Chemistry, like any science, requires precision. The data representation system in this field of knowledge has been developed for centuries, and the current standard is an optimized structure that contains all the necessary information for further theoretical work with each specific element.
When writing formulas and equations, it is extremely inconvenient to use integers, and today one or two letters are used for this purpose - the chemical symbols of elements.
Story
In the ancient world, as well as in the Middle Ages, scientists used symbolic images to denote various elements, but these signs were not standardized. It was not until the 13th century that attempts were made to systematize the symbols of substances and elements, and from the 15th century, newly discovered metals began to be designated by the first letters of their names. A similar naming strategy is used in chemistry to this day.
The current state of the naming system
To date, more than one hundred and twenty chemical elements are known, some of which are extremely problematic to find in nature. It is not surprising that even in the middle of the 19th century, science knew about the existence of only 63 of them, and there was neither a single naming system nor an integral system for presenting chemical data.
The last problem was solved in the second half of the same century by the Russian scientist D. I. Mendeleev, relying on the unsuccessful attempts of his predecessors. The naming process continues today - there are several elements with numbers from 119 and above, conventionally indicated in the table by the Latin abbreviation of their serial number. The pronunciation of the symbols of chemical elements of this category is carried out according to the Latin rules for reading numerals: 119 - ununenny (lit. "one hundred and nineteenth"), 120 - unbinilium ("one hundred and twentieth") and so on.
Most of the elements have their own names, derived from Latin, Greek, Arabic, German roots, in some cases reflecting the objective characteristics of substances, and in others acting as unmotivated symbols.
Etymology of some elements
As mentioned above, some names and symbols of chemical elements are based on objectively observable features.
The name of phosphorus, glowing in the dark, comes from the Greek phrase "bring light". When translated into Russian, quite a lot of "speaking" names are found: chlorine - "greenish", bromine - "bad smelling", rubidium - "dark red", indium - "indigo color". Since the chemical symbols of the elements are given in Latin letters, the direct connection of the name with the substance for a Russian speaker usually goes unnoticed.
There are also more subtle naming associations. So, the name of selenium comes from the Greek word meaning "Moon". This happened because in nature this element is a satellite of tellurium, whose name in the same Greek means "Earth".
Niobium is named similarly. According to Greek mythology, Niobe is the daughter of Tantalus. The chemical element tantalum was discovered earlier and is similar in its properties to niobium - thus, the logical connection "father-daughter" was projected onto the "relationship" of chemical elements.
Moreover, tantalum got its name in honor of the famous mythological character not by chance. The fact is that obtaining this element in its pure form was fraught with great difficulties, due to which scientists turned to the phraseological unit “Tantalum flour”.
Another curious historical fact is that the name of platinum literally translates as "silver", i.e. something similar, but not as valuable as silver. The reason is that this metal melts much more difficult than silver, and therefore for a long time it was not used and was not of particular value.
General principle of naming elements
When looking at the periodic table, the first thing that catches your eye is the names and symbols of the chemical elements. It is always one or two Latin letters, the first of which is capital. The choice of letters is due to the Latin name of the element. Despite the fact that the roots of words come from ancient Greek, and from Latin, and from other languages, according to the naming standard, Latin endings are added to them.
It is interesting that most of the characters will be intuitively understandable to a native Russian speaker: a student easily remembers aluminum, zinc, calcium or magnesium from the first time. The situation is more complicated with those names that differ in the Russian and Latin versions. The student may not immediately remember that silicon is silicium, and mercury is hydrargyrum. Nevertheless, you will have to remember this - the graphic representation of each element is focused on the Latin name of the substance, which will appear in chemical formulas and reactions as Si and Hg, respectively.
To remember such names, it is useful for students to perform exercises like: "Make a correspondence between the symbol of a chemical element and its name."
Other ways of naming
The names of some elements originated from the Arabic language and were "stylized" in Latin. For example, sodium takes its name from a root stem meaning "bubbling substance". Arabic roots can also be traced to the names of potassium and zirconium.
The German language also had its influence. From it come the names of such elements as manganese, cobalt, nickel, zinc, tungsten. The logical connection is not always obvious: for example, nickel is an abbreviation for the word meaning "copper devil".
In rare cases, the names were translated into Russian in the form of tracing paper: hydrogenium (literally "giving birth to water") turned into hydrogen, and carboneum into carbon.
