How to make up the structural formulas of oxygen-containing acids. Extracurricular lesson - acids

Well, to complete our acquaintance with alcohols, I will also give the formula of another well-known substance - cholesterol. Not everyone knows what he is monohydric alcohol!

|`/`\\`|<`|w>`\`/|<`/w$color(red)HO$color()>\/`|0/`|/\<`|w>|_q_q_q<-dH>:a_q|0<|dH>`/<`|wH>`\|dH; #a_(A-72)<_(A-120,d+)>-/-/<->`\

I marked the hydroxyl group in it in red.

Carboxylic acids

Any winemaker knows that wine should be stored without access to air. Otherwise it will turn sour. But chemists know the reason - if you add another oxygen atom to an alcohol, you get an acid.
Let's look at the formulas of acids that are obtained from alcohols already familiar to us:

Substance			Skeletal formula	Gross formula
Methane acid (formic acid)	H/C`|O|\OH	HCOOH	O//\OH
Ethanoic acid (acetic acid)	H-C-C\O-H; H|#C|H	CH3-COOH	/`|O|\OH
Propanic acid (methylacetic acid)	H-C-C-C\O-H; H|#2|H; H|#3|H	CH3-CH2-COOH	\/`|O|\OH
Butanoic acid (butyric acid)	H-C-C-C-C\O-H; H|#2|H; H|#3|H; H|#4|H	CH3-CH2-CH2-COOH	/\/`|O|\OH
Generalized formula	(R)-C\O-H	(R)-COOH or (R)-CO2H	(R)/`|O|\OH

Distinctive feature organic acids is the presence of a carboxyl group (COOH), which gives such substances acidic properties.

Anyone who has tried vinegar knows that it is very sour. The reason for this is the presence of acetic acid in it. Typically table vinegar contains between 3 and 15% acetic acid, with the rest (mostly) water. Consumption of acetic acid in undiluted form poses a danger to life.

Carboxylic acids can have multiple carboxyl groups. In this case they are called: dibasic, tribasic etc...

Food products contain many other organic acids. Here are just a few of them:

The name of these acids corresponds to those food products in which they are contained. By the way, please note that here there are acids that also have a hydroxyl group, characteristic of alcohols. Such substances are called hydroxycarboxylic acids(or hydroxy acids).
At the bottom, under each of the acids, there is a sign specifying the name of the group of organic substances to which it belongs.

Radicals

Radicals are another concept that has influenced chemical formulas. The word itself is probably known to everyone, but in chemistry radicals have nothing in common with politicians, rebels and other citizens with an active position.
Here these are just fragments of molecules. And now we will figure out what makes them special and get acquainted with a new way of writing chemical formulas.

Generalized formulas have already been mentioned several times in the text: alcohols - (R)-OH and carboxylic acids - (R)-COOH. Let me remind you that -OH and -COOH are functional groups. But R is a radical. It’s not for nothing that he is depicted as the letter R.

To be more specific, a monovalent radical is a part of a molecule lacking one hydrogen atom. Well, if you subtract two hydrogen atoms, you get a divalent radical.

Radicals in chemistry received their own names. Some of them even received Latin designations similar to the designations of the elements. And besides, sometimes in formulas radicals can be indicated in abbreviated form, more reminiscent of gross formulas.
All this is demonstrated in the following table.

Name	Structural formula	Designation	Brief formula	Example of alcohol
Methyl	CH3-()	Me	CH3	(Me)-OH	CH3OH
Ethyl	CH3-CH2-()	Et	C2H5	(Et)-OH	C2H5OH
I cut through	CH3-CH2-CH2-()	Pr	C3H7	(Pr)-OH	C3H7OH
Isopropyl	H3C\CH(*`/H3C*)-()	i-Pr	C3H7	(i-Pr)-OH	(CH3)2CHOH
Phenyl	`/`=`\//-\\-{}	Ph	C6H5	(Ph)-OH	C6H5OH

I think everything is clear here. I just want to draw your attention to the column where examples of alcohols are given. Some radicals are written in a form that resembles the gross formula, but the functional group is written separately. For example, CH3-CH2-OH turns into C2H5OH.
And for branched chains like isopropyl, structures with brackets are used.

There is also such a phenomenon as free radicals. These are radicals that, for some reason, have separated from functional groups. In this case, one of the rules with which we began studying the formulas is violated: the number of chemical bonds no longer corresponds to the valency of one of the atoms. Well, or we can say that one of the connections becomes open at one end. Free radicals usually live for a short time as the molecules tend to return to a stable state.

Introduction to nitrogen. Amines

I propose to get acquainted with another element that is part of many organic compounds. This nitrogen.
It is denoted by the Latin letter N and has a valency of three.

