Acids are complex substances whose molecules include hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.
Based on the presence or absence of oxygen in the molecule, acids are divided into oxygen-containing(H2SO4 sulfuric acid, H 2 SO 3 sulfurous acid, HNO 3 nitric acid, H 3 PO 4 phosphoric acid, H 2 CO 3 carbonic acid, H 2 SiO 3 silicic acid) and oxygen-free(HF hydrofluoric acid, HCl hydrochloric acid ( hydrochloric acid), HBr hydrobromic acid, HI hydroiodic acid, H 2 S hydrosulfide acid).
Depending on the number of hydrogen atoms in the acid molecule, acids are monobasic (with 1 H atom), dibasic (with 2 H atoms) and tribasic (with 3 H atoms). For example, nitric acid HNO 3 is monobasic, since its molecule contains one hydrogen atom, sulfuric acid H 2 SO 4 – dibasic, etc.
There are very few inorganic compounds containing four hydrogen atoms that can be replaced by a metal.
The part of an acid molecule without hydrogen is called an acid residue.
Acidic residues may consist of one atom (-Cl, -Br, -I) - these are simple acidic residues, or they may consist of a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.
In aqueous solutions, during exchange and substitution reactions, acidic residues are not destroyed:
H 2 SO 4 + CuCl 2 → CuSO 4 + 2 HCl
The word anhydride means anhydrous, that is, an acid without water. For example,
H 2 SO 4 – H 2 O → SO 3. Anoxic acids do not have anhydrides.
Acids get their name from the name of the acid-forming element (acid-forming agent) with the addition of the endings “naya” and less often “vaya”: H 2 SO 4 - sulfuric; H 2 SO 3 – coal; H 2 SiO 3 – silicon, etc.
The element can form several oxygen acids. In this case, the indicated endings in the name of the acids will be when the element exhibits higher valency(in an acid molecule great content oxygen atoms). If the element exhibits a lower valency, the ending in the name of the acid will be “empty”: HNO 3 - nitric, HNO 2 - nitrogenous.
Acids can be obtained by dissolving anhydrides in water. If the anhydrides are insoluble in water, the acid can be obtained by the action of another stronger acid on the salt of the required acid. This method is typical for both oxygen and oxygen-free acids. Oxygen-free acids are also obtained by direct synthesis from hydrogen and a non-metal, followed by dissolving the resulting compound in water:
H 2 + Cl 2 → 2 HCl;
H 2 + S → H 2 S.
Solutions of the resulting gaseous substances HCl and H 2 S are acids.
Under normal conditions, acids exist in both liquid and solid states.
Chemical properties of acids
Acid solutions act on indicators. All acids (except silicic) are highly soluble in water. Special substances - indicators allow you to determine the presence of acid.
Indicators are substances of complex structure. They change their color depending on their interaction with different chemicals. In neutral solutions they have one color, in solutions of bases they have another color. When interacting with an acid, they change their color: the methyl orange indicator turns red, and the litmus indicator also turns red.
Interact with bases with the formation of water and salt, which contains an unchanged acid residue (neutralization reaction):
H 2 SO 4 + Ca(OH) 2 → CaSO 4 + 2 H 2 O.
Interact with base oxides with the formation of water and salt (neutralization reaction). The salt contains the acidic residue of the acid that was used in the neutralization reaction:
H 3 PO 4 + Fe 2 O 3 → 2 FePO 4 + 3 H 2 O.
Interact with metals.
For acids to interact with metals, certain conditions must be met:
1. the metal must be sufficiently active with respect to acids (in the series of activity of metals it must be located before hydrogen). The further to the left a metal is in the activity series, the more intensely it interacts with acids;
2. the acid must be strong enough (that is, capable of donating hydrogen ions H +).
When leaking chemical reactions acids with metals, a salt is formed and hydrogen is released (except for the interaction of metals with nitric and concentrated sulfuric acids):
Zn + 2HCl → ZnCl 2 + H 2 ;
Cu + 4HNO 3 → CuNO 3 + 2 NO 2 + 2 H 2 O.
