Basics of general chemistry for self-study. Play slot machines for free and without registration online. Is it possible to learn chemistry quickly?
Chemistry. Self-instruction manual. Frenkel E.N.
M.: 20 1 7. - 3 51 p.
The tutorial is based on a technique that the author has been successfully using for more than 20 years. With her help, many schoolchildren were able to enter chemistry faculties and medical universities. This book is a Self-Teacher, not a Textbook. You will not encounter here a simple description of scientific facts and properties of substances. The material is structured in such a way that, if you encounter complex questions that cause difficulties, you will immediately find the author’s explanation. At the end of each chapter there are test tasks and exercises to consolidate the material. For an inquisitive reader who simply wants to expand his horizons, the Self-Teacher will give the opportunity to master this subject “from scratch.” After reading it, you cannot help but fall in love with this most interesting science - chemistry!
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Table of contents
From the author 7
PART 1. ELEMENTS OF GENERAL CHEMISTRY 9
Chapter 1. Basic concepts and laws of the subject “Chemistry” 9
1.1. The simplest concepts: substance, molecule, atom, chemical element 9
1.2. Simple and complex substances. Valence 13
1.3. Chemical reaction equations 17
Chapter 2. Main classes of inorganic compounds 23
2.1. Oxides 23
2.2. Acids 32
2.3. Bases 38
2.4. Salts 44
Chapter 3. Basic information about the structure of the atom 55
3.1. Structure of the Periodic Table of Mendeleev 55
3.2. Nucleus of an atom. Isotopes 57
3.3. Distribution of electrons in the field of the nucleus of an atom 60
3.4. Atomic structure and properties of elements 65
Chapter 4. The concept of chemical bonding 73
4.1. Ionic bond 73
4.2. Covalent bond 75
4.3. Chemical bonding and states of aggregation of matter. Crystal lattices 80
Chapter 5. Rate of chemical reaction 87
5.1. Dependence of the rate of a chemical reaction on various factors 87
5.2. Reversibility of chemical processes. Le Chatelier's principle 95
Chapter 6. Solutions 101
6.1. Concept of solutions 101
6.2. Electrolytic dissociation 105
6.3. Ionic-molecular reaction equations 111
6.4. The concept of pH (hydrogen value) 113
6.5. Hydrolysis of salts 116
Chapter 7. The concept of redox reactions123
PART 2. ELEMENTS OF INORGANIC CHEMISTRY 130
Chapter 8. General properties of metals 130
8.1. Internal structure and physical properties of metals 131
8.2. Alloys 133
8.3. Chemical properties of metals 135
8.4. Metal corrosion 139
Chapter 9. Alkali and alkaline earth metals 142
9.1. Alkali metals 142
9.2. Alkaline earth metals 145
Chapter 10. Aluminum 153
Chapter 11. Iron 158
11.1. Properties of iron and its compounds 158
11.2. Production of iron (iron and steel) 160
Chapter 12. Hydrogen and oxygen 163
12.1. Hydrogen 163
12.2. Oxygen 165
12.3. Water 166
Chapter 13. Carbon and silicon 170
13.1. Atomic structure and properties of carbon 170
13.2. Properties of carbon compounds 173
13.3. Atomic structure and properties of silicon 176
13.4. Silicic acid and silicates 178
Chapter 14. Nitrogen and phosphorus 182
14.1. Atomic structure and properties of nitrogen 182
14.2. Ammonia and ammonium salts 184
14.3. Nitric acid and its salts 187
14.4. Atomic structure and properties of phosphorus 189
14.5. Properties and significance of phosphorus compounds 191
Chapter 15. Sulfur 195
15.1. Atomic structure and properties of sulfur 195
15.2. Hydrogen sulfide 196
15.3. Sulfur dioxide and sulfurous acid 197
15.4. Sulfuric anhydride and sulfuric acid 198
Chapter 16. Halogens 202
16.1. Atomic structure and properties of halogens 202
16.2. Hydrochloric acid 205
SECTION 3. ELEMENTS OF ORGANIC CHEMISTRY 209
Chapter 17. Basic concepts of organic chemistry 210
17.1. Subject of organic chemistry. Theory of the structure of organic substances 210
17.2. Features of the structure of organic compounds 212
17.3. Classification of organic compounds 213
17.4. Formulas of organic compounds 214
17.5. Isomerism 215
17.6. Homologues 217
17.7. Names of hydrocarbons. Rules of international nomenclature 218
Chapter 18. Alkanes 225
18.1. Concept of alkanes 225
18.2. Homologous series, nomenclature, isomerism 225
18.3. Molecular structure 226
18.4. Properties of alkanes 226
18.5. Preparation and use of alkanes 229
Chapter 19. Alkenes 232
19.1. Homologous series, nomenclature, isomerism 232
19.2. Molecular structure 234
19.3. Properties of alkenes 234
19.4. Preparation and use of alkenes 238
19.5. The concept of alkadienes (dienes) 239
Chapter 20. Alkynes 244
20.1. Definition. Homologous series, nomenclature, isomerism 244
20.2. Molecular structure 245
20.3. Properties of alkynes 246
20.4. Preparation and use of acetylene 248
Chapter 21. Cyclic hydrocarbons. Arenas 251
21.1. The concept of cyclic hydrocarbons. Cycloalkanes 251
21.2. The concept of aromatic hydrocarbons 252
21.3. History of the discovery of benzene. Molecule structure 253
21.3. Homologous series, nomenclature, isomerism 255
21.4. Properties of benzene 256
21.5. Properties of benzene homologues 259
21.6. Preparation of benzene and its homologues 261
Chapter 22. Alcohols 263
22.1. Definition 263
22.2. Homologous series, nomenclature, isomerism 264
22.3. The structure of molecules 265
22.4. Properties of monohydric alcohols 266
22.5. Preparation and use of alcohols (using the example of ethyl alcohol) 268
22.6. Polyhydric alcohols 269
22.7. The concept of phenols 271
Chapter 23. Aldehydes 276
23.1. Definition. Homologous series, nomenclature, isomerism 276
23.2. Molecular structure 277
23.3. Properties of aldehydes 278
23.4. Preparation and use of aldehydes using the example of acetaldehyde 280
Chapter 24. Carboxylic acids 282
24.1. Definition 282
24.2. Homologous series, nomenclature, isomerism 283
24.3. Molecular structure 284
24.4. Properties of acids 285
24.5. Preparation and use of acids 287
Chapter 25. Esters. Fats 291
Chapter 26. Carbohydrates 297
Chapter 27. Nitrogen-containing compounds 304
27.1. Amines 304
27.2. Amino acids 306
27.3. Proteins 308
Chapter 28. Concept of polymers 313
PART 4. SOLVING PROBLEMS 316
Chapter 29. Basic calculation concepts 317
Chapter 30. Problems solved using standard formulas 320
30.1. Problems on the topic “Gases” 320
30.2. Problems on the topic “Methods of expressing the concentration of solutions” 324
Chapter 31. Problems solved using reaction equations 330
31.1. Preparation of calculations using reaction equations 330
31.2. Problems on the topic “Quantitative composition of mixtures” 333
31.3. Problems on “excess-deficiency” 337
31.4. Problems to establish the formula of a substance 342
31.5. Problems that take into account the “yield” of the resulting substance 349
Everything around us - on the street, on a robot, in public transport - is related to chemistry. And we ourselves consist of a number of chemical elements and processes. Therefore, the question of how to learn chemistry is quite relevant.