Let's see what substances are obtained if nitrogen is added to the familiar hydrocarbons:

Substance	Expanded structural formula	Simplified structural formula	Skeletal formula	Gross formula
Aminomethane (methylamine)	H-C-N\H;H|#C|H	CH3-NH2	\NH2
Aminoethane (ethylamine)	H-C-C-N\H;H|#C|H;H|#3|H	CH3-CH2-NH2	/\NH2
Dimethylamine	H-C-N<`|H>-C-H; H|#-3|H; H|#2|H	$L(1.3)H/N<_(A80,w+)CH3>\dCH3	/N<_(y-.5)H>\
Aminobenzene (Aniline)	H\N|C\\C|C<\H>`//C<|H>`\C<`/H>`||C<`\H>/	NH2|C\\CH|CH`//C<_(y.5)H>`\HC`||HC/	NH2|\|`/`\`|/_o
Triethylamine	$slope(45)H-C-C/N\C-C-H;H|#2|H; H|#3|H; H|#5|H;H|#6|H; #N`|C<`-H><-H>`|C<`-H><-H>`|H	CH3-CH2-N<`|CH2-CH3>-CH2-CH3	\/N<`|/>\|

As you probably already guessed from the names, all these substances are united under the general name amines. The functional group ()-NH2 is called amino group. Here are some general formulas of amines:

In general, there are no special innovations here. If these formulas are clear to you, then you can safely engage in further study of organic chemistry using a textbook or the Internet.
But I would also like to talk about the formulas in inorganic chemistry. You will see how easy it will be to understand them after studying the structure of organic molecules.

Rational formulas

It should not be concluded that inorganic chemistry is easier than organic chemistry. Of course, inorganic molecules tend to look much simpler because they don't tend to form complex structures like hydrocarbons. But then we have to study more than a hundred elements that make up the periodic table. And these elements tend to combine according to their chemical properties, but with numerous exceptions.

So, I won’t tell you any of this. The topic of my article is chemical formulas. And with them everything is relatively simple.
Most often used in inorganic chemistry rational formulas. And now we’ll figure out how they differ from those already familiar to us.

First, let's get acquainted with another element - calcium. This is also a very common element.
It is designated Ca and has a valency of two. Let's see what compounds it forms with the carbon, oxygen and hydrogen we know.

Substance	Structural formula	Rational formula	Gross formula
Calcium oxide	Ca=O	CaO
Calcium hydroxide	H-O-Ca-O-H	Ca(OH)2
Calcium carbonate	$slope(45)Ca`/O\C|O`|/O`\#1	CaCO3
Calcium bicarbonate	HO/`|O|\O/Ca\O/`|O|\OH	Ca(HCO3)2
Carbonic acid	H|O\C|O`|/O`|H	H2CO3

At first glance, you can see that the rational formula is something between a structural and a gross formula. But it is not yet very clear how they are obtained. To understand the meaning of these formulas, you need to consider the chemical reactions in which substances participate.

Calcium in its pure form is a soft white metal. It does not occur in nature. But it is quite possible to buy it at a chemical store. It is usually stored in special jars without access to air. Because in air it reacts with oxygen. Actually, that’s why it doesn’t occur in nature.
So, the reaction of calcium with oxygen:

2Ca + O2 -> 2CaO

The number 2 before the formula of a substance means that 2 molecules are involved in the reaction.
Calcium and oxygen produce calcium oxide. This substance also does not occur in nature because it reacts with water:

CaO + H2O -> Ca(OH2)

The result is calcium hydroxide. If you look closely at its structural formula (in the previous table), you can see that it is formed by one calcium atom and two hydroxyl groups, with which we are already familiar.
These are the laws of chemistry: if a hydroxyl group attaches to organic matter, it turns out alcohol, and if it is applied to a metal, it turns out to be hydroxide.

But calcium hydroxide does not occur in nature due to the presence of carbon dioxide in the air. I think everyone has heard about this gas. It is formed during the respiration of people and animals, the combustion of coal and petroleum products, during fires and volcanic eruptions. Therefore, it is always present in the air. But it also dissolves quite well in water, forming carbonic acid:

CO2 + H2O<=>H2CO3

Sign<=>indicates that the reaction can proceed in both directions under the same conditions.

Thus, calcium hydroxide, dissolved in water, reacts with carbonic acid and turns into slightly soluble calcium carbonate:

Ca(OH)2 + H2CO3 -> CaCO3"|v" + 2H2O

A down arrow means that as a result of the reaction the substance precipitates.
Upon further contact of calcium carbonate with carbon dioxide in the presence of water, a reversible reaction occurs to form an acidic salt - calcium bicarbonate, which is highly soluble in water

CaCO3 + CO2 + H2O<=>Ca(HCO3)2

This process affects the hardness of the water. When the temperature rises, bicarbonate turns back into carbonate. Therefore, in regions with hard water, scale forms in kettles.

Chalk, limestone, marble, tuff and many other minerals are largely composed of calcium carbonate. It is also found in corals, mollusk shells, animal bones, etc...
But if calcium carbonate is heated over very high heat, it will turn into calcium oxide and carbon dioxide.

This short story about the calcium cycle in nature should explain why rational formulas are needed. So, rational formulas are written so that the functional groups are visible. In our case it is:

In addition, individual elements - Ca, H, O (in oxides) - are also independent groups.

Ions

I think it's time to get acquainted with ions. This word is probably familiar to everyone. And after studying the functional groups, it doesn’t cost us anything to figure out what these ions are.

In general, the nature of chemical bonds is usually that some elements give up electrons while others gain them. Electrons are particles with a negative charge. An element with a full complement of electrons has zero charge. If he gave away an electron, then its charge becomes positive, and if he accepted it, then it becomes negative. For example, hydrogen has only one electron, which it gives up quite easily, turning into a positive ion. There is a special entry for this in chemical formulas:

H2O<=>H^+ + OH^-

Here we see that as a result electrolytic dissociation water breaks down into a positively charged hydrogen ion and a negatively charged OH group. The OH^- ion is called hydroxide ion. It should not be confused with the hydroxyl group, which is not an ion, but part of some kind of molecule. The + or - sign in the upper right corner shows the charge of the ion.
But carbonic acid never exists as an independent substance. In fact, it is a mixture of hydrogen ions and carbonate ions (or bicarbonate ions):

H2CO3 = H^+ + HCO3^-<=>2H^+ + CO3^2-

The carbonate ion has a charge of 2-. This means that two electrons have been added to it.

