| Anoxic: | Basicity | Salt name |
| HCl - hydrochloric (hydrochloric) | monobasic | chloride |
| HBr - hydrobromic | monobasic | bromide |
| HI - hydroiodide | monobasic | iodide |
| HF - hydrofluoric (hydrofluoric) | monobasic | fluoride |
| H 2 S - hydrogen sulfide | dibasic | sulfide |
| Oxygenated: | ||
| HNO 3 - nitrogen | monobasic | nitrate |
| H 2 SO 3 - sulfurous | dibasic | sulfite |
| H 2 SO 4 - sulfuric | dibasic | sulfate |
| H 2 CO 3 - coal | dibasic | carbonate |
| H 2 SiO 3 - silicon | dibasic | silicate |
| H 3 PO 4 - orthophosphoric | tripartite | orthophosphate |
Salts - complex substances that consist of metal atoms and acid residues. This is the most numerous class of inorganic compounds.
Classification. By composition and properties: medium, sour, basic, double, mixed, complex
Medium salts are products of the complete replacement of hydrogen atoms of a polybasic acid with metal atoms.
When dissociated, only metal cations (or NH 4 +) are produced. For example:
Na 2 SO 4 ® 2Na + +SO
CaCl 2 ® Ca 2+ + 2Cl -
Acid salts are products of incomplete substitution of hydrogen atoms of a polybasic acid for metal atoms.
When dissociated, they give metal cations (NH 4 +), hydrogen ions and anions of an acid residue, for example:
NaHCO 3 ® Na + + HCO « H + + CO .
Basic salts are products of incomplete substitution of OH groups - the corresponding base for acidic residues.
Upon dissociation, metal cations, hydroxyl anions and an acid residue are produced.
Zn(OH)Cl ® + + Cl - « Zn 2+ + OH - + Cl - .
double salts contain two metal cations and upon dissociation give two cations and one anion.
KAl(SO 4) 2 ® K + + Al 3+ + 2SO
Complex salts contain complex cations or anions.
Br ® + + Br - « Ag + +2 NH 3 + Br -
Na ® Na + + - « Na + + Ag + + 2 CN -
Genetic relationship between different classes of compounds
EXPERIMENTAL PART
Equipment and utensils: tripod with test tubes, washer, spirit lamp.
Reagents and materials: red phosphorus, zinc oxide, Zn granules, slaked lime powder Ca (OH) 2, 1 mol / dm 3 solutions of NaOH, ZnSO 4, CuSO 4, AlCl 3, FeCl 3, HCl, H 2 SO 4, universal indicator paper, solution phenolphthalein, methyl orange, distilled water.
Work order
1. Pour zinc oxide into two test tubes; add an acid solution (HCl or H 2 SO 4) to one, an alkali solution (NaOH or KOH) to the other and heat slightly on an alcohol lamp.
Observations: Does zinc oxide dissolve in a solution of acid and alkali?
Write Equations
Findings: 1. What type of oxides does ZnO belong to?
2. What properties do amphoteric oxides have?
Preparation and properties of hydroxides
2.1. Dip the tip of the universal indicator strip into an alkali solution (NaOH or KOH). Compare the obtained color of the indicator strip with the standard color scale.
Observations: Record the pH value of the solution.
2.2. Take four test tubes, pour 1 ml of ZnSO 4 solution into the first, СuSO 4 into the second, AlCl 3 into the third, FeCl 3 into the fourth. Add 1 ml of NaOH solution to each tube. Write observations and equations for the reactions that take place.
Observations: Does precipitation occur when alkali is added to a salt solution? Specify the color of the precipitate.
Write Equations ongoing reactions (in molecular and ionic form).
Findings: How can metal hydroxides be obtained?
2.3. Transfer half of the precipitates obtained in experiment 2.2 to other test tubes. On one part of the precipitate, act with a solution of H 2 SO 4 on the other - with a solution of NaOH.
Observations: Does precipitation dissolve when alkali and acid are added to precipitation?
Write Equations ongoing reactions (in molecular and ionic form).
Findings: 1. What type of hydroxides are Zn (OH) 2, Al (OH) 3, Сu (OH) 2, Fe (OH) 3?
2. What properties do amphoteric hydroxides have?
Getting salts.
3.1. Pour 2 ml of CuSO 4 solution into a test tube and lower the cleaned nail into this solution. (The reaction is slow, changes on the surface of the nail appear after 5-10 minutes).