This article is intended for persons over 18 years of age
Have you already turned 18?
Chemistry teaching methods
Not a single branch of industry or agriculture can do without this miracle science. Modern technologies use all possible developments to ensure that progress moves forward. Medicine and pharmacology, construction and light industry, cooking and our everyday life - they all depend on chemistry, its theory and research.
But not all young people of school age understand the need and importance of chemistry in our lives, do not attend lessons, do not listen to teachers and do not delve into the essence of the processes. To interest and instill a love for science and the school curriculum among students in grades 8, 9, 10, teachers use different methods and educational technologies, specific methods and use research technologies.
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Is it easy to learn chemistry on your own?
It often happens that after finishing a course in a certain subject in high school or college, a student realizes that he did not listen carefully and did not understand anything. This may be reflected in his annual grade, and may even cost him a budget place at the university. Therefore, many careless schoolchildren try to study chemistry on their own.
And here questions arise. Is this real? Is it possible to learn a difficult subject on your own? How to organize your time correctly and where to start? Of course, it is possible and quite realistic, the main thing is perseverance and the desire to achieve your goal. Where to start? No matter how trivial it may sound, motivation plays a decisive role in the entire process. It depends on whether you can sit over textbooks for a long time, learn formulas and tables, break down processes and do experiments.
Once you have identified a goal for yourself, you need to start implementing it. If you are starting to learn chemistry from scratch, you can stock up on textbooks for the 8th grade curriculum, guides for beginners, and laboratory notebooks where you will write down the results of your experiments. But there are often situations when home-based teaching is not effective and does not bring the desired results. There can be many reasons: lack of perseverance, lack of willpower, some aspects are unclear, without which further training makes no sense.
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Is it possible to learn chemistry quickly?
Many schoolchildren and students want to learn chemistry from scratch without spending a lot of effort and in a short time; they look online for ways to learn the subject in 5 minutes, in 1 day, in a week or a month. It is impossible to say how long it will take to learn chemistry. It all depends on the desire, motivation, abilities and capabilities of each individual student. And it is worth remembering that quickly learned information disappears from our memory just as quickly. Therefore, is it worth quickly learning the entire school chemistry course in a day? Or is it better to spend more time, but then pass all exams with flying colors?
Regardless of how long you plan to study chemistry, it is worth choosing convenient methods that will facilitate the already difficult task of learning the basics of organic and inorganic chemistry, the characteristics of chemical elements, formulas, acids, alkanes and much more.
The most popular method, which is used in secondary schools, preschool institutions, and in courses for studying a particular subject, is the game method. It allows you to remember a large amount of information in a simple and accessible form without spending a lot of effort. You can buy a young chemist’s kit (yes, don’t let this bother you) and see many important processes and reactions in a simple form, observe the interaction of different substances, and at the same time it is quite safe. In addition, use the method of cards or stickers, which you place on different objects (this is especially suitable for the kitchen) indicating the name of the chemical element, its properties, and formula. When you come across such pictures throughout the house, you will remember the necessary data on a subconscious level.
Alternatively, you can buy a book for children, which describes the initial and main points in a simple form, or you can watch an educational video where chemical reactions are explained based on home experiments.
Don’t forget to control yourself by doing tests and examples, solving problems - this is how you can consolidate your knowledge. Well, repeat the material you have already learned before, and the new material that you are learning now. It is the return and reminder that makes it possible to keep all the information in your head and not forget it before the exam.
An important point is the help of your smartphone or tablet, on which you can install special educational programs in order to learn chemistry. Such applications can be downloaded for free by selecting the desired level of knowledge - for beginners (if you are learning from scratch), intermediate (high school course) or advanced (for students of biological and medical faculties). The advantages of such devices are that you can repeat or learn something new from anywhere and at any time.
And finally. Whatever field you will succeed in the future: science, economics, fine arts, agriculture, military field or industry, remember that knowledge of chemistry will never be superfluous!
E.N.Frenkel
Chemistry tutorial
A manual for those who do not know, but want to learn and understand chemistry
Part I. Elements of general chemistry
(first difficulty level)
I, Frenkel Evgenia Nikolaevna, Honored Worker of Higher Education of the Russian Federation, graduate of the Faculty of Chemistry of Moscow State University in 1972, teaching experience 34 years. In addition, I am the mother of three children and grandmother of four grandchildren, the eldest of whom is in school.
I am concerned about the problem of school textbooks. The main problem of many of them is the difficult language, which requires additional “translation” into a language that students can understand to present educational material. Secondary school students often come to me with the following request: “Translate the text of the textbook so that it is clear.” Therefore, I wrote a “Self-Teacher in Chemistry”, in which many complex issues are presented in a completely accessible and at the same time scientific manner. Based on this “Self-Teacher”, which was written in 1991, I developed the program and content of the preparatory courses. Hundreds of schoolchildren studied there. Many of them started from scratch and after 40 lessons understood the subject so much that they passed exams with “4” and “5”. That’s why in our city my self-teaching manuals are selling like hotcakes.
Maybe others will find my work useful too?
The article was prepared with the support of the MakarOFF training center. The training center offers you to take manicure courses in Moscow inexpensively. The professional manicure school provides training in manicure, pedicure, nail extensions and design, as well as courses for general nail technicians, eyelash extensions, microblading, sugaring and waxing. The center issues diplomas after training and guaranteed employment. Detailed information about all training programs, prices, schedules, promotions and discounts, contacts on the website: www.akademiyauspeha.ru.
Preface
Dear readers! The “Chemistry Self-Teacher” we bring to your attention is not an ordinary textbook. It does not simply state some facts or describe the properties of substances. The “self-teacher” explains and teaches even if, unfortunately, you do not know or understand chemistry, and you cannot or are embarrassed to turn to the teacher for clarification. In manuscript form, this book has been used by schoolchildren since 1991, and there has not been a single student who failed the chemistry exam both at school and in universities. Moreover, many of them did not know chemistry at all.