Negatively charged ions are called anions. Typically these include acidic residues.
Positively charged ions - cations. Most often these are hydrogen and metals.

And here you can probably fully understand the meaning of rational formulas. The cation is written in them first, followed by the anion. Even if the formula does not contain any charges.

You probably already guess that ions can be described not only by rational formulas. Here is the skeletal formula of the bicarbonate anion:

Here the charge is indicated directly next to the oxygen atom, which received an extra electron and therefore lost one line. Simply put, each extra electron reduces the number of chemical bonds depicted in the structural formula. On the other hand, if some node of the structural formula has a + sign, then it has an additional stick. As always, this fact needs to be demonstrated with an example. But among the substances familiar to us there is not a single cation that consists of several atoms.
And such a substance is ammonia. Its aqueous solution is often called ammonia and is included in any first aid kit. Ammonia is a compound of hydrogen and nitrogen and has the rational formula NH3. Let's consider chemical reaction which occurs when ammonia is dissolved in water:

NH3 + H2O<=>NH4^+ + OH^-

The same thing, but using structural formulas:

H|N<`/H>\H + H-O-H<=>H|N^+<_(A75,w+)H><_(A15,d+)H>`/H + O`^-# -H

On the right side we see two ions. They were formed as a result of one hydrogen atom moving from a water molecule to an ammonia molecule. But this atom moved without its electron. The anion is already familiar to us - it is a hydroxide ion. And the cation is called ammonium. It exhibits properties similar to metals. For example, it may combine with an acidic residue. The substance formed by combining ammonium with a carbonate anion is called ammonium carbonate: (NH4)2CO3.
Here is the reaction equation for the interaction of ammonium with a carbonate anion, written in the form of structural formulas:

2H|N^+<`/H><_(A75,w+)H>_(A15,d+)H + O^-\C|O`|/O^-<=>H|N^+<`/H><_(A75,w+)H>_(A15,d+)H`|0O^-\C|O`|/O^-|0H_(A-15,d-)N^+<_(A105,w+)H><\H>`|H

But in this form the reaction equation is given for demonstration purposes. Typically equations use rational formulas:

2NH4^+ + CO3^2-<=>(NH4)2CO3

Hill system

So, we can assume that we have already studied structural and rational formulas. But there is another issue that is worth considering in more detail. How do gross formulas differ from rational ones?
We know why the rational formula of carbonic acid is written H2CO3, and not some other way. (The two hydrogen cations come first, followed by the carbonate anion.) But why is the gross formula written CH2O3?

In principle, the rational formula of carbonic acid may well be considered a true formula, because it has no repeating elements. Unlike NH4OH or Ca(OH)2.
But an additional rule is very often applied to gross formulas, which determines the order of elements. The rule is quite simple: carbon is placed first, then hydrogen, and then the remaining elements in alphabetical order.
So CH2O3 comes out - carbon, hydrogen, oxygen. This is called the Hill system. It is used in almost all chemical reference books. And in this article too.

A little about the easyChem system

Instead of a conclusion, I would like to talk about the easyChem system. It is designed so that all the formulas that we discussed here can be easily inserted into the text. Actually, all the formulas in this article are drawn using easyChem.

Why do we even need some kind of system for deriving formulas? The thing is that the standard way to display information in Internet browsers is hypertext markup language (HTML). It is focused on processing text information.

Rational and gross formulas can be depicted using text. Even some simplified structural formulas can also be written in text, for example alcohol CH3-CH2-OH. Although for this you would have to use the following entry in HTML: CH ₃-CH ₂-OH.
This of course creates some difficulties, but you can live with them. But how to depict the structural formula? In principle, you can use a monospace font:

H H | | H-C-C-O-H | | H H Of course it doesn’t look very nice, but it’s also doable.

The real problem comes when trying to depict benzene rings and when using skeletal formulas. There is no other way left except connecting a raster image. Rasters are stored in separate files. Browsers can include images in gif, png or jpeg format.
To create such files, a graphic editor is required. For example, Photoshop. But I have been familiar with Photoshop for more than 10 years and I can say for sure that it is very poorly suited for depicting chemical formulas.
Molecular editors cope with this task much better. But when large quantities formulas, each of which is stored in a separate file, it is quite easy to get confused in them.
For example, the number of formulas in this article is . They are displayed in the form of graphic images (the rest using HTML tools).

The easyChem system allows you to store all formulas directly in an HTML document in text form. In my opinion, this is very convenient.
In addition, the gross formulas in this article are calculated automatically. Because easyChem works in two stages: first the text description is converted into an information structure (graph), and then various actions can be performed on this structure. Among them are the following functions: calculation molecular weight, conversion to a gross formula, checking for the possibility of output as text, graphic and text rendering.

Thus, to prepare this article, I only used a text editor. Moreover, I didn’t have to think about which of the formulas would be graphic and which would be text.

Here are a few examples that reveal the secret of preparing the text of an article: Descriptions from the left column are automatically turned into formulas in the second column.
In the first line, the description of the rational formula is very similar to the displayed result. The only difference is that the numerical coefficients are displayed interlinearly.
In the second line, the expanded formula is given in the form of three separate chains separated by a symbol; I think it is easy to see that the textual description is in many ways reminiscent of the actions that would be required to depict the formula with a pencil on paper.
The third line demonstrates the use of slanted lines using the \ and / symbols. The ` (backtick) sign means the line is drawn from right to left (or bottom to top).