Observations: Are there any changes to the surface of the nail? What is being deposited?
Write an equation for a redox reaction.
Findings: Taking into account a number of stresses of metals, indicate the method for obtaining salts.
3.2. Place one zinc granule in a test tube and add HCl solution.
Observations: Is there any gas evolution?
Write an equation
Findings: Explain this method of obtaining salts?
3.3. Pour a little powder of slaked lime Ca (OH) 2 into a test tube and add a solution of HCl.
Observations: Is there an evolution of gas?
Write an equation the ongoing reaction (in molecular and ionic form).
Conclusion: 1. What type of reaction is the interaction of hydroxide and acid?
2. What substances are the products of this reaction?
3.5. Pour 1 ml of salt solutions into two test tubes: in the first - copper sulfate, in the second - cobalt chloride. Add to both tubes drop by drop sodium hydroxide solution until precipitation is formed. Then add an excess of alkali to both test tubes.
Observations: Indicate the color changes of the precipitates in the reactions.
Write an equation the ongoing reaction (in molecular and ionic form).
Conclusion: 1. As a result of what reactions are basic salts formed?
2. How can basic salts be converted to medium salts?
Control tasks:
1. From the listed substances, write out the formulas of salts, bases, acids: Ca (OH) 2, Ca (NO 3) 2, FeCl 3, HCl, H 2 O, ZnS, H 2 SO 4, CuSO 4, KOH
Zn (OH) 2, NH 3, Na 2 CO 3, K 3 PO 4.
2. Specify the oxide formulas corresponding to the listed substances H 2 SO 4, H 3 AsO 3, Bi (OH) 3, H 2 MnO 4, Sn (OH) 2, KOH, H 3 PO 4, H 2 SiO 3, Ge ( OH) 4 .
3. What hydroxides are amphoteric? Write the reaction equations characterizing the amphotericity of aluminum hydroxide and zinc hydroxide.
4. Which of the following compounds will interact in pairs: P 2 O 5 , NaOH, ZnO, AgNO 3 , Na 2 CO 3 , Cr(OH) 3 , H 2 SO 4 . Make equations of possible reactions.
Laboratory work No. 2 (4 hours)
Subject: Qualitative analysis of cations and anions
Target: to master the technique of carrying out qualitative and group reactions to cations and anions.
THEORETICAL PART
The main task of qualitative analysis is to establish the chemical composition of substances found in various objects (biological materials, drugs, food, environmental objects). In this paper, we consider the qualitative analysis of inorganic substances that are electrolytes, i.e., in fact, the qualitative analysis of ions. From the totality of occurring ions, the most important in medical and biological terms were selected: (Fe 3+, Fe 2+, Zn 2+, Ca 2+, Na +, K +, Mg 2+, Cl -, PO, CO, etc. ). Many of these ions are found in various drugs and foods.
In qualitative analysis, not all possible reactions are used, but only those that are accompanied by a distinct analytical effect. The most common analytical effects are: the appearance of a new color, the release of gas, the formation of a precipitate.
There are two fundamentally different approaches to qualitative analysis: fractional and systematic . In a systematic analysis, group reagents are necessarily used to separate the ions present into separate groups, and in some cases into subgroups. To do this, some of the ions are transferred to the composition of insoluble compounds, and some of the ions are left in solution. After separating the precipitate from the solution, they are analyzed separately.
For example, in solution there are A1 3+, Fe 3+ and Ni 2+ ions. If this solution is exposed to an excess of alkali, a precipitate of Fe (OH) 3 and Ni (OH) 2 precipitates, and ions [A1 (OH) 4] - remain in the solution. The precipitate containing hydroxides of iron and nickel, when treated with ammonia, will partially dissolve due to the transition to a solution of 2+. Thus, with the help of two reagents - alkali and ammonia, two solutions were obtained: one contained ions [А1(OH) 4 ] - , the other contained ions 2+ and a precipitate of Fe(OH) 3 . With the help of characteristic reactions, the presence of certain ions in solutions and in the precipitate, which must first be dissolved, is proved.
Systematic analysis is mainly used to detect ions in complex multicomponent mixtures. It is very time-consuming, but its advantage lies in the easy formalization of all actions that fit into a clear scheme (methodology).