The “Self-Teacher” is designed for independent work by the student. The main thing is to answer the questions that appear in the text as you read. If you could not answer the question, then read the text carefully again - all the answers are nearby. It is also advisable to perform all the exercises that occur during the explanation of new material. Numerous training algorithms that are practically not found in other textbooks will help with this. With their help you will learn:
Draw up chemical formulas based on valency;
Draw up equations of chemical reactions, arrange coefficients in them, including in equations of redox processes;
Compose electronic formulas (including short electronic formulas) of atoms and determine the properties of the corresponding chemical elements;
Predict the properties of certain compounds and determine whether a given process is possible or not.
The manual has two difficulty levels. Self-instruction manual first difficulty level consists of three parts.
Part I. Elements of general chemistry ( published).
Part II. Elements of inorganic chemistry.
Part III. Elements of organic chemistry.
Books second difficulty level also three.
Theoretical foundations of general chemistry.
Theoretical foundations of inorganic chemistry.
Theoretical foundations of organic chemistry.
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Chapter 1. Basic concepts of chemistry.
Chapter 2. The most important classes of inorganic compounds.
Chapter 3. Basic information about the structure of the atom. Periodic law of D.I.Mendeleev.
Chapter 4. The concept of chemical bonding. Chapter 5. Solutions. Chapter 6. Electrolytic dissociation.
Chapter 7. The concept of redox reactions. Chapter 8. Calculations using chemical formulas and equations.
Application. |
Chapter 1. Basic concepts of chemistry
What is chemistry? Where do we encounter chemical phenomena?
Chemistry is everywhere. Life itself is a countless variety of chemical reactions thanks to which we breathe, see the blue sky, smell the amazing smell of flowers.
What does chemistry study?
Chemistry studies substances, as well as the chemical processes in which these substances participate.
What is a substance?
Matter is what the world around us and ourselves are made of.
What is a chemical process (phenomenon)?
TO chemical phenomena These include processes that result in changes in the composition or structure of the molecules that form a given substance*. The molecules have changed - the substance has changed (it has become different), its properties have changed. For example, fresh milk turned sour, green leaves turned yellow, raw meat changed its smell when fried.
All these changes are a consequence of complex and diverse chemical processes. However, the signs of simple chemical reactions, as a result of which the composition and structure of molecules change, are the same: a change in color, taste or smell, the release of gas, light or heat, the appearance of a precipitate.
What are molecules, the change of which entails such diverse manifestations?
Molecules are the smallest particles of a substance, reflecting its qualitative and quantitative composition and its chemical properties.
By studying the composition and structure of one molecule, it is possible to predict many properties of a given substance as a whole. Such research is one of the main tasks of chemistry.
How are molecules structured? What are they made of?
Molecules are made up of atoms. The atoms in a molecule are connected by chemical bonds. Each atom is designated by symbol(chemical symbol). For example, H is a hydrogen atom, O is an oxygen atom.
The number of atoms in a molecule is indicated using index – numbers at the bottom right after the symbol.
For example:
Examples of molecules:
O 2 is an oxygen molecule consisting of two oxygen atoms;
H 2 O is a water molecule consisting of two hydrogen atoms and one oxygen atom.
If the atoms are not connected by a chemical bond, then their number is indicated using coefficient – numbers before the symbol:
The number of molecules is depicted similarly:
2H 2 – two hydrogen molecules;
3H 2 O – three water molecules.
Why do hydrogen and oxygen atoms have different names and different symbols? Because these are atoms of different chemical elements.
A chemical element is a type of atom with the same nuclear charge.
What is the nucleus of an atom? Why is the nuclear charge a sign that an atom belongs to a given chemical element? To answer these questions, it is necessary to clarify: do atoms change in chemical reactions, what does an atom consist of?
A neutral atom has no charge, although it consists of a positively charged nucleus and negatively charged electrons:
During chemical reactions the number of electrons of any atom can change, but the charge of the atomic nucleus does not change. Therefore, the charge of the nucleus of an atom is a kind of “passport” of a chemical element. All atoms with a nuclear charge of +1 belong to the chemical element called hydrogen. Atoms with a nuclear charge of +8 belong to the chemical element oxygen.
Each chemical element is assigned a chemical symbol (sign), a serial number in D.I. Mendeleev’s table (the serial number is equal to the charge of the atomic nucleus), a specific name, and for some chemical elements a special reading of the symbol in the chemical formula (Table 1).
Table 1
Symbols (signs) of chemical elements
| No. | No. in the table of D.I. Mendeleev | Symbol | Reading in the formula | Name |
| 1 | 1 | H | ash | Hydrogen |
| 2 | 6 | C | tse | Carbon |
| 3 | 7 | N | en | Nitrogen |
| 4 | 8 | O | O | Oxygen |
| 5 | 9 | F | fluorine | Fluorine |
| 6 | 11 | Na | sodium | Sodium |
| 7 | 12 | Mg | magnesium | Magnesium |
| 8 | 13 | Al | aluminum | Aluminum |
| 9 | 14 | Si | silicium | Silicon |
| 10 | 15 | P | pe | Phosphorus |
| 11 | 16 | S | es | Sulfur |
| 12 | 17 | Cl | chlorine | Chlorine |
| 13 | 19 | K | potassium | Potassium |
| 14 | 20 | Ca | calcium | Calcium |
| 15 | 23 | V | vanadium | Vanadium |
| 16 | 24 | Cr | chromium | Chromium |
| 17 | 25 | Mn | manganese | Manganese |
| 18 | 26 | Fe | ferrum | Iron |
| 19 | 29 | Cu | cuprum | Copper |
| 20 | 30 | Zn | zinc | Zinc |
| 21 | 35 | Br | bromine | Bromine |
| 22 | 47 | Ag | argentum | Silver |
| 23 | 50 | Sn | stannum | Tin |
| 24 | 53 | I | iodine | Iodine |
| 25 | 56 | Ba | barium | Barium |
| 26 | 79 | Au | aurum | Gold |
| 27 | 80 | Hg | hydrargyrum | Mercury |
| 28 | 82 | Pb | plumbum | Lead |
There are substances simple And complex . If a molecule consists of atoms of one chemical element, it is simple substance. Simple substances - Ca, Cl 2, O 3, S 8, etc.
Molecules complex substances consist of atoms of different chemical elements. Complex substances - H 2 O, NO, H 3 PO 4, C 12 H 22 O 11, etc.
Task 1.1. Indicate the number of atoms in the molecules of complex substances H 2 O, NO, H 3 PO 4, C 12 H 22 O 11, name these atoms.
The question arises: why is the formula H 2 O always written for water, and not HO or HO 2? Experience proves that the composition of water obtained by any method or taken from any source always corresponds to the formula H 2 O (we are talking about pure water).
The fact is that the atoms in a water molecule and in a molecule of any other substance are connected through chemical bonds. A chemical bond connects at least two atoms. Therefore, if a molecule consists of two atoms and one of them forms three chemical bonds, then the other also forms three chemical bonds.
Number of chemical bonds formed by an atom is called valence.