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Let's look at the most common ones in educational literature acid formulas:
It is easy to notice that all acid formulas have in common the presence of hydrogen atoms (H), which comes first in the formula.
Determination of the valence of an acid residue
From the above list it can be seen that the number of these atoms may differ. Acids that contain only one hydrogen atom are called monobasic (nitric, hydrochloric, and others). Sulfuric, carbonic, and silicic acids are dibasic, since their formulas contain two H atoms. A tribasic phosphoric acid molecule contains three hydrogen atoms.
Thus, the amount of H in the formula characterizes the basicity of the acid.
The atom or group of atoms that are written after hydrogen are called acid residues. For example, in hydrosulfide acid the residue consists of one atom - S, and in phosphoric, sulfurous and many others - of two, and one of them is necessarily oxygen (O). On this basis, all acids are divided into oxygen-containing and oxygen-free.
Each acid residue has a certain valency. It is equal to the number of H atoms in the molecule of this acid. The valence of the HCl residue is equal to one, since it is a monobasic acid. Residues of nitric, perchloric, and nitrous acids have the same valency. The valency of the sulfuric acid residue (SO 4) is two, since there are two hydrogen atoms in its formula. Trivalent phosphoric acid residue.
Acidic residues - anions
In addition to valence, acid residues have charges and are anions. Their charges are indicated in the solubility table: CO 3 2−, S 2−, Cl− and so on. Please note: the charge of the acidic residue is numerically the same as its valency. For example, in silicic acid, the formula of which is H 2 SiO 3, the acid residue SiO 3 has a valence of II and a charge of 2-. Thus, knowing the charge of the acidic residue, it is easy to determine its valence and vice versa.
Summarize. Acids are compounds formed by hydrogen atoms and acidic residues. From the point of view of the theory of electrolytic dissociation, another definition can be given: acids are electrolytes, in solutions and melts of which hydrogen cations and anions of acid residues are present.
Hints
Chemical formulas of acids are usually learned by heart, as are their names. If you have forgotten how many hydrogen atoms are in a particular formula, but you know what its acidic residue looks like, the solubility table will come to your aid. The charge of the residue coincides in modulus with the valence, and that with the amount of H. For example, you remember that the remainder of carbonic acid is CO 3 . Using the solubility table, you determine that its charge is 2-, which means it is divalent, that is, carbonic acid has the formula H 2 CO 3.
There is often confusion with the formulas of sulfuric and sulfurous, as well as nitric and nitrous acids. Here, too, there is one point that makes it easier to remember: the name of the acid from the pair in which there are more oxygen atoms ends in -naya (sulfuric, nitric). An acid with fewer oxygen atoms in the formula has a name ending in -istaya (sulphurous, nitrogenous).
However, these tips will only help if the acid formulas are familiar to you. Let's repeat them again.
| Acid formulas | Names of acids | Names of the corresponding salts |
| HClO4 | chlorine | perchlorates |
| HClO3 | hypochlorous | chlorates |
| HClO2 | chloride | chlorites |
| HClO | hypochlorous | hypochlorites |
| H5IO6 | iodine | periodates |
| HIO 3 | iodic | iodates |
| H2SO4 | sulfuric | sulfates |
| H2SO3 | sulfurous | sulfites |
| H2S2O3 | thiosulfur | thiosulfates |
| H2S4O6 | tetrathionic | tetrathionates |
| HNO3 | nitrogen | nitrates |
| HNO2 | nitrogenous | nitrites |
| H3PO4 | orthophosphoric | orthophosphates |
| HPO 3 | metaphosphoric | metaphosphates |
| H3PO3 | phosphorous | phosphites |
| H3PO2 | phosphorous | hypophosphites |
| H2CO3 | coal | carbonates |
| H2SiO3 | silicon | silicates |
| HMnO4 | manganese | permanganates |
| H2MnO4 | manganese | manganates |
| H2CrO4 | chrome | chromates |
| H2Cr2O7 | dichrome | dichromates |
| HF | hydrogen fluoride (fluoride) | fluorides |
| HCl | hydrochloric (hydrochloric) | chlorides |
| HBr | hydrobromic | bromides |
| HI | hydrogen iodide | iodides |
| H2S | hydrogen sulfide | sulfides |
| HCN | hydrogen cyanide | cyanides |
| HOCN | cyan | cyanates |
Let me briefly remind you of specific examples how to properly call salts.