Names and toponyms
More than a dozen elements are named after various scientists, including Albert Einstein, Dmitri Mendeleev, Enrico Fermi, Ernest Rutherford, Niels Bohr, Marie Curie and others.
Some names come from other proper names: the names of cities, states, countries. For example: moscovium, dubnium, europium, tennessine. Not all toponyms will seem familiar to a native speaker of the Russian language: it is unlikely that a person without cultural training will recognize the self-name of Japan in the word nihonium - Nihon (literally: the Land of the Rising Sun), and in hafnia - the Latin version of Copenhagen. Finding out even the name of your native country in the word ruthenium is not an easy task. Nevertheless, Russia in Latin is called Ruthenia, and it is in her honor that the 44th chemical element is named.
The names of cosmic bodies also appear in the periodic table: the planets Uranus, Neptune, Pluto, Ceres. In addition to the names of the characters of ancient Greek mythology (Tantalum, Niobium), there are also Scandinavian ones: thorium, vanadium.
Periodic table
In the periodic table familiar to us today, bearing the name of Dmitry Ivanovich Mendeleev, the elements are presented in series and periods. In each cell, a chemical element is indicated by a chemical symbol, next to which other data are presented: its full name, serial number, distribution of electrons over layers, relative atomic mass. Each cell has its own color, which depends on whether the s-, p-, d- or f- element is highlighted.
Recording principles
When writing isotopes and isobars, a mass number is placed on the top left of the element symbol - the total number of protons and neutrons in the nucleus. In this case, the atomic number is placed at the bottom left, which is the number of protons.
The charge of the ion is written on the top right, and the number of atoms is indicated on the same side below. Symbols for chemical elements always begin with a capital letter.
National spelling options
The Asia-Pacific region has its own spellings of the symbols of chemical elements, based on local writing methods. The Chinese notation system uses radical signs followed by characters in their phonetic meaning. Symbols of metals are preceded by the sign "metal" or "gold", gases - by the radical "steam", non-metals - by the hieroglyph "stone".
In European countries, there are also situations when the signs of elements during recording differ from those recorded in international tables. For example, in France, nitrogen, tungsten and beryllium have their own names in the national language and are denoted by the corresponding symbols.
Finally
Studying at school or even a higher educational institution, memorizing the contents of the entire periodic table is not required at all. In memory, you should keep the chemical symbols of the elements that are most often found in formulas and equations, and look at the little-used ones from time to time on the Internet or a textbook.
However, in order to avoid errors and confusion, it is necessary to know how the data is structured in the table, in which source to find the required data, and to clearly remember which element names differ in Russian and Latin versions. Otherwise, you can accidentally mistake Mg for manganese, and N for sodium.
To get practice at the initial stage, do the exercises. For example, specify the symbols for chemical elements for a randomly selected sequence of names from the periodic table. As you gain experience, everything will fall into place and the question of remembering this basic information will disappear by itself.
Modern symbols for chemical elements consist of the first letter or of the first and one of the following letters of the Latin name of the elements. In this case, only the first letter is capitalized. For example, H - hydrogen (lat. hydrogenium), N - nitrogen (lat. Nitrogenium), Ca - calcium (lat. Calcium), Pt - platinum (lat. Platinum) etc.
The metals discovered in the 15th-18th centuries - bismuth, zinc, cobalt - began to be denoted by the first letters of their names. At the same time, symbols of complex substances associated with their names appeared. For example, the sign of wine spirit is made up of the letters S and V (lat. spiritus vini). Signs of strong vodka (lat. aqua fortis) - nitric acid, and aqua regia (lat. aqua regis), mixtures of hydrochloric and nitric acids, are made up of the sign for water and the capital letters F and R, respectively. Glass sign (lat. vitrum) is formed from two letters V - straight and inverted. 
A.-L. Lavoisier, working on a new classification and nomenclature, proposed a very cumbersome system of chemical symbolism for elements and compounds. Attempts to streamline the ancient chemical signs continued until the end of the 18th century. A more appropriate sign system was proposed in 1787 by J.-A. Gassenfratz and P.-O. Ade; their chemical signs are already adapted to Lavoisier's anti-phlogistic theory and have some features that have been preserved later. They proposed to introduce symbols in the form of simple geometric shapes and letter designations as common for each class of substances, as well as straight lines drawn in various directions to designate the "true elements" - light and caloric, as well as elemental gases - oxygen, nitrogen and hydrogen. So, all metals were to be indicated by circles with the initial letter (sometimes two letters, and the second lower case) of the French name of the metal in the middle; all alkalis and alkaline earths (also classified by Lavoisier among the elements) - triangles arranged in various ways with Latin letters in the middle, etc.