If we designate each chemical bond with a dash, then for a molecule of two AB atoms we obtain AB, where three dashes indicate the three bonds formed by elements A and B between each other.
In this molecule, atoms A and B are trivalent.
It is known that the oxygen atom is divalent, the hydrogen atom is monovalent.
Question. How many hydrogen atoms can attach to one oxygen atom?
ANSWER: Two atoms. The composition of water is described by the formula H–O–H, or H 2 O.
REMEMBER! A stable molecule cannot have “free” or “extra” valences. Therefore, for a two-element molecule, the number of chemical bonds (valences) of the atoms of one element is equal to the total number of chemical bonds of the atoms of the other element.
Valence of atoms of some chemical elements constant(Table 2).
table 2
The value of constant valences of some elements
For other atoms, valence** can be determined (calculated) from the chemical formula of the substance. In this case, it is necessary to take into account the rule stated above about chemical bonds. For example, let's define the valency x manganese Mn according to the formula of the substance MnO 2:
The total number of chemical bonds formed by one and the other element (Mn and O) is the same:
x· 1 = 4; II · 2 = 4. Hence X= 4, i.e. In this chemical formula, manganese is tetravalent.
PRACTICAL CONCLUSIONS
1. If one of the atoms in the molecule is monovalent, then the valency of the second atom is equal to the number of atoms of the first element (see index!):
2. If the number of atoms in a molecule is the same, then the valence of the first atom is equal to the valence of the second atom:
3. If one of the atoms does not have an index, then its valency is equal to the product of the valency of the second atom and its index:
4. In other cases, put the valences “crosswise”, i.e. the valence of one element is equal to the index of another element:
Task 1.2. Determine the valencies of elements in compounds:
CO 2, CO, Mn 2 O 7, Cl 2 O, P 2 O 3, AlP, Na 2 S, NH 3, Mg 3 N 2.
Clue. First, indicate the valence of atoms for which it is constant. The valence of atomic groups OH, PO 4, SO 4, etc. is determined in the same way.
Task 1.3. Determine the valencies of atomic groups (underlined in the formulas):
H 3 P.O. 4 ,Ca( OH) 2 , Ca 3 ( P.O. 4) 2, H 2 SO 4,Cu SO 4 .
(Note! The same groups of atoms have the same valences in all compounds.)
Knowing the valencies of an atom or group of atoms, you can create a formula for a compound. To do this, use the following rules.
If the valencies of the atoms are the same, then the number of atoms is the same, i.e. We don’t put indexes:
If the valences are multiples (both are divided by the same number), then the number of atoms of the element with a lower valency is determined by division:
In other cases, the indices are determined “crosswise”:
Task 1.4. Make up the chemical formulas of the compounds:
Substances whose composition is reflected by chemical formulas can participate in chemical processes (reactions). The graphical notation corresponding to a given chemical reaction is called reaction equation. For example, when coal burns (interacts with oxygen), a chemical reaction occurs:
C + O 2 = CO 2.
The recording shows that one carbon atom C, combining with one molecule of oxygen O 2, forms one molecule of carbon dioxide CO 2. The number of atoms of each chemical element before and after the reaction must be the same. This rule is a consequence of the law of conservation of mass of matter. Law of conservation of mass: the mass of the starting substances is equal to the mass of the reaction products.
The law was discovered in the 18th century. M.V. Lomonosov and, independently of him, A.L. Lavoisier.
In fulfilling this law, it is necessary to arrange the coefficients in the equations of chemical reactions so that the number of atoms of each chemical element does not change as a result of the reaction. For example, the decomposition of Berthollet salt KClO 3 produces salt KCl and oxygen O 2:
KClO 3 KCl + O 2.
The number of potassium and chlorine atoms is the same, but the number of oxygen atoms is different. Let's equalize them:
Now the number of potassium and chlorine atoms before the reaction has changed. Let's equalize them:
Finally, you can put an equal sign between the right and left sides of the equation:
2KClO 3 = 2KСl + 3О 2.
The resulting record shows that the decomposition of the complex substance KClO 3 produces two new substances - the complex KCl and the simple one - oxygen O 2. The numbers in front of the formulas of substances in the equations of chemical reactions are called coefficients.
When selecting coefficients, it is not necessary to count individual atoms. If the composition of some atomic groups has not changed during the reaction, then the number of these groups can be taken into account, considering them as a single whole. Let's create an equation for the reaction of the substances CaCl 2 and Na 3 PO 4:
CaCl 2 + Na 3 PO 4 ……………….
Sequencing
1) Let's determine the valency of the starting atoms and the PO 4 group:
2) Let’s write the right side of the equation (without subscripts for now, the formulas of the substances in brackets need to be clarified):
3) Let’s compile the chemical formulas of the resulting substances based on the valences of their constituent parts:
4) Let's pay attention to the composition of the most complex compound Ca 3 (PO 4) 2 and equalize the number of calcium atoms (there are three of them) and the number of PO 4 groups (there are two):
5) The number of sodium and chlorine atoms before the reaction is now six. Let's put the corresponding coefficient on the right side of the diagram before the NaCl formula:
3CaCl 2 + 2Na 3 PO 4 = Ca 3 (PO 4) 2 + 6NaCl.
Using this sequence, it is possible to equalize the schemes of many chemical reactions (with the exception of more complex redox reactions, see Chapter 7).
Types of chemical reactions. Chemical reactions are of different types. The main four types are connection, decomposition, substitution and exchange.
1. Compound reactions– from two or more substances one substance is formed:
For example:
Ca + Cl 2 = CaCl 2.
2. Decomposition reactions– from one substance two or more substances are obtained:
For example:
Ca(HCO 3) 2 CaCO 3 + CO 2 + H 2 O.
3. Substitution reactions– simple and complex substances react, simple and complex substances are also formed, and the simple substance replaces part of the atoms of the complex substance:
A + BX AX + B.
For example:
Fe + CuSO 4 = Cu + FeSO 4.
4. Exchange reactions– here two complex substances react and two complex substances are obtained. During the reaction, complex substances exchange their constituent parts:
Exercises for Chapter 1
1. Learn the table. 1. Test yourself, write the chemical symbols: sulfur, zinc, tin, magnesium, manganese, potassium, calcium, lead, iron and fluorine.
2. Write the symbols of the chemical elements that are pronounced in formulas as: “ash”, “o”, “cuprum”, “es”, “pe”, “hydrargyrum”, “stannum”, “plumbum”, “en”, “ferrum” , "ce", "argentum". Name these elements.
3. Indicate the number of atoms of each chemical element in the formulas of the compounds:
Al 2 S 3, CaS, MnO 2, NH 3, Mg 3 P 2, SO 3.
4. Determine which substances are simple and which are complex:
Na 2 O, Na, O 2, CaCl 2, Cl 2.
Read the formulas of these substances.