There is much more detailed documentation on using the easyChem system here.

Let me finish this article and wish you good luck in studying chemistry.

A brief explanatory dictionary of terms used in the article

Hydrocarbons Substances consisting of carbon and hydrogen. They differ from each other in the structure of their molecules. Structural formulas schematic representations of molecules, where atoms are designated with Latin letters, A chemical bonds- dashes. Structural formulas are expanded, simplified and skeletal. Expanded structural formulas are structural formulas where each atom is represented as a separate node. Simplified structural formulas are those structural formulas where hydrogen atoms are written next to the element with which they are associated. And if more than one hydrogen is attached to one atom, then the amount is written as a number. We can also say that groups act as nodes in simplified formulas. Skeletal formulas are structural formulas where carbon atoms are depicted as empty nodes. The number of hydrogen atoms bonded to each carbon atom is equal to 4 minus the number of bonds that converge at the site. For knots formed not by carbon, the rules of simplified formulas apply. Gross formula (aka true formula) - list of all chemical elements, which are part of the molecule, indicating the number of atoms in the form of a number (if there is one atom, then the unit is not written) The Hill system is a rule that determines the order of atoms in the gross formula: carbon is placed first, then hydrogen, and then the remaining elements in alphabetical order. This is a system that is used very often. And all the gross formulas in this article are written according to the Hill system. Functional groups Stable combinations of atoms that are conserved during chemical reactions. Often functional groups have their own names and influence Chemical properties and scientific name of the substance

2. Bases react with acids to form salt and water (neutralization reaction). For example:

KOH + HC1 = KS1 + H 2 O;

Fe(OH) 2 + 2HNO 3 = Fe(NO 3) 2 + 2H 2 O

3. Alkalis react with acidic oxides to form salt and water:

Ca(OH) 2 + CO 2 = CaCO 2 + H 2 O.

4. Alkali solutions react with salt solutions if the result is the formation of an insoluble base or an insoluble salt. For example:

2NaOH + CuSO 4 = Cu(OH) 2 ↓ + Na 2 SO 4;

Ba(OH) 2 + Na 2 SO 4 = 2NaOH + BaSO 4 ↓

5. When heated, insoluble bases decompose into basic oxide and water.

2Fe(OH) 3 Fe 2 O 3 + ZH 2 O.

6. Alkali solutions interact with metals that form amphoteric oxides and hydroxides (Zn, Al, etc.).

2AI + 2KOH + 6H 2 O = 2K + 3H 2.

Getting grounds

Receipt soluble bases:

a) interaction of alkali and alkaline earth metals with water:

2Na + 2H 2 O = 2NaOH + H 2;

b) interaction of oxides of alkali and alkaline earth metals with water:

Na 2 O + H 2 O = 2NaOH.

2. Receipt insoluble bases the action of alkalis on soluble metal salts:

2NaOH + FeSO 4 = Fe(OH) 2 ↓ + Na 2 SO 4.

Acids ‑ complex substances, when dissociated in water, hydrogen ions H + and no other cations are formed.

Chemical properties

The general properties of acids in aqueous solutions are determined by the presence of H + ions (or rather H 3 O +), which are formed as a result of the electrolytic dissociation of acid molecules:

1. Acids change the color of indicators equally (Table 6).

2. Acids interact with bases.

For example:

H 3 PO 4 + 3NaOH = Na 3 PO 4 + ZN 2 O;

H 3 PO 4 + 2NaOH = Na 2 HPO 4 + 2H 2 O;

H 3 PO 4 + NaOH = NaH 2 PO 4 + H 2 O;

3. Acids interact with basic oxides:

2HCl + CaO = CaC1 2 + H 2 O;

H 2 SO 4 + Fe 2 O 3 = Fe 2 (SO 4) 3 + ZN 2 O.

4. Acids interact with amphoteric oxides:

2HNO 3 + ZnO = Zn(NO 3) 2 + H 2 O.

5. Acids react with some intermediate salts to form a new salt and a new acid; reactions are possible if the result is an insoluble salt or a weaker (or more volatile) acid than the original. For example:

2HC1+Na2CO3 = 2NaCl+H2O +CO2;

2NaCl + H 2 SO 4 = 2HCl + Na 2 SO 4.

6. Acids interact with metals. The nature of the products of these reactions depends on the nature and concentration of the acid and on the activity of the metal. For example, diluted sulfuric acid, hydrochloric acid and other non-oxidizing acids interact with metals that are in the series of standard electrode potentials (see Chapter 7.) to the left of hydrogen. As a result of the reaction, salt and hydrogen gas are formed:

H 2 SO 4 (dil)) + Zn = ZnSO 4 + H 2;

2HC1 + Mg = MgCl 2 + H 2.

Oxidizing acids (concentrated sulfuric acid, nitric acid HNO 3 of any concentration) also interact with metals that are in the series of standard electrode potentials after hydrogen to form a salt and an acid reduction product. For example:

2H 2 SO 4 (conc) + Zn = ZnSO 4 + SO 2 + 2H 2 O;

Obtaining acids

1. Anoxic acids are obtained by synthesis from simple substances and subsequent dissolution of the product in water.

S + H 2 = H 2 S.

2. Oxoacids are obtained by reacting acid oxides with water.

SO 3 + H 2 O = H 2 SO 4.

