparation of the substance under study, its physical properties, relationship to oxidizing agents (aqueous solution of KMnO 4), interaction with halogens in aqueous solutions, test for explosion hazard and combustion reaction are demonstrated. For greater safety, copper spirals are inserted into the gas outlet tubes. A separate experiment is carried out to study the special properties of the substances being studied.
The teacher prepares a supply of glassware and reagents for the lesson in advance. Due to the fact that methane, ethylene and acetylene are gaseous substances, and experiments with them are carried out at the time of receipt, there is no time left to discuss each property after its demonstration. Therefore, it is necessary to prepare students to perceive all experiments, quickly carry out these experiments, then write down the corresponding observations, reaction equations and conclusions. It is advisable to carry out such preparation of students by first sketching a table on the board in accordance with the name of the substance that is being studied in this lesson.
Production and properties of methane. In a mortar, stir the mixture of anhydrous sodium acetate and soda lime into volumetrically 1:3. Instead of soda lime, you can just as easily take a mixture of equal volumes of anhydrous sodium acetate, sodium hydroxide and calcium carbonate (chalk), mixed in a mortar. Fill a large dry test tube 1/4 full with the resulting mixture. Close the test tube with a stopper with a gas outlet tube with an extended end, into which place a copper spiral and secure it in the tripod leg, with a slight tilt towards the stopper
Figure 2. Installation for methane production.
Just before producing methane, prepare 4 50 ml glasses. Pour into them, respectively, 30 ml of clean water, a diluted solution of potassium permanganate (light pink color), iodine water (straw yellow color) and 10 ml of a foaming solution (solution of soap, shampoo, washing powder) to test for explosiveness.
To obtain methane, heat the entire test tube evenly, and then strongly heat the part of it where the main part of the mixture is located. First, air will be displaced from the test tube, then methane will begin to be released:
CH 3 COONa + NaOH CH 4 + Na 2 CO 3 .
Physical properties of methane. Pass the methane through a gas outlet tube through clean water. Bubbles of colorless gas - methane - are observed. Typically, methane is collected by displacing water, which leads students to assume that this gas is insoluble in water. The teacher confirms this conclusion. Prove that methane is lighter than air most quickly and clearly by filling a flask balanced upside down on a scale with this gas, as shown in the figure.
Figure 3. Proof of the relative lightness of methane.
The ratio of methane to an aqueous solution of potassium permanganate and iodine water. Insert the gas outlet tube into a glass with a solution of potassium permanganate and let methane pass through for a few seconds. Then carry out the same procedure with iodine water. Note. Due to the fact that unsaturated hydrocarbons may be among the by-products of the methane production reaction, these experiments should not be carried out for too long. The solutions do not change their color, which indicates that methane room temperature does not interact with aqueous solution potassium permanganate and iodine water.
Explosiveness test (testing methane for purity). Dip the gas outlet tube into the foaming solution so that the released gas forms foam. When the glass is filled with foam, remove the gas outlet tube and bring a burning splinter to the foam. Ignition and rapid combustion of methane is observed. If the flash is accompanied by a sharp sound, it means that the methane released from the device contains impurities of atmospheric oxygen. In this case, it is dangerous to ignite gas at the gas outlet pipe. Therefore, the cleanliness check must be repeated again after some time. Only pure methane (like hydrogen), without air admixture, can be ignited during the experiment.
Combustion of methane in the air. Ignite the methane at the end of the gas outlet tube; it will light up with a non-luminous bluish flame:
CH 4 + 2O 2 -> CO 2 + 2H 2 O.
If you place a porcelain cup into a methane flame, a black soot stain will not form on it. The color of the flame turns orange due to the presence of sodium ions in the glass from which the tube is made.
Combustion of methane in chlorine. Get chlorine in a tall transparent container in advance. Close the opening of the vessel with a cotton swab moistened with sodium thiosulfate solution. To demonstrate the interaction of methane with chlorine, replace the straight gas outlet tube with a tube with a curved end, ignite the gas, and add it to the vessel with chlorine, as shown in Figure 4.
Figure 4. Combustion of methane in chlorine.
The entire experiment, with proper preparation, takes about 5 minutes. After which the results of the experiment are discussed, the table is filled out and conclusions are drawn about the correspondence of the properties of methane to the structure of its molecule.
Properties of methane homologues. Pour 3 ml of water into a test tube, add 1 ml of hexane (you can take another saturated hydrocarbon or a mixture thereof). Note the physical properties of the substance, its insolubility in water, and its relative density compared to that of water.
Add a few drops of potassium permanganate solution to the mixture and make sure there is no interaction. Add a little hexane to iodine water (3 ml) and shake the test tube, note the absence of interaction of the hydrocarbon with the halogen. However, due to the better solubility of iodine in hexane, halogen is extracted into the hydrocarbon layer.