For fractional analysis, only characteristic reactions are used. It is obvious that the presence of other ions can significantly distort the results of the reaction (imposition of colors on top of each other, undesirable precipitation, etc.). To avoid this, fractional analysis mainly uses highly specific reactions that give an analytical effect with a small number of ions. For successful reactions, it is very important to maintain certain conditions, in particular, pH. Very often, in fractional analysis, one has to resort to masking, i.e., to the conversion of ions into compounds that are not capable of producing an analytical effect with the selected reagent. For example, dimethylglyoxime is used to detect the nickel ion. A similar analytical effect with this reagent gives the Fe 2+ ion. To detect Ni 2+, the Fe 2+ ion is converted into a stable fluoride complex 4- or oxidized to Fe 3+, for example, with hydrogen peroxide.
Fractional analysis is used to detect ions in simpler mixtures. The analysis time is significantly reduced, however, the experimenter is required to have a deeper knowledge of the patterns of chemical reactions, since it is quite difficult to take into account all possible cases of the mutual influence of ions on the nature of the observed analytical effects in one particular technique.
In analytical practice, the so-called fractional systematic method. With this approach, the minimum number of group reagents is used, which makes it possible to outline the tactics of analysis in general terms, which is then carried out by the fractional method.
According to the technique of carrying out analytical reactions, reactions are distinguished: sedimentary; microcrystalloscopic; accompanied by the release of gaseous products; carried out on paper; extraction; colored in solutions; flame coloring.
When carrying out sedimentary reactions, the color and nature of the precipitate (crystalline, amorphous) must be noted, if necessary, additional tests are carried out: the precipitate is checked for solubility in strong and weak acids, alkalis and ammonia, and an excess of the reagent. When carrying out reactions accompanied by the evolution of gas, its color and smell are noted. In some cases, additional tests are carried out.
For example, if it is assumed that the evolved gas is carbon monoxide (IV), it is passed through an excess of lime water.
In fractional and systematic analysis, reactions are widely used, during which a new color appears, most often these are complexation reactions or redox reactions.
In some cases, it is convenient to carry out such reactions on paper (drop reactions). Reagents that do not decompose under normal conditions are applied to paper in advance. So, to detect hydrogen sulfide or sulfide ions, paper impregnated with lead nitrate is used [blackening occurs due to the formation of lead (II) sulfide]. Many oxidizing agents are detected using starch iodine paper, i. paper impregnated with solutions of potassium iodide and starch. In most cases, the necessary reagents are applied to the paper during the reaction, for example, alizarin for the A1 3+ ion, cupron for the Cu 2+ ion, etc. To enhance the color, extraction into an organic solvent is sometimes used. Flame color reactions are used for preliminary tests.
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, acidic 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
Acids are such chemical compounds that are capable of donating an electrically charged hydrogen ion (cation), as well as accepting two interacting electrons, as a result of which a covalent bond is formed.
In this article, we will look at the main acids that are studied in the middle classes of comprehensive schools, and also learn a lot of interesting facts about a wide variety of acids. Let's get started.
Acids: types
In chemistry, there are many different acids that have a variety of properties. Chemists distinguish acids by their oxygen content, volatility, solubility in water, strength, stability, belonging to an organic or inorganic class of chemical compounds. In this article, we will look at a table that presents the most famous acids. The table will help you remember the name of the acid and its chemical formula.
So, everything is clearly visible. This table presents the most famous acids in the chemical industry. The table will help you remember the names and formulas much faster.
Hydrosulphuric acid
H 2 S is hydrosulfide acid. Its peculiarity lies in the fact that it is also a gas. Hydrogen sulfide is very poorly soluble in water, and also interacts with many metals. Hydrosulphuric acid belongs to the group of "weak acids", examples of which we will consider in this article.
H 2 S has a slightly sweet taste and a very strong smell of rotten eggs. In nature, it can be found in natural or volcanic gases, and it is also released when protein rots.
The properties of acids are very diverse, even if the acid is indispensable in industry, it can be very unhealthy for human health. This acid is highly toxic to humans. When a small amount of hydrogen sulfide is inhaled, a person wakes up with a headache, severe nausea and dizziness begin. If a person inhales a large amount of H 2 S, then this can lead to convulsions, coma, or even instant death.
Sulfuric acid
H 2 SO 4 is a strong sulfuric acid that children get acquainted with in chemistry lessons as early as the 8th grade. Chemical acids such as sulfuric are very strong oxidizing agents. H 2 SO 4 acts as an oxidizing agent on many metals, as well as basic oxides.
H 2 SO 4 causes chemical burns on contact with skin or clothing, but is not as toxic as hydrogen sulfide.