3. Most acids can be obtained by reacting salts with acids.

Na 2 SiO 3 + H 2 SO 4 = H 2 SiO 3 + Na 2 SO 4.

Amphoteric hydroxides

1. In a neutral environment (pure water), amphoteric hydroxides practically do not dissolve and do not dissociate into ions. They dissolve in acids and alkalis. The dissociation of amphoteric hydroxides in acidic and alkaline media can be expressed by the following equations:

Zn+ OH - Zn(OH)H + + ZnO

A1 3+ + ZON - Al(OH) 3 H + + AlO+ H 2 O

2. Amphoteric hydroxides react with both acids and alkalis, forming salt and water.

Interaction of amphoteric hydroxides with acids:

Zn(OH) 2 + 2HCl + ZnCl 2 + 2H 2 O;

Sn(OH) 2 + H 2 SO 4 = SnSO 4 + 2H 2 O.

Interaction of amphoteric hydroxides with alkalis:

Zn(OH) 2 + 2NaOH Na 2 ZnO 2 + 2H 2 O;

Zn(OH) 2 + 2NaOH Na 2 ;

Pb(OH) 2 + 2NaOHNa 2 .

Salts – products of the replacement of hydrogen atoms in an acid molecule with metal atoms or the replacement of a hydroxide ion in a base molecule with acidic residues.

General chemical properties of salts

1. Salts in aqueous solutions dissociate into ions:

a) medium salts dissociate into metal cations and anions of acidic residues:

NaCN =Na + +СN - ;

6) acid salts dissociate into metal cations and complex anions:

KHSO 3 = K + + HSO 3 -;

c) basic salts dissociate into complex cations and anions of acidic residues:

AlOH(CH 3 COO) 2 = AlOH 2+ + 2CH 3 COO - .

2. Salts react with metals to form a new salt and a new metal. This metal can displace from salt solutions only those metals that are to the right of it in the electrochemical voltage series:

CuSO 4 + Fe = FeSO 4 + Cu.

Soluble salts react with alkalis to form a new salt and a new base. The reaction is possible if the resulting base or salt precipitates.

For example:

FeCl 3 +3KOH = Fe(OH) 3 ↓+3KS1;

K 2 CO 3 + Ba(OH) 2 = BaCO 3 ↓+ 2KOH.

4. Salts react with acids to form a new weaker acid or a new insoluble salt:

Na 2 CO 3 + 2HC1 = 2NaCl + CO 2 + H 2 O.

When a salt reacts with an acid that forms a given salt, an acidic salt is obtained (this is possible if the salt is formed by a polybasic acid).

For example:

Na 2 S + H 2 S = 2NaHS;

CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2.

5. Salts can interact with each other to form new salts if one of the salts precipitates:

AgNO 3 + KC1 = AgCl↓ + KNO 3.

6. Many salts decompose when heated:

MgCO 3 MgO+ CO 2;

2NaNO 3 2NaNO 2 + O 2 .

7. Basic salts react with acids to form medium salts and water:

Fe(OH) 2 NO 3 +HNO 3 = FeOH(NO 3) 2 +H 2 O;

FeOH(NO 3) 2 + HNO 3 = Fe(NO 3) 3 + H 2 O.

8. Acidic salts react with alkalis to form medium salts and water:

NaHSO 4 + NaOH = Na 2 SO 3 + H 2 O;

KN 2 RO 4 + KON = K 2 NRO 4 + H 2 O.

Obtaining salts

All methods of obtaining salts are based on the chemical properties of the most important classes inorganic compounds. Ten classical methods for obtaining salts are presented in the table. 7.

In addition to general methods for obtaining salts, some private methods are also possible:

1. Interaction of metals whose oxides and hydroxides are amphoteric with alkalis.

2. Fusion of salts with certain acid oxides.

K 2 CO 3 + SiO 2 K 2 SiO 3 + CO 2 .

3. Interaction of alkalis with halogens:

2KOH + Cl 2 KCl + KClO + H 2 O.

4. Interaction of halides with halogens:

2KVg + Cl 2 = 2KS1 + Br 2.

When graphically depicting the formulas of substances, the sequence of arrangement of atoms in the molecule is indicated using the so-called valence strokes (the term “valence stroke” was proposed in 1858 by A. Cooper to denote the chemical forces of cohesion of atoms), otherwise called a valence line (each valence line, or valence prime, equivalent to one pair of electrons in covalent compounds or one electron involved in the formation of an ionic bond). Often misunderstood graphic image formulas for structural formulas acceptable only for compounds with covalent bond and showing the relative arrangement of atoms in a molecule.

Yes, the formulaNa-CLis not structural, since NaCI is an ionic compound; there are no molecules in its crystal lattice (molecules NаСLexist only in the gas phase). At the nodes of the crystal lattice NaCI are ions, and each Na+ is surrounded by six chloride ions. This is a graphic representation of the formula of a substance, showing that sodium ions are not bonded to each other, but to chloride ions. Chloride ions do not combine with each other; they are connected with sodium ions.

Let's show this with examples. Mentally, we first “split” a sheet of paper into several columns and perform actions according to algorithms for graphically depicting the formulas of oxides, bases, acids, and salts in the following order.