In 1814, Berzelius detailed a system of chemical symbolism based on designating elements with one or two letters of the element's Latin name; the number of atoms of an element was proposed to be indicated by superscript numerical indices (the currently accepted indication of the number of atoms by subscript numbers was proposed in 1834 by Justus Liebig). The Berzelius system has received universal recognition and has survived to the present day. In Russia, the first printed report on the chemical signs of Berzelius was made in Moscow by the doctor I. Ya. Zatsepin.
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An excerpt characterizing the Symbols of chemical elements
The friends were silent. Neither of them began to speak. Pierre glanced at Prince Andrei, Prince Andrei rubbed his forehead with his small hand."Let's go to dinner," he said with a sigh, getting up and heading for the door.
They entered the elegant, newly decorated dining room. Everything, from napkins to silver, faience and crystal, bore that special imprint of novelty that happens in the household of young spouses. In the middle of dinner, Prince Andrei leaned on his elbows and, like a man who has long had something in his heart and suddenly decides to speak out, with an expression of nervous irritation in which Pierre had never seen his friend before, he began to say:
“Never, never marry, my friend; here is my advice to you: do not marry until you tell yourself that you have done everything you could, and until you stop loving the woman you have chosen, until you see her clearly; otherwise you will make a cruel and irreparable mistake. Marry an old man, worthless ... Otherwise, everything that is good and lofty in you will be lost. Everything is wasted on trifles. Yes Yes Yes! Don't look at me with such surprise. If you expect anything from yourself ahead, then at every step you will feel that everything is over for you, everything is closed, except for the drawing room, where you will stand on the same board with the court lackey and the idiot ... Yes, what! ...
He waved his hand vigorously.
Pierre took off his glasses, which made his face change, showing even more kindness, and looked in surprise at his friend.
“My wife,” continued Prince Andrei, “is a wonderful woman. This is one of those rare women with whom you can be dead for your honor; but, my God, what would I not give now not to be married! This I tell you alone and first, because I love you.
Prince Andrei, saying this, was even less like than before, that Bolkonsky, who was sitting lounging in Anna Pavlovna's armchair and squinting through his teeth, uttering French phrases. His dry face kept trembling with the nervous animation of every muscle; eyes, in which the fire of life had previously seemed extinguished, now shone with a radiant, bright brilliance. It was evident that the more lifeless he seemed at ordinary times, the more energetic he was in those moments of almost painful irritation.
“You don’t understand why I say this,” he continued. “It's a whole life story. You say Bonaparte and his career,” he said, although Pierre did not talk about Bonaparte. – You are talking to Bonaparte; but Bonaparte, when he worked, went step by step towards the goal, he was free, he had nothing but his goal - and he reached it. But bind yourself to a woman, and like a chained convict, you lose all freedom. And everything that is in you of hope and strength, everything only weighs you down and torments you with repentance. Drawing rooms, gossip, balls, vanity, insignificance - this is a vicious circle from which I cannot get out. I am now going to war, to the greatest war that has ever been, and I know nothing and am no good. Je suis tres aimable et tres caustique, [I am very sweet and very eater,] continued Prince Andrei, “and Anna Pavlovna is listening to me. And this stupid society, without which my wife cannot live, and these women ... If only you could know what it is toutes les femmes distinguees [all these women of good society] and women in general! My father is right. Selfishness, vanity, stupidity, insignificance in everything - these are women when everything is shown as they are. You look at them in the light, it seems that there is something, but nothing, nothing, nothing! Yes, don’t marry, my soul, don’t marry, ”Prince Andrei finished.
“It’s funny to me,” said Pierre, “that you yourself, you consider yourself incapable, your life a spoiled life. You have everything, everything is ahead. And you…
He did not say that you were, but his tone already showed how highly he appreciated his friend and how much he expected from him in the future.