Example 1. The salt K 2 SO 4 is formed by a sulfuric acid residue (SO 4) and metal K. Salts of sulfuric acid are called sulfates. K 2 SO 4 - potassium sulfate.
Example 2. FeCl 3 - the salt contains iron and a hydrochloric acid residue (Cl). Name of salt: iron (III) chloride. Please note: in in this case we must not only name the metal, but also indicate its valency (III). In the previous example, this was not necessary, since the valency of sodium is constant.
Important: the name of the salt should indicate the valence of the metal only if the metal has a variable valency!
Example 3. Ba(ClO) 2 - the salt contains barium and the remainder of hypochlorous acid (ClO). Salt name: barium hypochlorite. The valency of the metal Ba in all its compounds is two; it does not need to be indicated.
Example 4. (NH 4) 2 Cr 2 O 7. The NH 4 group is called ammonium, the valence of this group is constant. Name of salt: ammonium dichromate (dichromate).
In the above examples we only encountered the so-called. medium or normal salts. Acidic, basic, double and complex salts, salts of organic acids will not be discussed here.
If you are interested not only in the nomenclature of salts, but also in the methods of their preparation and Chemical properties, I recommend turning to the relevant sections of the chemistry reference book: "
Acids are complex substances whose molecules include hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.
Based on the presence or absence of oxygen in the molecule, acids are divided into oxygen-containing(H 2 SO 4 sulfuric acid, H 2 SO 3 sulfurous acid, HNO 3 nitric acid, H 3 PO 4 phosphoric acid, H 2 CO 3 carbonic acid, H 2 SiO 3 silicic acid) and oxygen-free(HF hydrofluoric acid, HCl hydrochloric acid (hydrochloric acid), HBr hydrobromic acid, HI hydroiodic acid, H 2 S hydrosulfide acid).
Depending on the number of hydrogen atoms in the acid molecule, acids are monobasic (with 1 H atom), dibasic (with 2 H atoms) and tribasic (with 3 H atoms). For example, nitric acid HNO 3 is monobasic, since its molecule contains one hydrogen atom, sulfuric acid H 2 SO 4 – dibasic, etc.
There are very few inorganic compounds containing four hydrogen atoms that can be replaced by a metal.
The part of an acid molecule without hydrogen is called an acid residue.
Acidic residues may consist of one atom (-Cl, -Br, -I) - these are simple acidic residues, or they may consist of a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.
In aqueous solutions, during exchange and substitution reactions, acidic residues are not destroyed:
H 2 SO 4 + CuCl 2 → CuSO 4 + 2 HCl
The word anhydride means anhydrous, that is, an acid without water. For example,
H 2 SO 4 – H 2 O → SO 3. Anoxic acids do not have anhydrides.
Acids get their name from the name of the acid-forming element (acid-forming agent) with the addition of the endings “naya” and less often “vaya”: H 2 SO 4 - sulfuric; H 2 SO 3 – coal; H 2 SiO 3 – silicon, etc.
The element can form several oxygen acids. In this case, the indicated endings in the names of acids will be when the element exhibits a higher valency (the acid molecule contains a high content of oxygen atoms). If the element exhibits a lower valency, the ending in the name of the acid will be “empty”: HNO 3 - nitric, HNO 2 - nitrogenous.
Acids can be obtained by dissolving anhydrides in water. If the anhydrides are insoluble in water, the acid can be obtained by the action of another stronger acid on the salt of the required acid. This method is typical for both oxygen and oxygen-free acids. Oxygen-free acids are also obtained by direct synthesis from hydrogen and a non-metal, followed by dissolving the resulting compound in water:
H 2 + Cl 2 → 2 HCl;
H 2 + S → H 2 S.