To demonstrate the flammability of hexane, pour a few drops of it into a porcelain cup and set it on fire with a long burning splinter. Discuss the results of the experiment, write the corresponding reaction equations and draw conclusions about the properties of methane homologues determined by the structure of the molecules.
Preparation and properties of ethylene. Pour 2–3 ml of 96% ethyl alcohol into a test tube and slowly add 6–9 ml of concentrated sulfuric acid. Stir carefully. To avoid shocks during boiling, add a pinch of dry calcium sulfate or barium sulfate to ensure even boiling. The mixture for producing ethylene can be prepared in advance and stored for a long time. Close the test tube with a stopper with a gas outlet tube.
Figure 5. Installation for ethylene production.
Before obtaining ethylene, prepare solutions of reagents in four glasses, as recommended above to demonstrate the properties of methane.
Carefully heat the entire test tube first, and then heat the part where the upper boundary of the liquid is located. The temperature should be above 140 o C.
Physical properties of ethylene. Using a gas vent tube, pass the ethylene gas through clean water, lowering the tube to the bottom of the glass. Bubbles of a colorless gas, ethylene, are observed. Ethylene is collected by displacing water, which leads students to assume that this gas is insoluble in water. The teacher confirms this conclusion.
The ratio of ethylene to an aqueous solution of potassium permanganate and iodine water. Lower the gas outlet tube to the bottom of the glass with a light pink solution of potassium permanganate. The released gas passes through the potassium permanganate solution and gradually discolors it:
3H 2 C=CH 2 + 2KMnO 4 + 4H 2 O -> 2KOH + 2MnO 2 + 3CH 2 (OH)-CH 2 (OH).
Similarly, pass the resulting ethylene through a straw-yellow solution of iodine water. The solution becomes colorless:
H 2 C=CH 2 + I 2 -> C 2 H 4 I 2.
Explosion test (testing ethylene for purity). The demonstration of this experiment is carried out as described above for methane.
Combustion of ethylene in air and chlorine. For these experiments, bring the flame of a burning splinter to the end of the gas outlet tube. Ethylene ignites and burns with a luminous flame. When a porcelain cup is placed into a flame, a black spot of soot forms on it, the appearance of which can be explained by the higher content (%) of carbon in the ethylene molecule and its incomplete oxidation:
H 2 C = CH 2 + O 2 -> CO 2; WITH; H 2 O
When a bent tube with burning ethylene is introduced into a cylinder with chlorine (see experiments with methane), it continues to burn, releasing even more soot:
C 2 H 4 + Cl 2 = 2 C + 4HCl
The entire experiment takes only a few minutes. After which the results of the experiment are discussed, the table is filled out and conclusions are drawn about the correspondence of the properties of ethylene to the structure of its molecule (in comparison with the structure and properties of methane).
Preparation and properties of acetylene. To obtain acetylene, place 8-10 pea-sized pieces of calcium carbide in the flask of the device. Connect a flexible hose to the tube, at the end of which there should be a glass tube with an extended end and a copper spiral inside, as in Figure 6. Pour a few milliliters of a diluted (1:20) sulfuric acid solution from the separating funnel (the reaction proceeds more calmly):
Figure 6. Installation for acetylene production.
CaC 2 + 2H 2 O -> C 2 H 2 + Ca(OH) 2.
Before obtaining acetylene, prepare 4 glasses of 50 ml with solutions as for experiments with methane and ethylene.
Physical properties of acetylene. Using a gas outlet tube, pass the released gas through the water, lowering the end of the tube to the glass. Bubbles of a colorless gas, acetylene, are observed. Acetylene is collected by displacing water, which gives students reason to assume that this gas is insoluble or poorly soluble in water. The teacher confirms this conclusion.
Note. Acetylene is slightly soluble in water. To confirm this fact, you can add 1-2 drops of iodine water, which becomes discolored, to a glass of water through which acetylene has been passed.
The ratio of acetylene to an aqueous solution of potassium permanganate and iodine water. Pass the evolved gas successively through a dilute solution (pink) of potassium permanganate, and then through a light yellow solution of iodine:
HCCH + 4O -> COOH-COOH (oxalic acid);
HCCH + 2I 2 -> C 2 H 2 I 4 (tetraiodoethane).
Discoloration of solutions is observed. Note. The reactions proceed relatively slower than in the case of ethylene, so solutions of substances for the experiment must be very dilute, with barely noticeable color.
Explosion test (testing acetylene for purity). The demonstration of this experiment is carried out as described above for methane. Ignition and rapid combustion of acetylene with the release of soot is observed.