"How can he say that!" thought Pierre. Pierre considered Prince Andrei the model of all perfections precisely because Prince Andrei combined to the highest degree all those qualities that Pierre did not have and which can be most closely expressed by the concept of willpower. Pierre was always amazed at Prince Andrei's ability to deal calmly with all kinds of people, his extraordinary memory, erudition (he read everything, knew everything, had an idea about everything), and most of all his ability to work and study. If Pierre was often struck by the lack of the ability of dreamy philosophizing in Andrei (which Pierre was especially prone to), then he saw this not as a flaw, but as a strength.
In the best, friendly, and simple relations, flattery or praise is necessary, as grease is necessary for wheels to keep them moving.
- Je suis un homme fini, [I am a finished man,] - said Prince Andrei. - What to say about me? Let's talk about you," he said after a pause and smiled at his comforting thoughts.
This smile was immediately reflected on Pierre's face.
- And what to say about me? - said Pierre, spreading his mouth into a carefree, cheerful smile. – What am I? Je suis un batard [I am an illegitimate son!] - And he suddenly blushed crimson. It was evident that he made a great effort to say this. - Sans nom, sans fortune ... [No name, no fortune ...] And well, right ... - But he did not say that he was right. - I'm free for now, and I'm fine. I just don't know what to start with. I wanted to seriously consult with you.
Prince Andrew looked at him with kind eyes. But in his look, friendly, affectionate, all the same, the consciousness of his superiority was expressed.
“You are dear to me, especially because you are the only living person among our entire world. You feel good. Choose what you want; it does not matter. You will be good everywhere, but one thing: stop going to these Kuragins, to lead this life. So it doesn’t suit you: all these revels, and hussars, and that’s all ...
“Que voulez vous, mon cher,” said Pierre, shrugging his shoulders, “les femmes, mon cher, les femmes!” [What do you want, my dear, women, my dear, women!]
“I don’t understand,” Andrei answered. - Les femmes comme il faut, [Decent women,] is another matter; but les femmes Kuragin, les femmes et le vin, [Kuragin's women, women and wine,] I don't understand!
Pierre lived with Prince Vasily Kuragin and participated in the wild life of his son Anatole, the same one who was going to be married to the sister of Prince Andrei for correction.
“You know what,” said Pierre, as if he had an unexpectedly happy thought, “seriously, I have been thinking about this for a long time. With this life, I can neither decide nor think about anything. Headache, no money. Today he called me, I will not go.
“Give me your word of honor that you won’t ride?”
- Honestly!
It was already two o'clock in the morning when Pierre went out from his friend. The night was a June, Petersburg, duskless night. Pierre got into a cab with the intention of driving home. But the closer he drove, the more he felt the impossibility of falling asleep that night, which was more like evening or morning. Far away it was visible along the empty streets. Dear Pierre remembered that Anatole Kuragin was supposed to have a usual gambling society that evening, after which there was usually a drinking bout, ending in one of Pierre's favorite amusements.
"It would be nice to go to Kuragin," he thought.
But at once he remembered his word of honor given to Prince Andrei not to visit Kuragin. But immediately, as happens with people who are called spineless, he so passionately wanted to once again experience this dissolute life so familiar to him that he decided to go. And immediately the thought occurred to him that this word meant nothing, because even before Prince Andrei, he also gave Prince Anatole the word to be with him; finally, he thought that all these words of honor were such conditional things that had no definite meaning, especially if one realized that perhaps tomorrow either he would die or something so unusual would happen to him that there would be no more honest , nor dishonorable. This kind of reasoning, destroying all his decisions and assumptions, often came to Pierre. He went to Kuragin.
Arriving at the porch of a large house near the horse guard barracks in which Anatole lived, he climbed onto the illuminated porch, onto the stairs, and entered the open door. There was no one in the hall; there were empty bottles, raincoats, galoshes; there was a smell of wine, a distant voice and a cry could be heard.
The game and dinner were already over, but the guests had not yet left. Pierre threw off his cloak and entered the first room, where there were the remnants of dinner and one footman, thinking that no one could see him, was secretly finishing his unfinished glasses. From the third room came fuss, laughter, cries of familiar voices and the roar of a bear.
About eight young people crowded preoccupiedly near the open window. Three were busy with a young bear, which one dragged on a chain, scaring the other with it.
“I hold a hundred for Stevens!” one shouted.
– Look not to support! shouted another.
- I'm for Dolokhov! shouted a third. - Take it apart, Kuragin.
- Well, drop Mishka, there's a bet.
- In one spirit, otherwise it is lost, - shouted the fourth.