Graphic representation of oxide formulas (for example, A l 2 O 3 )

III II

1. Determine the valence of atoms of elements in A l 2 O 3

2. Write it down chemical signs metal atoms in first place (first column). If there is more than one metal atom, then we write it in one column and denote the valency (the number of bonds between atoms) with valence strokes

H. The second place (column), also in one column, is occupied by the chemical signs of oxygen atoms, and each oxygen atom must have two valence strokes, since oxygen is divalent

lll ll l

Graphic representation of base formulas(For example F e(OH) 3)

1. Determine the valence of atoms of elements Fe(OH) 3

2. In the first place (first column) we write the chemical symbols of the metal atoms, denoting their valence F e

H. The second place (column) is occupied by the chemical signs of oxygen atoms, which are attached by one bond to the metal atom, the second bond is still “free”

4. The third place (column) is occupied by the chemical signs of hydrogen atoms joining to the “free” valence of oxygen atoms

Graphic representation of acid formulas (for example, H 2 SO 4 )

lVlll

1. Determine the valence of atoms of elements H 2 SO 4 .

2. In the first place (first column) we write the chemical signs of hydrogen atoms in one column with the designation of valence

N—

N—

H. The second place (column) is occupied by oxygen atoms, joining a hydrogen atom with one valence bond, while the second valence of each oxygen atom is still “free”

BUT -

BUT -

4. The third place (column) is occupied by the chemical signs of the acid-forming atoms with the designation of valence

5. Oxygen atoms are added to the “free” valences of the acid-forming atom according to the valency rule

Graphic representation of salt formulas

Medium salts (For example,Fe 2 SO 4 ) 3) In medium salts, all the hydrogen atoms of the acid are replaced by metal atoms, therefore, when graphically depicting their formulas, the first place (first column) is occupied by the chemical signs of the metal atoms with the designation of valency, and then - as in acids, that is, the second place (column) occupied by the chemical signs of the oxygen atoms, the third place (column) is the chemical signs of the acid-forming atoms, there are three of them and they are attached to six oxygen atoms. Oxygen atoms are added to the “free” valencies of the acid former according to the valency rule

Acid salts ( for example, Ba(H 2 P.O. 4 ) 2) Acid salts can be considered as products of partial replacement of hydrogen atoms in an acid with metal atoms, therefore, when compiling graphic formulas of acid salts, the chemical signs of the metal and hydrogen atoms with the designation of valency are written in the first place (first column)

N—

N—

Va =

N—

N—

The second place (column) is occupied by the chemical signs of oxygen atoms

7. Acids. Salt. Relationship between classes of inorganic substances

7.1. Acids

Acids are electrolytes, upon the dissociation of which only hydrogen cations H + are formed as positively charged ions (more precisely, hydronium ions H 3 O +).

Another definition: acids are complex substances consisting of a hydrogen atom and acid residues (Table 7.1).

Table 7.1

Formulas and names of some acids, acid residues and salts

Acid formula	Acid name	Acid residue (anion)	Name of salts (average)
HF	Hydrofluoric (fluoric)	F −	Fluorides
HCl	Hydrochloric (hydrochloric)	Cl −	Chlorides
HBr	Hydrobromic	Br−	Bromides
HI	Hydroiodide	I −	Iodides
H2S	Hydrogen sulfide	S 2−	Sulfides
H2SO3	Sulphurous	SO 3 2 −	Sulfites
H2SO4	Sulfuric	SO 4 2 −	Sulfates
HNO2	Nitrogenous	NO2−	Nitrites
HNO3	Nitrogen	NO 3 −	Nitrates
H2SiO3	Silicon	SiO 3 2 −	Silicates
HPO 3	Metaphosphoric	PO 3 −	Metaphosphates
H3PO4	Orthophosphoric	PO 4 3 −	Orthophosphates (phosphates)
H4P2O7	Pyrophosphoric (biphosphoric)	P 2 O 7 4 −	Pyrophosphates (diphosphates)
HMnO4	Manganese	MnO 4 −	Permanganates
H2CrO4	Chrome	CrO 4 2 −	Chromates
H2Cr2O7	Dichrome	Cr 2 O 7 2 −	Dichromates (bichromates)
H2SeO4	Selenium	SeO 4 2 −	Selenates
H3BO3	Bornaya	BO 3 3 −	Orthoborates
HClO	Hypochlorous	ClO –	Hypochlorites
HClO2	Chloride	ClO2−	Chlorites
HClO3	Chlorous	ClO3−	Chlorates
HClO4	Chlorine	ClO 4 −	Perchlorates
H2CO3	Coal	CO 3 3 −	Carbonates
CH3COOH	Vinegar	CH 3 COO −	Acetates
HCOOH	Ant	HCOO −	Formiates

Under normal conditions, acids can be solids (H 3 PO 4, H 3 BO 3, H 2 SiO 3) and liquids (HNO 3, H 2 SO 4, CH 3 COOH). These acids can exist both individually (100% form) and in the form of diluted and concentrated solutions. For example, H 2 SO 4 , HNO 3 , H 3 PO 4 , CH 3 COOH are known both individually and in solutions.

A number of acids are known only in solutions. These are all hydrogen halides (HCl, HBr, HI), hydrogen sulfide H 2 S, hydrogen cyanide (hydrocyanic HCN), carbonic H 2 CO 3, sulfurous H 2 SO 3 acid, which are solutions of gases in water. For example, hydrochloric acid is a mixture of HCl and H 2 O, carbonic acid is a mixture of CO 2 and H 2 O. It is clear that using the expression “solution of hydrochloric acid" wrong.