Acetylene combustion in air. When the experiments are done and acetylene is released from the device without air, bring the flame of a burning splinter to the end of the gas outlet tube. Acetylene ignites and burns with a glowing, smoky flame.
Reaction of acetylene with chlorine. In a tall vessel pre-filled with chlorine (see experiments with methane), add a spoon for burning substances with a piece of calcium carbide moistened with a dilute solution of sulfuric acid ( carefully!). The released acetylene flashes in a chlorine atmosphere and burns, releasing a large amount of soot:
C 2 H 2 + Cl 2 -> 2C + 2HCl.
The entire experiment takes a few minutes. After which the results of the experiment are discussed, the table is filled out and conclusions are drawn about the correspondence of the properties of ethylene to the structure of its molecule (in comparison with the structure and properties of methane and ethylene).
Study of the properties of benzene. Unlike the hydrocarbons discussed above, benzene is a liquid, and it does not require experiments to obtain it in the lesson. Therefore, you can sequentially study its properties, conduct a discussion after each experiment, and then write down the reaction equation.
Physical properties of benzene. Add 1-2 ml of benzene to a test tube with 3–4 ml of water and mix the liquids. The liquids do not mix, therefore benzene does not dissolve in water. A layer of benzene collects above the surface of the water (the phase boundary is visible), therefore the density of benzene is less than unity (0.874 at 20 o C). Place the same test tube in a cup with a cooling mixture (for example, a mixture of potassium nitrate or urea with melting ice or snow). After some time (2–3 minutes), remove the test tube. Benzene solidified, but water remained liquid. Therefore, the solidification temperature of benzene is above 0 o C (+5.4 o C). Then heat the same test tube (not too much) in the burner flame. The top layer (benzene) will begin to boil, but the bottom layer (water) will not. Therefore, the boiling point of benzene is below 100 o C (80.4 o C).
Ratio of benzene to potassium permanganate solution and iodine water(or proof that benzene does not react to unsaturation). Pour 1–2 ml of benzene into a test tube, and then a little potassium permanganate solution (light pink). Shake the mixture. No discoloration occurs (even when heated). Carry out a similar experiment with iodine water. Discoloration also does not occur, but the phenomenon of extraction is observed (iodine goes into upper layer benozla and colors it).
Burning benzene in air. Dip a glass rod into a flask of benzene, then remove it and add a drop of benzene to the flame. Benzene ignites and burns with a highly smoky flame. The appearance of soot is explained in the same way as in the experiment with acetylene.
Nitration of benzene. Pour 1 ml of benzene into a test tube and add an equal volume of the nitrating mixture (a mixture of concentrated sulfuric and nitric acids in a volume ratio of 2:1). Heat the mixture to a boil, then cool it by pouring it into a glass (30–50 ml). It is easy to detect nitrobenzene in the resulting mixture by the smell of bitter almonds:
C 6 H 6 + HONO 2 -> C 6 H 5 NO 2 + H 2 O.
Oxidation of benzene homologues. Pour 2-3 ml of a diluted solution of potassium permanganate into a test tube, acidify it with 2-3 drops of diluted sulfuric acid, add about 1 ml of toluene to the mixture and shake well. Heat the mixture and observe the discoloration of the solution due to the oxidation of toluene into benzoic acid: C 6 H 5 CH 3 + 3O -> C 6 H 5 COOH + H 2 O.
Carry out the xylene oxidation reaction in the same way; in this case, dibasic phthalic acid C 6 H 4 (COOH) 2 is formed.
Note. When studying each subsequent representative of hydrocarbons, similarities and differences with previously studied substances are discussed. A conclusion is drawn about the dependence of properties on the structure of substances. By thus implementing a unified approach to studying the properties of hydrocarbons, the teacher achieves a clearer understanding by students of the characteristics different groups hydrocarbons, and as a result - a more durable consolidation of the material in the students’ memory.
Additional experiment for performing in chemistry classes or during elective courses
Determination of halogens by Beilstein test. Heat the copper wire in the flame of the burner until the flame stops coloring. With the end of the wire (can be hot), touch the substance being analyzed (chloroform, bromobenzene, chloroacetic acid, iodoform, polyvinyl chloride, etc.) and add it to a colorless flame (you can light a little ethanol in a porcelain cup). If the analyzed substance contains chlorine or bromine, then the flame turns a beautiful emerald green color, if iodine, the flame becomes green. The method was proposed in 1872 by F. Beilstein (1838-1906).
Composition of natural or liquefied gas . Place it on gas stove large saucepan with cold water (3-5 l) and light the gas. After a while, you will see droplets of liquid appear on the cold outer surface of the pan. This is water. Where did she come from? Obviously, when gas burns, hydrogen oxide is released. This means that one of the components of natural gas is hydrogen.