5. Learn the table. 2. Make up chemical formulas of substances based on the known valency of elements and atomic groups:
6. Determine the valence of chemical elements in compounds:
N 2 O, Fe 2 O 3, PbO 2, N 2 O 5, HBr, SiH 4, H 2 S, MnO, Al 2 S 3.
7. Arrange the coefficients and indicate the types of chemical reactions:
a) Mg + O 2 MgO;
b) Al + CuCl 2 AlCl 3 + Cu;
c) NaNO 3 NaNO 2 + O 2;
d) AgNO 3 + BaCl 2 AgCl + Ba(NO 3) 2;
e) Al + HCl AlCl 3 + H 2;
e) KOH + H 3 PO 4 K 3 PO 4 + H 2 O;
g) CH 4 C 2 H 2 + H 2 .
* There are substances that are not built from molecules. But these substances will be discussed later (see Chapter 4).
** Strictly speaking, according to the rules below, it is not the valency that is determined, but the oxidation state (see Chapter 7). However, in many compounds the numerical values of these concepts coincide, so the valence can also be determined using the formula of a substance.
Reprinted with continuation
E.N.Frenkel
Chemistry tutorial
A manual for those who do not know, but want to learn and understand chemistry
Part I. Elements of general chemistry
(first difficulty level)
I, Frenkel Evgenia Nikolaevna, Honored Worker of Higher Education of the Russian Federation, graduate of the Faculty of Chemistry of Moscow State University in 1972, teaching experience 34 years. In addition, I am the mother of three children and grandmother of four grandchildren, the eldest of whom is in school.
I am concerned about the problem of school textbooks. The main problem of many of them is the difficult language, which requires additional “translation” into a language that students can understand to present educational material. Secondary school students often come to me with the following request: “Translate the text of the textbook so that it is clear.” Therefore, I wrote a “Self-Teacher in Chemistry”, in which many complex issues are presented in a completely accessible and at the same time scientific manner. Based on this “Self-Teacher”, which was written in 1991, I developed the program and content of the preparatory courses. Hundreds of schoolchildren studied there. Many of them started from scratch and after 40 lessons understood the subject so much that they passed exams with “4” and “5”. That’s why in our city my self-teaching manuals are selling like hotcakes.
Maybe others will find my work useful too?
The article was prepared with the support of the MakarOFF training center. The training center offers you to take manicure courses in Moscow inexpensively. The professional manicure school provides training in manicure, pedicure, nail extensions and design, as well as courses for general nail technicians, eyelash extensions, microblading, sugaring and waxing. The center issues diplomas after training and guaranteed employment. Detailed information about all training programs, prices, schedules, promotions and discounts, contacts on the website: www.akademiyauspeha.ru.
Preface
Dear readers! The “Chemistry Self-Teacher” we bring to your attention is not an ordinary textbook. It does not simply state some facts or describe the properties of substances. The “self-teacher” explains and teaches even if, unfortunately, you do not know or understand chemistry, and you cannot or are embarrassed to turn to the teacher for clarification. In manuscript form, this book has been used by schoolchildren since 1991, and there has not been a single student who failed the chemistry exam both at school and in universities. Moreover, many of them did not know chemistry at all.
The “Self-Teacher” is designed for independent work by the student. The main thing is to answer the questions that appear in the text as you read. If you could not answer the question, then read the text carefully again - all the answers are nearby. It is also advisable to perform all the exercises that occur during the explanation of new material. Numerous training algorithms that are practically not found in other textbooks will help with this. With their help you will learn:
Draw up chemical formulas based on valency;
Draw up equations of chemical reactions, arrange coefficients in them, including in equations of redox processes;
Compose electronic formulas (including short electronic formulas) of atoms and determine the properties of the corresponding chemical elements;
Predict the properties of certain compounds and determine whether a given process is possible or not.
The manual has two difficulty levels. Self-instruction manual first difficulty level consists of three parts.
Part I. Elements of general chemistry ( published).
Part II. Elements of inorganic chemistry.
Part III. Elements of organic chemistry.
Books second difficulty level also three.
Theoretical foundations of general chemistry.
Theoretical foundations of inorganic chemistry.
Theoretical foundations of organic chemistry.
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Chapter 1. Basic concepts of chemistry.
Chapter 2. The most important classes of inorganic compounds.
Chapter 3. Basic information about the structure of the atom. Periodic law of D.I.Mendeleev.
Chapter 4. The concept of chemical bonding. Chapter 5. Solutions. Chapter 6. Electrolytic dissociation.
Chapter 7. The concept of redox reactions. Chapter 8. Calculations using chemical formulas and equations.
Application. |
Chapter 1. Basic concepts of chemistry
What is chemistry? Where do we encounter chemical phenomena?
Chemistry is everywhere. Life itself is a countless variety of chemical reactions thanks to which we breathe, see the blue sky, smell the amazing smell of flowers.
What does chemistry study?
Chemistry studies substances, as well as the chemical processes in which these substances participate.
What is a substance?
Matter is what the world around us and ourselves are made of.
What is a chemical process (phenomenon)?
TO chemical phenomena These include processes that result in changes in the composition or structure of the molecules that form a given substance*. The molecules have changed - the substance has changed (it has become different), its properties have changed. For example, fresh milk turned sour, green leaves turned yellow, raw meat changed its smell when fried.
All these changes are a consequence of complex and diverse chemical processes. However, the signs of simple chemical reactions, as a result of which the composition and structure of molecules change, are the same: a change in color, taste or smell, the release of gas, light or heat, the appearance of a precipitate.
What are molecules, the change of which entails such diverse manifestations?
Molecules are the smallest particles of a substance, reflecting its qualitative and quantitative composition and its chemical properties.
By studying the composition and structure of one molecule, it is possible to predict many properties of a given substance as a whole. Such research is one of the main tasks of chemistry.
How are molecules structured? What are they made of?
Molecules are made up of atoms. The atoms in a molecule are connected by chemical bonds. Each atom is designated by symbol(chemical symbol). For example, H is a hydrogen atom, O is an oxygen atom.
The number of atoms in a molecule is indicated using index – numbers at the bottom right after the symbol.
For example:
Examples of molecules:
O 2 is an oxygen molecule consisting of two oxygen atoms;
H 2 O is a water molecule consisting of two hydrogen atoms and one oxygen atom.
If the atoms are not connected by a chemical bond, then their number is indicated using coefficient – numbers before the symbol:
The number of molecules is depicted similarly:
2H 2 – two hydrogen molecules;
3H 2 O – three water molecules.
Why do hydrogen and oxygen atoms have different names and different symbols? Because these are atoms of different chemical elements.
A chemical element is a type of atom with the same nuclear charge.
What is the nucleus of an atom? Why is the nuclear charge a sign that an atom belongs to a given chemical element? To answer these questions, it is necessary to clarify: do atoms change in chemical reactions, what does an atom consist of?