Most acids are soluble in water; silicic acid H 2 SiO 3 is insoluble. The vast majority of acids have molecular structure. Examples of structural formulas of acids:

In most oxygen-containing acid molecules, all hydrogen atoms are bonded to oxygen. But there are exceptions:

Acids are classified according to a number of characteristics (Table 7.2).

Table 7.2

Classification of acids

Classification sign	Acid type	Examples
Number of hydrogen ions formed upon complete dissociation of an acid molecule	Monobase	HCl, HNO3, CH3COOH
	Dibasic	H2SO4, H2S, H2CO3
	Tribasic	H3PO4, H3AsO4
The presence or absence of an oxygen atom in a molecule	Oxygen-containing (acid hydroxides, oxoacids)	HNO2, H2SiO3, H2SO4
	Oxygen-free	HF, H2S, HCN
Degree of dissociation (strength)	Strong (completely dissociate, strong electrolytes)	HCl, HBr, HI, H2SO4 (diluted), HNO3, HClO3, HClO4, HMnO4, H2Cr2O7
	Weak (partially dissociate, weak electrolytes)	HF, HNO 2, H 2 SO 3, HCOOH, CH 3 COOH, H 2 SiO 3, H 2 S, HCN, H 3 PO 4, H 3 PO 3, HClO, HClO 2, H 2 CO 3, H 3 BO 3, H 2 SO 4 (conc)
Oxidative properties	Oxidizing agents due to H + ions (conditionally non-oxidizing acids)	HCl, HBr, HI, HF, H 2 SO 4 (dil), H 3 PO 4, CH 3 COOH
	Oxidizing agents due to anion (oxidizing acids)	HNO 3, HMnO 4, H 2 SO 4 (conc), H 2 Cr 2 O 7
	Anion reducing agents	HCl, HBr, HI, H 2 S (but not HF)
Thermal stability	Exist only in solutions	H 2 CO 3, H 2 SO 3, HClO, HClO 2
	Easily decomposes when heated	H 2 SO 3 , HNO 3 , H 2 SiO 3
	Thermally stable	H 2 SO 4 (conc), H 3 PO 4

All general chemical properties of acids are due to the presence in their aqueous solutions of excess hydrogen cations H + (H 3 O +).

1. Due to the excess of H + ions, aqueous solutions of acids change the color of litmus violet and methyl orange to red (phenolphthalein does not change color and remains colorless). In an aqueous solution of weak carbonic acid, litmus is not red, but pink; a solution over a precipitate of very weak silicic acid does not change the color of the indicators at all.

2. Acids interact with basic oxides, bases and amphoteric hydroxides, ammonia hydrate (see Chapter 6).

Example 7.1. To carry out the transformation BaO → BaSO 4 you can use: a) SO 2; b) H 2 SO 4; c) Na 2 SO 4; d) SO 3.

Solution. The transformation can be carried out using H 2 SO 4:

BaO + H 2 SO 4 = BaSO 4 ↓ + H 2 O

BaO + SO 3 = BaSO 4

Na 2 SO 4 does not react with BaO, and in the reaction of BaO with SO 2 barium sulfite is formed:

BaO + SO 2 = BaSO 3

Answer: 3).

3. Acids react with ammonia and its aqueous solutions with the formation of ammonium salts:

HCl + NH 3 = NH 4 Cl - ammonium chloride;

H 2 SO 4 + 2NH 3 = (NH 4) 2 SO 4 - ammonium sulfate.

4. Non-oxidizing acids react with metals located in the activity series up to hydrogen to form a salt and release hydrogen:

H 2 SO 4 (diluted) + Fe = FeSO 4 + H 2

2HCl + Zn = ZnCl 2 = H 2

The interaction of oxidizing acids (HNO 3, H 2 SO 4 (conc)) with metals is very specific and is considered when studying the chemistry of elements and their compounds.

5. Acids interact with salts. The reaction has a number of features:

a) in most cases, when a stronger acid reacts with a salt of a weaker acid, a salt of a weak acid and a weak acid are formed, or, as they say, a stronger acid displaces a weaker one. The series of decreasing strength of acids looks like this:

Examples of reactions occurring:

2HCl + Na 2 CO 3 = 2NaCl + H 2 O + CO 2

H 2 CO 3 + Na 2 SiO 3 = Na 2 CO 3 + H 2 SiO 3 ↓

2CH 3 COOH + K 2 CO 3 = 2CH 3 COOK + H 2 O + CO 2

3H 2 SO 4 + 2K 3 PO 4 = 3K 2 SO 4 + 2H 3 PO 4

Do not interact with each other, for example, KCl and H 2 SO 4 (diluted), NaNO 3 and H 2 SO 4 (diluted), K 2 SO 4 and HCl (HNO 3, HBr, HI), K 3 PO 4 and H 2 CO 3, CH 3 COOK and H 2 CO 3;

b) in some cases, a weaker acid displaces a stronger one from a salt:

CuSO 4 + H 2 S = CuS↓ + H 2 SO 4

3AgNO 3 (dil) + H 3 PO 4 = Ag 3 PO 4 ↓ + 3HNO 3.

Such reactions are possible when the precipitates of the resulting salts do not dissolve in the resulting dilute strong acids (H 2 SO 4 and HNO 3);

c) in the case of the formation of precipitates that are insoluble in strong acids, a reaction may occur between a strong acid and a salt formed by another strong acid:

BaCl 2 + H 2 SO 4 = BaSO 4 ↓ + 2HCl

Ba(NO 3) 2 + H 2 SO 4 = BaSO 4 ↓ + 2HNO 3

AgNO 3 + HCl = AgCl↓ + HNO 3

Example 7.2. Indicate the row containing the formulas of substances that react with H 2 SO 4 (diluted).