Rinse glass jar lime water, drain off the excess so that large drops of solution remain on the walls of the vessel. Hold the jar over the flame of a gas burner ( Beware of burns!), and you will see that the droplets of lime water have become cloudy. This indicates the presence of carbon dioxide. This means that the second component of the gas is carbon.
In addition, in the composition of compounds forming natural gas, there are nitrogen, oxygen, and sulfur in small quantities.
The chemical bond between hydrogen and sulfur is stronger than between hydrogen and carbon. Place a small piece of paraffin the size of a grain of wheat and the same amount of sulfur in a vessel. Heat the mixture. This releases hydrogen sulfide ( smell carefully!) and free carbon.
Properties of gasoline.a) Add a drop of iodine tincture and an equal volume of gasoline to a test tube with 2 ml of water. Shake the mixture well. After liquid separation, two options are possible. First, the color has disappeared, therefore, the sample is cracked gasoline and contains unsaturated hydrocarbons. Second, iodine was extracted in the upper gasoline layer. This means that you have straight distilled gasoline (does not contain unsaturated compounds). In addition, you are convinced that iodine dissolves better in gasoline than in water.
b) Grind a few sunflower seeds or a piece of walnut with 2-3 ml of gasoline. Drain the clear liquid and place one drop on filter paper. After the gasoline evaporates, a greasy stain remains on the paper. Using gasoline, oil is extracted (extracted) from oilseeds at oil extraction plants. Use gasoline to clean clothes from grease stains. Pour a few drops of gasoline into the bottom of a dry and clean metal tin can and set it on fire with a long splinter. (The container with gasoline must be placed on a fireproof stand.) Gasoline is very flammable and burns quickly without soot.
Sublimation of naphthalene. Place mothballs in the bottom of a wide-neck glass bottle (ketchup bottle) or other similar container. Then place a dry branched twig into the bottle. Cover the neck of the vessel with a piece of cotton wool. Now place the bottle in a cold sand bath and start heating (do the experiment in a fume hood). When heated (50 o C), naphthalene sublimes and condenses on the cold walls and branches in the form shiny scales(when sublimation begins, stop heating). Please note that sublimation can be used to purify a substance. Make a guess about the type of naphthalene crystal lattice.
Determination of quantitative relationships in combustion reactions of gaseous hydrocarbons in oxygen. Collect in eudiometer<рисунок 7>oxygen and one of the gaseous hydrocarbons in various volumetric ratios.
Figure 7. Eudiometer.
Set the mixture on fire, after establishing the initial temperature, note the volume of gas above the liquid in the eudiometer and draw appropriate conclusions in accordance with Gay-Lussac's law of volumetric relations.
Questions and tasks to consolidate, clarify and systematize the topic
Any experiments in chemistry lessons must be discussed from the point of view of theoretical principles, from the point of view of using the considered properties of substances in practice; We offer several options for discussion questions.
- Check availability natural sources hydrocarbons in your region. What are their modern role and prospects for use in the regional economy?
- Find out how much natural or liquefied gas your family consumes per year. Calculate the volume of oxygen required to burn this amount of gas and the volume carbon dioxide, standing out at the same time. Discuss your results. How much heat is generated in this process?
- If your home uses other energy sources, such as electricity, make a guess as to which source is cheaper and more environmentally friendly.
- In road transport, compressed propane-butane mixture in cylinders is widely used as motor fuel. Why is cheaper and more accessible natural gas or methane not used for these purposes?
- By studying the physical properties of the simplest saturated hydrocarbons, you became convinced that they are odorless. Why does household gas (natural or in cylinders) have an odor?
- As the number of carbon atoms in hydrocarbon molecules increases, the number of their isomers increases. For example, for dean C 10 H the 22nd number possible isomers equals 75; for more complex compounds this number reaches hundreds and thousands. Do you think it is possible to obtain all these isomers practically?
- Take a close look at a regular lighter. Understand for yourself the meaning of every detail. Pay attention to the principle of its operation, the structure of the flame, and the possibility of its regulation. Write a Treatise on the Lighter. In addition to the description appearance, indicate the composition and properties of the fuel and substances from which the parts are made, as well as the physical and chemical processes, occurring when using modern flint.
P.S. Description of others learning experiences can be found in the work: Shtrempler G.I. METHOD OF EDUCATIONAL CHEMICAL EXPERIMENT AT SCHOOL. Educational and methodological manual for students of chemical specialties. 2008 284 p. Published on the website of the Faculty of Chemistry of Saratov State University: http://www.sgu.ru/faculties/chemical/uch/ped/default.php.