The acid is a constituent. Acids: classification and chemical properties
Names of some inorganic acids and salts
| Acid formulas | Names of acids | Names of the corresponding salts |
| HClO 4 | chloride | perchlorates |
| HClO 3 | chlorine | chlorates |
| HClO 2 | chloride | chlorites |
| HClO | hypochlorous | hypochlorites |
| H5IO6 | iodine | periodates |
| HIO 3 | iodine | iodates |
| H2SO4 | sulfuric | sulfates |
| H2SO3 | sulphurous | sulfites |
| H2S2O3 | thiosulfuric | thiosulfates |
| H2S4O6 | tetrathionic | tetrathionates |
| H NO 3 | nitric | nitrates |
| H NO 2 | nitrogenous | nitrites |
| H3PO4 | orthophosphoric | orthophosphates |
| HPO3 | metaphosphoric | metaphosphates |
| H3PO3 | phosphorous | phosphites |
| H3PO2 | phosphorous | hypophosphites |
| H2CO3 | coal | carbonates |
| H2SiO3 | silicon | silicates |
| HMnO 4 | manganese | permanganates |
| H2MnO4 | manganese | manganates |
| H2CrO4 | chrome | chromates |
| H2Cr2O7 | dichrome | dichromates |
| HF | hydrofluoric (hydrofluoric) | fluorides |
| HCl | hydrochloric (hydrochloric) | chlorides |
| HBr | hydrobromic | bromides |
| HI | hydroiodic | iodides |
| H 2 S | hydrogen sulfide | sulfides |
| HCN | hydrocyanic | cyanides |
| HOCN | cyanic | cyanates |
Let me briefly remind concrete examples how to properly name salts.
Example 1. Salt K 2 SO 4 is formed by the rest of sulfuric acid (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 residue of hydrochloric acid(Cl). Name of the salt: iron(III) chloride. Please note: 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: in the name of the salt, the valency of the metal should be indicated only if this metal has a variable valency!
Example 3. Ba (ClO) 2 - the composition of the salt includes barium and the remainder of hypochlorous acid (ClO). Name of salt: barium hypochlorite. The valency of the Ba metal in all its compounds is two, it is not necessary to indicate it.
Example 4. (NH 4) 2 Cr 2 O 7. The NH 4 group is called ammonium, the valence of this group is constant. Salt name: ammonium dichromate (bichromate).
In the above examples, we met only the so-called. medium or normal salts. Sour, basic, double and complex salts, salts of organic acids will not be discussed here.
Do not underestimate the role of acids in our lives, because many of them are simply irreplaceable in Everyday life. First, let's remember what acids are. This complex substances. The formula is written as follows: HnA, where H is hydrogen, n is the number of atoms, A is the acid residue.
The main properties of acids include the ability to replace the molecules of hydrogen atoms with metal atoms. Most of them are not only caustic, but also very poisonous. But there are also those that we encounter constantly, without harm to our health: vitamin C, lemon acid, lactic acid. Consider the basic properties of acids.
Physical properties
The physical properties of acids often provide a clue to their character. Acids can exist in three forms: solid, liquid and gaseous. For example: nitrogen (HNO3) and sulfuric acid(H2SO4) are colorless liquids; boric (H3BO3) and metaphosphoric (HPO3) are solid acids. Some of them have color and smell. Different acids dissolve differently in water. There are also insoluble ones: H2SiO3 - silicon. Liquid substances have a sour taste. The name of some acids was given by the fruits in which they are found: malic acid, citric acid. Others got their name from the chemical elements contained in them.
Acid classification
Usually acids are classified according to several criteria. The very first is, according to the oxygen content in them. Namely: oxygen-containing (HClO4 - chlorine) and anoxic (H2S - hydrogen sulfide).
By the number of hydrogen atoms (by basicity):
- Monobasic - contains one hydrogen atom (HMnO4);
- Dibasic - has two hydrogen atoms (H2CO3);
- Tribasic, respectively, have three hydrogen atoms (H3BO);
- Polybasic - have four or more atoms, are rare (H4P2O7).