Nitric acid
Strong acids are very important in our world. Examples of such acids: HCl, H 2 SO 4 , HBr, HNO 3 . HNO 3 is the well-known nitric acid. It has found wide application in industry as well as in agriculture. It is used for the manufacture of various fertilizers, in jewelry, in photographic printing, in the production of medicines and dyes, as well as in the military industry.
Chemical acids such as nitric acid are very harmful to the body. Vapors of HNO 3 leave ulcers, cause acute inflammation and irritation of the respiratory tract.
Nitrous acid
Nitrous acid is often confused with nitric acid, but there is a difference between them. The fact is that it is much weaker than nitrogen, it has completely different properties and effects on the human body.
HNO 2 has found wide application in the chemical industry.
Hydrofluoric acid
Hydrofluoric acid (or hydrogen fluoride) is a solution of H 2 O with HF. The formula of the acid is HF. Hydrofluoric acid is very actively used in the aluminum industry. It dissolves silicates, etchs silicon, silicate glass.
Hydrogen fluoride is very harmful to the human body, depending on its concentration it can be a light drug. When it comes into contact with the skin, at first there are no changes, but after a few minutes, a sharp pain and a chemical burn may appear. Hydrofluoric acid is very harmful to the environment.
Hydrochloric acid
HCl is hydrogen chloride and is a strong acid. Hydrogen chloride retains the properties of acids belonging to the group of strong acids. In appearance, the acid is transparent and colorless, but smokes in air. Hydrogen chloride is widely used in the metallurgical and food industries.
This acid causes chemical burns, but it is especially dangerous if it gets into the eyes.
Phosphoric acid
Phosphoric acid (H 3 PO 4) is a weak acid in its properties. But even weak acids can have the properties of strong ones. For example, H 3 PO 4 is used in industry to recover iron from rust. In addition, phosphoric (or phosphoric) acid is widely used in agriculture - a wide variety of fertilizers are made from it.
The properties of acids are very similar - almost each of them is very harmful to the human body, H 3 PO 4 is no exception. For example, this acid also causes severe chemical burns, nosebleeds, and tooth decay.
Carbonic acid
H 2 CO 3 is a weak acid. It is obtained by dissolving CO 2 (carbon dioxide) in H 2 O (water). Carbonic acid is used in biology and biochemistry.
Density of various acids
The density of acids occupies an important place in the theoretical and practical parts of chemistry. Thanks to the knowledge of density, it is possible to determine the concentration of an acid, solve chemical problems, and add the correct amount of acid to complete the reaction. The density of any acid varies with concentration. For example, the greater the percentage of concentration, the greater the density.
General properties of acids
Absolutely all acids are (that is, they consist of several elements of the periodic table), while they necessarily include H (hydrogen) in their composition. Next, we will look at which are common:
- All oxygen-containing acids (in the formula of which O is present) form water during decomposition, and also anoxic acids decompose into simple substances (for example, 2HF decomposes into F 2 and H 2).
- Oxidizing acids interact with all metals in the metal activity series (only with those located to the left of H).
- They interact with various salts, but only with those that were formed by an even weaker acid.
According to their physical properties, acids differ sharply from each other. After all, they can have a smell and not have it, as well as be in a variety of aggregate states: liquid, gaseous and even solid. Solid acids are very interesting for studying. Examples of such acids: C 2 H 2 0 4 and H 3 BO 3.
Concentration
Concentration is a quantity that determines the quantitative composition of any solution. For example, chemists often need to determine how much pure sulfuric acid is in dilute H 2 SO 4 acid. To do this, they pour a small amount of dilute acid into a beaker, weigh it, and determine the concentration from a density table. The concentration of acids is closely related to the density, often there are calculation tasks to determine the concentration, where you need to determine the percentage of pure acid in the solution.
Classification of all acids according to the number of H atoms in their chemical formula
One of the most popular classifications is the division of all acids into monobasic, dibasic and, accordingly, tribasic acids. Examples of monobasic acids: HNO 3 (nitric), HCl (hydrochloric), HF (hydrofluoric) and others. These acids are called monobasic, since only one H atom is present in their composition. There are many such acids, it is impossible to remember absolutely every one. You just need to remember that acids are also classified by the number of H atoms in their composition. Dibasic acids are defined similarly. Examples: H 2 SO 4 (sulphuric), H 2 S (hydrogen sulfide), H 2 CO 3 (coal) and others. Tribasic: H 3 PO 4 (phosphoric).