Solutions of the resulting gaseous substances HCl and H 2 S are acids.
Under normal conditions, acids exist in both liquid and solid states.
Chemical properties of acids
Acid solutions act on indicators. All acids (except silicic) are highly soluble in water. Special substances - indicators allow you to determine the presence of acid.
Indicators are substances of complex structure. They change color depending on their interaction with different chemicals. In neutral solutions they have one color, in solutions of bases they have another color. When interacting with an acid, they change their color: the methyl orange indicator turns red, and the litmus indicator also turns red.
Interact with bases with the formation of water and salt, which contains an unchanged acid residue (neutralization reaction):
H 2 SO 4 + Ca(OH) 2 → CaSO 4 + 2 H 2 O.
Interact with base oxides with the formation of water and salt (neutralization reaction). The salt contains the acidic residue of the acid that was used in the neutralization reaction:
H 3 PO 4 + Fe 2 O 3 → 2 FePO 4 + 3 H 2 O.
Interact with metals.
For acids to interact with metals, certain conditions must be met:
1. the metal must be sufficiently active with respect to acids (in the series of activity of metals it must be located before hydrogen). The further to the left a metal is in the activity series, the more intensely it interacts with acids;
2. the acid must be strong enough (that is, capable of donating hydrogen ions H +).
When chemical reactions of acid with metals occur, salt is formed and hydrogen is released (except for the interaction of metals with nitric and concentrated sulfuric acids):
Zn + 2HCl → ZnCl 2 + H 2 ;
Cu + 4HNO 3 → CuNO 3 + 2 NO 2 + 2 H 2 O.
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Acids- electrolytes, upon dissociation of which only H + ions are formed from positive ions:
HNO 3 ↔ H + + NO 3 - ;
CH 3 COOH↔ H + +CH 3 COO — .
All acids are classified into inorganic and organic (carboxylic), which also have their own (internal) classifications.
Under normal conditions, a significant amount of inorganic acids exist in a liquid state, some in a solid state (H 3 PO 4, H 3 BO 3).
Organic acids with up to 3 carbon atoms are highly mobile, colorless liquids with a characteristic pungent odor; acids with 4-9 carbon atoms are oily liquids with an unpleasant odor, and acids with a large number of carbon atoms are solids insoluble in water.
Chemical formulas of acids
Let us consider the chemical formulas of acids using the example of several representatives (both inorganic and organic): hydrochloric acid - HCl, sulfuric acid - H 2 SO 4, phosphoric acid - H 3 PO 4, acetic acid - CH 3 COOH and benzoic acid - C 6 H5COOH. The chemical formula shows the quality and quantitative composition molecules (how many and which atoms are included in a particular compound) Using the chemical formula, you can calculate the molecular weight of acids (Ar(H) = 1 amu, Ar(Cl) = 35.5 amu, Ar( P) = 31 amu, Ar(O) = 16 amu, Ar(S) = 32 amu, Ar(C) = 12 amu) :
Mr(HCl) = Ar(H) + Ar(Cl);
Mr(HCl) = 1 + 35.5 = 36.5.
Mr(H 2 SO 4) = 2×Ar(H) + Ar(S) + 4×Ar(O);
Mr(H 2 SO 4) = 2×1 + 32 + 4×16 = 2 + 32 + 64 = 98.
Mr(H 3 PO 4) = 3×Ar(H) + Ar(P) + 4×Ar(O);
Mr(H 3 PO 4) = 3×1 + 31 + 4×16 = 3 + 31 + 64 = 98.
Mr(CH 3 COOH) = 3×Ar(C) + 4×Ar(H) + 2×Ar(O);
Mr(CH 3 COOH) = 3×12 + 4×1 + 2×16 = 36 + 4 + 32 = 72.
Mr(C 6 H 5 COOH) = 7×Ar(C) + 6×Ar(H) + 2×Ar(O);
Mr(C 6 H 5 COOH) = 7 × 12 + 6 × 1 + 2 × 16 = 84 + 6 + 32 = 122.