By class chemical compounds, divided into organic and inorganic acids. The former are mainly found in plant products: acetic, lactic, nicotinic, ascorbic acids. Inorganic acids include: sulfuric, nitric, boric, arsenic. The range of their application is quite wide from industrial needs (production of dyes, electrolytes, ceramics, fertilizers, etc.) to cooking or cleaning sewers. Acids can also be classified according to strength, volatility, stability and solubility in water.
Chemical properties
Consider the main Chemical properties acids.
- The first is interaction with indicators. As indicators, litmus, methyl orange, phenolphthalein and universal indicator paper are used. In acid solutions, the color of the indicator will change color: litmus and universal ind. paper will turn red, methyl orange - pink, phenolphthalein will remain colorless.
- The second is the interaction of acids with bases. This reaction is also called neutralization. The acid reacts with the base, resulting in salt + water. For example: H2SO4+Ca(OH)2=CaSO4+2 H2O.
- Since almost all acids are highly soluble in water, neutralization can be carried out with both soluble and insoluble bases. The exception is silicic acid, which is almost insoluble in water. To neutralize it, bases such as KOH or NaOH are required (they are soluble in water).
- The third is the interaction of acids with basic oxides. This is where the neutralization reaction takes place. Basic oxides are close "relatives" of bases, hence the reaction is the same. We very often use these oxidizing properties of acids. For example, to remove rust from pipes. The acid reacts with the oxide to become a soluble salt.
- The fourth is the reaction with metals. Not all metals react equally well with acids. They are divided into active (K, Ba, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Ni, Sn. Pb) and inactive (Cu, Hg, Ag, Pt, Au). It is also worth paying attention to the strength of the acid (strong, weak). For example, hydrochloric and sulfuric acids are able to react with all inactive metals, while citric and oxalic acids are so weak that they react very slowly even with active metals.
- The fifth is the reaction of oxygen-containing acids to heating. Almost all acids of this group, when heated, decompose into oxygen oxide and water. The exceptions are carbonic (H3PO4) and sulfurous acids (H2SO4). When heated, they decompose into water and gas. This must be remembered. That's all the basic properties of acids.
Acids can be classified according to different criteria:
1) The presence of oxygen atoms in the acid
2) Acid basicity
The basicity of an acid is the number of "mobile" hydrogen atoms in its molecule, capable of splitting off from the acid molecule in the form of hydrogen cations H + during dissociation, and also being replaced by metal atoms:
4) Solubility
5) Sustainability
7) Oxidizing properties
Chemical properties of acids
1. Ability to dissociate
Acids dissociate in aqueous solutions into hydrogen cations and acid residues. As already mentioned, acids are divided into well-dissociating (strong) and low-dissociating (weak). When writing the dissociation equation for strong monobasic acids, either one arrow pointing to the right () or an equal sign (=) is used, which actually shows the irreversibility of such dissociation. For example, the dissociation equation for strong hydrochloric acid can be written in two ways:
or in this form: HCl \u003d H + + Cl -
or in this: HCl → H + + Cl -
In fact, the direction of the arrow tells us that the reverse process of combining hydrogen cations with acidic residues (association) in strong acids practically does not occur.
In case we want to write the equation for the dissociation of a weak monobasic acid, we must use two arrows instead of the sign in the equation. This sign reflects the reversibility of the dissociation of weak acids - in their case, the reverse process of combining hydrogen cations with acidic residues is strongly pronounced:
CH 3 COOH CH 3 COO - + H +
Polybasic acids dissociate in steps, i.e. hydrogen cations are not detached from their molecules simultaneously, but in turn. For this reason, the dissociation of such acids is expressed not by one, but by several equations, the number of which is equal to the basicity of the acid. For example, the dissociation of tribasic phosphoric acid proceeds in three steps with the successive detachment of H + cations:
H 3 PO 4 H + + H 2 PO 4 —
H 2 PO 4 - H + + HPO 4 2-
HPO 4 2- H + + PO 4 3-
It should be noted that each next stage of dissociation proceeds to a lesser extent than the previous one. That is, H 3 PO 4 molecules dissociate better (to a greater extent) than H 2 PO 4 — ions, which, in turn, dissociate better than HPO 4 2- ions. This phenomenon is associated with an increase in the charge of acidic residues, as a result of which the strength of the bond between them and positive H + ions increases.