A neutral atom has no charge, although it consists of a positively charged nucleus and negatively charged electrons:
During chemical reactions the number of electrons of any atom can change, but the charge of the atomic nucleus does not change. Therefore, the charge of the nucleus of an atom is a kind of “passport” of a chemical element. All atoms with a nuclear charge of +1 belong to the chemical element called hydrogen. Atoms with a nuclear charge of +8 belong to the chemical element oxygen.
Each chemical element is assigned a chemical symbol (sign), a serial number in D.I. Mendeleev’s table (the serial number is equal to the charge of the atomic nucleus), a specific name, and for some chemical elements a special reading of the symbol in the chemical formula (Table 1).
Table 1
Symbols (signs) of chemical elements
| No. | No. in the table of D.I. Mendeleev | Symbol | Reading in the formula | Name |
| 1 | 1 | H | ash | Hydrogen |
| 2 | 6 | C | tse | Carbon |
| 3 | 7 | N | en | Nitrogen |
| 4 | 8 | O | O | Oxygen |
| 5 | 9 | F | fluorine | Fluorine |
| 6 | 11 | Na | sodium | Sodium |
| 7 | 12 | Mg | magnesium | Magnesium |
| 8 | 13 | Al | aluminum | Aluminum |
| 9 | 14 | Si | silicium | Silicon |
| 10 | 15 | P | pe | Phosphorus |
| 11 | 16 | S | es | Sulfur |
| 12 | 17 | Cl | chlorine | Chlorine |
| 13 | 19 | K | potassium | Potassium |
| 14 | 20 | Ca | calcium | Calcium |
| 15 | 23 | V | vanadium | Vanadium |
| 16 | 24 | Cr | chromium | Chromium |
| 17 | 25 | Mn | manganese | Manganese |
| 18 | 26 | Fe | ferrum | Iron |
| 19 | 29 | Cu | cuprum | Copper |
| 20 | 30 | Zn | zinc | Zinc |
| 21 | 35 | Br | bromine | Bromine |
| 22 | 47 | Ag | argentum | Silver |
| 23 | 50 | Sn | stannum | Tin |
| 24 | 53 | I | iodine | Iodine |
| 25 | 56 | Ba | barium | Barium |
| 26 | 79 | Au | aurum | Gold |
| 27 | 80 | Hg | hydrargyrum | Mercury |
| 28 | 82 | Pb | plumbum | Lead |
There are substances simple And complex . If a molecule consists of atoms of one chemical element, it is simple substance. Simple substances - Ca, Cl 2, O 3, S 8, etc.
Molecules complex substances consist of atoms of different chemical elements. Complex substances - H 2 O, NO, H 3 PO 4, C 12 H 22 O 11, etc.
Task 1.1. Indicate the number of atoms in the molecules of complex substances H 2 O, NO, H 3 PO 4, C 12 H 22 O 11, name these atoms.
The question arises: why is the formula H 2 O always written for water, and not HO or HO 2? Experience proves that the composition of water obtained by any method or taken from any source always corresponds to the formula H 2 O (we are talking about pure water).
The fact is that the atoms in a water molecule and in a molecule of any other substance are connected through chemical bonds. A chemical bond connects at least two atoms. Therefore, if a molecule consists of two atoms and one of them forms three chemical bonds, then the other also forms three chemical bonds.
Number of chemical bonds formed by an atom is called valence.
If we designate each chemical bond with a dash, then for a molecule of two AB atoms we obtain AB, where three dashes indicate the three bonds formed by elements A and B between each other.
In this molecule, atoms A and B are trivalent.
It is known that the oxygen atom is divalent, the hydrogen atom is monovalent.
Question. How many hydrogen atoms can attach to one oxygen atom?
ANSWER: Two atoms. The composition of water is described by the formula H–O–H, or H 2 O.
REMEMBER! A stable molecule cannot have “free” or “extra” valences. Therefore, for a two-element molecule, the number of chemical bonds (valences) of the atoms of one element is equal to the total number of chemical bonds of the atoms of the other element.
Valence of atoms of some chemical elements constant(Table 2).
table 2
The value of constant valences of some elements
For other atoms, valence** can be determined (calculated) from the chemical formula of the substance. In this case, it is necessary to take into account the rule stated above about chemical bonds. For example, let's define the valency x manganese Mn according to the formula of the substance MnO 2:
The total number of chemical bonds formed by one and the other element (Mn and O) is the same:
x· 1 = 4; II · 2 = 4. Hence X= 4, i.e. In this chemical formula, manganese is tetravalent.
PRACTICAL CONCLUSIONS
1. If one of the atoms in the molecule is monovalent, then the valency of the second atom is equal to the number of atoms of the first element (see index!):
2. If the number of atoms in a molecule is the same, then the valence of the first atom is equal to the valence of the second atom:
3. If one of the atoms does not have an index, then its valency is equal to the product of the valency of the second atom and its index:
4. In other cases, put the valences “crosswise”, i.e. the valence of one element is equal to the index of another element:
Task 1.2. Determine the valencies of elements in compounds:
CO 2, CO, Mn 2 O 7, Cl 2 O, P 2 O 3, AlP, Na 2 S, NH 3, Mg 3 N 2.
Clue. First, indicate the valence of atoms for which it is constant. The valence of atomic groups OH, PO 4, SO 4, etc. is determined in the same way.
Task 1.3. Determine the valencies of atomic groups (underlined in the formulas):
H 3 P.O. 4 ,Ca( OH) 2 , Ca 3 ( P.O. 4) 2, H 2 SO 4,Cu SO 4 .
(Note! The same groups of atoms have the same valences in all compounds.)
Knowing the valencies of an atom or group of atoms, you can create a formula for a compound. To do this, use the following rules.
If the valencies of the atoms are the same, then the number of atoms is the same, i.e. We don’t put indexes:
If the valences are multiples (both are divided by the same number), then the number of atoms of the element with a lower valency is determined by division:
In other cases, the indices are determined “crosswise”:
Task 1.4. Make up the chemical formulas of the compounds:
Substances whose composition is reflected by chemical formulas can participate in chemical processes (reactions). The graphical notation corresponding to a given chemical reaction is called reaction equation. For example, when coal burns (interacts with oxygen), a chemical reaction occurs:
C + O 2 = CO 2.
The recording shows that one carbon atom C, combining with one molecule of oxygen O 2, forms one molecule of carbon dioxide CO 2. The number of atoms of each chemical element before and after the reaction must be the same. This rule is a consequence of the law of conservation of mass of matter. Law of conservation of mass: the mass of the starting substances is equal to the mass of the reaction products.
The law was discovered in the 18th century. M.V. Lomonosov and, independently of him, A.L. Lavoisier.
In fulfilling this law, it is necessary to arrange the coefficients in the equations of chemical reactions so that the number of atoms of each chemical element does not change as a result of the reaction. For example, the decomposition of Berthollet salt KClO 3 produces salt KCl and oxygen O 2:
KClO 3 KCl + O 2.