- Yakov, give me a bottle, Yakov! - Shouted the owner himself, a tall handsome man, standing in the middle of the crowd in one thin shirt, open in the middle of his chest. - Stop, gentlemen. Here he is Petrusha, dear friend, - he turned to Pierre.
The decision on the need to maintain such a notebook did not come immediately, but gradually, with the accumulation of work experience.
At first it was a place at the end of the workbook - a few pages for writing down the most important definitions. Then the most important tables were placed there. Then came the realization that in order to learn how to solve problems, most students need strict algorithmic prescriptions, which they, first of all, must understand and remember.
It was then that the decision came to maintain, in addition to the workbook, another obligatory chemistry notebook - a chemical dictionary. Unlike workbooks, which can even be two during one academic year, a dictionary is a single notebook for the entire chemistry course. It is best if this notebook has 48 sheets and a strong cover.
We arrange the material in this notebook as follows: at the beginning - the most important definitions that the guys write out from the textbook or write down under the dictation of the teacher. For example, in the first lesson in the 8th grade, this is the definition of the subject “chemistry”, the concept of “chemical reactions”. During the school year in the 8th grade, they accumulate more than thirty. According to these definitions, I conduct surveys in some lessons. For example, an oral question in a chain, when one student asks a question to another, if he answered correctly, then he already asks the next question; or, when one student is asked questions by other students, if he does not cope with the answer, then they answer themselves. In organic chemistry, these are mainly definitions of classes of organic substances and main concepts, for example, “homologues”, “isomers”, etc.
At the end of our reference book, material is presented in the form of tables and diagrams. On the last page is the very first table “Chemical elements. Chemical signs". Then the tables “Valence”, “Acids”, “Indicators”, “Electrochemical series of voltages of metals”, “Series of electronegativity”.
I especially want to dwell on the contents of the table “Correspondence of acids to acid oxides”:
| Correspondence of acids to acid oxides | ||||
| acid oxide | Acid | |||
| Name | Formula | Name | Formula | Acid residue, valence |
| carbon monoxide (II) | CO2 | coal | H2CO3 | CO 3 (II) |
| sulfur(IV) oxide | SO2 | sulphurous | H2SO3 | SO3(II) |
| sulfur(VI) oxide | SO 3 | sulfuric | H2SO4 | SO4(II) |
| silicon(IV) oxide | SiO2 | silicon | H2SiO3 | SiO 3 (II) |
| nitric oxide (V) | N 2 O 5 | nitric | HNO3 | NO 3 (I) |
| phosphorus(V) oxide | P2O5 | phosphoric | H3PO4 | PO 4 (III) |
Without understanding and memorizing this table, it is difficult for students of the 8th grade to compile equations for the reactions of acid oxides with alkalis.
When studying the theory of electrolytic dissociation, at the end of the notebook we write down schemes and rules.
Rules for compiling ionic equations:
1. In the form of ions, write down the formulas of strong electrolytes that are soluble in water.
2. In molecular form, write down the formulas of simple substances, oxides, weak electrolytes and all insoluble substances.
3. The formulas of poorly soluble substances on the left side of the equation are written in ionic form, on the right - in molecular form.
When studying organic chemistry, we write in the dictionary summarizing tables for hydrocarbons, classes of oxygen- and nitrogen-containing substances, schemes for genetic relationships.
| Physical quantities | |||
| Designation | Name | Units | Formulas |
| amount of substance | mole | = N / N A ; = m / M; V / V m (for gases) |
|
| N A | Avogadro's constant | molecules, atoms and other particles | N A = 6.02 10 23 |
| N | number of particles | molecules, atoms and other particles |
N = N A |
| M | molar mass | g/mol, kg/kmol | M = m / ; / M/ = M r |
| m | weight | g, kg | m = M ; m = V |
| Vm | molar volume of gas | l / mol, m 3 / kmol | Vm \u003d 22.4 l / mol \u003d 22.4 m 3 / kmol |
| V | volume | l, m 3 | V = V m (for gases) ; |
| density | g/ml; | = m/V; M / V m (for gases) |
|
During the 25 years of teaching chemistry at school, I had to work on different programs and textbooks. At the same time, it was always surprising that practically no textbook teaches how to solve problems. At the beginning of the study of chemistry, in order to systematize and consolidate knowledge in the dictionary, the students and I compile a table “Physical quantities” with new quantities:
When teaching students how to solve computational problems, I attach great importance to algorithms. I believe that the strict prescription of the sequence of actions allows a weak student to understand the solution of problems of a certain type. For strong students, this is an opportunity to reach the creative level of their further chemical education and self-education, since first you need to confidently master a relatively small number of standard techniques. On the basis of this, the ability to correctly apply them at different stages of solving more complex problems will develop. Therefore, I have compiled algorithms for solving computational problems for all types of school course problems and for extracurricular activities.