1) Zn, Al 2 O 3, KCl (p-p); 3) NaNO 3 (p-p), Na 2 S, NaF; 2) Cu(OH) 2, K 2 CO 3, Ag; 4) Na 2 SO 3, Mg, Zn(OH) 2.

Solution. All substances of row 4 interact with H 2 SO 4 (dil):

Na 2 SO 3 + H 2 SO 4 = Na 2 SO 4 + H 2 O + SO 2

Mg + H 2 SO 4 = MgSO 4 + H 2

Zn(OH) 2 + H 2 SO 4 = ZnSO 4 + 2H 2 O

In row 1) the reaction with KCl (p-p) is not feasible, in row 2) - with Ag, in row 3) - with NaNO 3 (p-p).

Answer: 4).

6. Concentrated sulfuric acid behaves very specifically in reactions with salts. This is a non-volatile and thermally stable acid, therefore it displaces all strong acids from solid (!) salts, since they are more volatile than H2SO4 (conc):

KCl (tv) + H 2 SO 4 (conc.) KHSO 4 + HCl

2KCl (s) + H 2 SO 4 (conc) K 2 SO 4 + 2HCl

Salts formed by strong acids (HBr, HI, HCl, HNO 3, HClO 4) react only with concentrated sulfuric acid and only when in a solid state

Example 7.3. Concentrated sulfuric acid, unlike dilute one, reacts:

3) KNO 3 (tv);

Solution. Both acids react with KF, Na 2 CO 3 and Na 3 PO 4, and only H 2 SO 4 (conc.) react with KNO 3 (solid).

Answer: 3).

Methods for producing acids are very diverse.

Anoxic acids receive:

• by dissolving the corresponding gases in water:

HCl (g) + H 2 O (l) → HCl (p-p)

H 2 S (g) + H 2 O (l) → H 2 S (solution)

• from salts by displacement with stronger or less volatile acids:

FeS + 2HCl = FeCl 2 + H 2 S

KCl (tv) + H 2 SO 4 (conc) = KHSO 4 + HCl

Na 2 SO 3 + H 2 SO 4 Na 2 SO 4 + H 2 SO 3

Oxygen-containing acids receive:

• by dissolving the corresponding acidic oxides in water, while the degree of oxidation of the acid-forming element in the oxide and acid remains the same (with the exception of NO 2):

N2O5 + H2O = 2HNO3

SO 3 + H 2 O = H 2 SO 4

P 2 O 5 + 3H 2 O 2H 3 PO 4

• oxidation of non-metals with oxidizing acids:

S + 6HNO 3 (conc) = H 2 SO 4 + 6NO 2 + 2H 2 O

• by displacing a strong acid from a salt of another strong acid (if a precipitate insoluble in the resulting acids precipitates):

Ba(NO 3) 2 + H 2 SO 4 (diluted) = BaSO 4 ↓ + 2HNO 3

AgNO 3 + HCl = AgCl↓ + HNO 3

• by displacing a volatile acid from its salts with a less volatile acid.

For this purpose, non-volatile, thermally stable concentrated sulfuric acid is most often used:

NaNO 3 (tv) + H 2 SO 4 (conc.) NaHSO 4 + HNO 3

KClO 4 (tv) + H 2 SO 4 (conc.) KHSO 4 + HClO 4

• displacement of a weaker acid from its salts by a stronger acid:

Ca 3 (PO 4) 2 + 3H 2 SO 4 = 3CaSO 4 ↓ + 2H 3 PO 4

NaNO 2 + HCl = NaCl + HNO 2

K 2 SiO 3 + 2HBr = 2KBr + H 2 SiO 3 ↓

Acids- these are complex substances whose molecules consist of hydrogen atoms that can be replaced and acidic residues.

The acid residue has a negative charge.

Oxygen-free acids: HCl, HBr, H 2 S, etc.

An element that, together with hydrogen and oxygen atoms, forms an oxygen-containing acid molecule is called acid-forming.

According to the number of hydrogen atoms in the molecule, acids are divided into monobasic And polybasic.

Monobasic acids contain one hydrogen atom: HCl, HNO 3, HBr, etc.

Polybasic acids contain two or more hydrogen atoms: H 2 SO 4 (dibasic), H 3 PO 4 (tribasic).

In oxygen-free acids, to the name of the element that forms the acid, add the connecting vowel “o” and the words “... hydrogen acid" For example: HF – hydrofluoric acid.

If the acid-forming element exhibits the maximum oxidation state (it corresponds to the group number), then add “...naya acid". Butexample:

HNO 3 – nitrogen and I acid (because the nitrogen atom has a maximum oxidation state of +5)

If the oxidation state of the element is below the maximum, then add "...tired acid":

1+3-2
HNO 2 – nitrogen exhausted acid (since the acid-forming element N has a minimum oxidation state).

H3PO4 – ortho phosphoric acid.

HPO 3 – meta phosphoric acid.

Structural formulas of acids.

In a molecule of an oxygen-containing acid, a hydrogen atom is bonded to an atom of the acid-forming element through an oxygen atom. Therefore, when compiling a structural formula, all hydroxide ions must first be attached to the atom of the acid-forming element.

Then connect the remaining oxygen atoms with two dashes directly to the atoms of the acid-forming element (Fig. 2).