Structural (graphic) formulas of acids
The structural (graphic) formula of a substance is more visual. It shows how atoms are connected to each other within a molecule. Let us indicate the structural formulas of each of the above compounds:
Rice. 1. Structural formula hydrochloric acid.
Rice. 2. Structural formula of sulfuric acid.
Rice. 3. Structural formula of phosphoric acid.
Rice. 4. Structural formula of acetic acid.
Rice. 5. Structural formula of benzoic acid.
Ionic formulas
All inorganic acids are electrolytes, i.e. capable of dissociating in an aqueous solution into ions:
HCl ↔ H + + Cl - ;
H 2 SO 4 ↔ 2H + + SO 4 2- ;
H 3 PO 4 ↔ 3H + + PO 4 3- .
Examples of problem solving
EXAMPLE 1
| Exercise | With complete combustion 6 g organic matter 8.8 g of carbon monoxide (IV) and 3.6 g of water were formed. Determine the molecular formula of the burned substance if it is known that its molar mass is 180 g/mol. |
| Solution | Let's draw a diagram of the combustion reaction organic compound denoting the number of carbon, hydrogen and oxygen atoms as “x”, “y” and “z” respectively: C x H y O z + O z →CO 2 + H 2 O. Let us determine the masses of the elements that make up this substance. Values of relative atomic masses taken from the Periodic Table of D.I. Mendeleev, round to whole numbers: Ar(C) = 12 amu, Ar(H) = 1 amu, Ar(O) = 16 amu. m(C) = n(C)×M(C) = n(CO 2)×M(C) = ×M(C); m(H) = n(H)×M(H) = 2×n(H 2 O)×M(H) = ×M(H); Let's calculate the molar masses of carbon dioxide and water. As is known, the molar mass of a molecule is equal to the sum of the relative atomic masses of the atoms that make up the molecule (M = Mr): M(CO 2) = Ar(C) + 2×Ar(O) = 12+ 2×16 = 12 + 32 = 44 g/mol; M(H 2 O) = 2×Ar(H) + Ar(O) = 2×1+ 16 = 2 + 16 = 18 g/mol. m(C) = ×12 = 2.4 g; m(H) = 2 × 3.6 / 18 × 1 = 0.4 g. m(O) = m(C x H y O z) - m(C) - m(H) = 6 - 2.4 - 0.4 = 3.2 g. Let's define chemical formula connections: x:y:z = m(C)/Ar(C) : m(H)/Ar(H) : m(O)/Ar(O); x:y:z= 2.4/12:0.4/1:3.2/16; x:y:z= 0.2: 0.4: 0.2 = 1: 2: 1. Means simplest formula CH 2 O compounds molar mass 30 g/mol. To find the true formula of an organic compound, we find the ratio of the true and resulting molar masses: M substance / M(CH 2 O) = 180 / 30 = 6. This means that the indices of carbon, hydrogen and oxygen atoms should be 6 times higher, i.e. the formula of the substance will be C 6 H 12 O 6. This is glucose or fructose. |
| Answer | C6H12O6 |
EXAMPLE 2
| Exercise | Derive the simplest formula of a compound in which the mass fraction of phosphorus is 43.66%, and the mass fraction of oxygen is 56.34%. |
| Solution | Mass fraction element X in a molecule of composition HX is calculated using the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let us denote the number of phosphorus atoms in the molecule by “x”, and the number of oxygen atoms by “y” Let's find the corresponding relative atomic masses elements of phosphorus and oxygen (relative atomic mass values taken from D.I. Mendeleev’s Periodic Table, rounded to whole numbers). Ar(P) = 31; Ar(O) = 16. We divide the percentage content of elements into the corresponding relative atomic masses. Thus we will find the relationship between the number of atoms in the molecule of the compound: x:y = ω(P)/Ar(P) : ω (O)/Ar(O); x:y = 43.66/31: 56.34/16; x:y: = 1.4: 3.5 = 1: 2.5 = 2: 5. This means that the simplest formula for combining phosphorus and oxygen is P 2 O 5 . It is phosphorus(V) oxide. |
| Answer | P2O5 |