I will give examples of some of them.
Algorithm for solving problems by chemical equations.
1. Briefly write down the condition of the problem and make a chemical equation.
2. Above the formulas in the chemical equation, write the data of the problem, write the number of moles under the formulas (determined by the coefficient).
3. Find the amount of a substance, the mass or volume of which is given in the condition of the problem, using the formulas:
M/M; \u003d V / V m (for gases V m \u003d 22.4 l / mol).
Write the resulting number above the formula in the equation.
4. Find the amount of a substance whose mass or volume is unknown. To do this, reason according to the equation: compare the number of moles according to the condition with the number of moles according to the equation. Proportion if necessary.
5. Find the mass or volume using the formulas: m = M ; V = V m .
This algorithm is the basis that the student must master so that in the future he can solve problems using equations with various complications.
Tasks for excess and deficiency.
If in the condition of the problem the quantities, masses or volumes of two reacting substances are known at once, then this is a problem for excess and deficiency.
When solving it:
1. It is necessary to find the amounts of two reacting substances according to the formulas:
M/M; = V/V m .
2. The resulting numbers of moles are inscribed above the equation. Comparing them with the number of moles according to the equation, draw a conclusion about which substance is given in deficiency.
3. By deficiency, make further calculations.
Tasks for the share of the yield of the reaction product, practically obtained from the theoretically possible.
According to the reaction equations, theoretical calculations are carried out and theoretical data are found for the reaction product: theor. , m theor. or V theor. . When carrying out reactions in the laboratory or in industry, losses occur, so the practical data obtained are practical. ,
m practical or V practical. is always less than theoretically calculated data. The yield fraction is denoted by the letter (eta) and is calculated by the formulas:
(this) = pract. / theor. = m practical. / m theor. = V practical. / V theor.
It is expressed as a fraction of a unit or as a percentage. There are three types of tasks:
If the data for the starting substance and the share of the yield of the reaction product are known in the condition of the problem, then you need to find the practical. , m practical or V practical. reaction product.
Solution order:
1. Calculate according to the equation, based on the data for the original substance, find the theory. , m theor. or V theor. reaction product;
2. Find the mass or volume of the reaction product, practically obtained, according to the formulas:
m practical = m theor. ; V pract. = V theor. ; practical = theor. .
If in the condition of the problem the data for the starting substance and practice are known. , m practical or V practical. of the obtained product, while it is necessary to find the share of the yield of the reaction product.
Solution order:
1. Calculate according to the equation, based on the data for the starting substance, find
Theor. , m theor. or V theor. reaction product.
2. Find the share of the yield of the reaction product using the formulas:
Prakt. / theor. = m practical. / m theor. = V practical. /V theor.
If in the condition of the problem are known pract. , m practical or V practical. of the resulting reaction product and the share of its yield, in this case, you need to find data for the starting substance.
Solution order:
1. Find theor., m theor. or V theor. reaction product according to the formulas:
Theor. = practical / ; m theor. = m practical. / ; V theor. = V practical. / .
2. Calculate according to the equation, based on theor. , m theor. or V theor. reaction product and find data for the starting material.
Of course, we consider these three types of problems gradually, we work out the skills of solving each of them using the example of a number of problems.
Problems on mixtures and impurities.
A pure substance is that which is more in the mixture, the rest is impurities. Designations: the mass of the mixture - m cm, the mass of the pure substance - m q.v., the mass of impurities - m approx. , mass fraction of a pure substance - h.v.
The mass fraction of a pure substance is found by the formula: h.v. = m q.v. / m see, express it in fractions of a unit or as a percentage. We distinguish 2 types of tasks.
If in the condition of the problem the mass fraction of a pure substance or the mass fraction of impurities is given, then the mass of the mixture is given. The word "technical" also means the presence of a mixture.
Solution order:
1. Find the mass of a pure substance using the formula: m p.m. = q.v. m see.
If the mass fraction of impurities is given, then first you need to find the mass fraction of a pure substance: = 1 - approx.