Of the polybasic acids, sulfuric acid is an exception. Since this acid dissociates well in both steps, it is permissible to write the equation of its dissociation in one stage:
H 2 SO 4 2H + + SO 4 2-
2. Interaction of acids with metals
The seventh point in the classification of acids, we indicated their oxidizing properties. It was pointed out that acids are weak oxidizing agents and strong oxidizers. The vast majority of acids (practically all except H 2 SO 4 (conc.) and HNO 3) are weak oxidizing agents, since they can show their oxidizing ability only due to hydrogen cations. Such acids can oxidize from metals only those that are in the activity series to the left of hydrogen, while the salt of the corresponding metal and hydrogen are formed as products. For example:
H 2 SO 4 (diff.) + Zn ZnSO 4 + H 2
2HCl + Fe FeCl 2 + H 2
As for strong oxidizing acids, i.e. H 2 SO 4 (conc.) and HNO 3, then the list of metals on which they act is much wider, and it includes both all metals up to hydrogen in the activity series, and almost everything after. That is, concentrated sulfuric acid and nitric acid of any concentration, for example, will oxidize even such inactive metals as copper, mercury, and silver. In more detail, the interaction of nitric acid and concentrated sulfuric acid with metals, as well as some other substances due to their specificity, will be considered separately at the end of this chapter.
3. Interaction of acids with basic and amphoteric oxides
Acids react with basic and amphoteric oxides. Silicic acid, since it is insoluble, does not react with low-active basic oxides and amphoteric oxides:
H 2 SO 4 + ZnO ZnSO 4 + H 2 O
6HNO 3 + Fe 2 O 3 2Fe (NO 3) 3 + 3H 2 O
H 2 SiO 3 + FeO ≠
4. Interaction of acids with bases and amphoteric hydroxides
HCl + NaOH H2O + NaCl
3H 2 SO 4 + 2Al (OH) 3 Al 2 (SO 4) 3 + 6H 2 O
5. Interaction of acids with salts
This reaction proceeds if a precipitate, a gas, or a substantially weaker acid than the one that reacts is formed. For example:
H 2 SO 4 + Ba(NO 3) 2 BaSO 4 ↓ + 2HNO 3
CH 3 COOH + Na 2 SO 3 CH 3 COONa + SO 2 + H 2 O
HCOONa + HCl HCOOH + NaCl
6. Specific oxidizing properties of nitric and concentrated sulfuric acids
As mentioned above, nitric acid in any concentration, as well as sulfuric acid exclusively in a concentrated state, are very strong oxidizing agents. In particular, unlike other acids, they oxidize not only metals that are up to hydrogen in the activity series, but also almost all metals after it (except platinum and gold).
For example, they are able to oxidize copper, silver and mercury. However, it should be firmly grasped the fact that a number of metals (Fe, Cr, Al), despite the fact that they are quite active (they are up to hydrogen), nevertheless, do not react with concentrated HNO 3 and concentrated H 2 SO 4 without heating on due to the passivation phenomenon - a protective film of solid oxidation products is formed on the surface of such metals, which does not allow molecules of concentrated sulfuric and concentrated nitric acids to penetrate deep into the metal for the reaction to proceed. However, with strong heating, the reaction still proceeds.
In the case of interaction with metals, the required products are always the salt of the corresponding metal and the acid used, as well as water. A third product is also always isolated, the formula of which depends on many factors, in particular, such as the activity of metals, as well as the concentration of acids and the temperature of the reactions.