Basic classification of acids
One of the most popular classifications of acids is their division into oxygen-containing and anoxic acids. How to remember, without knowing the chemical formula of a substance, that it is an oxygen-containing acid?
All oxygen-free acids in the composition lack the important element O - oxygen, but they contain H. Therefore, the word "hydrogen" is always attributed to their name. HCl is a H 2 S - hydrogen sulfide.
But even by the names of acid-containing acids, you can write a formula. For example, if the number of O atoms in a substance is 4 or 3, then the suffix -n- is always added to the name, as well as the ending -aya-:
- H 2 SO 4 - sulfuric (number of atoms - 4);
- H 2 SiO 3 - silicon (number of atoms - 3).
If the substance has less than three oxygen atoms or three, then the suffix -ist- is used in the name:
- HNO 2 - nitrogenous;
- H 2 SO 3 - sulfurous.
General properties
All acids taste sour and often slightly metallic. But there are other similar properties, which we will now consider.
There are substances that are called indicators. Indicators change their color, or the color remains, but its hue changes. This happens when some other substances, such as acids, act on the indicators.
An example of a color change is such a product familiar to many as tea and citric acid. When lemon is thrown into tea, the tea gradually begins to noticeably lighten. This is due to the fact that lemon contains citric acid.
There are other examples as well. Litmus, which in a neutral medium has a lilac color, turns red when hydrochloric acid is added.
With tensions up to hydrogen in the series, gas bubbles are released - H. However, if a metal that is in the tension series after H is placed in a test tube with acid, then no reaction will occur, there will be no gas evolution. So, copper, silver, mercury, platinum and gold will not react with acids.
In this article, we examined the most famous chemical acids, as well as their main properties and differences.
7. Acids. Salt. Relationship between classes of inorganic substances
7.1. acids
Acids are electrolytes, during 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 | Name of the acid | Acid residue (anion) | Name of salts (medium) |
|---|---|---|---|
| HF | Hydrofluoric (hydrofluoric) | F- | Fluorides |
| HCl | Hydrochloric (hydrochloric) | Cl- | chlorides |
| HBr | Hydrobromic | Br- | Bromides |
| HI | Hydroiodic | I- | iodides |
| H 2 S | Hydrogen sulfide | S2− | Sulfides |
| H2SO3 | sulphurous | SO 3 2 - | Sulfites |
| H2SO4 | sulfuric | SO 4 2 - | sulfates |
| HNO 2 | nitrogenous | NO 2 - | 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 (two-phosphoric) | P 2 O 7 4 - | Pyrophosphates (diphosphates) |
| HMnO 4 | manganese | MnO 4 - | Permanganates |
| H2CrO4 | Chrome | CrO 4 2 - | Chromates |
| H2Cr2O7 | dichrome | Cr 2 O 7 2 - | Dichromates (bichromates) |
| H 2 SeO 4 | Selenic | SeO 4 2 − | selenates |
| H3BO3 | Bornaya | BO 3 3 - | Orthoborates |
| HClO | hypochlorous | ClO- | Hypochlorites |
| HClO 2 | Chloride | ClO 2 - | Chlorites |
| HClO 3 | Chlorine | ClO 3 - | Chlorates |
| HClO 4 | Chloric | ClO 4 - | Perchlorates |
| H2CO3 | Coal | CO 3 3 - | Carbonates |
| CH3COOH | Acetic | CH 3 COO − | Acetates |
| HCOOH | Formic | HCOO- | Formates |
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 in individual (100% form) and in the form of dilute 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 hydrohalic (HCl, HBr, HI), hydrogen sulfide H 2 S, hydrocyanic (hydrocyanic HCN), coal 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, coal is a mixture of CO 2 and H 2 O. It is clear that it is wrong to use the expression "hydrochloric acid solution".
Most acids are soluble in water, silicic acid H 2 SiO 3 is insoluble. The vast majority of acids have a 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 features (Table 7.2).