2. Based on the mass of a pure substance, make further calculations according to the equation.
If the condition of the problem gives the mass of the initial mixture and n, m or V of the reaction product, then you need to find the mass fraction of the pure substance in the initial mixture or the mass fraction of impurities in it.
Solution order:
1. Calculate according to the equation, based on the data for the reaction product, and find n hours. and m h.v.
2. Find the mass fraction of a pure substance in a mixture using the formula: q.v. = m q.v. / m see and mass fraction of impurities: approx. = 1 - h.c.
The law of volumetric ratios of gases.
The volumes of gases are related in the same way as their quantities of substances:
V 1 / V 2 = 1 / 2
This law is used in solving problems by equations in which the volume of a gas is given and it is necessary to find the volume of another gas.
The volume fraction of gas in the mixture.
Vg / Vcm, where (phi) is the volume fraction of gas.
Vg is the volume of gas, Vcm is the volume of the mixture of gases.
If the volume fraction of the gas and the volume of the mixture are given in the condition of the problem, then, first of all, you need to find the volume of the gas: Vg = Vcm.
The volume of the mixture of gases is found by the formula: Vcm \u003d Vg /.
The volume of air spent on burning a substance is found through the volume of oxygen found by the equation:
Vair \u003d V (O 2) / 0.21
Derivation of formulas of organic substances by general formulas.
Organic substances form homologous series that have common formulas. This allows:
1. Express the relative molecular weight in terms of the number n.
M r (C n H 2n + 2) = 12n + 1 (2n + 2) = 14n + 2.
2. Equate M r expressed in terms of n to the true M r and find n.
3. Compose reaction equations in general form and perform calculations on them.
Derivation of formulas of substances by combustion products.
1. Analyze the composition of the combustion products and draw a conclusion about the qualitative composition of the burnt substance: H 2 O -> H, CO 2 -> C, SO 2 -> S, P 2 O 5 -> P, Na 2 CO 3 -> Na, C.
The presence of oxygen in the substance requires verification. Designate the indices in the formula as x, y, z. For example, CxHyOz (?).
2. Find the amount of substances of combustion products using the formulas:
n = m / M and n = V / Vm.
3. Find the amounts of elements contained in the burnt substance. For example:
n (C) \u003d n (CO 2), n (H) \u003d 2 ћ n (H 2 O), n (Na) \u003d 2 ћ n (Na 2 CO 3), n (C) \u003d n (Na 2 CO 3) etc.
4. If a substance of unknown composition burned out, then it is imperative to check whether it contained oxygen. For example, СxНyОz (?), m (O) \u003d m in-va - (m (C) + m (H)).
b) if relative density is known: M 1 = D 2 M 2 , M = D H2 2, M = D O2 32,
M = D air. 29, M = D N2 28, etc.
1 way: find the simplest formula of a substance (see the previous algorithm) and the simplest molar mass. Then compare the true molar mass with the simplest and increase the indices in the formula by the required number of times.
2 way: find the indices using the formula n = (e) Mr / Ar (e).
If the mass fraction of one of the elements is unknown, then it must be found. To do this, subtract the mass fraction of another element from 100% or from unity.
Gradually, in the course of studying chemistry in the chemical dictionary, there is an accumulation of algorithms for solving problems of different types. And the student always knows where to find the right formula or the right information to solve the problem.
Many students like to keep such a notebook, they themselves supplement it with various reference materials.
As for extracurricular activities, the students and I also start a separate notebook for writing algorithms for solving problems that go beyond the scope of the school curriculum. In the same notebook, for each type of task, we write down 1-2 examples, they solve the rest of the tasks in another notebook. And, if you think about it, among the thousands of different tasks encountered in the exam in chemistry in all universities, one can distinguish tasks of 25 - 30 different types. Of course, there are many variations among them.
In developing algorithms for solving problems in optional classes, A.A. Kushnarev. (Learning to solve problems in chemistry, - M., School - press, 1996).
The ability to solve problems in chemistry is the main criterion for the creative assimilation of the subject. It is through solving problems of various levels of complexity that a chemistry course can be effectively mastered.
If a student has a clear idea of all possible types of problems, has solved a large number of problems of each type, then he is able to cope with passing the exam in chemistry in the form of the Unified State Examination and entering universities.