The high oxidizing power of concentrated sulfuric and concentrated nitric acids allows them to react not only with practically all metals of the activity range, but even with many solid non-metals, in particular, with phosphorus, sulfur, and carbon. The table below clearly shows the products of the interaction of sulfuric and nitric acids with metals and non-metals, depending on the concentration:
7. Reducing properties of anoxic acids
All anoxic acids (except HF) can exhibit reducing properties due to the chemical element that is part of the anion, under the action of various oxidizing agents. So, for example, all hydrohalic acids (except HF) are oxidized by manganese dioxide, potassium permanganate, potassium dichromate. In this case, halide ions are oxidized to free halogens:
4HCl + MnO 2 MnCl 2 + Cl 2 + 2H 2 O
18HBr + 2KMnO 4 2KBr + 2MnBr 2 + 8H 2 O + 5Br 2
14НI + K 2 Cr 2 O 7 3I 2 ↓ + 2Crl 3 + 2KI + 7H 2 O
Among all hydrohalic acids, hydroiodic acid has the greatest reducing activity. Unlike other hydrohalic acids, even ferric oxide and salts can oxidize it.
6HI + Fe 2 O 3 2FeI 2 + I 2 ↓ + 3H 2 O
2HI + 2FeCl 3 2FeCl 2 + I 2 ↓ + 2HCl
Hydrosulfide acid H 2 S also has a high reducing activity. Even an oxidizing agent such as sulfur dioxide can oxidize it.
Substances that dissociate in solutions to form hydrogen ions are called.
Acids are classified according to their strength, basicity, and the presence or absence of oxygen in the composition of the acid.
By strengthacids are divided into strong and weak. The most important strong acids are nitric HNO 3 , sulfuric H 2 SO 4 , and hydrochloric HCl .
By the presence of oxygen distinguish oxygen-containing acids ( HNO3, H3PO4 etc.) and anoxic acids ( HCl, H 2 S , HCN, etc.).
By basicity, i.e. according to the number of hydrogen atoms in an acid molecule that can be replaced by metal atoms to form a salt, acids are divided into monobasic (for example, HNO 3, HCl), dibasic (H 2 S, H 2 SO 4), tribasic (H 3 PO 4 ), etc.
The names of oxygen-free acids are derived from the name of the non-metal with the addition of the ending -hydrogen: HCl - hydrochloric acid, H 2 S e - hydroselenic acid, HCN - hydrocyanic acid.
The names of oxygen-containing acids are also formed from the Russian name of the corresponding element with the addition of the word "acid". At the same time, the name of the acid in which the element is in the highest oxidation state ends in "naya" or "ova", for example, H2SO4 - sulfuric acid, HClO 4 - perchloric acid, H 3 AsO 4 - arsenic acid. With a decrease in the degree of oxidation of the acid-forming element, the endings change in the following sequence: “oval” ( HClO 3 - chloric acid), "pure" ( HClO 2 - chlorous acid), "wobbly" ( H O Cl - hypochlorous acid). If the element forms acids, being in only two oxidation states, then the name of the acid corresponding to the lowest oxidation state of the element receives the ending "pure" ( HNO3 - Nitric acid, HNO 2 - nitrous acid).