Table 7.2
Acid classification
| Classification sign | Acid type | Examples |
|---|---|---|
| The number of hydrogen ions formed during the complete dissociation of an acid molecule | Monobasic | HCl, HNO 3 , CH 3 COOH |
| Dibasic | H 2 SO 4 , H 2 S, H 2 CO 3 | |
| Tribasic | H 3 PO 4 , H 3 AsO 4 | |
| The presence or absence of an oxygen atom in the molecule | Oxygen-containing (acid hydroxides, oxoacids) | HNO 2 , H 2 SiO 3 , H 2 SO 4 |
| Anoxic | HF, H2S, HCN | |
| Degree of dissociation (strength) | Strong (completely dissociate, strong electrolytes) | HCl, HBr, HI, H 2 SO 4 (diff), HNO 3 , HClO 3 , HClO 4 , HMnO 4 , H 2 Cr 2 O 7 |
| 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) | |
| Oxidizing properties | Oxidizing agents due to H + ions (conditionally non-oxidizing acids) | HCl, HBr, HI, HF, H 2 SO 4 (diff), H 3 PO 4 , CH 3 COOH |
| Oxidizing agents due to the 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 | Exists only in solutions | H 2 CO 3 , H 2 SO 3 , HClO, HClO 2 |
| Easily decomposed when heated | H 2 SO 3 , HNO 3 , H 2 SiO 3 | |
| Thermally stable | H 2 SO 4 (conc), H 3 PO 4 |
All the general chemical properties of acids are due to the presence in their aqueous solutions of an excess of hydrogen cations H + (H 3 O +).
1. Due to an excess of H + ions, aqueous solutions of acids change the color of violet and methyl orange litmus to red (phenolphthalein does not change color, remains colorless). In an aqueous solution of weak carbonic acid, the 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 Ch. 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) SO3.
Decision. The transformation can be carried out using H 2 SO 4:
BaO + H 2 SO 4 \u003d 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 to form ammonium salts:
HCl + NH 3 \u003d NH 4 Cl - ammonium chloride;
H 2 SO 4 + 2NH 3 = (NH 4) 2 SO 4 - ammonium sulfate.
4. Non-oxidizing acids with the formation of a salt and the release of hydrogen react with metals located in the row of activity to hydrogen:
H 2 SO 4 (diff) + Fe = FeSO 4 + H 2
2HCl + Zn \u003d ZnCl 2 \u003d H 2
The interaction of oxidizing acids (HNO 3 , H 2 SO 4 (conc)) with metals is very specific and is considered in the study of 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 is formed and a weak acid, or, as they say, a stronger acid displaces a weaker one. The series of decreasing strength of acids looks like this:
Examples of ongoing reactions:
2HCl + Na 2 CO 3 \u003d 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 \u003d 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 (diff), NaNO 3 and H 2 SO 4 (diff), 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 the salt:
CuSO 4 + H 2 S \u003d CuS ↓ + H 2 SO 4
3AgNO 3 (razb) + 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 between a strong acid and a salt formed by another strong acid is possible:
BaCl 2 + H 2 SO 4 \u003d 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 series in which the formulas of substances that react with H 2 SO 4 are given (diff).
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.
Decision. All substances of series 4 interact with H 2 SO 4 (razb):
Na 2 SO 3 + H 2 SO 4 \u003d Na 2 SO 4 + H 2 O + SO 2
Mg + H 2 SO 4 \u003d 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. It is a non-volatile and thermally stable acid, therefore it displaces all strong acids from solid (!) Salts, since they are more volatile than H 2 SO 4 (conc):
KCl (tv) + H 2 SO 4 (conc) KHSO 4 + HCl
2KCl (tv) + 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 in the solid state
Example 7.3. Concentrated sulfuric acid, unlike dilute sulfuric acid, reacts:
3) KNO 3 (TV);
Decision. 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 (tv).
Answer: 3).
Methods for obtaining acids are very diverse.
Anoxic acids receive:
- by dissolving the corresponding gases in water:
HCl (g) + H 2 O (g) → HCl (p-p)
H 2 S (g) + H 2 O (g) → H 2 S (solution)
- from salts by displacement by stronger or less volatile acids:
FeS + 2HCl \u003d 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
oxygenated acids receive:
- by dissolving the corresponding acid oxides in water, while the oxidation state of the acid-forming element in the oxide and acid remains the same (NO 2 is an exception):
N 2 O 5 + H 2 O \u003d 2HNO 3
SO 3 + H 2 O \u003d 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 forms that is insoluble in the resulting acids):
Ba (NO 3) 2 + H 2 SO 4 (razb) \u003d BaSO 4 ↓ + 2HNO 3
AgNO 3 + HCl = AgCl↓ + HNO 3
- displacement of a volatile acid from its salts by 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
- by displacing a weaker acid from its salts with 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 ↓