The number of potassium and chlorine atoms is the same, but the number of oxygen atoms is different. Let's equalize them:
Now the number of potassium and chlorine atoms before the reaction has changed. Let's equalize them:
Finally, you can put an equal sign between the right and left sides of the equation:
2KClO 3 = 2KСl + 3О 2.
The resulting record shows that the decomposition of the complex substance KClO 3 produces two new substances - the complex KCl and the simple one - oxygen O 2. The numbers in front of the formulas of substances in the equations of chemical reactions are called coefficients.
When selecting coefficients, it is not necessary to count individual atoms. If the composition of some atomic groups has not changed during the reaction, then the number of these groups can be taken into account, considering them as a single whole. Let's create an equation for the reaction of the substances CaCl 2 and Na 3 PO 4:
CaCl 2 + Na 3 PO 4 ……………….
Sequencing
1) Let's determine the valency of the starting atoms and the PO 4 group:
2) Let’s write the right side of the equation (without subscripts for now, the formulas of the substances in brackets need to be clarified):
3) Let’s compile the chemical formulas of the resulting substances based on the valences of their constituent parts:
4) Let's pay attention to the composition of the most complex compound Ca 3 (PO 4) 2 and equalize the number of calcium atoms (there are three of them) and the number of PO 4 groups (there are two):
5) The number of sodium and chlorine atoms before the reaction is now six. Let's put the corresponding coefficient on the right side of the diagram before the NaCl formula:
3CaCl 2 + 2Na 3 PO 4 = Ca 3 (PO 4) 2 + 6NaCl.
Using this sequence, it is possible to equalize the schemes of many chemical reactions (with the exception of more complex redox reactions, see Chapter 7).
Types of chemical reactions. Chemical reactions are of different types. The main four types are connection, decomposition, substitution and exchange.
1. Compound reactions– from two or more substances one substance is formed:
For example:
Ca + Cl 2 = CaCl 2.
2. Decomposition reactions– from one substance two or more substances are obtained:
For example:
Ca(HCO 3) 2 CaCO 3 + CO 2 + H 2 O.
3. Substitution reactions– simple and complex substances react, simple and complex substances are also formed, and the simple substance replaces part of the atoms of the complex substance:
A + BX AX + B.
For example:
Fe + CuSO 4 = Cu + FeSO 4.
4. Exchange reactions– here two complex substances react and two complex substances are obtained. During the reaction, complex substances exchange their constituent parts:
Exercises for Chapter 1
1. Learn the table. 1. Test yourself, write the chemical symbols: sulfur, zinc, tin, magnesium, manganese, potassium, calcium, lead, iron and fluorine.
2. Write the symbols of the chemical elements that are pronounced in formulas as: “ash”, “o”, “cuprum”, “es”, “pe”, “hydrargyrum”, “stannum”, “plumbum”, “en”, “ferrum” , "ce", "argentum". Name these elements.
3. Indicate the number of atoms of each chemical element in the formulas of the compounds:
Al 2 S 3, CaS, MnO 2, NH 3, Mg 3 P 2, SO 3.
4. Determine which substances are simple and which are complex:
Na 2 O, Na, O 2, CaCl 2, Cl 2.
Read the formulas of these substances.
5. Learn the table. 2. Make up chemical formulas of substances based on the known valency of elements and atomic groups:
6. Determine the valence of chemical elements in compounds:
N 2 O, Fe 2 O 3, PbO 2, N 2 O 5, HBr, SiH 4, H 2 S, MnO, Al 2 S 3.
7. Arrange the coefficients and indicate the types of chemical reactions:
a) Mg + O 2 MgO;
b) Al + CuCl 2 AlCl 3 + Cu;
c) NaNO 3 NaNO 2 + O 2;
d) AgNO 3 + BaCl 2 AgCl + Ba(NO 3) 2;
e) Al + HCl AlCl 3 + H 2;
e) KOH + H 3 PO 4 K 3 PO 4 + H 2 O;
g) CH 4 C 2 H 2 + H 2 .
* There are substances that are not built from molecules. But these substances will be discussed later (see Chapter 4).
** Strictly speaking, according to the rules below, it is not the valency that is determined, but the oxidation state (see Chapter 7). However, in many compounds the numerical values of these concepts coincide, so the valence can also be determined using the formula of a substance.
Reprinted with continuation
Chapter 1.
General chemical and environmental patterns.
Where does chemistry begin?
Is this a difficult question? Everyone will answer it differently.
In secondary school, students study chemistry over a number of years. Many people do quite well on their final exam in chemistry. However…
Conversations with applicants and then first-year students indicate that residual knowledge in chemistry after secondary school is insignificant. Some get confused in various definitions and chemical formulas, while others cannot even reproduce the basic concepts and laws of chemistry, not to mention the concepts and laws of ecology.
Their chemistry never started.
Chemistry, apparently, begins with a deep mastery of its fundamentals, and above all, the basic concepts and laws.
1.1. Basic chemical concepts.
In D.I. Mendeleev’s table there are numbers next to the element symbol. One number indicates the atomic number of the element, and the second atomic mass. The serial number has its own physical meaning. We will talk about it later, here we will focus on atomic mass and highlight in what units it is measured.
It should be noted right away that the atomic mass of an element given in the table is a relative value. The unit of relative atomic mass is taken to be 1/12 of the mass of a carbon atom, an isotope with a mass number of 12, and is called the atomic mass unit /amu/. Therefore, 1 amu equal to 1/12 of the mass of the carbon isotope 12 C. And it is equal to 1.667 * 10 –27 kg. /The absolute mass of a carbon atom is 1.99*10 –26 kg./
Atomic mass, given in the table, is the mass of the atom expressed in atomic mass units. The quantity is dimensionless. Specifically for each element, atomic mass shows how many times the mass of a given atom is greater or less than 1/12 of the mass of a carbon atom.
The same can be said about molecular weight.
Molecular mass is the mass of a molecule expressed in atomic mass units. The magnitude is also relative. The molecular mass of a particular substance is equal to the sum of the masses of the atoms of all the elements that make up the molecule.
An important concept in chemistry is the concept of “mole”. Mole– such an amount of substance that contains 6.02 * 10 23 structural units /atoms, molecules, ions, electrons, etc./. Mole of atoms, mole of molecules, mole of ions, etc.
The mass of one mole of a given substance is called its molar / or molar / mass. It is measured in g/mol or kg/mol and is designated by the letter “M”. For example, the molar mass of sulfuric acid M H 2 SO4 = 98 g/mol.
The next concept is “Equivalent”. Equivalent/E/ is the weight amount of a substance that interacts with one mole of hydrogen atoms or replaces such an amount in chemical reactions. Therefore, the equivalent of hydrogen E H is equal to one. /E N =1/. The oxygen equivalent E O is equal to eight /E O =8/.