Abstract keywords: Chemical elements, signs of chemical elements.
In chemistry, the concept is very important. "chemical element"(The word "element" in Greek means "component"). To understand its essence, remember how mixtures and chemical compounds differ.
For example, iron and sulfur retain their properties in the mixture. Therefore, it can be argued that a mixture of iron powder with sulfur powder consists of two simple substances - iron and sulfur. Since the chemical compound iron sulfide is formed from simple substances - iron and sulfur, I would like to argue that iron sulfide also consists of iron and sulfur. But having become acquainted with the properties of iron sulfide, we understand that this cannot be argued. This, formed as a result of chemical interaction, has completely different properties than the original substances. Because the composition of complex substances does not include simple substances, but atoms of a certain type.
A CHEMICAL ELEMENT is a certain type of atom.
So, for example, all oxygen atoms, regardless of whether they are part of oxygen molecules or water molecules, are the chemical element oxygen. All atoms of hydrogen, iron, sulfur are, respectively, the chemical elements hydrogen, iron, sulfur, etc.
At present, 118 different types of atoms are known, i.e. 118 chemical elements. From the atoms of this relatively small number of elements, a huge variety of substances is formed. (The concept of "chemical element" will be clarified and expanded in future notes).
Using the concept of "chemical element", we can clarify the definitions: SIMPLE are substances that consist of atoms of one chemical element. COMPLEX are substances that consist of atoms of different chemical elements.
It is necessary to distinguish between concepts "simple substance" and "chemical element" , although their names are in most cases the same. Therefore, every time we meet the words "oxygen", "hydrogen", "iron", "sulphur", etc., we need to understand what we are talking about - a simple substance or a chemical element. If, for example, they say: “Fish breathe oxygen dissolved in water”, “Iron is a metal that is attracted by a magnet”, this means that we are talking about simple substances - oxygen and iron. If they say that oxygen or iron is part of a substance, then they mean oxygen and iron as chemical elements.
Chemical elements and the simple substances they form can be divided into two large groups: metals and non-metals. Examples of metals are iron, aluminum, copper, gold, silver, etc. Metals are plastic, have a metallic luster, and conduct electric current well. Examples of non-metals are sulfur, phosphorus, hydrogen, oxygen, nitrogen, etc. The properties of non-metals are varied.
Signs of chemical elements
Each chemical element has its own name. For a simplified designation of chemical elements, use chemical symbolism. A chemical element is denoted by the initial or initial and one of the subsequent letters of the Latin name of this element. So, hydrogen (lat. hydrogenium - hydrogenium) is denoted by the letter H, mercury (lat. hydrargyrum - hydrargyrum) - in letters hg etc. The Swedish chemist J. J. Berzelius proposed modern chemical symbolism in 1814
The abbreviations for chemical elements are signs(or symbols) chemical elements. The chemical symbol (chemical sign) denotes one atom of a given chemical element .
You already know the symbols of some chemical elements.
What does the chemical symbol show?
1) Denotes a chemical element (give a name);
2) one atom of this element;
3) by the symbol, you can determine the place of the element in the periodic system of D.I. Mendeleev;
4) the periodic system can be used to determine the relative atomic mass of an element.
Let's take an example.
Chemical element symbol - Cu
1) The chemical element is copper.
2) one copper atom;
3) Copper is in the periodic system of elements in period 4, group 1, serial number - 29.
4) Ar(Cu)=64
Let us summarize the information known to us, which contains a chemical formula.
Table. Information contained in a chemical formula.
Example: HNO3 - nitric acid
| 1. Qualitative composition | 1. A molecule consists of atoms of three chemical elements: H, N, O |
| 2. Quantitative composition | 2. The molecule consists of five atoms: one hydrogen atom, one nitrogen atom, three oxygen atoms |
| 3. Relative molecular weight | 3.Mr(HNO3)= 1 1+14 1+16 3=63 |
| 4. Mass of the molecule | 4. mm(HNO3)= 1a.u.m. 1+ 14 amu 1+ 16 amu 3=63 amu |
| 5. Mass fractions of elements | 5.ω(H) = Ar(H) 1 / Mr(HNO3)= 1 1/63=0.016 or 1.6% ω(N)= Ar(N) 1 /Mr(HNO3)= ω(O)= Ar(O) 3 /Mr(HNO3)= |
Complete the task in the workbook by analogy
Summarizing
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