Table - The most important acids and their salts
|
Acid |
Names of the corresponding normal salts |
|
|
Name |
Formula |
|
|
Nitrogen |
HNO3 |
Nitrates |
|
nitrogenous |
HNO 2 |
Nitrites |
|
Boric (orthoboric) |
H3BO3 |
Borates (orthoborates) |
|
Hydrobromic |
Bromides |
|
|
Hydroiodine |
iodides |
|
|
Silicon |
H2SiO3 |
silicates |
|
manganese |
HMnO 4 |
Permanganates |
|
Metaphosphoric |
HPO 3 |
Metaphosphates |
|
Arsenic |
H 3 AsO 4 |
Arsenates |
|
Arsenic |
H 3 AsO 3 |
Arsenites |
|
orthophosphoric |
H3PO4 |
Orthophosphates (phosphates) |
|
Diphosphoric (pyrophosphoric) |
H4P2O7 |
Diphosphates (pyrophosphates) |
|
dichrome |
H2Cr2O7 |
Dichromates |
|
sulfuric |
H2SO4 |
sulfates |
|
sulphurous |
H2SO3 |
Sulfites |
|
Coal |
H2CO3 |
Carbonates |
|
Phosphorous |
H3PO3 |
Phosphites |
|
Hydrofluoric (hydrofluoric) |
Fluorides |
|
|
Hydrochloric (hydrochloric) |
chlorides |
|
|
Chloric |
HClO 4 |
Perchlorates |
|
Chlorine |
HClO 3 |
Chlorates |
|
hypochlorous |
HClO |
Hypochlorites |
|
Chrome |
H2CrO4 |
Chromates |
|
Hydrogen cyanide (hydrocyanic) |
cyanides |
|
Obtaining acids
1. Anoxic acids can be obtained by direct combination of non-metals with hydrogen:
H 2 + Cl 2 → 2HCl,
H 2 + S H 2 S.
2. Oxygen-containing acids can often be obtained by directly combining acid oxides with water:
SO 3 + H 2 O \u003d H 2 SO 4,
CO 2 + H 2 O \u003d H 2 CO 3,
P 2 O 5 + H 2 O \u003d 2 HPO 3.
3. Both oxygen-free and oxygen-containing acids can be obtained by exchange reactions between salts and other acids:
BaBr 2 + H 2 SO 4 \u003d BaSO 4 + 2HBr,
CuSO 4 + H 2 S \u003d H 2 SO 4 + CuS,
CaCO 3 + 2HBr \u003d CaBr 2 + CO 2 + H 2 O.
4. In some cases, redox reactions can be used to obtain acids:
H 2 O 2 + SO 2 \u003d H 2 SO 4,
3P + 5HNO 3 + 2H 2 O = 3H 3 PO 4 + 5NO.
Chemical properties of acids
1. The most characteristic chemical property of acids is their ability to react with bases (as well as with basic and amphoteric oxides) to form salts, for example:
H 2 SO 4 + 2NaOH \u003d Na 2 SO 4 + 2H 2 O,
2HNO 3 + FeO \u003d Fe (NO 3) 2 + H 2 O,
2 HCl + ZnO \u003d ZnCl 2 + H 2 O.
2. The ability to interact with some metals in the series of voltages up to hydrogen, with the release of hydrogen:
Zn + 2HCl \u003d ZnCl 2 + H 2,
2Al + 6HCl \u003d 2AlCl 3 + 3H 2.
3. With salts, if a poorly soluble salt or volatile substance is formed:
H 2 SO 4 + BaCl 2 = BaSO 4 ↓ + 2HCl,
2HCl + Na 2 CO 3 \u003d 2NaCl + H 2 O + CO 2,
2KHCO 3 + H 2 SO 4 \u003d K 2 SO 4 + 2SO 2+ 2H2O.
Note that polybasic acids dissociate in steps, and the ease of dissociation in each of the steps decreases, therefore, for polybasic acids, acid salts are often formed instead of medium salts (in the case of an excess of the reacting acid):
Na 2 S + H 3 PO 4 \u003d Na 2 HPO 4 + H 2 S,
NaOH + H 3 PO 4 = NaH 2 PO 4 + H 2 O.
4. A special case of acid-base interaction is the reaction of acids with indicators, leading to a change in color, which has long been used for the qualitative detection of acids in solutions. So, litmus changes color in an acidic environment to red.
5. When heated, oxygen-containing acids decompose into oxide and water (preferably in the presence of a water-removing P2O5):
H 2 SO 4 \u003d H 2 O + SO 3,
H 2 SiO 3 \u003d H 2 O + SiO 2.
M.V. Andryukhova, L.N. Borodin