A distinction is made between the chemical equivalent of an element and the chemical equivalent of a complex substance.
The equivalent of an element is a variable quantity. It depends on the atomic mass /A/ and valence /B/ that the element has in a particular compound. E=A/B. For example, let's determine the equivalent of sulfur in the oxides SO 2 and SO 3. In SO 2 E S =32/4=8, and in SO 3 E S =32/6=5.33.
The molar mass of an equivalent, expressed in grams, is called equivalent mass. Therefore, the equivalent mass of hydrogen ME H = 1 g/mol, the equivalent mass of oxygen ME O = 8 g/mol.
The chemical equivalent of a complex substance /acid, hydroxide, salt, oxide/ is the amount of the corresponding substance that interacts with one mole of hydrogen atoms, i.e. with one equivalent of hydrogen or replaces that amount of hydrogen or any other substance in chemical reactions.
Acid equivalent/E K/ is equal to the quotient of the molecular weight of the acid divided by the number of hydrogen atoms participating in the reaction. For the acid H 2 SO 4, when both hydrogen atoms react H 2 SO 4 +2NaOH=Na 2 SO+2H 2 O the equivalent will be equal to EN 2 SO4 = M H 2 SO 4 /n H =98/2=49
Hydroxide equivalent /E hydr. / is defined as the quotient of the molecular weight of the hydroxide divided by the number of hydroxo groups that react. For example, the equivalent of NaOH will be equal to: E NaOH = M NaOH / n OH = 40/1 = 40.
Salt equivalent/E salt/ can be calculated by dividing its molecular weight by the product of the number of metal atoms that react and their valency. Thus, the equivalent of the salt Al 2 (SO 4) 3 will be equal to E Al 2 (SO 4) 3 = M Al 2 (SO 4) 3 /6 = 342/2.3 = 342/6 = 57.
Oxide equivalent/E ok / can be defined as the sum of the equivalents of the corresponding element and oxygen. For example, the equivalent of CO 2 will be equal to the sum of the equivalents of carbon and oxygen: E CO 2 = E C + E O = 3 + 8 = 7.
For gaseous substances it is convenient to use equivalent volumes /E V /. Since under normal conditions a mole of gas occupies a volume of 22.4 liters, based on this value it is easy to determine the equivalent volume of any gas. Let's consider hydrogen. The molar mass of hydrogen 2g occupies a volume of 22.4 liters, then its equivalent mass of 1g occupies a volume of 11.2 liters / or 11200 ml /. Therefore E V N =11.2l. The equivalent volume of chlorine is 11.2 l /E VCl = 11.2 l/. The equivalent volume of CO is 3.56 /E VC O =3.56 l/.
The chemical equivalent of an element or complex substance is used in stoichiometric calculations of exchange reactions, and in the corresponding calculations of redox reactions, oxidative and reduction equivalents are used.
Oxidative equivalent is defined as the quotient of the molecular weight of the oxidizing agent divided by the number of electrons it accepts in a given redox reaction.
The reducing equivalent is equal to the molecular weight of the reducing agent divided by the number of electrons it gives up in a given reaction.
Let's write the redox reaction and determine the equivalent of the oxidizing agent and reducing agent:
5N 2 aS+2KMnO 4 +8H 2 SO 4 =S+2MnSO 4 +K 2 SO 4 +5Na 2 SO 4 +8H 2 O
The oxidizing agent in this reaction is potassium permanganate. The equivalent of the oxidizing agent will be equal to the mass of KMnO 4 divided by the number of electrons accepted by the oxidizing agent in the reaction (ne=5). E KMnO 4 =M KMnO 4 /ne=158/5=31.5. The molar mass of the equivalent of the oxidizing agent KMnO 4 in an acidic medium is 31.5 g/mol.
The equivalent of the reducing agent Na 2 S will be: E Na 4 S = M Na 4 S / ne = 78/2 = 39. The molar mass of Na 2 S equivalent is 39 g/mol.
In electrochemical processes, in particular during the electrolysis of substances, an electrochemical equivalent is used. The electrochemical equivalent is determined as the quotient of the chemical equivalent of the substance released at the electrode divided by the Faraday number /F/. The electrochemical equivalent will be discussed in more detail in the corresponding paragraph of the course.
Valence. When atoms interact, a chemical bond is formed between them. Each atom can only form a certain number of bonds. The number of bonds determines such a unique property of each element, which is called valence. In its most general form, valency refers to the ability of an atom to form a chemical bond. One chemical bond that a hydrogen atom can form is taken as a unit of valence. In this regard, hydrogen is a monovalent element, and oxygen is a divalent element, because No more than two hydrogens can form a bond with an oxygen atom.
The ability to determine the valence of each element, including in a chemical compound, is a necessary condition for successfully mastering a chemistry course.
Valence is also related to such a concept of chemistry as oxidation state. The oxidation substate is the charge that an element has in an ionic compound or would have in a covalent compound if the shared electron pair were completely shifted to a more electronegative element. The oxidation state has not only a numerical expression, but also a corresponding charge sign (+) or (–). Valence does not have these signs. For example, in H 2 SO 4 the oxidation state is: hydrogen +1, oxygen –2, sulfur +6, and the valency, accordingly, will be 1, 2, 6.
Valency and oxidation state in numerical values do not always coincide in value. For example, in a molecule of ethyl alcohol CH 3 –CH 2 –OH the valence of carbon is 6, hydrogen is 1, oxygen is 2, and the oxidation state, for example, of the first carbon is –3, the second is –1: –3 CH 3 – –1 CH 2 –OH.
1.2. Basic environmental concepts.
Recently, the concept of “ecology” has deeply entered our consciousness. This concept, introduced back in 1869 by E. Haeckel, comes from the Greek oikos- house, place, dwelling, logos– the teaching / is disturbing humanity more and more.
In biology textbooks ecology defined as the science of the relationship between living organisms and their environment. An almost consonant definition of ecology is given by B. Nebel in his book “Science of the Environment” - Ecology is the science of various aspects of the interaction of organisms with each other and with the environment. A broader interpretation can be found in other sources. For example, Ecology – 1/. The science that studies the relationship between organisms and their systemic assemblies and the environment; 2/. A set of scientific disciplines that study the relationship of systemic biological structures /from macromolecules to the biosphere/ among themselves and with the environment; 3/. A discipline that studies the general laws of functioning of ecosystems at various hierarchical levels; 4/. A comprehensive science that studies the habitat of living organisms; 5/. Study of the position of man as a species in the biosphere of the planet, his connections with ecological systems and the impact on them; 6/. The science of environmental survival. / N.A. Agidzhanyan, V.I. Torshik. Human ecology./. However, the term “ecology” refers not only to ecology as a science, but to the state of the environment itself and its impact on humans, flora and fauna.
